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PubMed1991

Effect of the herbicide Bentanex on soil microorganisms and their activity.

The effect of the herbicide Bentanex, especially of its effective component bentazone, on selected soil bacteria and fungi, on their growth and reproduction and on some important physiological activities ensuring a regular nutrient cycle in nature was investigated. Bentazone affected growth and reproduction of soil bacteria and micromycetes in dependence on the concentration and species of the microorganism. Physiological and biochemical activities of bacteria with respect to nitrogen fixation, nitrification and CO2 production were negatively influenced by high concentrations of the herbicide. These concentrations were used to observe the effect on selected activities of soil microorganisms and were much higher than those actually used in agriculture.

Bacteria↗
PubMed1991

Effect of the fungicides tridemorph and vinclozolin on soil microorganisms and nitrogen metabolism.

The effects of tridemorph and vinclozolin were studied on different types of microorganisms, urea hydrolysis and nitrification in soil and in culture. The fungicides adversely affected the population of bacteria, fungi and actinomycetes as a function of time of incubation. Urea hydrolysis both in culture and soil were also inhibited by the fungicides, and tridemorph was more detrimental. In soil, 45 micrograms/g of tridemorph inhibited 50% of ammonification of urea, ID50 for nitrite production was 750 micrograms/g. In urea-hydrolyzing cultures, 80, 75 and 77 mg/L of tridemorph were the ID50 values for urea hydrolysis by Micrococcus sp., Proteus sp. and P. vulgaris respectively.

Actinomycetales↗
PubMed2005

Effects of slow-release urea fertilizers on urease activity, microbial biomass, and nematode communities in an aquic brown soil.

A field experiment was carried out at the Shenyang Experimental Station of Ecology (CAS) in order to study the effects of slow-release urea fertilizers high polymer-coated urea (SRU1), SRU1 mixed with dicyandiamide DCD (SRU2), and SRU1 mixed with calcium carbide CaC2 (SRU3) on urease activity, microbial biomass C and N, and nematode communities in an aquic brown soil during the maize growth period. The results demonstrated that the application of slow-release urea fertilizers inhibits soil urease activity and increases the soil NH4+-N content. Soil available N increment could promote its immobilization by microorganisms. Determination of soil microbial biomass N indicated that a combined application of coated urea and nitrification inhibitors increased the soil active N pool. The population of predators/omnivores indicated that treatment with SRU2 could provide enough soil NH4+-N to promote maize growth and increased the food resource for the soil fauna compared with the other treatments.

Acetylene↗
PubMed1981

Effect of some sulphur compounds on soil microflora of spruce rhizosphere.

The effect of a long-term application of sulphite, thiosulphate and sodium sulphate on the soil microflora and spruce seedlings was investigated in a pot experiment. Sulphur compounds decreased the concentration of bacteria, including thiobacilli, increased the concentration of microscopic fungi and sulphate-reducing bacteria; they inhibited respiration, nitrification and oxidation of thiosulphate, stimulated ammonification and oxidation of elemental sulphur. In certain cases the spruce rhizosphere exhibited just the opposite effect. In the rhizosphere the sulphate-reducing bacteria was suppressed together with thiobacilli, whose unit oxidative activity increased substantially. Growth of seedlings was inhibited by sulphite and stimulated by thiosulphate and sulphate. Sulphite, the effects of which were similar to those of sulphur dioxide immissions, was the most effective compound. In regions influenced by immissions the soil is apparently intoxicated by the absorbed sulphite.

Bacteria↗
PubMed2002

Nitrate dynamics in an Alpine forest site (Mühleggerköpfl). O and N stable isotope analysis in natural water samples.

Stable isotope analysis of 15N/14N and 18O/16O-nitrate was used to investigate the nitrate dynamics and potential groundwater pollution in an Alpine forest stand in Tyrol/Austria. The dynamics of delta15-N(nitrate) values were followed in a forest ecosystem. The stable isotopic values of the throughfall are comparable with other studies. The completely decoupled dynamics of the delta15-N(nitrate) of the precipitation and the surface water was observed. High variations in delta15N-nitrate values in rainfall indicate that nitrate of different sources is deposited at that site. A significant correlation between the delta15N(nitrate) values of the surface water and soil water was obtained, while no significant correlation between the delta15N(nitrate) values of any precipitation sample with the surface water could be found. This suggests that the main source of nitrate in soil water originates from microbiological activity such as nitrification reactions and less from nitrate input by deposition. The results of delta18O(nitrate) measurements strongly supported the microbiological origin of nitrate in the surface and soil water In an additional lysimeter experiment, 15N-labelled nitrate was applied to study nitrate transport in soil. After 130 days and the collection of 300 L leachate, a total of 52% of the applied nitrate was detected in seepage water.

Environmental Monitoring↗
PubMed2000

Intramolecular stable isotope ratios of N2O in the tropical swamp forest in Thailand.

The dry-wet cycle is a common climatic phenomenon in the tropical regions of monsoon-affected Asia. An intermittent increase in N2O was clearly observed in the Bang Nara River, with a tropical swamp catchment at the beginning of rainy season of November 1997. The intramolecular distribution of isotopes clearly demonstrated that nitrification is the major process for the production of N2O. Using stable isotope data, the production mechanism of N2O in the study areas was found to vary in time and space with changes in the redox boundary along the water flow.

Nitrogen Isotopes↗
PubMed2005

Insights on the evolution of metabolic networks of unicellular translationally biased organisms from transcriptomic data and sequence analysis.

Codon bias is related to metabolic functions in translationally biased organisms, and two facts are argued about. First, genes with high codon bias describe in meaningful ways the metabolic characteristics of the organism; important metabolic pathways corresponding to crucial characteristics of the lifestyle of an organism, such as photosynthesis, nitrification, anaerobic versus aerobic respiration, sulfate reduction, methanogenesis, and others, happen to involve especially biased genes. Second, gene transcriptional levels of sets of experiments representing a significant variation of biological conditions strikingly confirm, in the case of Saccharomyces cerevisiae, that metabolic preferences are detectable by purely statistical analysis: the high metabolic activity of yeast during fermentation is encoded in the high bias of enzymes involved in the associated pathways, suggesting that this genome was affected by a strong evolutionary pressure that favored a predominantly fermentative metabolism of yeast in the wild. The ensemble of metabolic pathways involving enzymes with high codon bias is rather well defined and remains consistent across many species, even those that have not been considered as translationally biased, such as Helicobacter pylori, for instance, reveal some weak form of translational bias for this genome. We provide numerical evidence, supported by experimental data, of these facts and conclude that the metabolic networks of translationally biased genomes, observable today as projections of eons of evolutionary pressure, can be analyzed numerically and predictions of the role of specific pathways during evolution can be derived. The new concepts of Comparative Pathway Index, used to compare organisms with respect to their metabolic networks, and Evolutionary Pathway Index, used to detect evolutionarily meaningful bias in the genetic code from transcriptional data, are introduced.

Ammonia↗
PubMed2005

Short-term wavelike dynamics of bacterial populations in response to nutrient input from fresh plant residues.

The objectives of the research were to investigate short-term dynamics of bacterial populations in soil after a disturbance in the form of fresh organic matter incorporation and to investigate how these dynamics are linked to those of some environmental parameters. To reach these objectives, soil bacterial populations, mineral nitrogen, pH, and redox potential (ROP) were monitored daily for 1 month after incorporation of clover-grass (CG) plant material in microcosm experiments. Colony-forming units (CFUs) and direct microscopic counts of FDA-stained and FTTC-stained bacteria increased immediately after incorporation of the plant material, dropped within 2 days, and fluctuated thereafter. Harmonics analysis demonstrated that there were significant wavelike fluctuations with three or four significant peaks within 1 month after incorporation of clover-grass material. Peaks in CFUs were 1-2 days ahead of those in direct counts. Ammonium (NH4) concentrations increased from the start of the experiments until nitrification commenced. Nitrate (NO3) concentrations dropped immediately after plant incorporation, and then rose monotonically until the end of the experiments. There were no wavelike fluctuations in NH4 and NO3 concentrations, so that bacterial fluctuations could not be attributed to alternating mineral N shortages and sufficiencies. pH levels rose and declined with NH4 levels. ROP dropped shortly before NH4 concentrations rose, and increased before NH4 concentrations decreased; there were no regular fluctuations in ROP, so that temporary oxygen shortages may not have been responsible for the observed fluctuations in bacterial populations. Thus, for the first time, regular wavelike dynamics were demonstrated for bacterial populations after perturbation by addition of fresh organic matter to soil, and several potential reasons for the death phase of the fluctuations could be excluded from further consideration.

Bacteria↗
PubMed2001

Influence of Initial C/N Ratio on Chemical and Microbial Composition during Long Term Composting of Straw.

Shredded straw of Miscanthus was composted in 800-L boxes with different amounts of pig slurry added as nitrogen source. The impact of the different initial C/N ratios (11, 35, 47, 50, and 54) on the composting process and the end product was evaluated by examining chemical and microbiological parameters during 12 months of composting. Low initial C/N ratios caused a fast degradation of fibers during the first three months of composting (hemicellulose: 50-80%, cellulose: 40-60%), while high initial C/N ratios resulted in 10-20% degradation of both hemicellulose and cellulose. These differences were reflected in the microbial biomass and respiration, which initially were higher in low C/N treatments than in high C/N treatments. After 12 months of composting, this situation was reversed. Composts with high initial C/N ratios had high microbial biomass (15-20 mg ATP g-1 OM) and respiration rates (200 mg CO2 h-1 g-1 OM) compared to treatments with low initial C/N ratios (less than 10 mg ATP g-1 OM and 25 mg CO2 h-1 g-1 OM). This could be explained by the microorganisms being nitrogen limited in the high C/N ratio treatments. In the low C/N ratio treatments, without nitrogen limitation, the high activity in the beginning decreased with time because of exhaustion of easily available carbon. Different nitrogen availability was also seen in the nitrification patterns, since nitrate was only measured in significant amounts in the treatments with initial C/N ratios of 11 and 35. The microbial community structure (measured as phospholipid fatty acid, PLFA, profile) was also affected by the initial C/N ratios, with lower fungal/bacterial ratios in the low compared to the high C/N treatments after 12 months of composting. However, in the low C/N treatments higher levels of PLFAs indicative of thermophilic gram-positive bacteria were found compared to the high C/N treatments. This was caused by the initial heating phase being longer in the low than in the high C/N treatments. The different fungal/bacterial ratios could also be explained by the initial heating phase, since a significant correlation between this ratio and heat generated during the initial composting phase was found.

Journal Article↗
PubMed1999

Assessment of Three Methods for Detection and Quantification of Nitrite-Oxidizing Bacteria and Nitrobacter in Freshwater Sediments (MPN-PCR, MPN-Griess, Immunofluorescence).

> Abstract Nitrification in freshwater, a key process in the nitrogen cycle, is now well known to take place predominantly on suspended particles and in sediment. Nitrobacter is the most commonly isolated nitrite oxidizing bacteria from water environments. Three methods for counting nitrite oxidizing communities (especially Nitrobacter) in sediment were investigated: MPN-Griess, fluorescent antibodies (immunofluorescence), and a more recent molecular method coupling specific DNA amplification by PCR and statistical MPN quantification. After preliminary adjustments of the MPN-PCR technique, the detection level and the yield of each method were determined by inoculating a sediment with a pure Nitrobacter culture. The best recovery yield was obtained with the immunofluorescence technique (21.3%) and the lowest detection level was reached with the MPN-Griess method (10(3) Nitrobacter/g dry weight sediment). The MPN-PCR method resulted in the lowest recovery yields and needs further adaptation to become a reliable and precise tool for investigations of nitrifying bacteria in sediment.

Journal Article↗
PubMed2002

Hydraulic selection pressure-induced nitrifying granulation in sequencing batch reactors.

The effect of hydraulic selection pressure on the development of nitrifying granules was investigated in four column-type sequencing batch reactors (SBR). The nature of SBR is cycle operation, thus SBR cycle time can serve as a main hydraulic selection pressure imposed on the microbial community in the system. No nitrifying granulation was observed in the SBR operated at the longest cycle time of 24 h, due to a very weak hydraulic selection pressure, while the washout of nitrifying sludge was found in the SBR run at the shortest cycle time of 3 h, and led to a failure of nitrifying granulation. Excellent nitrifying granules with a mean diameter of 0.25 mm and specific gravity of 1.014 were developed in a SBR operated at cycle times of 6 h and 12 h, respectively. The results further showed that a short cycle time would stimulate microbial activity, production of cell polysaccharides and also improve the cell hydrophobicity. These hydraulic selection pressure-induced microbial changes favour the formation of nitrifying granules. This work, probably for the first time, shows that nitrifying granules can be developed at a proper hydraulic selection pressure in terms of SBR cycle time. Nitrifying granulation is a novel biotechnology which has a great potential for wastewater nitrification.

Bacteria↗
PubMed2005

DGGE analysis of 16S rDNA of ammonia-oxidizing bacteria in chemical-biological flocculation and chemical coagulation systems.

Microbial community DNA was extracted from activated sludge samples taken from a chemical bioflocculation process and a chemical coagulation process in Shanghai, China. 16S rDNA of ammonia-oxidizing bacteria (AOB)was amplified by nested polymerase chain reaction and fingerprinted by denaturing gradient gel electrophoresis for microbial structure analysis. The Shannon diversity index of each sample was determined. The results indicated that the microbial structure of AOB in chemical bioflocculation process was comparable at two operational conditions. The ammonia-oxidizing bacterial communities were similar in three channels of the chemical bioflocculation process and in three serial tanks in the chemical coagulation process at the same condition. The diversity of microbial structures in the chemical bioflocculation process was higher than in the chemical coagulation process, in which the microbial structure was similar to that in the influent. Although the microbial study provides insights to the nitrification removal, higher microbial diversity of AOB does not necessarily mean higher ammonia oxidization. Molecular analysis should be combined with chemical assays to optimize operational conditions.

Ammonia↗
PubMed2005

Single-stage autotrophic nitrogen-removal process using a composite matrix immobilizing nitrifying and sulfur-denitrifying bacteria.

We developed a novel single-stage autotrophic nitrogen-removal process comprised of two composite immobilized biomass layers-one of nitrifying bacteria and one of sulfur-denitrifying bacteria and elemental sulfur-in a Fe-Ni fibrous slag matrix. Nitrification and consumption of dissolved oxygen occurred in the outer part and sulfur denitrification in the anoxic inner part of the composite matrix, thus realizing autotrophic nitrogen removal in a single reactor. The complete conversion of ammonia into N2 in a single reactor was demonstrated in both batch-mode incubation and continuous-feed operation. The spatial profiles of the ammonia-oxidizing bacteria and denitrifying bacteria were evaluated by real-time PCR, targeting their functional genes, and stratification of these two types was observed in the matrix after several months of incubation. This process does not require any specific reactor type or conditions and thus has the potential to be applied to many different wastewater treatment processes due to its simplicity in both operation and construction.

Aerobiosis↗
PubMed2001

Nitrate reduction by Citrobacter diversus under aerobic environment.

A new aerobic denitrifier, Citrobacter diversus, was isolated from both nitrification and denitrification sludge. To monitor the variation in the concentration of nitrogen oxides, aerobic denitrification by C. diversus was carried out in a batch reactor. When the nitrate concentration was greater than 180 mg N l(-1), the nitrate reduction rate became stable. The effect of the C/N ratio on the denitrification activity was also investigated. The results showed that the optimum denitrification activity was obtained when the C/N ratio was 4-5. The range of the C/N ratio was higher than that for traditional anoxic denitrification. The effect of the dissolved oxygen concentration was further studied; and it was found that the range of dissolved oxygen concentrations, both for specific growth rates and for specific denitrification rates, was 2-6 mg(-1). From these results, it can be concluded that both the concentration of dissolved oxygen and the C/N ratio are key factors in the aerobic denitrification by C. diversus.

Aerobiosis↗
PubMed2001

Evaluation of nitric oxide production by lactobacilli.

Six strains of Lactobacillus fermentum and Lactobacillus plantarum were investigated for nitric oxide (NO) production. First, the potential presence of NO synthase was examined. None of the strains of L. fermentum and L. plantarum examined produced NO from L-arginine under aerobic conditions. Interestingly, all L. fermentum strains expressed strong L-arginine deiminase activity. All L. fermentum strains produced NO in MRS broth, but the NO was found to be chemically derived from nitrite, which was produced by L. fermentum from nitrate present in the medium. Indeed all L. fermentum strains express nitrate reductase under anaerobic conditions. Moreover, one strain, L. fermentum LF1, had nitrate reductase activity under aerobic conditions. It was also found that L. fermentum strains JCM1173 and LF1 possessed ammonifying nitrite reductase. The latter strain also had denitrifying nitrite reductase activity at neutral pH under both anaerobic and aerobic conditions. The LF1 strain is thus capable of biochemically converting nitrate to NO. NO and nitrite produced from nitrate by lactobacilli may constitute a potential antimicrobial mechanism. studied in a rat acute liver injury model (Adawi et al. 1997). The results indicate that Lactobacillus plantarum DSM 9842 may possess NOS (Adawi et al. 1997). However, NO production from L-arginine has not been investigated in pure cultures of L. plantarum. According to the results of a 15N enrichment experiment, traces of (NO2-+NO3-)-N (total oxidised nitrogen: TON), which seemed to be formed by the resting cells of Lactobacillus fermentum IFO3956, appeared to be derived from L-arginine (Morita et al. 1997). Therefore, it was suggested that L. fermentum may possess a NOS. However, NO produced from L-arginine was not directly measured and a NOS inhibitor test was not performed by Morita et al. (1997). It is known that L-arginine deiminase (ADI) in bacteria may convert L-arginine to NH4+ (Cunin et al. 1986), which may be further oxidised to TON via nitrification by bacteria. Therefore, 15N enrichment experiments could not definitely conclude that L. fermentum possess NOS to convert L-arginine directly to NO. In this study, six Lactobacillus strains belonging to L. plantarum and L. fermentum were measured for NO production in MRS broth. The metabolism of nitrate and L-arginine by the Lactobacillus cell suspensions was also studied. The possibility that NO and nitrite production by lactobacilli may be a potential probiotic trait is also discussed.

Arginine↗
PubMed2001

Application of rRNA-targeted oligonucleotide probes in biotechnology.

Ribosomal RNA-targeted oligonucleotide probes have become valuable tools for the detection of microorganisms involved in important biotechnological processes. Microorganisms which are of major importance for processes such as wastewater treatment, microbial leaching or methane production can be detected and quantified in situ within a complex microbial community. For certain processes, such as nitrification or biological phosphate removal, new microorganisms have become the focus of interest and have led to an improved understanding of these bioremediation techniques. Hybridization techniques have become fast and reliable alternatives to conventional cultivation techniques in the food industry as a control method for starter cultures for fermentation processes or product control. Recent analytical tools such as flow cytometry and digital image processing have improved the efficiency of these techniques. This review is intended to present a summary of methodological aspects of rRNA-based hybridization techniques and their application in biotechnology.

Bioreactors↗
PubMed2001

Aerobic treatment of a concentrated urea wastewater with simultaneous stripping of ammonia.

An industrial wastewater containing a total Kjeldahl nitrogen (TKN) of 12.80 g l(-1) was treated in a continuously fed activated sludge reactor. The main contaminant was urea (21.52 g l(-1)), together with minor amounts of the nitrification inhibitor dicyandiamide (0.46 g l(-1)) and free ammonia (0.56 g l(-1)). The wastewater was diluted 1:1 with water and treated under alkaline conditions (pH 9.4), enabling the simultaneous hydrolysis of urea and stripping of free ammonia in one aerobic reactor. Experiments were conducted to eliminate the remaining ammonia in a separate treatment unit by nitrification/denitrification. An adapted nitrifying bacterial population was isolated which was able to nitrify at a rate of 0.1 g nitrogen l(-1) day(-1) at a dicyandiamide concentration of 0.22 g l(-1). However, this was found to be too slow for an industrial-scale operation. Therefore, separate stripping with air or steam after pH adjustment to > or =10.5 is proposed. The diluted wastewater was treated with a hydraulic retention time of 6 days, corresponding to a volumetric nitrogen loading rate of 1.1 g nitrogen l(-1) day(-1) with an overall TKN reduction of 78.0%.

Aerobiosis↗
PubMed2006

Quality and quantity of leachate in aerobic pilot-scale landfills.

In this study, two pilot-scale aerobic landfill reactors with (A1) and without (A2) leachate recirculation are used to obtain detailed information on the quantity and quality of leachate in aerobic landfills. The observed parameters of leachate quality are pH, chloride (Cl-), chemical oxygen demand (COD), biological oxygen demand (BOD), total Kjeldahl nitrogen (TKN), ammonia nitrogen (NH3-N), and nitrate (NO3(-)-N). pH values of the leachate increased to 7 after 50 days in reactor A1 and after 70 days in reactor A2. Cl- concentrations increased rapidly to 6100 (A1) and 6900 (A2) mg/L after 80 days, from initial values of 3000 and 2800 mg/L, respectively. COD and BOD values decreased rapidly in the A1 landfill reactor, indicating the rapid oxidation of organic matter. The BOD/COD ratio indicates that leachate recirculation slightly increases the degradation of solid waste in aerobic landfills. NH3-N concentrations decreased as a result of the nitrification process. Denitrification occurred in parts of the reactors as a result of intermittent aeration; this process causes a decrease in NO3(-) concentrations. There is a marked difference between the A1 and A2 reactors in terms of leachate quantity. Recirculated leachate made up 53.3% of the leachate generated from the A1 reactor during the experiment, while leachate quantity decreased by 47.3% with recirculation when compared with the aerobic dry landfill reactor.

Aerobiosis↗