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PubMed2006

Biodegradability of activated sludge organics under anaerobic conditions.

From an experimental and theoretical investigation of the continuity of activated sludge organic (COD) compounds along the link between the fully aerobic or N removal activated sludge and anaerobic digestion unit operations, it was found that the unbiodegradable particulate organics (i) originating from the influent wastewater and (ii) generated by the activated sludge endogenous process, as determined from response of the activated sludge system, are also unbiodegradable under anaerobic digestion conditions. This means that the activated sludge biodegradable organics that can be anaerobically digested can be calculated from the active fraction of the waste activated sludge based on the widely accepted ordinary heterotrophic organism (OHO) endogenous respiration/death regeneration rates and unbiodegradable fraction. This research shows that the mass balances based steady state and dynamic simulation activated sludge, aerobic digestion and anaerobic digestion models provide internally consistent and externally compatible elements that can be coupled to produce plant wide steady state and dynamic simulation WWTP models.

Anaerobiosis↗
PubMed2006

Effect of pH, temperature and substrate on N2O, NO and CO2 production by Alcaligenes faecalis p.

AIMS: To study the effect of pH, temperature and substrate on the magnitude of N(2)O and NO production by heterotrophic nitrifiers. METHODS AND RESULTS: The change in N(2)O and NO production by the heterotrophic nitrifiers Alcaligenes faecalis subsp. parafaecalis and Paracoccus pantotrophus because of variations in pH, temperature and substrate was studied in chemostat cultures under steady-state conditions. N(2)O, NO and CO(2) production increased with temperature between 4 and 32 degrees C. For N(2)O an optimum temperature of 28 degrees C was observed. No optimum temperature was found for NO. Highest N(2)O and CO(2) productions were observed at a pH of 7.0. However, besides having an optimum at pH 7.0, especially NO production but also N(2)O production increased significantly at pH <or= 4.0. This increase in NO production under acidic conditions was partly because of chemo-denitrification, which contributed up to 62% of total NO production at pH 3.0 (0.8% for N(2)O). Furthermore, we could demonstrate that substrate quality significantly affects N(2)O, NO and CO(2) production. N(2)O and especially NO production by A. faecalis p. was significantly lower on an ammonium citrate medium when compared with rates obtained for a peptone-meat extract medium. CONCLUSIONS: The results indicate that heterotrophic nitrifiers are suitable model organisms to study the influence of environmental factors on microbial N trace gas production. SIGNIFICANCE IMPACT OF THE STUDY: The results allow an improved description, e.g. of the pH dependency of N trace gas production by microbes and/or chemo-denitrification in process-oriented models describing the exchange of N trace gases between soils and the atmosphere.

Alcaligenes faecalis↗
PubMed2004

Development and evaluation of an online CO(2) evolution test and a multicomponent biodegradation test system.

Well-established biodegradation tests use biogenously evolved carbon dioxide (CO(2)) as an analytical parameter to determine the ultimate biodegradability of substances. A newly developed analytical technique based on the continuous online measurement of conductivity showed its suitability over other techniques. It could be demonstrated that the method met all criteria of established biodegradation tests, gave continuous biodegradation curves, and was more reliable than other tests. In parallel experiments, only small variations in the biodegradation pattern occurred. When comparing the new online CO(2) method with existing CO(2) evolution tests, growth rates and lag periods were similar and only the final degree of biodegradation of aniline was slightly lower. A further test development was the unification and parallel measurement of all three important summary parameters for biodegradation--i.e., CO(2) evolution, determination of the biochemical oxygen demand (BOD), and removal of dissolved organic carbon (DOC)--in a multicomponent biodegradation test system (MCBTS). The practicability of this test method was demonstrated with aniline. This test system had advantages for poorly water-soluble and highly volatile compounds and allowed the determination of the carbon fraction integrated into biomass (heterotrophic yield). The integrated online measurements of CO(2) and BOD systems produced continuous degradation curves, which better met the stringent criteria of ready biodegradability (60% biodegradation in a 10-day window). Furthermore the data could be used to calculate maximal growth rates for the modeling of biodegradation processes.

Aniline Compounds↗
PubMed1989

Characterization of the bacterial population structure in an anaerobic-aerobic activated sludge system on the basis of respiratory quinone profiles.

Bacterial respiratory quinones were used as biomarkers for studying the bacterial population structure, especially the content of Acinetobacter species, in a laboratory-scale anaerobic-aerobic activated sludge system and in the standard aerobic system. All tested sludges contained both ubiquinone and menaquinone, with a molar ratio of about 1:0.5. High-performance liquid chromatography showed that ubiquinone with eight isoprene units (Q-8) was present as the predominant ubiquinone, Q-10 was the second most common type, and Q-9 and other homologs were minor components in the anaerobic-aerobic sludge and the standard aerobic sludge. Bacteriological examination indicated that, in both sludge systems, Q-8-containing bacteria constituted a large proportion of the aerobic heterotrophic bacterial flora, but only a few strains with Q-9 were found. These findings demonstrate that the population of Acinetobacter species, which contain Q-9 as the major quinone, is negligible in those environments. The present results suggest that the introduction of anaerobic conditions into the aerobic batch process has little influence on the bacterial community structure.

Aerobiosis↗
PubMed2005

Effect of plants and filter materials on bacteria removal in pilot-scale constructed wetlands.

Due to the lack of testing units or appropriate experimental approaches, only little is known about the removal of bacteria in constructed wetlands. However, improved performance in terms of water sanitation requires a detailed understanding of the ongoing processes. Therefore, we analyzed the microbial diversity and the survival of Enterobacteriaceae in six pilot-scale constructed wetland systems treating domestic wastewater: two vertical sand filters, two vertical expanded clay filters and two horizontal sand filters (each planted and unplanted). Samples were taken from the in- and outflow, from the rhizosphere, and from the bulk soil at various depths. Colony-forming units of heterotrophic bacteria and coliforms were analyzed and the removal of bacteria between the in- and outflow was determined to within 1.5-2.5 orders of magnitude. To access the taxon-specific biodiversity of potential pathogens in the filters and to reduce the complexity of the analysis, specific primers for Enterobacteriaceae were developed. While performing PCR-SSCP analyses, a pronounced decrease in diversity from the inflow to the outflow of treated wastewater was observed. No differences were observed between the bulk soil of planted and unplanted vertical filters. Some bands appeared in the rhizosphere that were not present in the bulk soil, indicating the development of specific communities stimulated by the plants. The fingerprinting of the rhizosphere of plants grown on sand or expanded clay exhibited many differences, which show that different microbial communities exist depending on the soil type of the filters. The use of the taxon-specific primers enabled us to evaluate the fate of the Enterobacteriaceae entering the wetlands and to localize harboring in the rhizosphere. The most abundant bands of the profiles were sequenced: Pantoea agglomerans was found in nearly all samples from the soil but not in the effluent, whereas Citrobacter sp. could not be removed by the horizontal unplanted sand and vertical planted expanded clay filters. These results show that the community in wetland system is strongly influenced by the filtration process, the filter material and the plants.

Aluminum Silicates↗
PubMed2002

Bacterivory by heterotrophic flagellates: community structure and feeding strategies.

Heterotrophic flagellates (HF) are known as most important grazers of bacteria in many aquatic ecosystem. HF cannot be treated as a black box since HF generally contain a diverse community of species significantly differing in their feeding behaviour and other ecological properties. Today it seems that the dominant taxonomic groups among heterotrophic nano- and microflagellate communities within different marine, brackish and limnetic pelagic communities (heterokont taxa, dinoflagellates, choanoflagellates, kathablepharids) and benthic communities (euglenids, bodonids, thaumatomonads, apusomonads, cercomonads) are relatively similar. HF among protista incertae sedis, often neglected in ecological studies, are abundant bacterivores in all investigated habitats. Recent studies of flagellate feeding processes indicated that there are significant species-specific differences and individual variability regarding the food uptake and food selection of bacterivorous flagellates: Variability of bacterivory is discussed regarding the prevailing feeding modes, the energy budgets, the considerable importance of slight deviations in the time budgets of feeding phases, the ingestion rates and the feeding microhabitat, respectively. The significant flexibility of the grazing impact of bacterivorous flagellate communities creates a complex top-down pressure on bacteria which should have lead to the evolution of efficient predator avoidance mechanisms in bacteria and should be at least partly responsible for the diversity of present bacteria.

Animals↗
PubMedDate not supplied

The use of stoichiometric relations for the description and analysis of microbial cultures.

A general method is described, which enables the derivation of predictive fermentation equations for any microbiological process. The method combines the well-known achievements of the elemental balance approach with microscopic, metabolic balances and biochemical restrictions, using the key intermediates concept. Special attention is paid to the distinction between independent and dependent flow variables of a system. The method is fully illustrated for the very simple example of heterotrophic growth on a single substrate without product formation. Other examples include growth on mixed substrates and the description of catabolic and anabolic product formation.

Adenosine Triphosphate↗
PubMed2004

Bacterial competition in activated sludge: theoretical analysis of varying solids retention times on diversity.

A mechanistic model for activated sludge sewage treatment was developed to predict exploitative competition of six aerobic heterotrophic bacterial species competing for three essential resources. The central hypothesis of the model is that in a multispecies/limiting resource system the number of coexisting bacterial species, N, exceeds the number of limiting resources, K, available for them. The explanation for this is that for certain species combinations, the dynamics of the competition process generate oscillations in the abundances of species, and these oscillations allow the coexistence of greater number of species than the number of limiting resources ( N > K). This result is a direct contradiction of an existing activated sludge steady state competition theory, "the principle of competitive exclusion," which states that the competition process proceeds to equilibrium, allowing only N </= K species to coexist. The model was used to investigate the effect of varying solids retention times on the diversity of species using the conventional, completely mixed activated sludge configuration. The results of model simulations showed that for a certain range of solids retention times (2.28-5.66 days) the competition of six species for three essential resources produces oscillations within the structure of the bacterial community allowing for the sustained growth of more than three species on three resources.

Bacterial Physiological Phenomena↗
PubMed2001

The effects of the flow pattern on organic oxidation and nitrification in aerated submerged biofilters.

Previous research has shown that a submerged biofilter is effective in removing organic matter and total organic nitrogen. Upflow and downflow biofilters were set up to investigate the different oxidative efficiencies on organic matter and ammonia nitrogen of different biofilter positions and to compare the biological activities of the upflow and downflow patterns. A comparison of the operational characteristics of the two types of biofilters is discussed. The main COD removal zone is 0-20 cm in the upflow biofilter, but in the downflow biofilter it occurs in the submerged zone. The nitrification process is dependent on the HRT and the residual COD. In the downflow biofilter, the efficiency of the nitrification increases with the HRT. The growth of nitrifying bacteria has a tendency to take place in higher zones in the downflow biofilter, especially for a longer HRT. Batch tests measured the biological activity of heterotrophs and nitrifying autotrophs with decomposition rates. In the upflow biofilter, the nitrification rates increased while the COD oxidative rates decreased with the height of the biofilter, so the effect of the HRT on the activity of the nitrifying autotrophs is significant. However, in the down biofilter, the activity of the nitrifying autotrophs was similar at different heights in the same HRT runs with the maximum nitrifying autotrophs activity being at an HRT of 6 hours.

Bacteria↗
PubMed2005

Prospects in diatom research.

Diatoms are unicellular photosynthetic eukaryotes that play a major role in the global cycling of carbon and silicon. They are believed to have arisen from a secondary endosymbiotic event between two eukaryotes, a red alga and a flagellated heterotroph. Recent analysis of a diatom genome indeed reveals a 'mosaic' nature, with genes derived from plant, animal and bacterial lineages. Advances in molecular genomics are facilitating the use of diatom-specific genes or pathways for biotechnology. Another interest is in understanding the artistry of the amorphous silica shell and the underlying biomineralization process. Materials scientists and chemists are now exploiting diatoms to develop new biomimetic approaches and to create silicon-based microdevices with specific features.

Biotechnology↗
PubMed2004

Belowground carbon dynamics in loblolly pine (Pinus taeda) immediately following diammonium phosphate fertilization.

Forest soils store an immense quantity of labile carbon (C) and a may be a large potential sink for atmospheric C. Forest management practices such as fertilization may enhance overall C storage in soils, yet changes in physiological processes following nutrient amendments have not been widely investigated. We intensively monitored belowground C dynamics for nearly 200 days following diammonium phosphate fertilization of pot-grown loblolly pine (Pinus taeda L.) seedlings in an effort to examine the short-term effects of fertilization on processes involved in soil C sequestration. Soil respiration rates initially increased in fertilized pots relative to controls, followed by a brief reversal in this trend and then a final sustained pattern of elevated rates of soil respiration in the fertilized treatment. Patterns in soil respiration rates over time reflected changes in autotrophic (root) and heterotrophic (microbial) components of soil respiration. Root respiration rates were greater in the fertilized treatment 49 days following fertilization and returned to control rates by the end of the study. In contrast, microbial respiration rates and microbial activity per soil C concentration remained depressed over the same time period. Compared with control seedlings, total root biomass was 27% greater in fertilized seedlings harvested at the end of the study, indicating that the elevated soil respiration rates observed toward the end of the study were a result of increased respiring root biomass. We conclude that fertilization, at least over the short-term, may increase soil C sequestration by increasing belowground biomass production and reducing microbial driven C turnover.

Biomass↗
PubMed1990

Assessment of the bacteriological activity associated with granular activated carbon treatment of drinking water.

Bacteriological analyses were performed on the effluent from a conventional water treatment pilot plant in which granular activated carbon (GAC) had been used as the final process to assess the impact of GAC on the microbial quality of the water produced. Samples were collected twice weekly for 160 days from the effluents of six GAC columns, each of which used one of four different empty-bed contact times (7.5, 15, 30, and 60 min). The samples were analyzed for heterotrophic plate counts and total coliforms. Effluent samples were also exposed to chloramines and free chlorine for 60 min (pH 8.2, 23 degrees C). Bacterial identifications were performed on the disinfected and nondisinfected effluents. Additional studies were conducted to assess the bacteriological activity associated with released GAC particles. The results indicated that heterotrophic plate counts in the effluents from all columns increased to 10(5) CFU/ml within 5 days and subsequently stabilized at 10(4) CFU/ml. The heterotrophic plate counts did not differ at different empty-bed contact times. Coliforms (identified as Enterobacter spp.) were recovered from the nondisinfected effluent on only two occasions. The disinfection results indicated that 1.5 mg of chloramines per liter inactivated approximately 50% more bacteria than did 1.0 mg of free chlorine per liter after 1 h of contact time. Chloramines and chlorine selected for the development of different bacterial species--Pseudomonas spp. and Flavobacterium spp., respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adsorption↗
PubMed1992

Release of heptapeptide toxin (microcystin) during the decomposition process of Microcystis aeruginosa.

The decomposition process of toxic blue-green alga (cyanobacteria), Microcystis aeruginosa, under dark and aerobic condition was investigated in relation to the change of the amounts of heptapeptide toxins (microcystins YR and LR) by two experiments: one with Microcystis cells and the other with two purified microcystins. In the experiment with Microcystis cells, an increase of heterotrophic bacteria observed from the beginning of the experiment, was followed by decomposition of the algal cells and the subsequent release of microcystins into the filtrate fraction. The amounts of the toxins initially present in the cells were quantitatively detected in the filtrate fraction on the 35th day. The decomposition of microcystin YR began on the 42nd day. The decomposition rate of the two toxins was different. The decomposition rate of purified microcystins YR and LR, compared in distilled water and culture medium, respectively, indicated clearly that microcystin YR was more labile to decomposition than microcystin LR in the culture medium. At the end of the experiment (45th day) microcystin YR decreased to 58.6%, while 86.2% of microcystin LR remained.

Bacterial Toxins↗
PubMed2006

Why are plastid genomes retained in non-photosynthetic organisms?

The evolution of the plastid from a photosynthetic bacterial endosymbiont involved a dramatic reduction in the complexity of the plastid genome, with many genes either discarded or transferred to the nucleus of the eukaryotic host. However, this evolutionary process has not gone to completion and a subset of genes remains in all plastids examined to date. The various hypotheses put forward to explain the retention of the plastid genome have tended to focus on the need for photosynthetic organisms to retain a genetic system in the chloroplast, and they fail to explain why heterotrophic plants and algae, and the apicomplexan parasites all retain a genome in their non-photosynthetic plastids. Here we consider two additional explanations: the 'essential tRNAs' hypothesis and the 'transfer-window' hypothesis.

Animals↗
PubMed2006

Biodegradation of p-nitrophenol by aerobic granules in a sequencing batch reactor.

In this study, aerobic granules to treat wastewater containing p-nitrophenol (PNP) were successfully developed in a sequencing batch reactor (SBR) using activated sludge as inoculum. A key step was the conditioning of the activated sludge seed to enrich for biomass with improved settleability and higher PNP degradation activity by implementing progressive decreases in settling time and stepwise increases in PNP concentration. The aerobic granules were cultivated at a PNP loading rate of 0.6 kg/ m3 x day, with glucose to boost the growth of PNP-degrading biomass. The granules had a clearly defined shape and appearance, settled significantly faster than activated sludge, and were capable of nearly complete PNP removal. The granules had specific PNP degradation rates that increased with PNP concentration from 0 to 40.1 mg of PNP/L, peaked at 19.3 mg of PNP/(g of VSS) x h (VSS = volatile suspended solids), and declined with further increases in PNP concentration as substrate inhibition effects became significant. Batch incubation experiments show that the PNP-degrading granules could also degrade other phenolic compounds, such as hydroquinone, p-nitrocatechol, phenol, 2,4-dichlorophenol, and 2,6-dichlorophenol. The PNP-degrading granules contained diverse microbial morphotypes, and PNP-degrading bacteria accounted for 49% of the total culturable heterotrophic bacteria. Denaturing gradient gel electrophoresis analysis of 16S rRNA gene fragments showed a gradual temporal shift in microbial community succession as the granules developed from the activated sludge seed. Specific oxygen utilization rates at 100 mg/L PNP were found to increase with the evolution of smaller granules to large granules, suggesting that the granulation process can enhance metabolic efficiency toward biodegradation of PNP. The results in this study demonstrate that it is possible to use aerobic granules for PNP biodegradation and broadens the benefits of using the SBR to target treatment of toxic and recalcitrant organic compounds.

Aerobiosis↗
PubMed1967

Biogenesis of chloroplast membranes. I. Plastid dedifferentiation in a dark-grown algal mutant (Chlamydomonas reinhardi).

This paper describes the morphology and photosynthetic activity of a mutant of Chlamydomonas reinhardi (y-1) which is unable to synthesize chlorophyll in the dark. When grown heterotrophically in the light, the mutant is indistinguishable from the wild type Chlamydomonas. When grown in the dark, chlorophyll is diluted through cell division and the photosynthetic activity (oxygen evolution, Hill reaction, and photoreduction of NADP) decays at a rate equal to or faster than that of chlorophyll dilution. However, soluble enzymes associated with the photosynthetic process (alkaline FDPase, NADP-linked G-3-P dehydrogenase, RuDP carboxylase), as well as cytochrome f and ferredoxin, continue to be present in relatively high concentrations. The enzymes involved in the synthesis of the characteristic lipids of the chloroplast (including mono- and digalactoside glycerides, phosphatidyl glycerol, and sulfolipid) are still detectable in dark-grown cells. Such cells accumulate large amounts of starch granules in their plastids. On onset of illumination, dark-grown cells synthesize chlorophyll rapidly, utilizing their starch reserve in the process. At the morphological level, it was observed that during growth in the dark the chloroplast lamellar system is gradually disorganized and drastically decreased in extent, while other subchloroplast components are either unaffected (pyrenoid and its tubular system, matrix) or much less affected (eyespot, ribosomes). It is concluded that the dark-grown mutant possesses a partially differentiated plastid and the enzymic apparatus necessary for the synthesis of the chloroplast membranes (discs). The advantage provided by such a system for the study of the biogenesis of the chloroplast photosynthetic membranes is discussed.

Autoradiography↗
PubMed2000

Microbial ecology of nitrifying bacteria in wastewater treatment process examined by fluorescence in situ hybridization.

The microbial ecology of nitrifying bacteria in various types of wastewater treatment processes and the dynamic response of the microbial ecology in biofilms were investigated using fluorescence in situ hybridization (FISH) with 16S rRNA-targeted oligonucleotide probes. Nitrifying bacteria were found to exhibit various organizational forms under different conditions of substrate composition and concentration. Ammonia-oxidizing bacteria were dominant in ammonia-rich inorganic wastewater, while heterotrophic bacteria and ammonia-oxidizing bacteria were localized at different positions in the biofilm in organic wastewater. The dynamics of the microbial ecology in the biofilm with regard to the spatial distribution of ammonia-oxidizing bacteria and heterotrophic bacteria caused by a gradual change in substrate composition was successfully monitored by FISH analysis.

Journal Article↗
PubMed2005

Sabella spallanzanii filter-feeding on bacterial community: ecological implications and applications.

The filtration process of Sabella spallanzanii Gmelin on bacterial community was studied in a coastal area of the Northern Ionian Sea (Mediterranean Sea) at three sites, S. Vito, Lido Gandoli and Lido Silvana, where some specimens of S. spallanzanii were transplanted. Analyses were performed both on water and worm samples. A total of six microbial groups were examined: culturable heterotrophic bacteria, total culturable bacteria at 37 degrees C, culturable vibrios, total and fecal coliforms and fecal streptococci. The bacterial densities were usually orders of magnitude higher in the worm homogenates than in the corresponding seawater and the highest values were observed in August. The ability of S. spallanzanii to accumulate the microbial pollution indicators suggests this species can be employed as a bioindicator for monitoring water quality. Moreover, the accumulation capability of S. spallanzanii for specific micro-organisms provides a potential role in sewage bioremediation.

Analysis of Variance↗