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PubMed2003

Calorimetric assessment of activity in WWTP biomass.

A heat flux bench-scale calorimeter (Bio-RC1) has been used to assess the metabolic activity of microbial populations involved in wastewater treatment biological processes under aerobic, anoxic and anaerobic conditions. Under strictly aerobic conditions, a linear correlation was observed between oxygen uptake rate and heat flux for heterotrophic and nitrifying bacterial populations. Using the same calorimetric approach and the same apparatus, toxicity and biodegradability of a pesticides factory wastewater were investigated. The activity of heterotrophic and nitrifying aerobic communities was monitored considering both oxygen consumption and heat dissipation, whereas, under anoxic conditions, calorimetric data were compared to the traditional NUR (nitrate uptake rate) test. Heterotrophic activity was found to be 52% inhibited after toxic wastewater exposure under both aerobic and anoxic conditions and 30% inhibition was observed on autotrophic ammonia oxidation. Additionally, calorimetric measurements have been successfully applied to investigate anaerobic digestion. The thermal response of a mesophilic granular sludge to repetitive glucose pulses has been evaluated and a toxicity test has been performed by exposing the biomass to increasing concentrations of formaldehyde.

Ammonia↗
PubMed2002

Nitrifying and heterotrophic population dynamics in biofilm reactors: effects of hydraulic retention time and the presence of organic carbon.

Two biofilm reactors operated with hydraulic retention times of 0.8 and 5.0 h were used to study the links between population dynamics and reactor operation performance during a shift in process operation from pure nitrification to combined nitrification and organic carbon removal. The ammonium and the organic carbon loads were identical for both reactors. The composition and dynamics of the microbial consortia were quantified by fluorescence in situ hybridization (FISH) with rRNA-targeted oligonucleotide probes combined with confocal laser scanning microscopy, and digital image analysis. In contrast to past research, after addition of acetate as organic carbon nitrification performance decreased more drastically in the reactor with longer hydraulic retention time. FISH analysis showed that this effect was caused by the unexpected formation of a heterotrophic microorganism layer on top of the nitrifying biofilm that limited nitrifiers oxygen supply. Our results demonstrate that extension of the hydraulic retention time might be insufficient to improve combined nitrification and organic carbon removal in biofilm reactors.

Acetates↗
PubMed1995

The bifunctional cytochrome c reductase/processing peptidase complex from plant mitochondria.

Cytochrome c reductase from potato has been extensively studied with respect to its catalytic activities, its subunit composition, and the biogenesis of individual subunits. Molecular characterization of all 10 subunits revealed that the high-molecular-weight subunits exhibit striking homologies with the components of the general mitochondrial processing peptidase (MPP) from fungi and mammals. Some of the other subunits show differences in the structure of their targeting signals or in their molecular composition when compared to their counterparts from heterotrophic organisms. The proteolytic activity of MPP was found in the cytochrome c reductase complexes from potato, spinach, and wheat, suggesting that the integration of the protease into this respiratory complex is a general feature of higher plants.

Amino Acid Sequence↗
PubMed2002

Active heterotrophic and autotrophic biomass distribution between fixed and suspended systems in a hybrid biological reactor.

This paper presents the results obtained when modifying sludge retention time (SRT 8, 5, and 3.7 days during phases A, B and C respectively) for a hybrid biological reactor (HR) compared with a classical activated sludge process. The study was conducted by following active biomass evolution and distribution for two lab-scale pilots plants operating with the same conditions, one acting as HR and the other as the control reactor (CR) without support material. At the end of phase C, support material was split into two fractions between both reactors to study the effect of support to reactor volume ratio (Fr). Active biomasses in suspended and fixed systems were calculated using respirometric techniques. Evolutions of active autotrophic and heterotrophic biomasses for both reactors are presented during all the operational periods and it is observed that in the HR biomass concentrations are up to double that in the CR, mainly due to the presence of support material. When studying biomass distribution in HR, autotrophic biomass is mainly located over the support material (from 95% to 99% during periods A and C respectively) while only about 60% of heterotrophic biomass is located over the support.

Bacteria↗
PubMedDate not supplied

[Participation of bdellovibrios in sewage self-purification processes].

The participation of bacterial parasites belonging to the genus Bdellovibrio in the processes of sewage self-purification was studied in refineries of Pushchino. The lytic activity of Bdellovibrio resulting in a decrease of the number of heterotrophic Gram-negative bacteria and E. coli in sewage was found to depend on the temperature factor influencing the intensity of interaction between the parasite and the host bacterium. The maximal p/h (parasite/host) index was found at the water temperature of 26 degrees C and the minimal one at 19 degrees C. Sewage purified at 26 degrees C and transferred to a precipitation tank contained 800 cells of E. coli in 1 ml while that purified at 19 degrees C contained 4000 cells in 1 ml. The number of interacting organisms varied in sewage which was typical of the "parasite-host" relations. Therefore, Bdellovibrio should be involved in the self-purification of sewage from the intestinal microflora at 26 degrees C; to a lesser extent, at 23.5 degrees C; and not at all, at 19 degrees C.

Bdellovibrio↗
PubMed2006

Monitoring biodegradation of diesel fuel in bioventing processes using in situ respiration rate.

An in situ measuring system of respiration rate was applied for monitoring biodegradation of diesel fuel in a bioventing process for bioremediation of diesel contaminated soil. Two laboratory-scale soil columns were packed with 5 kg of soil that was artificially contaminated by diesel fuel as final TPH (total petroleum hydrocarbon) concentration of 8,000 mg/kg soil. Nutrient was added to make a relative concentration of C:N:P = 100:10:1. One soil column was operated with continuous venting mode, and the other one with intermittent (6 h venting/6 h rest) venting mode. On-line O2 and CO2 gas measuring system was applied to measure O2 utilisation and CO2 production during biodegradation of diesel for 5 months. Biodegradation rate of TPH was calculated from respiration rate measured by the on-line gas measuring system. There were no apparent differences between calculated biodegradation rates from two columns with different venting modes. The variation of biodegradation rates corresponded well with trend of the remaining TPH concentrations comparing other biodegradation indicators, such as C17/pristane and C18/phytane ratio, dehydrogenase activity, and the ratio of hydrocarbon utilising bacteria to total heterotrophic bacteria. These results suggested that the on-line measuring system of respiration rate would be applied to monitoring biodegradation rate and to determine the potential applicability of bioventing process for bioremediation of oil contaminated soil.

Aerobiosis↗
PubMed2004

UV disinfection in a model distribution system:; biofilm growth and microbial community.

Two model distribution systems were operated in parallel to investigate the impact of UV disinfection on water distribution system biofilms and microbial community composition. One system received an influent irradiated with UV light, whereas the control received the same influent with no treatment. The biofilm in the UV system, as compared to the control, was more responsive (i.e., had a greater increase in steady-state density of heterotrophic bacteria) to the increased nutrient availability afforded by a decrease in HRT from 12 to 2 h. However, the UV treatment did not have a consistent impact on the biofilm community, indicating the processes controlling HPC density were independent of the specific strains of bacteria forming the biofilm. There was evidence that particle shielding contributed to the survival of UV-susceptible bacteria. This hypothesis was consistent with the presence of UV-susceptible bacteria in the UV system, as well as the high similarity of the biofilm communities in the UV and control systems in one of the experiments. To simulate an intrusion event, opportunistic pathogens were added to each system after the biofilm community reached steady-state. Opportunistic pathogen attachment was not affected by the UV treatment, but was instead correlated to the biofilm density of heterotrophic bacteria.

Bacteria↗
PubMed2005

The Aspergillus nidulans phytochrome FphA represses sexual development in red light.

Phytochrome photoreceptors sense red and far-red light through photointerconversion between two stable conformations, a process mediated by a linear tetrapyrrole chromophore. Originally, phytochromes were thought to be confined to photosynthetic organisms including cyanobacteria, but they have been recently discovered in heterotrophic bacteria and fungi, where little is known about their functions. It was shown previously in the ascomycetous fungus Aspergillus nidulans that asexual sporulation is stimulated and sexual development repressed by red light. The effect was reminiscent of a phytochrome response, and indeed phytochrome-like proteins were detected in several fungal genomes. All fungal homologs are more similar to bacterial than plant phytochromes and have multifunctional domains where the phytochrome region and histidine kinase domain are combined in a single protein with a C-terminal response-regulator domain. Here, we show that the A. nidulans phytochrome FphA binds a biliverdin chromophore, acts as a red-light sensor, and represses sexual development under red-light conditions. FphA-GFP is cytoplasmic and excluded from the nuclei, suggesting that red-light photoperception occurs in the cytoplasm. This is the first phytochrome experimentally characterized outside the plant and bacterial kingdoms and the second type of fungal protein identified that functions in photoperception.

Amino Acid Sequence↗
PubMed1985

Heavy metal toxicity to microbe-mediated ecologic processes: a review and potential application to regulatory policies.

Microorganisms are sensitive to heavy metal pollution as are other components of the biota. However, most studies on the interactions between microbes and heavy metals have been conducted in synthetic media or in altered (e.g., sterilized) environmental samples and usually have used only single species. Few studies have evaluated the effects of heavy metals on the activities of natural heterogeneous microbial populations, both autotrophic and heterotrophic, in terrestrial and aquatic environments. These latter studies have shown that heavy metals inhibit primary productivity, nitrogen fixation, the mineralization of carbon, nitrogen, sulfur, and phosphorus, litter decomposition, and enzyme synthesis and activity in soils, sediments, and surface waters. The potential adverse effects of heavy metals on such microbe-mediated ecologic processes need to be incorporated into the methodologies used by regulatory agencies, such as the U.S. Environmental Protection Agency, to prepare environmental risk assessments which, in turn, are used to formulate environmental criteria, such as the Water Quality Criteria, and to evaluate the safety to the environment of exposure to "new chemical substances," as mandated by the U.S. Toxic Substances Control Act of 1976. To provide appropriate data that can be assimilated into regulatory policy, it is essential that microbial ecotoxicity tests be standardized, are neither costly nor difficult to train personnel to conduct, and produce data that can be quantitated.

Bacteria↗
PubMed2026

Microbial succession and assembly shaped by sulfur, spatial partitioning, and water flow in a volcanic acidic river of northern Patagonia.

Extreme acidic environments represent natural laboratories for investigating the mechanisms of microbial community assembly, yet the ecological processes structuring these communities remain incompletely understood. Here, we investigate how spatial partitioning, hydrodynamics, and colonization history shape microbial succession in a unique sulfur-rich, acidic river of volcanic origin in northern Patagonia. We combined 16S rRNA gene profiling and shotgun metagenomics with a multi-scale experimental framework encompassing water column fractionation and colonization assays under native and controlled conditions. Microbial diversity was strongly influenced by spatial fractionation, with free-living communities exhibiting higher richness and temporal variability than particle-associated assemblages. Water flow modulated community structure, increasing evenness in free-living fractions under high-flow conditions, but had limited impact on particle-attached communities. Colonization of sulfur-beads followed a structured successional trajectory, with autotrophic sulfur oxidizers dominating early stages and heterotrophs adapted to biofilm lifestyles increasing over time. Ex situ recolonization assays revealed strong priority effects, with initial colonizers determining successional trajectories. Turnover analyses revealed that the balance among stochastic and deterministic assembly processes shifted across communities with pronounced stochasticity in the water column and flow-dependent effects in free-living communities, while biofilm associated communities on sulfur-beads exhibited stronger contribution of deterministic selection. These ecological patterns were mirrored by functional differentiation, with gene enrichment analyses revealing adaptive signatures of substrate attachment and resource acquisition. By integrating fine-scale environmental variation with colonization dynamics, this study reveals how microscale habitat structure and temporal fluxes jointly modulate microbial community assembly rules, offering a nuanced framework to dissect ecological processes in extreme systems.

Sulfur↗
PubMed2003

Experimental evidence that terrestrial carbon subsidies increase CO2 flux from lake ecosystems.

Subsidies are donor-controlled inputs of nutrients and energy that can affect ecosystem-level processes in a recipient environment. Lake ecosystems receive large inputs of terrestrial carbon (C) in the form of dissolved organic matter (DOM). DOM inputs may energetically subsidize heterotrophic bacteria and determine whether lakes function as sources or sinks of atmospheric CO(2). I experimentally tested this hypothesis using a series of mesocosm experiments in New England lakes. In the first experiment, I observed that CO(2) flux increased by 160% 4 days following a 1,000 microM C addition in the form of DOM. However, this response was relatively short lived, as there was no effect of DOM enrichment on CO(2) flux beyond 8 days. In a second experiment, I demonstrated that peak CO(2) flux from mesocosms in two lakes increased linearly over a broad DOM gradient (slope for both lakes=0.02+/-0.001 mM CO(2).m(-2) day(-1) per microM DOC, mean+/-SE). Concomitant changes in bacterial productivity and dissolved oxygen strengthen the inference that increasing CO(2) flux resulted from the metabolism of DOM. I conducted two additional studies to test whether DOM-correlated attributes were responsible for the observed change in plankton metabolism along the subsidy gradient. First, terrestrial DOM reduced light transmittance, but experimental shading revealed that this was not responsible for the observed patterns of CO(2) flux. Second, organically bound nitrogen (N) and phosphorus (P) accompanied DOM inputs, but experimental nutrient additions (without organic C) caused mesocosms to be saturated with CO(2). Together, these results suggest that C content of terrestrial DOM may be an important subsidy for freshwater bacteria that can influence whether recipient aquatic ecosystems are sources or sinks of atmospheric CO(2).

Carbon↗
PubMed1985

Isotope effects associated with the anaerobic oxidation of sulfite and thiosulfate by the photosynthetic bacterium, Chromatium vinosum.

The purple photosynthetic bacterium Chromatium vinosum, strain D, catalyzes several oxidations of reduced sulfur compounds under anaerobic conditions in the light: e.g., sulfide --> sulfur --> sulfate, sulfite --> sulfate, and thiosulfate --> sulfur + sulfate. Here it is shown that no sulfur isotope effect is associated with the last of these processes; isotopic compositions of the sulfur and sulfate produced can differ, however, if the sulfane and sulfonate positions within the thiosulfate have different isotopic compositions. In the second process, an observed change from an inverse to a normal isotope effect during oxidation of sulfite may indicate the operation of 2 enzymatic pathways. In contrast to heterotrophic anaerobic reduction of oxidized sulfur compounds, anaerobic oxidations of inorganic sulfur compounds by photosynthetic bacteria are characterized by relatively small isotope effects.

Anaerobiosis↗
PubMed2004

Heterotrophic and mixotrophic growth of Micractinium pusillum Fresenius in the presence of acetate and glucose: effect of light and acetate gradient concentration.

The main objective of this study was to determine the importance of secondary mechanism of organic carbon utilization (mixotrophic and heterotrophic modes) in addition to CO2 fixation (photoautotrophic mode) in the green alga, Micractinium pusillum Fresenius (chlorophyta), isolated from a waste stabilization pond. The growth was studied in the presence of acetate and glucose. The incorporation rate of 14C- acetate was measured in the light and in the dark at different concentrations. Finally, in order to underline the role of photosynthesis and respiration processes in the acetate assimilation, the effect of two specific metabolic inhibitors, a specific inhibitor of photosystem II (DCMU) and an uncoupler respiratory (DNP), has been studied. The obtained results showed that M. pusillum grows in the presence of organic substrates, i.e., glucose and acetate, in the light (mixotrophic growth) as well as in the dark (Heterotrophic growth). The growth was much more important in the light than in the dark and more in the presence of glucose than of acetate. In the light, the presence of acetate led to a variation of growth parameters mumax, iotaopt, and beta. The effect of acetate gradient on the growth of the microalga was severe as soon as its concentration in the medium was higher. The acetate uptake followed a Michaelis-Menten kinetic in the light as well as in the dark. The capacity of assimilation was slightly higher in the dark. The utilization of DNP and DCMU indicates that acetate incorporation is an active process depending on both anabolic (photosynthesis) and catabolic (respiration) metabolisms, corroborating the model of the Michaelis-Menten kinetic.

Acetates↗
PubMedDate not supplied

Particle handling during interception feeding by four species of heterotrophic nanoflagellates.

High resolution video-microscopy was used to observe grazing patterns of the heterotrophic nanoflagellates Cafeteria roenbergensis, Bodo saltans, Spumella sp., and Ochromonas sp. Spumella and Ochromonas enclose food particles with pseudopodia while Cafeteria and Bodo engulf particles by invagination of the cell surface. The following parameters of the feeding process were quantified: frequency of flagellar beating, speed of particles in different positions of the feeding current, food size selection, feeding rate, and the time budget for the handling of particles. The mean handling times differed between 94 s for Cafeteria and 4 s for Ochromonas for ingested particles. Handling times for ingested particles were significantly longer than for non-captured particles. Long handling times were calculated to be disadvantageous only for flagellates which propel a high water volume per hour (esp. Ochromonas) or live in a bacteria-rich environment. Our model calculations may provide a reasonable theoretical explanation for a concentration-dependent behavioural variability of the feeding strategy of different heterotrophic nanoflagellates (HNF) species.

Animals↗
PubMed2002

Chlorination of model drinking water biofilm: implications for growth and organic carbon removal.

The influence of chlorine on biofilm in low organic carbon environments typical of drinking water or industrial process water was examined by comparing biomass and kinetic parameters for biofilm growth in a chlorinated reactor to those in a non-chlorinated control. Mixed-population heterotrophic biofilms were developed in rotating annular reactors under low concentration, carbon-limited conditions (< 2 mg/L as carbon) using three substrate groups (amino acids, carbohydrates and humic substances). Reactors were operated in parallel under identical conditions with the exception that chlorine was added to one reactor at a dose sufficient to maintain a free chlorine residual of 0.09-0.15 mg/L in the effluent. The presence of free chlorine resulted in development of less biofilm biomass compared to the control for all substrates investigated. However, specific growth and organic carbon removal rates were on the average five times greater for chlorinated biofilm compared to the control. Observed yield values were less for chlorinated biofilm. Although chlorinated biofilm's specific organic carbon removal rate was high, the low observed yield indicated organic carbon was being utilized for purposes other than creating new cell biomass. The impacts of free chlorine on mixed-population biofilms in low-nutrient environments were different depending upon the available substrate. Biofilms grown using amino acids exhibited the least difference between control and chlorinated kinetic parameters; biofilm grown using carbohydrates had the greatest differences. These findings are particularly relevant to the fundamental kinetic parameters used in models of biofilm growth in piping systems that distribute chlorinated, low-carbon-concentration water.

Biofilms↗
PubMed2002

Hydrogenotrophic denitrification in a microporous membrane bioreactor.

Hydrogenotrophic denitrification of nitrate contaminated groundwater in a bench-scale microporous membrane bioreactor has been investigated. To prevent microbial contamination of the effluent from the reactor the nitrate-laden water treated was separated from the denitrifying culture with a 0.02 microm pore diameter membrane. Equal pressure was maintained across the membrane and nitrate was removed by molecular diffusion through the membrane and into the denitrifying culture. The system was operated with a hydrogenotrophic denitrification culture to circumvent the addition of an organic substrate to the water. Removal efficiencies ranging from 96% to 92% were achieved at influent concentrations ranging from 20 to 40 mg/L NO3(-)-N. The flux values achieved in this study were 2.7-5.3 g NO3-N m 2d(-1). The microporous membrane served as an effective barrier for preventing microbial contamination of the product water as evidenced by the effluent heterotrophic plate count of 9 (+/- 3.5) CFU/mL. The hydrogenotrophic culture was analyzed using available 16S and 23S rRNA-targeted oligonucleotide probes. It was determined that the enrichment process selected for organisms belonging to the beta subclass of Proteobacteria. Further analysis of the hydrogenotrophic culture indicated that the organisms may belong to the beta-3 subgroup of Proteobacteria and have yet to be identified as hydrogenotrophic denitrifiers.

Bioreactors↗
PubMed2001

Impacts of solar ultraviolet-B radiation on terrestrial ecosystems of Tierra del Fuego (southern Argentina). An overview of recent progress.

The southern part of Tierra del Fuego, in the southernmost tip of South America, is covered by dense Nothofagus spp. forests and Sphagnum-dominated peat bogs, which are subjected to the influence of ozone depletion and to increased levels of solar ultraviolet-B radiation (UV-B). Over the last 5 years we have studied some of the biological impacts of solar UV-B on natural ecosystems of this region. We have addressed two general problems: (i) do the fluctuations in UV-B levels under the influence of the Antarctic ozone 'hole' have any measurable biological impact, and (ii) what are the long-term effects of solar (ambient) UV-B on the Tierra del Fuego ecosystems? In this paper, we provide an overview of the progress made during the first 4 years of the project. We highlight and discuss the following results: (1) ambient UV-B has subtle but significant inhibitory effects on the growth of herbaceous and graminoid species of this region (growth reduction < or = 12%), whereas no consistent inhibitory effects could be detected in woody perennials; (2) in the species investigated in greatest detail, Gunnera magellanica, the inhibitory effect of solar UV-B is accompanied by increased levels of DNA damage in leaf tissue, and the DNA damage density in the early spring is clearly correlated with the dose of weighted UV-B measured at ground level; (3) the herbaceous species investigated thus far show little or no acclimation responses to ambient UV-B such as increased sunscreen levels and DNA repair capacity; and (4) ambient UV-B has significant effects on heterotrophic organisms, included marked inhibitory effects on insect herbivory. The results from the experiments summarized in this review clearly indicate that UV-B influences several potentially important processes and ecological interactions in the terrestrial ecosystems of Tierra del Fuego.

Animals↗
PubMed2001

The role of solar UV radiation in the ecology of alpine lakes.

Solar ultraviolet radiation (UVR, 290-400 nm) is a crucial environmental factor in alpine lakes because of the natural increase of the UVR flux with elevation and the high water transparency of these ecosystems. The ecological importance of UVR, however, has only recently been recognized. This review, examines the general features of alpine lakes regarding UVR, summarizes what is known about the role of solar UVR in the ecology of alpine lakes, and identifies future research directions. Unlike the pattern observed in most lowland lakes, variability of UV attenuation in alpine lakes is poorly explained by differences in dissolved organic carbon (DOC) concentrations, and depends mainly on optical characteristics (absorption) of the chromophoric dissolved organic matter (CDOM). Within the water column of lakes with low DOC concentrations (0.2-0.4 mg l(-1)), UV attenuation is influenced by phytoplankton whose development at depth (i.e. the deep chlorophyll maximum) causes important changes in UV attenuation. Alpine aquatic organisms have developed a number of strategies to minimize UV damage. The widespread synthesis or bioaccumulation of different compounds that directly or indirectly absorb UV energy is one such strategy. Although most benthic and planktonic primary producers and crustacean zooplankton are well adapted to high intensities of solar radiation, heterotrophic protists, bacteria, and viruses seem to be particularly sensitive to UVR. Understanding the overall impact of UVR on alpine lakes would need to consider synergistic and antagonistic processes resulting from the pronounced climatic warming, which have the potential to modify the UV underwater climate and consequently the stress on aquatic organisms.

Altitude↗