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PubMed2026

Two worlds beneath: Distinct microbial strategies of the rock-attached and planktonic subsurface biosphere.

BACKGROUND: Microorganisms in groundwater ecosystems exist either as planktonic cells or as attached communities on aquifer rock surfaces. Attached cells outnumber planktonic ones by at least three orders of magnitude, suggesting a critical role in aquifer ecosystem function. However, particularly in consolidated carbonate aquifers, where research has predominantly focused on planktonic microbes, the metabolic potential and ecological roles of attached communities remain poorly understood. RESULTS: To investigate the differences between attached and planktonic communities, we sampled the attached microbiome from passive samplers filled with crushed carbonate rock exposed to oxic and anoxic groundwater in the Hainich Critical Zone Exploratory and compared it to a previously published, extensive dataset of planktonic communities from the same aquifer ecosystem. Microbial lifestyle (attached vs. planktonic) explained more variance in community composition than redox conditions, prompting us to further investigate its role in shaping functional and activity profiles. Metagenomic analysis revealed a striking taxonomic and functional segregation: the 605 metagenome-assembled genomes (MAGs) from attached communities were dominated by Proteobacteria (358 MAGs) and were enriched in genes for biofilm formation, chemolithoautotrophy, and redox cycling (e.g., iron and sulfur metabolism). In contrast, the 891 MAGs from planktonic communities were dominated by Cand. Patescibacteria (464 MAGs) and Nitrospirota (60 MAGs) and showed lower functional versatility. Only a few genera were shared, and even closely related MAGs (> 90% average nucleotide identity) differed in assembly size and metabolic traits, demonstrating lifestyle-specific functional adaptation. Analysis of active replication indicated that the active fraction of the attached community was primarily represented by the most abundant MAGs. Planktonic communities featured a higher fraction of active MAGs compared to attached communities, but overall with lower relative abundances. CONCLUSIONS: The high abundance, metabolic specialization, and carbon fixation potential of attached microbes suggest that they are key drivers of subsurface biogeochemical processes. Carbonate aquifers may act as much larger inorganic carbon sinks than previously estimated based on CO2 fixation rates of the planktonic communities alone. Our findings underscore the need to incorporate attached microbial communities into models of subsurface ecosystem function. Video Abstract.

Plankton↗

PubMed2005

Chemical characterization of exopolysaccharides from Antarctic marine bacteria.

Exopolysaccharides (EPS) may have an important role in the Antarctic marine environment, possibly acting as ligands for trace metal nutrients such as iron or providing cryoprotection for growth at low temperature and high salinity. Ten bacterial strains, isolated from Southern Ocean particulate material or from sea ice, were characterized. Whole cell fatty acid profiles and 16S rRNA gene sequences showed that the isolates included representatives of the genera Pseudoalteromonas, Shewanella, Polaribacter, and Flavobacterium as well as one strain, which constituted a new bacterial genus in the family Flavobacteriaceae. The isolates are, therefore, members of the "Gammaproteobacteria" and Cytophaga-Flexibacter-Bacteroides, the taxonomic groups that have been shown to dominate polar sea ice and seawater microbial communities. Exopolysaccharides produced by Antarctic isolates were characterized. Chemical composition and molecular weight data revealed that these EPS were very diverse, even among six closely related Pseudoalteromonas isolates. Most of the EPS contained charged uronic acid residues; several also contained sulfate groups. Some strain produced unusually large polymers (molecular weight up to 5.7 MDa) including one strain in which EPS synthesis is stimulated by low temperature. This study represents a first step in the understanding of the role of bacterial EPS in the Antarctic marine environment.

Antarctic Regions↗

PubMed2004

Molecular ecological analysis of the gastrointestinal microbiota: a review.

The gastrointestinal (GI) microbiota of mammals is characterized by its high population density, wide diversity and complexity of interactions. While all major groups of microbes are represented, bacteria predominate. Importantly, bacterial cells outnumber animal (host) cells by a factor of ten and have a profound influence on nutritional, physiological and immunological processes in the host animal. Our knowledge of the molecular and cellular bases of host-microbe interactions is limited, though critically needed to determine if and how the GI microbiota contributes to various enteric disorders in humans and animals. Traditionally, GI bacteria have been studied via cultivation-based techniques, which are labor intensive and require previous knowledge of individual nutritional and growth requirements. Recently, findings from culture-based methods have been supplemented with molecular ecology techniques that are based on the 16S rRNA gene. These techniques enable characterization and quantification of the microbiota, while also providing a classification scheme to predict phylogenetic relationships. The choice of a particular molecular-based approach depends on the questions being addressed. Clone libraries can be sequenced to identify the composition of the microbiota, often to the species level. Microbial community structure can be analyzed via fingerprinting techniques, while dot blot hybridization or fluorescent in situ hybridization can measure abundance of particular taxa. Emerging approaches, such as those based on functional genes and their expression and the combined use of stable isotopes and biomarkers, are being developed and optimized to study metabolic activities of groups or individual organisms in situ. Here, a critical summary is provided of current molecular ecological approaches for studying the GI microbiota.

Digestive System↗

PubMed2006

Molecular diversity studies of bacterial communities of oil polluted microbial mats from the Etang de Berre (France).

The biodiversity of microbial mats inhabiting the oil-contaminated lagoon Etang de Berre was determined by molecular approaches. The fingerprint of denaturing gradient gel electrophoresis (DGGE) and automatic ribosomal intergenic spacer analysis (ARISA) of mats exposed to different pollution levels showed specific microbial communities for each site but similar diversity richness. Species composition of the mats were compared by constructing 16S rRNA libraries. Amplified rDNA restriction analysis (ARDRA) of clone libraries confirmed their similar level of diversity richness. Phylogenetic analysis of the 16S rRNA sequences showed that the classes gamma and alpha of Proteobacteria were abundantly present in both sites whereas phylotypes related to the delta-Proteobacteria and to the uncultured WS3 group were mainly found in the site with the highest pollution. Identification of the species involved in oil degradation by combining culture-based approaches and DGGE, showed that enrichment cultures were constituted by members of the Rhodobacterales and species related to Rhodococcus, Sphingomonas, Xanthomonas and Microbacterium, all of them known for their ability to degrade hydrocarbons. Our findings suggest that oil pollution has not affected the biodiversity richness of the mats. However, the populations involved in hydrocarbon degradation represent a minor fraction of the mat communities in the Etang de Berre.

Bacteria↗

PubMed1994

Development of an rRNA-targeted oligonucleotide probe specific for the genus Acinetobacter and its application for in situ monitoring in activated sludge.

Enhanced biological phosphate removal in an anaerobic-aerobic activated sludge system has generally been ascribed to members of the genus Acinetobacter. A genus-specific 16S rRNA-targeted oligonucleotide probe was developed to investigate the role of Acinetobacter spp. in situ. Nonisotopic dot blot hybridization to 66 reference strains, including the seven described Acinetobacter spp., demonstrated the expected probe specificity. Fluorescent derivatives were used for in situ monitoring of Acinetobacter spp. in the anaerobic and aerobic compartments of a sewage treatment plant with enhanced biological phosphate removal. Microbial community structures were further analyzed with oligonucleotide probes specific for the alpha, beta, or gamma subclasses of the class Proteobacteria, for the Cytophaga-Flavobacterium cluster, for gram-positive bacteria with a high G + C DNA content, and for all bacteria. Total cell counts were determined by 4',6-diamidino-2-phenylindole staining. In both the anaerobic and the aerobic basins, the activated sludge samples were dominated by members of the class Proteobacteria belonging to the beta subclass and by gram-positive bacteria with a high G + C DNA content. Acinetobacter spp. constituted less than 10% of all bacteria. For both basins, the microbial community structures determined with molecular techniques were compared with the compositions of the heterotrophic saprophytic microbiota determined with agar plating techniques. Isolates on nutrient-rich medium were classified by whole-cell hybridization with rRNA-targeted probes and fatty acid analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Acinetobacter↗

PubMed2026

Donor Microbiota Features Associated With Liver Transplant Recipient Infectious Complications: A Pilot Study Using Deep Intestinal Sampling During Liver Procurement.

BACKGROUND: The gut microbiota of living organ donors has been linked to transplant outcomes. However, little is known about the characteristics of the deceased donor gut microbiota or its potential impact on recipient outcomes. METHODS: We analyzed the deep intestinal microbiota from 24 deceased donors. Samples included luminal stool from the right and left colon as well as bile. Microbial composition was characterized using 16S V4 rRNA sequencing. α- and β-diversity analyses were performed to compare microbial communities between donor enteric sites and against stool samples from 28 healthy community controls, 14 critically ill intensive care comparators, and 12 matched liver transplant recipients. Machine learning models and logistic regression analysis were applied to explore whether features of the donor microbiota could predict recipient post-transplant complications. FINDINGS: The deceased donor microbiota showed an absence of the expected compositional variability between sampling sites, with no significant differences in either α- or β-diversity observed between bile, right and left colonic samples (all p > 0.05). Donor samples exhibited distinct microbial profiles compared with stool from both healthy and ICU comparators, including increased abundance of potential pathogens within the Enterobacteriaceae family (all p < 0.001). Features of the donor microbiota, particularly enrichment of Enterobacteriaceae, were associated with an increased risk of early post-transplant infection in recipients (≤ 30 days; p = 0.011). INTERPRETATION: The deceased donor gut microbiota may represent a distinct microbial community with potential clinical relevance. Microbial profiling of donor enteric microbiota may help identify recipients at heightened risk of early post-transplant infectious complications.

Enterobacteriaceae↗

PubMed2026

Benchmarking DNA extraction protocols across use cases for culture-independent Nanopore metagenomics.

Oxford Nanopore Technologies (ONT) sequencing offers several advantages for metagenomics, including long reads, rapid turnaround, low upfront cost, scalability and portability. However, for ONT metagenomics, DNA yield, quality and integrity are important considerations when selecting an extraction method. Many metagenomic extraction methods use harsh lysis conditions to extract a wide range of species and provide an accurate community composition, but these conditions can compromise DNA fragment length. Therefore, extraction methods for ONT metagenomics must balance DNA shearing and recovery with representative community lysis. We systematically evaluated DNA extraction methods for ONT metagenomic sequencing using a use case-oriented framework. Among nearly 50 extraction methods screened, 7 were selected for detailed comparison based on suitability for metagenomics, variation in methodology, availability, cost and processing time: Norgen BioTek Corp's Stool DNA Isolation (NG), Zymo Research's ZymoBIOMICS Quick-DNA HMW MagBead (ZMG), Qiagen's DNeasy Blood and Tissue (QBT), Macherey-Nagel's NucleoMag DNA Microbiome (MN), Zymo Research's ZymoBIOMICS DNA Mini Prep (ZMI), Qiagen's DNeasy PowerSoil/QIAamp PowerFecal Pro (PS) and Qiagen's QIAamp Fast DNA Stool Mini (QIA). Methods were tested using Zymo Research's ZymoBIOMICS Microbial Community Standard (MCS), a matrix-free mock community with known composition. DNA extracts were sequenced on an ONT PromethION using the Rapid Barcoding Kit, except QIA due to insufficient DNA yield. Metrics for the method, DNA extracts, sequencing and genomes were evaluated, revealing trade-offs between methods. The two magnetic bead methods, MN and ZMG, produced the highest mean read length N50 values (13.9 and 16.5 kb, respectively) but showed apparent community compositions skewed towards Gram-negative bacteria. In contrast, ZMI and PS maintained a community composition close to expected, with reduced mean read length N50 values (4.5 vs. 7.5 kb). Performance across various metrics is presented in the context of the following use cases: maximizing genome coverage and assembly completeness, preserving composition accuracy, targeting specific species and limiting required resources (equipment, time or budget). The metrics and use case considerations presented offer practical guidance for informed selection of DNA extraction methods for ONT metagenomics. For accurate community composition, ZMI or PS are recommended, while PS and ZMG perform best at maximizing genome coverage and assembly completeness. NG and QBT may be the most economical options, though performance trade-offs were observed. Finally, PS may be the preferred method for time-sensitive diagnostic or field applications.

Metagenomics↗

PubMed2006

Denitrifier community composition along a nitrate and salinity gradient in a coastal aquifer.

Nitrogen flux into the coastal environment via submarine groundwater discharge may be modulated by microbial processes such as denitrification, but the spatial scales at which microbial communities act and vary are not well understood. In this study, we examined the denitrifying community within the beach aquifer at Huntington Beach, California, where high-nitrate groundwater is a persistent feature. Nitrite reductase-encoding gene fragments (nirK and nirS), responsible for the key step in the denitrification pathway, were PCR amplified, cloned, and sequenced from DNAs extracted from aquifer sediments collected along a cross-shore transect, where groundwater ranged in salinity from 8 to 34 practical salinity units and in nitrate concentration from 0.5 to 330 muM. We found taxonomically rich and novel communities, with all nirK clones exhibiting <85% identity and nirS clones exhibiting <92% identity at the amino acid level to those of cultivated denitrifiers and other environmental clones in the database. Unique communities were found at each site, despite being located within 40 m of each other, suggesting that the spatial scale at which denitrifier diversity and community composition vary is small. Statistical analyses of nir sequences using the Monte Carlo-based program integral-Libshuff confirmed that some populations were indeed distinct, although further sequencing would be required to fully characterize the highly diverse denitrifying communities at this site.

Bacteria↗

PubMed2003

Leitbakteria of microbial biofilm communities causing occlusion of biliary stents.

Biliary stents inserted to relieve obstructive jaundice caused by biliary or pancreatic malignancies inevitably become occluded by microbial growth in the form of diverse microbial community biofilms. The scarce information available on these communities is based on cultivation methods, but such methods usually provide distorted overviews of community composition, so commonalities and differences in biliary stent communities are uncertain. We extracted DNA and RNA from the microbial communities of 11 biliary stents explanted from nine patients in hospitals from two different countries, amplified 16S rRNA and rDNA sequences, analysed the amplicons by the single-strand conformation polymorphism (SSCP) method, and sequenced and deduced phylogenetic assignments of the major amplicons representing the major biofilm community members. We used a Modified Robbins Device (MRD) to study de novo development of a stent biofilm from a patient stent microbial community. Single-strand conformation polymorphism fingerprinting revealed the same six abundant bacterial species, here designated Leitbakteria, namely Klebsiella pneumoniae, Enterococcus faecalis, Pseudomonas aeruginosa, Enterobacter aerogenes, and two unculturable bacteria distantly related to E. coli and Shigella sonnei, in all of the stent biofilm communities. In the experimental biliary stent system, a sequential colonization of the stent surface was observed, with P. aeruginosa being the pioneer colonizer, followed by K. pneumoniae and one of the unculturable Leitbakteria, followed by the remainder of the community. The overview of microbial biofilm communities of biliary stents gained by the use of culture-independent methods revealed new unculturable bacteria as major members of biliary stent biofilms, and the diversity of the abundant members of the stent biofilms is considerably lower than suggested from earlier studies based on cultivation methods, and that communities from different stents from different patients in different countries are remarkably similar and have similar major members, the stent Leitbakteria.

Aged↗

PubMed2005

Structure and topology of microbial communities in the major gut compartments of Melolontha melolontha larvae (Coleoptera: Scarabaeidae).

Physicochemical gut conditions and the composition and topology of the intestinal microbiota in the major gut compartments of the root-feeding larva of the European cockchafer (Melolontha melolontha) were studied. Axial and radial profiles of pH, O2, H2, and redox potential were measured with microsensors. Terminal restriction fragment length polymorphism (T-RFLP) analysis of bacterial 16S rRNA genes in midgut samples of individual larvae revealed a simple but variable and probably nonspecific community structure. In contrast, the T-RFLP profiles of the hindgut samples were more diverse but highly similar, especially in the wall fraction, indicating the presence of a gut-specific community involved in digestion. While high acetate concentrations in the midgut and hindgut (34 and 15 mM) corroborated the presence of microbial fermentation in both compartments, methanogenesis was confined to the hindgut. Methanobrevibacter spp. were the only methanogens detected and were restricted to this compartment. Bacterial 16S rRNA gene clone libraries of the hindgut were dominated by clones related to the Clostridiales. Clones related to the Actinobacteria, Bacillales, Lactobacillales, and gamma-Proteobacteria were restricted to the lumen, whereas clones related to the beta- and delta-Proteobacteria were found only on the hindgut wall. Results of PCR-based analyses and fluorescence in situ hybridization of whole cells with group-specific oligonucleotide probes documented that Desulfovibrio-related bacteria comprise 10 to 15% of the bacterial community at the hindgut wall. The restriction of the sulfate-reducer-specific adenosine-5'-phosphosulfate reductase gene apsA to DNA extracts of the hindgut wall in larvae from four other populations in Europe suggested that sulfate reducers generally colonize this habitat.

Animals↗

PubMed2002

Analysis of bacterial community composition by oligonucleotide fingerprinting of rRNA genes.

One of the first steps in characterizing an ecosystem is to describe the organisms inhabiting it. For microbial studies, experimental limitations have hindered the ability to depict diverse communities. Here we describe oligonucleotide fingerprinting of rRNA genes (OFRG), a method that permits identification of arrayed rRNA genes (rDNA) through a series of hybridization experiments using small DNA probes. To demonstrate this strategy, we examined the bacteria inhabiting two different soils. Analysis of 1,536 rDNA clones revealed 766 clusters grouped into five major taxa: Bacillus, Actinobacteria, Proteobacteria, and two undefined assemblages. Soil-specific taxa were identified and then independently confirmed through cluster-specific PCR of the original soil DNA. Near-species-level resolution was obtained by this analysis as clones with average sequence identities of 97% were grouped in the same cluster. A comparison of these OFRG results with the results obtained in a denaturing gradient gel electrophoresis analysis of the same two soils demonstrated the significance of this methodological advance. OFRG provides a cost-effective means to extensively analyze microbial communities and should have applications in medicine, biotechnology, and ecosystem studies.

Bacteria↗

PubMed1985

Fourier transform-infrared spectroscopic methods for microbial ecology: analysis of bacteria, bacteria-polymer mixtures and biofilms.

Fourier transform-infrared (FT-IR) spectroscopy has been used to rapidly and nondestructively analyze bacteria, bacteria-polymer mixtures, digester samples and microbial biofilms. Diffuse reflectance FT-IR (DRIFT) analysis of freeze-dried, powdered samples offered a means of obtaining structural information. The bacteria examined were divided into two groups. The first group was characterized by a dominant amide I band and the second group of organisms displayed an additional strong carbonyl stretch at approximately 1740 cm-1. The differences illustrated by the subtraction spectra obtained for microbes of the two groups suggest that FT-IR spectroscopy can be utilized to recognize differences in microbial community structure. Calculation of specific band ratios has enabled the composition of bacteria and extracellular or intracellular storage product polymer mixtures to be determined for bacteria-gum arabic (amide I/carbohydrate C-O approximately 1150 cm-1) and bacteria-poly-beta-hydroxybutyrate (amide I/carbonyl approximately 1740 cm-1). The key band ratios correlate with the compositions of the material and provide useful information for the application of FT-IR spectroscopy to environmental biofilm samples and for distinguishing bacteria grown under differing nutrient conditions. DRIFT spectra have been obtained for biofilms produced by Vibrio natriegens on stainless steel disks. Between 48 and 144 h, an increase in bands at approximately 1440 and 1090 cm-1 was seen in FT-IR spectra of the V. natriegens biofilm. DRIFT spectra of mixed culture effluents of anaerobic digesters show differences induced by shifts in input feedstocks. The use of flow-through attenuated total reflectance has permitted in situ real-time changes in biofilm formation to be monitored and provides a powerful tool for understanding the interactions within adherent microbial consortia.

Bacterial Physiological Phenomena↗

PubMed2026

Association Between the Root Canal Microbiome and Apical Lesion Size: An Observational Shotgun Metagenomic Study.

AIM: The aim was to characterize the taxonomic and functional composition of the microbiome involved in primary endodontic infections and to evaluate their association with the periapical lesion size using shotgun metagenomic sequencing. METHODOLOGY: Samples from primary root canal infections diagnosed with apical periodontitis were analysed with shotgun sequencing. Samples were classified according to the lesion size as small (< 3 mm) or large (> 7 mm). The bacterial DNA copies in each group were quantified by qPCR. Taxonomic and functional annotations were made using Bracken/Kraken2 and HUMAnN3 software. Species richness, Shannon, Simpson and Pielou indices were used to measure alpha diversity. The similarity of the bacterial communities between study groups was evaluated by Principal Coordinate Analysis based on Bray-Curtis distances. The ALDEx2 package was used to infer the differences between species, and the edgeR package for KEGG pathways. For all statistical analyses, p < 0.05 was considered as significant. RESULTS: A total of 49 samples were analysed, 27 with small lesions and 22 with large lesions. Species richness and Shannon indices showed differences between both groups, whereas no differences were seen according to Simpson and Pielou indices. A different community composition (PERMANOVA, p = 0.0019) was observed between the two groups. Three species were significantly enriched in the large lesion samples, Filifactor alocis, Lachnospiraceae bacterium oral taxon 500 and Olsenella uli, while three others were enriched in small lesion samples, Acinetobacter baumannii, Acinetobacter pittii and Cutibacterium acnes. Functionally, benzoate, flavonoid and steroid degradation, the sphingolipid signalling pathway and proteasome function were enriched in samples with large lesions. Monoterpenoid biosynthesis, phospholipase D signalling, the sulphur relay system and staurosporine biosynthesis were enriched in small lesions. CONCLUSIONS: Teeth with large periapical lesions harbour greater bacterial loads and exhibit a more diverse microbial community than those with small lesions. Differences in species-level taxonomic composition were observed between both groups. Functionally, large lesions are enriched in pathways associated with immune evasion and pro-inflammatory activity, whereas small lesions are characterized by pathways related to apoptosis, metabolic adaptation and anti-inflammatory processes. These findings suggest that lesion severity is also shaped by the functional potential of the microbiome to modulate host inflammation.

Humans↗

PubMed1996

Characterization of universal small-subunit rRNA hybridization probes for quantitative molecular microbial ecology studies.

Universal oligonucleotide hybridization probes targeting the small-subunit rRNA are commonly used to quantify total microbial representation in environmental samples. Universal probes also serve to normalize results obtained with probes targeting specific phylogenetic groups of microorganisms. In this study, six universal probes were evaluated for stability of probe-target duplexes by using rRNA from nine organisms representing the three domains of Bacteria, Archaea, and Eucarya. Domain-specific variations in dissociation temperatures were observed for all probes. This could lead to a significant bias when these probes are used to quantify microbial populations in environmental samples. We suggest lowering the posthybridization wash stringency for two of the universal probes (S-*-Univ-1390-a-A-18 and S-*-Univ-1392-a-A-15) examined. These two probes were evaluated with traditional and modified hybridization conditions to characterize defined mixtures of rRNAs extracted from pure cultures and rRNA samples obtained from anaerobic digester samples. Probe S-*-Univ-1390-a-A-18 provided excellent estimations of domain-level community composition of these samples and is recommended for future use in microbial ecology studies.

Archaea↗

PubMed2003

Life under nutrient limitation in oligotrophic marine environments: an eco/physiological perspective of Sphingopyxis alaskensis (formerly Sphingomonas alaskensis).

The oceans of the world are nutrient-limited environments that support a dynamic diversity of microbial life. Heterotrophic prokaryotes proliferate in oligotrophic regions and affect nutrient transformation and remineralization thereby impacting directly on the all marine biota. An important challenge in studying the microbial ecology of oligotrophic environments has been the isolation of ecologically important species. This goal has been recognized not only for its relevance in defining the dynamics of community composition, but for enabling physiological studies of competitive species and inferring their impact on the microbial food web. This review describes the successful isolation attempts of the ultramicrobacterium, Sphingopyxis alaskensis (formerly described as Sphingomonas alaskensis) using extinction dilution culturing methods. It then provides a comprehensive perspective of the unique physiological and genetic properties that have been identified that distinguish it from typical copiotrophic species. These properties are described through studies of the growth phase and growth rate control of macromolecular synthesis, stress resistance and global gene expression (proteomics). We also discuss the importance of integrating ecological and physiological approaches for studying microorganisms in marine environments.

Alaska↗

PubMed2000

Depositional facies and aqueous-solid geochemistry of travertine-depositing hot springs (Angel Terrace, Mammoth Hot Springs, Yellowstone National Park, U.S.A.).

Petrographic and geochemical analyses of travertine-depositing hot springs at Angel Terrace, Mammoth Hot Springs, Yellowstone National Park, have been used to define five depositional facies along the spring drainage system. Spring waters are expelled in the vent facies at 71 to 73 degrees C and precipitate mounded travertine composed of aragonite needle botryoids. The apron and channel facies (43-72 degrees C) is floored by hollow tubes composed of aragonite needle botryoids that encrust sulfide-oxidizing Aquificales bacteria. The travertine of the pond facies (30-62 degrees C) varies in composition from aragonite needle shrubs formed at higher temperatures to ridged networks of calcite and aragonite at lower temperatures. Calcite "ice sheets", calcified bubbles, and aggregates of aragonite needles ("fuzzy dumbbells") precipitate at the air-water interface and settle to pond floors. The proximal-slope facies (28-54 degrees C), which forms the margins of terracette pools, is composed of arcuate aragonite needle shrubs that create small microterracettes on the steep slope face. Finally, the distal-slope facies (28-30 degrees C) is composed of calcite spherules and calcite "feather" crystals. Despite the presence of abundant microbial mat communities and their observed role in providing substrates for mineralization, the compositions of spring-water and travertine predominantly reflect abiotic physical and chemical processes. Vigorous CO2 degassing causes a +2 unit increase in spring water pH, as well as Rayleigh-type covariations between the concentration of dissolved inorganic carbon and corresponding delta 13C. Travertine delta 13C and delta 18O are nearly equivalent to aragonite and calcite equilibrium values calculated from spring water in the higher-temperature (approximately 50-73 degrees C) depositional facies. Conversely, travertine precipitating in the lower-temperature (< approximately 50 degrees C) depositional facies exhibits delta 13C and delta 18O values that are as much as 4% less than predicted equilibrium values. This isotopic shift may record microbial respiration as well as downstream transport of travertine crystals. Despite the production of H2S and the abundance of sulfide oxidizing microbes, preliminary delta 34S data do not uniquely define the microbial metabolic pathways present in the spring system. This suggests that the high extent of CO2 degassing and large open-system solute reservoir in these thermal systems overwhelm biological controls on travertine crystal chemistry.

Calcium Carbonate↗

PubMed1996

Characterization of Bacterial Communities from Activated Sludge: Culture-Dependent Numerical Identification Versus In Situ Identification Using Group- and Genus-Specific rRNA-Targeted Oligonucleotide Probes

The structures of bacterial communities were studied in activated sludge samples obtained from the aerobic and anaerobic zones of a wastewater treatment plant showing enhanced phosphorous removal. Samples were analyzed by in situ hybridization with oligonucleotide probes complementary to selected regions of the 16S and 23S ribosomal RNA (rRNA) characteristic for defined phylogenetic entities (genera and larger groups). The microbial community structures revealed by molecular techniques were compared with the compositions of culturable bacterial communities, obtained from the characterization of 255 isolates from tryptone-soy (TS) agar and R2A agar. These isolates were characterized by 89 physiological tests and their cellular fatty acid patterns, and identified. Culture-dependent techniques indicated the following distribution: different Aeromonas spp. (2.7-8.3% on R2A agar; 45.0-63.7% on TS agar), Acinetobacter spp. (5.4-9.0% on R2A agar; 5.0-9.1% on TS agar), Pseudomonas spp. (up to 10% on R2A agar) and Shewanella putrefaciens (up to 3.0% on R2A agar), all members of the gamma subclass of Proteobacteria, were isolated most frequently. The relatively rare isolates of the beta subclass were identified as Acidovorax spp., Alcaligenes spp., and Comamonas spp.. The Gram-positive bacteria (high DNA G+C) were assigned mainly to Arthrobacter spp., Microbacterium spp., and Mycobacterium phlei. In order to assess the in situ abundance of the most frequently isolated genus, Aeromonas, two rRNA-targeted oligonucleotide probes were developed. The two gamma proteobacterial genera Aeromonas and Acinetobacter constituted less than 5% of all bacteria. In situ, Proteobacteria belonging to the beta subclass and high G+C Gram-positive bacteria were dominant. From filamentous bacteria, Sphaerotilus spp. and Leptothrix spp. could be detected occasionally. In addition, one sample contained a high proportion of the morphologically distinct filaments of Microthrix parvicella.

Journal Article↗

PubMed2002

Recent developments in molecular techniques for identification and monitoring of xenobiotic-degrading bacteria and their catabolic genes in bioremediation.

The pollution of soil and water with xenobiotics is widespread in the environment and is creating major health problems. The utilization of microorganisms to clean up xenobiotics from a polluted environment represents a potential solution to such environmental problems. Recent developments in molecular-biology-based techniques have led to rapid and accurate strategies for monitoring, discovery and identification of novel bacteria and their catabolic genes involved in the degradation of xenobiotics. Application of these techniques to bioremediation has also improved our understanding of the composition, phylogeny, and physiology of metabolically active members of the microbial community in the environment. This review provides an overview of recent developments in molecular-biology-based techniques and their application in bioremediation of xenobiotics.

Bacteria↗