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PubMed1990

Changes in bacterial populations during red tides caused by Mesodinium rubrum and Gymnodinium catenatum in North West Coast of Spain.

Heterotrophic bacterial communities associated with four red tides caused by Mesodinium rubrum and Gymnodinium catenatum in two Galician Rias (North West Spain) were examined. Three of these were produced by the Mesodinium rubrum and the causative organism of a toxic bloom was Gymnodinium catenatum. In early stages of all the blooms, the diversity decreased but the total marine bacterial counts increased by one or two logs. Vibrio numbers were also incremented by two logs in two blooms of M. rubrum, while in the other bloom of this organism and in the red tide caused by G. catenatum a decrease in number of these bacteria was observed. A total of 116 bacterial strains were identified at the genus level and grouped into 12 phena. During the decomposition processes of two blooms of M. rubrum a zooplanktonic-type bacterial succession was observed (Vibrio, pseudomonads and Moraxella-Acinetobacter). On the other hand, during decomposition of the other red tide of M. rubrum and the bloom of G. catenatum, a typical phytoplanktonic-type succession occurred, as Pseudomonas and Moraxella groups became dominant for all the process. These results support the conflicting taxonomical position of M. rubrum. After the blooms, the changes in the community point towards the restablishment of the normal bacterial flora of the estuary (increase in diversity and decreases of bacterial numbers). Only the Vibrio strains, isolated from the non-toxic first and second red tides, displayed cytotoxic activities. A relationship among bacterial cytotoxicity and toxic effects of blooms cannot therefore be established.

Animals↗
PubMed2004

Solid phase treatment of an aged soil contaminated by polycyclic aromatic hydrocarbons.

Laboratory scale tests were carried out in order to evaluate the removal efficiency of polyaromatic hydrocarbons (PAHs) during the different biological treatments of a Manufacturing Gas Plant site aged soil, heavily contaminated by high molecular weight compounds. Biodegradation studies were carried out at nearly 25 degrees C in solid phase reactors. Three tests were performed, over a period of 100 days for each test. In the first test (P1-bioaugmentated), soil was mixed with wood chips and urea at the start of the treatment and after six weeks from the beginning of the test was also periodically inoculated (at 42, 54, 69, 82, and 96 days) with selected consortia of autochthonous PAH-degrading bacteria. The second test (P2-biostimulated) was performed similarly to the previous one, but without any inoculations. In the third test (P3-control) only soil was introduced. All systems were aerated daily and humidified at the occurrence. PAH concentration, total cultivable heterotrophs, PAH-degrading bacteria, mycetes, pH, ATP concentration, and enzymatic activities were monitored every two weeks during the treatments. Tests showed that nearly 50% of light (three rings) PAHs, 35% of benzo-PAHs and 40% of the total PAHs could be removed in the reactor P2 following 100 days of treatment. Lower removal efficiency could be observed for light PAHs (28%) in the inoculated reactor (P1) at the end of the treatment: comparable abatements were obtained for benzo- and total PAHs. In the reactor P3 (control), the concentration of all polyaromatic hydrocarbons was nearly always constant, suggesting that the physical losses were negligible during the solid phase treatments. Therefore the C to N ratio balance resulted to be the key factor in promoting the biodegradation process of all PAHs.

Biodegradation, Environmental↗
PubMed2001

Simultaneous carbon and nitrogen removal from high strength domestic wastewater in an aerobic RBC biofilm.

High strength domestic wastewater discharges after no/partial treatment through sewage treatment plants or septic tank seepage field systems have resulted in a large build-up of groundwater nitrates in Rajasthan, India. The groundwater table is very deep and nitrate concentrations of 500-750 mg/l (113-169 as NO3(-)-N) are commonly found. A novel biofilm in a 3-stage lab-scale rotating biological contactor (RBC) was developed by the incorporation of a sulphur oxidising bacterium Thiosphaera pantotropha which exhibited high simultaneous removal of carbon and nitrogen in fully aerobic conditions. T. pantotropha has been shown to be capable of simultaneous heterotrophic nitrification and aerobic denitrification thereby helping the steps of carbon oxidation, nitrification and denitrification to be carried out concurrently. The first stage having T. pantotropha dominated biofilm showed high carbon and NH4(+)-N removal rates of 8.7-25.9 g COD/m2 d and 0.81-1.85 g N/m2 d for the corresponding loadings of 10.0-32.0 g COD/m2 d and 1.0-3.35 g N/m2 d. The ratio of carbon removed to nitrogen removed was close to 12.0. The nitrification rate increased from 0.81 to 1.8 g N/m2 d with the increasing nitrogen loading rates despite a high simultaneous organic loading rate. However, it fell to 1.53 g N/m2 d at a high load of 3.35 g N/m2 d and 32 g COD/m2 d showing a possible inhibition of the process. A simultaneous 44-63% removal of nitrogen was also achieved without any significant NO2(-)-N or NO3(-)-N build-up. The second and third stages, almost devoid of any organic carbon, acted only as autotrophic nitrification units, converting the NH4(+)-N from stage 1 to nitrite and nitrate. Such a system would not need a separate carbon oxidation step to increase nitrification rates and no external carbon source for denitrification. The alkalinity compensation during denitrification for that destroyed in nitrification may also result in a high economy.

Biofilms↗
PubMed1987

Nickel uptake in Bradyrhizobium japonicum.

Free-living Bradyrhizobium japonicum grown heterotrophically with 1 microM 63Ni2+ accumulated label. Strain SR470, a Hupc mutant, accumulated almost 10-fold more 63Ni2+ on a per-cell basis than did strain SR, the wild type. Nongrowing cells were also able to accumulate nickel over a 2-h period, with the Hupc mutant strain SR470 again accumulating significantly more 63Ni2+ than strain SR. These results suggest that this mutant is constitutive for nickel uptake as well as for hydrogenase expression. The apparent Kms for nickel uptake in strain SR and strain SR470 were found to be similar, approximately 26 and 50 microM, respectively. The Vmax values, however, were significantly different, 0.29 nmol of Ni/min per 10(8) cells for SR and 1.40 nmol of Ni/min per 10(8) cells for SR470. The uptake process was relatively specific for nickel; only Cu2+ and Zn2+ (10 microM) were found to appreciably inhibit the uptake of 1 microM Ni, while a 10-fold excess of Mg2+, Co2+, Fe3+, or Mn2+ did not affect Ni2+ uptake. The lack of inhibition by Mg2+ indicates that nickel is not transported by a magnesium uptake system. Nickel uptake was also inhibited by cold (53% inhibition at 4 degrees C) and slightly by the ionophores nigericin and carbonyl cyanide m-chlorophenylhydrazone. Other ionophores did not appreciably affect nickel uptake, even though they significantly stimulated O2 uptake. The cytochrome c oxidase inhibitors azide, cyanide, and hydroxylamine did not inhibit Ni2+ uptake, even at concentrations (of cyanide and hydroxylamine) that inhibited O2 uptake. The addition of oxidizable substrates such as succinate or gluconate did not increase nickel uptake, even though they increased respiratory activity. Nickel update showed a pH dependence with an optimum at 6.0. Most (approximately 85%) of the 63Ni2+ taken up in 1 min by strain SR470 was not exchangeable with cold nickel.

Biological Transport↗
PubMed2000

Carbon and nitrogen fluxes in a closed seawater facility.

A variety of empirical and calculated data from the largest tank at the New Jersey State Aquarium were used to quantify the fluxes of carbon and nitrogen before and after the installation of denitrification in this facility. Before denitrification, the stock of dissolved inorganic carbon (DIC) in Ocean Tank exhibited a decrease of 6.9 kg C/month and sodium bicarbonate had to be added to maintain DIC in steady state. We were able to explain the DIC decrease by two non-conservative processes: the formation of carbonaceous precipitates (removes 4.2 kg C/month) and outgassing of carbon dioxide due to acidity from nitrification (independently determined to remove 3.2 kg C/month). Nitrogen budget in Ocean Tank before denitrification is in contrast to that of carbon, and it shows an increase of 4.8 kg N/month in the form of nitrate. Denitrification is currently removing 53.3 kg N/month (in the form of nitrogen gas), so this element should eventually reach steady state. The use of methanol for denitrification has resulted in a flux of 26.3 kg C/month into the aquarium and, as predicted, an increase in Ocean Tank DIC stock has been observed without any additions of sodium bicarbonate. Our approach can be used to model carbon and nitrogen balances in closed seawater facilities that host heterotrophic organisms and operate either with or without a biological denitrification system.

Carbon↗
PubMed2001

Biogenic carbon cycling in the upper ocean: effects of microbial respiration.

Food-web processes are important controls of oceanic biogenic carbon flux and ocean-atmosphere carbon dioxide exchange. Two key controlling parameters are the growth efficiencies of the principal trophic components and the rate of carbon remineralization. We report that bacterial growth efficiency is an inverse function of temperature. This relationship permits bacterial respiration in the euphotic zone to be computed from temperature and bacterial production. Using the temperature-growth efficiency relationship, we show that bacterial respiration generally accounts for most community respiration. This implies that a larger fraction of assimilated carbon is respired at low than at high latitudes, so a greater proportion of production can be exported in polar than in tropical regions. Because bacterial production is also a function of temperature, it should be possible to compute euphotic zone heterotrophic respiration at large scales using remotely sensed information.

Atmosphere↗
PubMed2026

Influence of microplastics on microalgal performance during wastewater polishing.

Microplastics (MPs) are emerging contaminants that are increasingly accumulating in aquatic ecosystems due to excessive anthropogenic activity and insufficient mitigation strategies, posing serious environmental and public health risks. Their impact on wastewater (WW) treatment processes remains poorly understood. This study evaluated the effects of five MPs commonly found in WW - polypropylene, polystyrene, polyamide, low-density polyethylene, and high-density polyethylene - on the physiology and bioremediation performance of the microalga Chlorella vulgaris in synthetic WW (SWW). Metabolic responses were assessed via esterase activity and intracellular reactive oxygen species (ROS), while nitrogen (N), phosphorus (P), and glucose removal were monitored to evaluate bioremediation efficiency. MPs inhibited esterase activity and elevated ROS levels, indicating oxidative stress. Nevertheless, C. vulgaris maintained a high bioremediation capacity (> 75 % N, > 60 % P, and > 70 % for glucose). Environmental conditions modulated microalga response to MPs exposure. Under N-limited conditions, C. vulgaris exhibited enhanced nutrient uptake and biomass production, but a 12 h/12 h light/dark photoperiod reduced N removal but stimulated glucose consumption via heterotrophic metabolism. In contrast, C-limited conditions exacerbated oxidative stress and compromised nutrient removal, resulting in residual concentrations exceeding legal limits. These findings highlight that environmental factors can either mitigate or exacerbate the physiological stress induced by MPs, ultimately affecting WW polishing. This work provides a comprehensive insight into the cellular and metabolic effects of MPs on microalgae and supports C. vulgaris as a resilient and sustainable approach for nutrient and carbon removal in MP-contaminated WW systems.

Microalgae↗
PubMed2004

Isolation and characterization of arsenate-reducing bacteria from arsenic-contaminated sites in New Zealand.

Two environmental sites in New Zealand were sampled (e.g., water and sediment) for bacterial isolates that could use either arsenite as an electron donor or arsenate as an electron acceptor under aerobic and anaerobic growth conditions, respectively. These two sites were subjected to widespread arsenic contamination from mine tailings generated from historic gold mining activities or from geothermal effluent. No bacteria were isolated from these sites that could utilize arsenite or arsenate under the respective growth conditions tested, but a number of chemoheterotrophic bacteria were isolated that could grow in the presence of high concentrations of arsenic species. In total, 17 morphologically distinct arsenic-resistant heterotrophic bacteria isolates were enriched from the sediment samples, and analysis of the 16S rRNA gene sequence of these bacteria revealed them to be members of the genera Exiguobacterium, Aeromonas, Bacillus, Pseudomonas, Escherichia, and Acinetobacter. Two isolates, Exiguobacterium sp. WK6 and Aeromonas sp. CA1, were of particular interest because they appeared to gain metabolic energy from arsenate under aerobic growth conditions, as demonstrated by an increase in cellular growth yield and growth rate in the presence of arsenate. Both bacteria were capable of reducing arsenate to arsenite via a non-respiratory mechanism. Strain WK6 was positive for arsB, but the pathway of arsenate reduction for isolate CA1 was via a hitherto unknown mechanism. These isolates were not gaining an energetic advantage from arsenate or arsenite utilization, but were instead detoxifying arsenate to arsenite. As a subsidiary process to arsenate reduction, the external pH of the growth medium increased (i.e., became more alkaline), allowing these bacteria to grow for extended periods of time.

Acinetobacter↗
PubMed1997

Stable-Isotope Analysis of a Combined Nitrification-Denitrification Sustained by Thermophilic Methanotrophs under Low-Oxygen Conditions.

To simulate growth conditions experienced by microbiota at O(inf2)-limited interfaces of organic matter in compost, an experimental system capable of maintaining dual limitations of oxygen and carbon for extended periods, i.e., a pO(inf2)-auxostat, has been used. (sup15)N tracer studies on thermophilic (53(deg)C) decomposition processes occurring in manure-straw aggregates showed the emission of dinitrogen gas from the reactor as a result of simultaneous nitrification and denitrification at low pO(inf2) values (0.1 to 2.0%, vol/vol). The N loss was confirmed by nitrogen budget studies of the system. Depending on the imposed pO(inf2), 0.6 to 1.4 mmol of N/day (i.e., 20 to 40% of input N) was emitted as N(inf2). When the pO(inf2) was raised, the rates of both nitrification and denitrification increased instantaneously, indicating that ammonia oxidation was limited by oxygen. In auxostats permanently running at pO(inf2) >= 2% (vol/vol), the free ammonium pool was almost completely oxidized and was converted to nitrite plus nitrate and N(inf2) gas. Labelling of the auxostat with [(sup13)C]carbonate was conducted to reveal whether nitrification was of autotrophic or heterotrophic origin. Incorporation of (sup13)CO(inf2) into population-specific cellular compounds was evaluated by profiling the saponifiable phospholipid fatty acids (FAs) by using capillary gas chromatography and subsequently analyzing the (sup13)C/(sup12)C ratios of the individual FAs, after their combustion to CO(inf2), by isotope ratio mass spectrometry. Apart from the observed label incorporation into FAs originating from a microflora belonging to the genus Methylococcus (type X group), supporting nitrification of a methylotrophic nature, this analysis also corroborated the absence of truly autotrophic nitrifying populations. Nevertheless, the extent to which ammonia oxidation continued to exist in this thermophilic community suggested that a major energy gain could be associated with it.

Journal Article↗
PubMed2006

Comparative genomic evidence for a close relationship between the dimorphic prosthecate bacteria Hyphomonas neptunium and Caulobacter crescentus.

The dimorphic prosthecate bacteria (DPB) are alpha-proteobacteria that reproduce in an asymmetric manner rather than by binary fission and are of interest as simple models of development. Prior to this work, the only member of this group for which genome sequence was available was the model freshwater organism Caulobacter crescentus. Here we describe the genome sequence of Hyphomonas neptunium, a marine member of the DPB that differs from C. crescentus in that H. neptunium uses its stalk as a reproductive structure. Genome analysis indicates that this organism shares more genes with C. crescentus than it does with Silicibacter pomeroyi (a closer relative according to 16S rRNA phylogeny), that it relies upon a heterotrophic strategy utilizing a wide range of substrates, that its cell cycle is likely to be regulated in a similar manner to that of C. crescentus, and that the outer membrane complements of H. neptunium and C. crescentus are remarkably similar. H. neptunium swarmer cells are highly motile via a single polar flagellum. With the exception of cheY and cheR, genes required for chemotaxis were absent in the H. neptunium genome. Consistent with this observation, H. neptunium swarmer cells did not respond to any chemotactic stimuli that were tested, which suggests that H. neptunium motility is a random dispersal mechanism for swarmer cells rather than a stimulus-controlled navigation system for locating specific environments. In addition to providing insights into bacterial development, the H. neptunium genome will provide an important resource for the study of other interesting biological processes including chromosome segregation, polar growth, and cell aging.

Alphaproteobacteria↗
PubMed2005

Feasibility study of bioremediation of a drilling-waste-polluted soil: stimulation of microbial activities and hydrocarbon removal.

The objective of this study was to determine the feasibility of bioremediation as a treatment option for an aged and chronically polluted drilling waste soil located at the Southeast of Mexico. The polluted drilling-waste site with a mean total petroleum hydrocarbon concentration (TPHs) of 39,397 +/- 858 mg/kg was treated with one dose of a nutrient-surfactant commercial product at 40 mg/kg soil and two doses of H2O2 (50 and 100 mg H2O2/kg soil). In this study, the parameters that were monitored include soil respiration, heterotrophic and hydrocarbon-degrading bacteria as biological indicators, catalase and dehydrogenase activities, and TPHs degradation as decontamination parameters. The results demonstrated that the microbial activities can be stimulated in a polluted drilling-waste site by the addition of H2O2 and commercial product, thereby resulting in increasing TPHs degradation. These aspects must be taken into account when biodegradation studies involve the application of a commercial product.

Analysis of Variance↗
PubMed2001

Toxic effects of linear alkylbenzene sulfonate on metabolic activity, growth rate, and microcolony formation of Nitrosomonas and Nitrosospira strains.

Strong inhibitory effects of the anionic surfactant linear alkylbenzene sulfonate (LAS) on four strains of autotrophic ammonia-oxidizing bacteria (AOB) are reported. Two Nitrosospira strains were considerably more sensitive to LAS than two Nitrosomonas strains were. Interestingly, the two Nitrosospira strains showed a weak capacity to remove LAS from the medium. This could not be attributed to adsorption or any other known physical or chemical process, suggesting that biodegradation of LAS took place. In each strain, the metabolic activity (50% effective concentration [EC(50)], 6 to 38 mg liter(-1)) was affected much less by LAS than the growth rate and viability (EC(50), 3 to 14 mg liter(-1)) were. However, at LAS levels that inhibited growth, metabolic activity took place only for 1 to 5 days, after which metabolic activity also ceased. The potential for adaptation to LAS exposure was investigated with Nitrosomonas europaea grown at a sublethal LAS level (10 mg liter(-1)); compared to control cells, preexposed cells showed severely affected cell functions (cessation of growth, loss of viability, and reduced NH(4)(+) oxidation activity), demonstrating that long-term incubation at sublethal LAS levels was also detrimental. Our data strongly suggest that AOB are more sensitive to LAS than most heterotrophic bacteria are, and we hypothesize that thermodynamic constraints make AOB more susceptible to surfactant-induced stress than heterotrophic bacteria are. We further suggest that AOB may comprise a sensitive indicator group which can be used to determine the impact of LAS on microbial communities.

Alkanesulfonic Acids↗
PubMed2002

The effect of drinking water treatment on the spatial heterogeneity of micro-organisms: implications for assessment of treatment efficiency and health risk.

The effect of drinking water treatment (ferric coagulation, floc blanket clarification, rapid sand filtration) on the spatial heterogeneity of five species of micro-organism was studied at pilot scale. It was found that the spatial heterogeneity of vegetative bacteria (namely total coliform and heterotrophic (22 degrees C; 3 d) bacteria) was little affected by treatment. Indeed, counts of total coliform bacteria within 500 l volumes of treated water were Poisson distributed (i.e. showed minimum variation). In contrast, treatment appeared to increase the spatial heterogeneity (or clustering) of both aerobic spores indigenous to the raw water and Bacillus subtilis var niger spores added to the raw water. Furthermore, B. subtilis var niger spores added to the raw water were detected in the treated water 25 h after termination of spiking to the raw water. The effect on C. parvum oocysts added to the raw water could not be determined because few oocysts broke through treatment into the treated water. Indeed oocyst removals of 5-6 logs were apparent. "Species-specific" differences in the removal ratios were also demonstrated. It is concluded that audits for treatment processes based on single 100 ml "spot" samples for spores will tend to over-estimate the net spore removal and hence underestimate the public health risk. Spatial heterogeneity of counts in treated water contributes to explaining why no "ideal" surrogate has been identified for treatment plant performance.

Animals↗
PubMed2002

A cyanobacterial gene in nonphotosynthetic protists--an early chloroplast acquisition in eukaryotes?

Since the incorporation of mitochondria and chloroplasts (plastids) into the eukaryotic cell by endosymbiosis, genes have been transferred from the organellar genomes to the nucleus of the host, via an ongoing process known as endosymbiotic gene transfer. Accordingly, in photosynthetic eukaryotes, nuclear genes with cyanobacterial affinity are believed to have originated from endosymbiotic gene transfer from chloroplasts. Analysis of the Arabidopsis thaliana genome has shown that a significant fraction (2%-9%) of the nuclear genes have such an endosymbiotic origin. Recently, it was argued that 6-phosphogluconate dehydrogenase (gnd)-the second enzyme in the oxidative pentose phosphate pathway-was one such example. Here we show that gnd genes with cyanobacterial affinity also are present in several nonphotosynthetic protistan lineages, such as Heterolobosea, Apicomplexa, and parasitic Heterokonta. Current data cannot definitively resolve whether these groups acquired the gnd gene by primary and/or secondary endosymbiosis or via an independent lateral gene transfer event. Nevertheless, our data suggest that chloroplasts were introduced into eukaryotes much earlier than previously thought and that several major groups of heterotrophic eukaryotes have secondarily lost photosynthetic plastids.

Arabidopsis↗
PubMed2005

Controversies on the origin of life.

Different viewpoints, many with deep philosophical and historical roots, have shaped the scientific study of the origin of life. Some of these argue that primeval life was based on simple anaerobic microorganisms able to use a wide inventory of abiotic organic materials (i.e. a heterotrophic origin), whereas others invoke a more sophisticated organization, one that thrived on simple inorganic molecules (i.e. an autotrophic origin). While many scientists assume that life started as a self-replicative molecule, the first gene, a primitive self-catalytic metabolic network has also been proposed as a starting point. Even the emergence of the cell itself is a contentious issue: did boundaries and compartments appear early or late during life's origin? Starting with a recent definition of life, based on concepts of autonomy and open-ended evolution, it is proposed here that, firstly, organic molecules self-organized in a primordial metabolism located inside protocells. The flow of matter and energy across those early molecular systems allowed the generation of more ordered states, forming the cradle of the first genetic records. Thus, the origin of life was a process initiated within ecologically interconnected autonomous compartments that evolved into cells with hereditary and true Darwinian evolutionary capabilities. In other words, the individual existence of life preceded its historical-collective dimension.

Biological Evolution↗
PubMed2006

Microbial community succession in an unvegetated, recently deglaciated soil.

Primary succession is a fundamental process in macroecosystems; however, if and how soil development influences microbial community structure is poorly understood. Thus, we investigated changes in the bacterial community along a chronosequence of three unvegetated, early successional soils ( approximately 20-year age gradient) from a receding glacier in southeastern Peru using molecular phylogenetic techniques. We found that evenness, phylogenetic diversity, and the number of phylotypes were lowest in the youngest soils, increased in the intermediate aged soils, and plateaued in the oldest soils. This increase in diversity was commensurate with an increase in the number of sequences related to common soil bacteria in the older soils, including members of the divisions Acidobacteria, Bacteroidetes, and Verrucomicrobia. Sequences related to the Comamonadaceae clade of the Betaproteobacteria were dominant in the youngest soil, decreased in abundance in the intermediate age soil, and were not detected in the oldest soil. These sequences are closely related to culturable heterotrophs from rock and ice environments, suggesting that they originated from organisms living within or below the glacier. Sequences related to a variety of nitrogen (N)-fixing clades within the Cyanobacteria were abundant along the chronosequence, comprising 6-40% of phylotypes along the age gradient. Although there was no obvious change in the overall abundance of cyanobacterial sequences along the chronosequence, there was a dramatic shift in the abundance of specific cyanobacterial phylotypes, with the intermediate aged soils containing the greatest diversity of these sequences. Most soil biogeochemical characteristics showed little change along this approximately 20-year soil age gradient; however, soil N pools significantly increased with soil age, perhaps as a result of the activity of the N-fixing Cyanobacteria. Our results suggest that, like macrobial communities, soil microbial communities are structured by substrate age, and that they, too, undergo predictable changes through time.

Bacteria↗
PubMed1998

Microbiology of a nitrite-oxidizing bioreactor.

The microbiology of the biomass from a nitrite-oxidizing sequencing batch reactor (NOSBR) fed with an inorganic salts solution and nitrite as the sole energy source that had been operating for 6 months was investigated by microscopy, by culture-dependent methods, and by molecular biological methods, and the seed sludge that was used to inoculate the NOSBR was investigated by molecular biological methods. The NOSBR sludge comprised a complex and diverse microbial community containing gram-negative and gram-positive rods, cocci, and filaments. By culture-dependent methods (i.e., micromanipulation and sample dilution and spread plate inoculation), 16 heterotrophs (6 gram positive and 10 gram negative) were identified in the NOSBR sludge (RC), but no autotrophs were isolated. 16S ribosomal DNA clone libraries of the two microbial communities revealed that the seed sludge (GC) comprised a complex microbial community dominated by Proteobacteria (29% beta subclass; 18% gamma subclass) and high G + C gram-positive bacteria (10%). Three clones (4%) were closely related to the autotrophic nitrite-oxidizer Nitrospira moscoviensis. The NOSBR sludge was overwhelmingly dominated by bacteria closely related to N. moscoviensis (89%). Two clone sequences were similar to those of the genus Nitrobacter. Near-complete insert sequences of eight RC and one GC N. moscoviensis clone were determined and phylogenetically analyzed. This is the first report of the presence of bacteria from the Nitrospira phylum in wastewater treatment systems, and it is hypothesized that these bacteria are the unknown nitrite oxidizers in these processes.

Bacteria↗
PubMedDate not supplied

Confusing selective feeding with differential digestion in bacterivorous nanoflagellates.

Food selectivity and the mechanisms of food selection were analyzed by video microscopy for three species (Spumella, Ochromonas, Cafeteria) of interception-feeding heterotrophic nanoflagellates. The fate of individual prey particles, either live bacteria and/or inert particles, was recorded during the different stages of the particle-flagellate-interaction, which included capture, ingestion, digestion, and egestion. The experiments revealed species-specific differences and new insights into the underlying mechanisms of particle selection by bacterivorous flagellates. When beads and bacteria were offered simultaneously, both particles were ingested unselectively at similar rates. However, the chrysomonads Spumella and Ochromonas egested the inert beads after a vacuole passage time of only 2-3 min, which resulted in an increasing proportion of bacteria in the food vacuoles. Vacuole passage time for starved flagellates was significantly longer compared to that of exponential-phase flagellates for Spumella and Ochromonas. The bicosoecid Cafeteria stored all ingested particles, beads as well as bacteria, in food vacuoles for more then 30 min. Therefore "selective digestion" is one main mechanism responsible for differential processing of prey particles. This selection mechanism may explain some discrepancies of former experiments using inert particles as bacterial surrogates for measuring bacterivory.

Animals↗