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PubMed1997

Microbial solubilization and immobilization of toxic metals: key biogeochemical processes for treatment of contamination.

Microorganisms play important roles in the environmental fate of toxic metals with a multiplicity of physico-chemical and biological mechanisms effecting transformations between soluble and insoluble phases. Such mechanisms are important components of natural biogeochemical cycles for metals and metalloids with some processes being of potential application to the treatment of contaminated materials. This paper will concentrate on three selected aspects which illustrate the key importance of microorganisms in effecting changes in metal(loid) solubility, namely toxic metal sulfide precipitation by sulfate-reducing bacteria, heterotrophic leaching by fungi, and microbial transformations of metalloids, which includes reduction and methylation. The basic microbiology of these processes is described as well as their environmental significance and use in bioremediation.

Bacteria↗

PubMed2004

Microbiological changes during bioremediation of explosives-contaminated soils in laboratory and pilot-scale bioslurry reactors.

Changes in the microbial community during bioremediation of explosives-contaminated soil in a molasses-fed bioslurry process were examined. Upon addition of molasses to laboratory-scale reactors, total culturable heterotrophs increased rapidly by three to four orders of magnitude. However, heat-shocked heterotrophs and the percentage of gram-positive bacterial isolates did not increase until the soluble concentrations of 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrobenzene (TNB) began to decrease. The number of identified phospholipid fatty acids (PLFA) and the total PLFA concentration also exhibited an immediate increase in response to molasses addition, while the concentration of branched PLFA, indicative of the gram-positive population, remained low until soluble TNT and TNB concentrations had significantly decreased. This same general relationship between explosives degradation and gram-positive-specific PLFA was observed during an experiment with a large field-scale bioslurry lagoon reactor. These results indicate that the gram-positive organisms, which have been shown to be severely impacted by even low concentrations of TNT and TNB [Current Microbiol. 35 (1997) 77; Environ. Toxicol. Chem. 17 (1998) 2185], are able to increase in concentrations after explosives compounds are reduced to non-inhibitory levels, and should therefore be able to reestablish themselves in remediated soils.

Biodegradation, Environmental↗

PubMed1990

Thiosulfate, polythionates and elemental sulfur assimilation and reduction in the bacterial world.

Among sulfur compounds, thiosulfate and polythionates are present at least transiently in many environments. These compounds have a similar chemical structure and their metabolism appears closely related. They are commonly used as energy sources for photoautotrophic or chemolithotrophic microorganisms, but their assimilation has been seldom studied and their importance in bacterial physiology is not well understood. Almost all bacterial strains are able to cleave these compounds since they possess thiosulfate sulfur transferase, thiosulfate reductase or S-sulfocysteine synthase activities. However, the role of these enzymes in the assimilation of thiosulfate or polythionates has not always been clearly established. Elemental sulfur is, on the contrary, very common in the environment. It is an energy source for sulfur-reducing eubacteria and archaebacteria and many sulfur-oxidizing archaebacteria. A phenomenon still not well understood is the 'excessive assimilatory sulfur metabolism' as observed in methanogens which perform a sulfur reduction which exceeds their anabolic needs without any apparent benefit. In heterotrophs, assimilation of elemental sulfur is seldom described and it is uncertain whether this process actually has a physiological significance. Thus, reduction of thiosulfate and elemental sulfur is a common but incompletely understood feature among bacteria. These activities could give bacteria a selective advantage, but further investigations are needed to clarify this possibility. Presence of thiosulfate, polythionates and sulfur reductase activities does not imply obligatorily that these activities play a role in thiosulfate, polythionates or sulfur assimilation as these compounds could be merely intermediates in bacterial metabolism. The possibility also exists that the assimilation of these sulfur compounds is just a side effect of an enzymatic activity with a completely different function. As long as these questions remain unanswered, our understanding of sulfur and thiosulfate metabolism will remain incomplete.

Archaea↗

PubMed2001

Two-step process for ketocarotenoid production by a green alga, Chlorococcum sp. strain MA-1.

The production of ketocarotenoids (KCs) from Chlorococcum sp. strain MA-1 was investigated by a two-step process. In the first step, 18 g biomass l(-1) was achieved by feeding glucose to the heterotrophic cultures; in the second step, the high-density cultures were treated with light illumination or chemical stress in dark, respectively, to induce KC synthesis. Light-treated cultures could produce 103 mg total KCs l(-1) and 32 mg astaxanthin l(-1), three times higher than those from chemical-treated cultures, in the 10 days of induction. The percentages of individual KCs (hydroxyechinenone, canthaxanthin, adonirubin and astaxanthin) in the total KCs were not markedly influenced by the different stress conditions. The developed two-step process provides a feasible strategy for commercial production of ketocarotenoids by the green microalga, Chlorococcum sp. strain MA-1.

Biomass↗

PubMed2004

Patterns of intramolecular carbon isotopic heterogeneity within amino acids of autotrophs and heterotrophs.

A survey of the intramolecular C isotopic composition of a variety of organisms was conducted to investigate the potential of intramolecular isotopic measurements as a tracer of biological or geochemical processes. Based on a consideration of inorganic C sources and enzymatic fractionations, contrasting predictions were made for the relative (13)C enrichments of the alpha-carboxyl carbons fixed by the anapleurotic (beta)-carboxylation pathway during amino acid synthesis by photoautotrophs and heterotrophs. To test the model predictions, the stable C isotopic compositions of the acid hydrolyzable C fraction, the total amino acid alpha-carboxyl C fraction and the alpha-carboxyl C of glutamate from a variety of autotrophic and heterotrophic organisms were compared. The relative (13)C enrichments of carboxyl carbons in the bulk amino acid fraction and in glutamate conformed qualitatively to model predictions. Macroalgal taxa possessed a significantly less enriched carboxyl C fraction than did either C3 or C4 vascular plants, indicating the presence of a different beta-carboxylation pathway operating in these organisms. In most multicellular heterotrophs, the isotopic composition of the amino acid carboxyl carbons closely resembled that of their food sources. Amino acids are apparently assimilated into tissue proteins directly from their diets without significant metabolic modification. However, shifts in the isotopic composition of the carboxyl C fractions in some organisms were detected that were consistent with the occurrence of significant resynthesis of amino acids from non-amino acid precursors. Comparison of plant leaves and roots provided evidence of environmentally controlled assimilate partitioning. Intramolecular isotopic measurements of biological molecules provide unique insights into the origins and transformations of bio-molecules.

Amino Acids↗

PubMed2001

Assessment of denitrification by the ordinary heterotrophic organisms in an NDBEPR activated sludge system.

The purpose of this study was to isolate and characterise the ordinary heterotrophic organisms (OHOs) present in a NDBEPR system in order to gain a better understanding of the organisms involved in denitrification as well as a more holistic and accurate evaluation of the OHO fraction attributable to denitrification in such a system. Heterotrophic bacteria were isolated from the pre- and secondary anoxic zones of the Darvill NDBEPR process and characterised according to their ability to reduce nitrates and/or nitrites under anoxic conditions. Results showed that the OHO fraction is more complex than currently accepted and, with respect to denitrification, can be more accurately subdivided into five functional groups, four of which interactively contribute to denitrification occurring in the system and one group that are non-denitrifying. These groups were defined as true denitrifiers (bacteria capable of both nitrate and nitrite reduction), incomplete denitrifiers (bacteria that reduced nitrates to nitrites with no further reduction of the nitrites produced), incomplete-nitrite reducers (bacteria capable of both nitrate and nitrite reduction, however, exhibiting severe inhibition of nitrite reduction by nitrates), exclusive nitrite reducers (bacteria only capable of reducing nitrites) and non-denitrifiers (bacteria not capable of nitrate or nitrite reduction).

Bacteria↗

PubMed2004

Bioaerosols from the land application of biosolids in the desert southwest USA.

This study evaluated bioaerosol emissions during land application of Class B biosolids in and around Tucson, Arizona, to aid in developing models of the fate and transport of bioaerosols generated from the land application of biosolids. Samples were collected for 20 min at distances between 2 m and 20 m downwind of point sources, using an SKC BioSampler impinger. A total of six samples were collected per sampling event, which consisted of a biosolid spray applicator applying liquid biosolids to a cotton field. Each application represented one exposure. Samples were collected in deionised water amended with peptone and antifoam agent. Ambient weather conditions were also monitored every 10 min following initiation of sampling. Concurrently with downwind samples, background (ambient) air samples were collected to compensate for any ambient airborne microorganisms. In addition, biosolids samples were collected for analysis of target indicator and pathogenic organisms. Soil samples were also collected and analysed. Significant numbers of heterotrophic plate count (HPC) bacteria were found in air samples collected during the biosolid application process. These could have arisen from soil particles being aerosolised during the land application process. Aerosolised soil may contribute significantly to the amount of aerosolised microorganisms. Soil particles may be able to more readily aerosolise, due to their low density, small particle size and low mass. Aerosolised HPC bacteria found during biosolids land application were similar to those found during normal tractor operation on non-biosolids applied fields. Coliforms and coliphages were not routinely detected even though they were found to be present in the biosolids at relatively high concentrations, 10(6) and 10(4)/g (dry weight) of biosolids respectively. This could be due to the die-off rate of aerosolised Gram-negative bacteria or sorption to the solid portion of the biosolids. Low numbers of aerosolised coliphages may likewise be due to sorption phenomena. We theorise that only organisms in the aqueous phase of the biosolids were available to desorb and be aerosolised. Animal viruses, which were not detected in the biosolids, were likewise not detected in the aerosol samples. Clostridium perfringens was detected in only a small percent of aerosol samples although it was detected during all weather conditions; other microorganisms were detected during more favourable environmental conditions (relative humidity >10%). Despite the fact that many of these organisms were present in the biosolids at significant concentrations, their presence in bioaerosols generated during the land application of biosolids was limited to only a small percentage of samples. Bacteria as well as viruses may sorb to biosolids, which contain a high percentage of organic matter, and desorption during land application of biosolids may not readily take place; therefore, these microorganisms may not be readily aerosolised.

Adsorption↗

PubMedDate not supplied

[Department of metabolism regulation. Biochemistry problems].

The publication represents main results of investigations, performed at the Department of Metabolism Regulation in 1950-1995. The problems of protein biosynthesis, fixation and the regulatory role of carboxylic acid in heterotrophic organisms were studied. The role of formic acid in metabolism and changes in metabolic processes at chronic alcoholism were investigated as well. The fundamental results were used as a basis for the solution of practical questions of medicine and animal husbandry.

Academies and Institutes↗

PubMed1977

[Influence of N-serve on mineral nitrogen forms and microorganisms of the soil (author's transl)].

In a model experiment with soil, 2 stages of nitrogen (without additional N and with 200 kg N/ha in the form of ammonia) and 3 N-Serve stages (without inhibitor and with 0.25 per cent and 1 per cent of inhibitor, relative to 200 kg of N/ha) were followed up over a period of 3 and 6 weeks, respectively, with respect to the dynamics of the nitrification process, the saprophytic soil microorganisms, and the autotrophic nitrifiers. In a second experiment, the ammonia form of nitrogen was substituted by the nitrate and nitrite form, respectively. No serious influence on the heterotrophic soil micro-organisms could be detected in any experimental variant; N-Serve was slightly stimulating, the autotrophic nitrifiers were noticeably depressed by N-Serve. The nitrification process could clearly be proved after 3 weeks already; by N-Serve it was remarkably delayed. Nitrite that had been added to the soil was scarcely transformed into nitrate, whereas it was somewhat more ammonified. The high loss of nitrogen in the nitrite variant cannot be caused by denitrification alone. When nitrate was used, the nitrification was not delayed.

Ammonia↗

PubMed1996

The molecular regulation of the reductive pentose phosphate pathway in Proteobacteria and Cyanobacteria.

In phototrophic and chemoautotrophic proteobacteria, genes encoding enzymes of the Calvin-Benson-Bassham pathway of CO2 fixation are often found in clusters that are transcribed from a single promoter under control of the LysR-type transcriptional activator, CbbR. Mutations affecting CbbR prevent induction of cbb genes. Gel-retardation assays have demonstrated CbbR binding to putative regulatory regions of cbb operons, and in two cases, footprinting experiments have delimited the nucleotide sequence protected by CbbR. Fusion of cbb control sequences to reporter genes has allowed the regions required for promoter activity to be defined, and recent experiments indicate that the cbb regulon in Rhodobacter is controlled by a global two-component signal transduction system that also regulates other metabolic processes in this organism. Different ways of regulating CBB cycle enzymes that also have roles in heterotrophic metabolism have recently been discovered. In cyanobacteria, the genes of the CBB pathway are organized and regulated differently, and these oxygen-evolving phototrophic bacteria have evolved different strategies to control the assimilation of CO2.

Bacteria↗

PubMed2002

Metabolism of Alcaligenes denitrificans in biofilm vs planktonic cells.

AIMS: To compare the effect of phosphorous concentration (200 mg P l(-1) and 20 mg P l(-1)) on the denitrifying efficiency of Alcaligenes denitrificans when in the form of planktonic cells or in the form of a biofilm, and to select the most adequate C/N ratio. METHODS AND RESULTS: Two types of assays were carried out: with planktonic cells and with cells in biofilm form. Anoxic bottles with the appropriate C/N and phosphorous concentration were incubated at 30 degrees C and submitted to orbital shaking at 150 rev min(-1). The specific activity of cells in biofilm form, in terms of substrate consumption, was significantly higher than cells in planktonic form. With regard to the effect of increasing phosphorous concentration, an increase in specific activity was also only evident when the cells were in biofilm form. CONCLUSIONS: The two forms showed different performances and phosphorous concentration only markedly affected the biofilm form. SIGNIFICANCE AND IMPACT OF THE STUDY: The importance of the C/N/P ratio in the denitrification process is demonstrated. As there was no report in the literature about the stoichiometric relationship of heterotrophic denitrification with citrate, its stoichiometry, including the requirement for cell synthesis, was determined.

Alcaligenes↗

PubMed2000

The responses of photosynthesis and oxygen consumption to short-term changes in temperature and irradiance in a cyanobacterial mat (Ebro Delta, Spain).

We have evaluated the effects of short-term changes in incident irradiance and temperature on oxygenic photosynthesis and oxygen consumption in a hypersaline cyanobacterial mat from the Ebro Delta, Spain, in which Microcoleus chthonoplastes was the dominant phototrophic organism. The mat was incubated in the laboratory at 15, 20, 25 and 30 degrees C at incident irradiances ranging from 0 to 1,000 micromol photons m(-2) s(-1). Oxygen microsensors were used to measure steady-state oxygen profiles and the rates of gross photosynthesis, which allowed the calculation of areal gross photosynthesis, areal net oxygen production, and oxygen consumption in the aphotic layer of the mat. The lowest surface irradiance that resulted in detectable rates of gross photosynthesis increased with increasing temperature from 50 micromol photons m(-2) s(-1) at 15 degrees C to 500 micromol photons m(-2) s(-1) at 30 degrees C. These threshold irradiances were also apparent from the areal rates of net oxygen production and point to the shift of M. chthonoplastes from anoxygenic to oxygenic photosynthesis and stimulation of sulphide production and oxidation rates at elevated temperatures. The rate of net oxygen production per unit area of mat at maximum irradiance, J0, did not change with temperature, whereas, JZphot, the flux of oxygen across the lower boundary of the euphotic zone increased linearly with temperature. The rate of oxygen consumption per volume of aphotic mat increased with temperature. This increase occurred in darkness, but was strongly enhanced at high irradiances, probably as a consequence of increased rates of photosynthate exudation, stimulating respiratory processes in the mat. The compensation irradiance (Ec) marking the change of the mat from a heterotrophic to an autotrophic community, increased exponentially in this range of temperatures.

Cyanobacteria↗

PubMed1990

Evolution of the first metabolic cycles.

There are two alternatives concerning the origin of life: the origin may be heterotrophic or autotrophic. The central problem within the theory of an autotrophic origin is the first process of carbon fixation. I here propose the hypothesis that this process is an autocatalytic cycle that can be retrodictively constructed from the extant reductive citric acid cycle by replacing thioesters by thioacids and by assuming that the required reducing power is obtained from the oxidative formation of pyrite (FeS2). This archaic cycle is strictly chemoautotrophic: photoautotrophy is not required. The cycle is catalytic for pyrite formation and autocatalytic for its own multiplication. It is a consequence of this hypothesis that the postulated cycle cannot exist as a single isolated cycle but must be a member of a network of concatenated homologous cycles, from which all anabolic pathways appear to have sprung.

Biological Evolution↗

PubMed2002

Minimization of sludge production in biological processes: an alternative solution for the problem of sludge disposal.

A combined system associating activated sludge and ozonation was evaluated for the treatment of urban wastewater. Experiments have shown that 70% reduction in sludge production can be reached (compared to a reference system running in low loaded conditions Y(obs) = 0.28 g VSS.g COD(-1)) by applying an ozone dosage of 0.05 g O3/g VSS(treated) Recycling of the ozonated sludge to the aeration tank induces a slight increase in effluent COD, but the biological treatment performance is maintained. Nitrification capabilities are not altered by the sludge reduction process and active biomass measurements revealed that autotrophic biomass seems to be less affected than the heterotrophs. Significant improvements in sludge settling characteristics are observed.

Cities↗

PubMed2006

Activity of bacteria in water of hot springs from Southern and Central Kamchatskaya geothermal provinces, Kamchatka Peninsula, Russia.

The hot-spring waters of numerous hot springs at the Kamchatka Peninsula, Russia differ in their chemical characteristics and elemental composition. Total bacterial abundance (TBA) as well as enzymatically active and respiring bacteria was enumerated in water samples collected from the Nalychevskie, Oksinskie, Apapelskie, and Dachnye hot springs. 5-Carboxyfluorescein diacetate activity was detected in all water samples and comprised 29-65% of the TBA as determined by 4',6-diamidino-2-phenylindol staining. The respiratory activity of iron-oxidizing bacteria was assayed by 5-cyano-2,3-ditolyltetrazolium chloride reduction. Respiring cells accounted for 9-14% of the TBA, indicating a positive correlation with the number of iron-oxidizing bacteria from the hot-spring biomats. Enumeration of heterotrophic bacteria revealed a high-density bacterial population only in the water of the Apapelskie hot spring, which has a temperature of 36 degrees C. Therefore, it appears that heterotrophic and iron-oxidizing bacteria inhabiting the hot-spring waters are essential for the geochemical processes occurring in hydrothermal systems.

Bacteria↗

PubMed2003

The hexokinase of the hyperthermophile Thermoproteus tenax. ATP-dependent hexokinases and ADP-dependent glucokinases, teo alternatives for glucose phosphorylation in Archaea.

The phosphorylation of glucose by different sugar kinases plays an essential role in Archaea because of the absence of a phosphoenolpyruvate-dependent transferase system characteristic for Bacteria. In the genome of the hyperthermophilic Archaeon Thermoproteus tenax a gene was identified with sequence similarity to glucokinases of the so-called ROK family (repressor protein, open reading frame, sugar kinase). The T. tenax enzyme, like the recently described ATP-dependent "glucokinase" from Aeropyrum pernix, shows the typical broad substrate specificity of hexokinases catalyzing not only phosphorylation of glucose but also of other hexoses such as fructose, mannose, or 2-deoxyglucose, and thus both enzymes represent true hexokinases. The T. tenax hexokinase shows strikingly low if at all any regulatory properties and thus fulfills no important control function at the beginning of the variant of the Embden-Meyerhof-Parnas pathway in T. tenax. Transcript analyses reveal that the hxk gene of T. tenax is cotranscribed with an upstream located orfX, which codes for an 11-kDa protein of unknown function. Growth-dependent studies and promoter analyses suggest that post-transcriptional RNA processing might be involved in the generation of the monocistronic hxk message, which is observed only under heterotrophic growth conditions. Data base searches revealed T. tenax hexokinase homologs in some archaeal, few eukaryal, and many bacterial genomes. Phylogenetic analyses confirm that the archaeal hexokinase is a member of the so-called ROK family, which, however, should be referred to as ROK group because it represents a group within the bacterial glucokinase fructokinase subfamily II of the hexokinase family. Thus, archaeal hexokinases represent a second major group of glucose-phosphorylating enzymes in Archaea beside the recently described archaeal ADP-dependent glucokinases, which were recognized as members of the ribokinase family. The distribution of the two types of sugar kinases, differing in their cosubstrate as well as substrate specificity, within Archaea is discussed on the basis of physiological constraints of the respective organisms.

Adenosine Diphosphate↗

PubMed2006

Selective enrichment and molecular characterization of a previously uncultured Nitrospira-like bacterium from activated sludge.

Previously uncultured nitrite-oxidizing bacteria affiliated to the genus Nitrospira have for the first time been successfully enriched from activated sludge from a municipal wastewater treatment plant. During the enrichment procedure, the abundance of the Nitrospira-like bacteria increased to approximately 86% of the total bacterial population. This high degree of purification was achieved by a novel enrichment protocol, which exploits physiological features of Nitrospira-like bacteria and includes the selective repression of coexisting Nitrobacter cells and heterotrophic contaminants by application of ampicillin in a final concentration of 50 microg ml(-1). The enrichment process was monitored by electron microscopy, fluorescence in situ hybridization (FISH) with rRNA-targeted probes and fatty acid profiling. Phylogenetic analysis of 16S rRNA gene sequences revealed that the enriched bacteria represent a novel Nitrospira species closely related to uncultured Nitrospira-like bacteria previously found in wastewater treatment plants and nitrifying bioreactors. The enriched strain is provisionally classified as 'Candidatus Nitrospira defluvii'.

Ampicillin↗

PubMed1997

Occurrence of gram-negative bacteria in drinking water undergoing softening treatment.

A study was carried out on the presence of Gram-negative bacteria in the municipal waters of Bologna (Italy) undergoing softening using domestic ion exchangers with an automatic disinfection mechanism. The softening process was seen to cause a 15 fold increase in 22 degrees C and 36 degrees C heterotrophic plate counts. There was a 30 fold increase in Gram-negative bacteria and their number correlated directly with temperature and inversely with active residual chlorine. Organic matter had no effect on bacterial growth. The most commonly found bacteria were various species of Pseudomonas (87.6%) (Ps. acidovorans, Ps. denitrificans, Ps. fluorescens and Ps. testosteroni) followed by Aeromonas hydrophila (5.6%) and Stenotrophomonas (Xantomonas) maltophilia (3.8% in outgoing water). Pseudomonas aeruginosa (present in 5.6% of incoming water samples and 0.4% of outgoing water) and Yersinia enterocolitica (present in 4.3% of incoming water samples and 1.1% of outgoing water) did not find favorable conditions for growth on the ion exchange resins.

Gram-Negative Bacteria↗