Changes In Microbial Populations Research Articles

Microbial community composition along a 50 000-year lacustrine sediment sequence

For decades, microbial community composition in subseafloor sediments has been the focus of extensive studies. In deep lacustrine sediments, however, the taxonomic composition of microbial communities remains undercharacterized. Greater knowledge on microbial diversity in lacustrine sediments would improve our understanding of how environmental factors, and resulting selective pressures, shape subsurface biospheres in marine and freshwater sediments. Using high-throughput sequencing of 16S rRNA genes across high-resolution climate intervals covering the last 50 000 years in Laguna Potrok Aike, Argentina, we identified changes in microbial populations in response to both past environmental conditions and geochemical changes of the sediment during burial. Microbial communities in Holocene sediments were most diverse, reflecting a layering of taxa linked to electron acceptors availability. In deeper intervals, the data show that salinity, organic matter and the depositional conditions over the Last Glacial-interglacial cycle were all selective pressures in the deep lacustrine assemblage resulting in a genetically distinct biosphere from the surface dominated primarily by Bathyarchaeota and Atribacteria groups. However, similar to marine sediments, some dominant taxa in the shallow subsurface persisted into the subsurface as minor fraction of the community. The subsequent establishment of a deep subsurface community likely results from a combination of paleoenvironmental factors that have shaped the pool of available substrates, together with substrate depletion and/or reworking of organic matter with depth.

Geraniol-Loaded Polymeric Nanoparticles Inhibit Enteric Pathogens on Spinach during Posttreatment Refrigerated and Temperature Abuse Storage

Post-harvest cross-contamination of produce with bacterial human pathogens reduces the usefulness of produce as a source of wholesome human food. The application of nano-encapsulated natural antimicrobials, including essential oil components of plants, can help protect produce safety by decontaminating produce from microbial pathogens. The primary objective of this research was to determine the efficacy of antimicrobial interventions on pathogen-inoculated spinach samples stored refrigerated (5 °C) for up to 10 days, or refrigerated (5 °C) for 5 days with subsequent moderate (15 °C) or severe (25 °C) temperature abuse thereafter until a total of 10 days had elapsed. The secondary objective of the study was to determine the capacity of antimicrobial interventions to inhibit and/or reduce pathogen numbers on spinach when inoculation followed intervention treatment, simulating cross-contamination of spinach following post-harvest sanitizing of spinach. Rinsed spinach was portioned into samples and inoculated with cocktailed antibiotic-resistant pathogens to 6.1±0.1 log10 CFU/cm2 for each pathogen. Treatments of geraniol-loaded polymeric nanoparticles (GPNs) (0.5 wt.% geraniol), unencapsulated geraniol (0.5 wt.%), and 200 ppm free and available chlorine (FAC; pH 7.0) were applied to pathogens-inoculated or non-inoculated spinach samples. Following treatment, samples were collected for determining pathogen survival or were covered and held to determine changes in microbial populations (inoculated pathogens and naturally contaminating microbial hygiene indicators) during post-treatment simulated refrigerated and/or temperature-abuse storage. Changes in pathogen numbers were assessed periodically over 10 days for refrigerated (5°C), moderately (15°C) or severely (25°C) temperature-abused spinach. Immediately following treatment by FAC, unencapsulated or nanoparticle-entrapped geraniol, E. coli O157:H7 and Salmonella counts on spinach ranged from 1.5 to 6.1 log10 CFU/cm2. Geraniol-loaded nanoparticles reduced pathogens to non-detectable numbers (detection limit: 0.5 log10 CFU/cm2) on refrigerated and moderately temperature-abused samples (15°C) within 7 days of storage post-treatment, and after 10 days of severe thermo-abuse storage (25°C). Conversely, FAC treatment did not reduce pathogens to non-detectable numbers for refrigerated spinach, and was not observed to inhibit pathogen growth in temperature-abused samples. Application of encapsulated geraniol can reduce pathogens on spinach surfaces, preventing their transmission to consumers, aiding the retention of produce wholesomeness and utility for human consumption and nutrition.

Microbial consortium culture and vermi-composting technologies for recycling on-farm wastes and food production

PurposeA study was conducted to characterize the ‘Madhyam culture’ (Excel Crop Care Limited.), an aerobic-composting microbial consortium culture, and understand composting dynamics, product quality and use in crop production vis-à-vis vermi-composting (using earthworms).Methods16S rDNA analysis was used to characterize aerobic-composting culture. Aerobic-composting and vermi-composting technologies were evaluated to decompose sorghum straw and dung biomass (80:20 ratio; primed with 0.5% urea and 4% rock phosphate) to study days to maturity and composting dynamics in terms of changes in temperature and microbial population. Compost quality was tested for macro-, micro-nutrients and C:N ratio, and evaluated for food production in on-farm trials.Results16S rDNA analysis screened sixteen bacterial isolates—eight related to genus Bacillus, three to each Halobacillus and Staphylococcus, one to each Microbacterium and Streptomyces. The population of bacteria was 4.5 cfu ml−1 at 10−7 dilution. Aerobic- and vermi-composts matured in around 50 and 60 days, respectively. Aerobic-composting throughout recorded relatively higher bacterial population, and higher temperatures during the initial phase. Aerobic-compost tested for high nutrient (1.55% N, 0.93% P, 1.00% K) content and stable C:N ratio (10.3) compared to vermi-compost (1.11% N, 0.43% P, 0.96% K and C:N ratio of 11.7). Field evaluation of both composts showed yield benefit and saving of chemical fertilizers up to 25%.ConclusionsAerobic-composting (using microbial consortium culture), like vermi-composting, proved to be an effective technology with advantage of no requirement to maintain ambient living conditions in lean periods as is required for earthworms in vermi-composting, but needs more energy/labor for biomass turnings.

Ex-vivo cow rumen fluid fermentation: changes in microbial populations and fermentation products with different forages

ABSTRACTThis study investigated the effects of three forage treatments [herbal plantain (PL), ryegrass-white clover pasture (RW) and root crop fodder beet (FB)] on ex-vivo rumen fluid fermentations. Quantitative real-time Polymerase Chain Reaction (qPCR) and PCR-single-stranded conformation polymorphism (PCR-SSCP) analyses were undertaken for aliquots collected from the fermentations. The FB treatment had the highest volatile fatty acid (VFA) and lowest pH compared with other treatments. The RW culture that had a higher fibre content, had higher Fibrobacter succinogenes(F. succinogenes) and anaerobic fungi levels when compared with the FB and PL. Protozoans were however the most abundant microorganisms in the FB cultures, and they had the highest water-soluble carbohydrate (WSC) content. The abundance of F. succinogenes increased in the RW fermentation up to 12 h, and the abundance of anaerobic fungi increased in the RW fermentation up to 24 h. In all the treatments, no effect was found on the overall abundance of bacteria. The findings confirmed that changes in rumen microbial community and fermentation products are partly related to the WSC and fibre content of two novel forages (i.e. PL and FB) increasingly used in animal production.

Changes of microbial population and N-cycling function genes with depth in three Chinese paddy soils.

Microbial communities play critical roles in soil nitrogen (N) cycle; however, we have limited understanding of the distribution of N-cycling microbial groups in deeper soil horizons. In this study, we used quantitative PCR to characterize the changes of microbial populations (16S rRNA and 18S rRNA) and five key N-cycling gene abundances involved in N fixation (nifH), ammonia oxidation (amoA) by ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA), and nitrite reduction (nirS and nirK) along profiles (0–100 cm depth) of different paddy soils from three regions (Hailun, Changshu, Yingtan) across China from north to south. We found that most microbial and N-cycling functional genes significantly decreased with soil depth; however, AOA were enriched in deeper soil layers (20–40 cm). The abundances of microbial and N-cycling functional genes generally decreased by one to two orders of magnitude in the deeper horizons relative to topsoils. The AOA gene abundance was higher than that of AOB in the paddy soil profile, and the nirS and nirK abundances were dominant in topsoil and deeper soil, respectively. All N functional genes except AOA were more abundant in Changshu than Hailun and Yingtan. High abundances and low vertical changes of N-cycling genes in Changshu suggest more dynamic N-transformations in this region. Correlation analysis showed that soil properties and climate parameters had a significant relationship with N-cycling gene abundances. Moreover, the abundance of different N-cycling genes was affected by different environmental parameters, which should be studied further to explore their roles in N cycling for sustainable agriculture and environmental management.

Microbial population changes in patients with medication-related osteonecrosis of the jaw treated with systemic antibiotics

This study aimed to investigate the bacterial population in patients with medication-related osteonecrosis of the jaw (MRONJ) after treatment with doxycycline and metronidazole. A total of 38 patients with MRONJ (age range 55-88, mean age 73 + 8.82 standard deviation) treated with doxycycline first and with metronidazole second were enrolled in this study. Two swabs were taken at the margin of the infected MRONJ lesion after applying pressure on the marginal mucosa, and visible pus was secreted. Real-time polymerase chain reaction was used to analyze 20 periopathogenic and commensal species and the total bacterial level. Bacterial counts were compared between antibiotic treatments and with a control group of orally healthy patients who didn't have periodontal pockets of more than 3 mm (n = 29) by means of a Mann-Whitney U test. Comparisons between the two antibiotic treatments were performed by a paired Wilcoxon signed rank test. The total bacterial level was significantly higher in the MRONJ patients treated with systemic antibiotics compared with the control group. However, significant lower bacterial amounts were found for 12 of the 20 investigated bacteria. We couldn't establish a significant advantage of metronidazole administration after doxycycline treatment. Our findings suggest that the total bacterial level in MRONJ patients is higher even when treated with systemic antibiotics. The significantly different bacterial amounts of the selected species suggest an alteration in the microbial population.

Impact of hydraulic retention time (HRT) and pH on dark fermentative hydrogen production from glycerol

Hydrogen is a promising alternative of clean energy carrier which can be biologically produced from glycerol-rich waste an abundant and economic source of substrate. However, continuous hydrogen-producing systems still need to be improved and in particular by manipulating the only few available operating conditions. The aim of this study was to investigate the effect of the two main operational parameters, ie. pH and hydraulic retention time (HRT) on hydrogen yields and microbial community structures. For that, a continuous stirred tank reactor (CSTR) was first inoculated with an enriched mixed microflora and was then fed with glycerol. A strong influence of these two operational parameters was shown on hydrogen yields where the maximum yield (0.58 ± 0.13 molH2mol−1glycerol) was achieved at pH 5.5 - HRT 12 h and was 28.5 times higher than the minimum (0.02 ± 0.02 molH2mol−1glycerol) obtained at pH 5.0 - HRT 14 h. Changes in most dominant microbial populations were mainly influenced by the pH. Interestingly, HRT parameter related to changes in the metabolic patterns and influenced the composition of subdominant microorganisms, suggesting they might have a key role in changing the ability of the consortium and/or the activity of dominant microorganisms to produce hydrogen.

Activity of Dehydrogenases as an Indicator of Soil Environment Quality

Activity of dehydrogenases (DHs) indicates the presence of viable and physiologically active (physiologically active or physiological activity) microorganisms. Their presence (activity) in soil is correlated with the content of organic carbon, microorganisms, nitrifying activity and microbial respiration. Determination of DHs activity allows to control changes in soil microbial population and is considered as an important parameter of soil quality. The aim of the study was to determine the effects of different farming systems on the enzymatic activity in soil under winter wheat. The research was conducted in the years 2014–2016 on long-term field experiment under two different farming systems (ecological and conventional) at the IUNG (PIB) Experimental Station located in Osiny (Lublin Voivodeship), Poland. Each farming system differs in crop rotation system and whole agrotechnics, which have been adapted to its specificity. Determination of DHs activity was performed using Casida et al.’s (1964) method with modifications. Measured DHs activity was expressed in milligrams of triphenyl formazan (TPF) per 100 g of soil within 24 hours. The results showed that ecological farming system beneficially influenced soil environment.

002 Effects of cold temperature and fat supplementation on rumen microbial populations in Korean cattle

In lower critical temperature, cattle increase their metabolic rate to supply more body heat. This increases nutrient requirements, particularly energy, and may affect rumen fermentation characteristics and thus the rumen microbial ecosystem. This study was performed to examine whether cold temperature and fat supplementation affects rumen microbial populations in Korean cattle. Six Korean cattle steers (average 17 mo of age and 375 kg of BW) were divided into a conventional control diet group (n = 3) and a 1.75% fat supplementation group (n = 3). Steers were allowed to receive daily a concentrate (1.5% of BW) and 3 kg of tall fescue hay. Steers were raised in metabolic cages in a temperature-controlled room with 2 different temperature conditions. Animals were grown in natural cold condition for 12 d with 2 different diets, and they were then grown in neutral normal temperature for 12 d. There was a 10-d resting period between the 2 temperature conditions in a feedlot with the control diet. The minimum ambient temperature (−6.24°C) of the cold environment was lower (P < 0.01) than that (15.8°C) of the normal temperature condition. Rumen fluid samples were obtained via stomach tube on the last day of each of 2 experimental periods 3 h after the morning feeding. Rumen fluids were frozen in liquid nitrogen and stored at −70°C. Genomic DNA was extracted and used for 16S rRNA metagenomics sequencing by an Illumina HiSeq 2000 system. Raw sequencing data was processed by QIIME. Statistical analysis was conducted by 2-way (diet and temperature) ANOVA. Bacteroidetes was the most abundant phylum followed by Firmicutes in all rumen fluid samples. Relative abundances of the genera Propionibacterium and Anaeroplasma were higher (P < 0.05) in cold temperature than in normal temperature, whereas those of Desulfovibrio and Mogibacterium were lower (P < 0.05) in cold temperature. Relative abundance of the family R4-45B was higher (P < 0.05) in the fat diet group than in control diet group, whereas that of Pyramidobacter was lower (P < 0.05) in fat diet group. Real-time PCR was performed to validate the metagenomics data and to identify the changes of microbial population at species levels with 19 microbial primers. Succinimonas amylolytica was higher (P < 0.05) in cold temperature than in normal temperature. Ruminococcus albus was higher (P < 0.05) in the fat diet group than in the control diet group. In conclusion, metagenomics and real-time PCR results reveals that cold temperature and fat supplement affect microbial populations in the rumen of beef cattle.

Breaking continuous potato cropping with legumes improves soil microbial communities, enzyme activities and tuber yield.

This study was conducted to explore the changes in soil microbial populations, enzyme activity, and tuber yield under the rotation sequences of Potato–Common vetch (P–C), Potato–Black medic (P–B) and Potato–Longdong alfalfa (P–L) in a semi–arid area of China. The study also determined the effects of continuous potato cropping (without legumes) on the above mentioned soil properties and yield. The number of bacteria increased significantly (p < 0.05) under P–B rotation by 78%, 85% and 83% in the 2, 4 and 7–year continuous cropping soils, respectively compared to P–C rotation. The highest fungi/bacteria ratio was found in P–C (0.218), followed by P–L (0.184) and then P–B (0.137) rotation over the different cropping years. In the continuous potato cropping soils, the greatest fungi/bacteria ratio was recorded in the 4–year (0.4067) and 7–year (0.4238) cropping soils and these were significantly higher than 1–year (0.3041), 2–year (0.2545) and 3–year (0.3030) cropping soils. Generally, actinomycetes numbers followed the trend P–L>P–C>P–B. The P–L rotation increased aerobic azotobacters in 2–year (by 26% and 18%) and 4–year (40% and 21%) continuous cropping soils compared to P–C and P–B rotation, respectively. Generally, the highest urease and alkaline phosphate activity, respectively, were observed in P–C (55.77 mg g–1) and (27.71 mg g–1), followed by P–B (50.72 mg mg–1) and (25.64 mg g–1) and then P–L (41.61 mg g–1) and (23.26 mg g–1) rotation. Soil urease, alkaline phosphatase and hydrogen peroxidase activities decreased with increasing years of continuous potato cropping. On average, the P–B rotation significantly increased (p <0.05) tuber yield by 19% and 18%, compared to P–C and P–L rotation respectively. P–L rotation also increased potato tuber yield compared to P–C, but the effect was lesser relative to P–B rotation. These results suggest that adopting potato–legume rotation system has the potential to improve soil biology environment, alleviate continuous cropping obstacle and increase potato tuber yield in semi–arid region.

What is adaptation by natural selection? Perspectives of an experimental microbiologist.

Ever since Darwin, the role of natural selection in shaping the morphological, physiological, and behavioral adaptations of animals and plants across generations has been central to understanding life and its diversity. New discoveries have shown with increasing precision how genetic, molecular, and biochemical processes produce and express those organismal features during an individual’s lifetime. When it comes to microorganisms, however, understanding the role of natural selection in producing adaptive solutions has historically been, and sometimes continues to be, contentious. This tension is curious because microbes enable one to observe the power of adaptation by natural selection with exceptional rigor and clarity, as exemplified by the burgeoning field of experimental microbial evolution. I trace the development of this field, describe an experiment with Escherichia coli that has been running for almost 30 years, and highlight other experiments in which natural selection has led to interesting dynamics and adaptive changes in microbial populations.

Performance assessment of improved composting system for food waste with varying aeration and use of microbial inoculum

Wet waste recycling at generation point will alleviate burden on the overflowing waste dumpsites in developing nations. Drum composting is a potential treatment option for such waste at individual or community level. The present study was aimed to produce compost from wet waste (primarily comprising food waste) in composting drums modified for improved natural air circulation. Effect of microbial inoculum and waste turning on composting process was also studied. The final results showed the production of matured and stable compost in the modified drums. Addition of the microbial inoculum resulted in thermophilic phase within a week time. The self-heating test and germination index (>80%) showed the production of non-phytotoxic and mature compost in the modified drums after 60days. The change in microbial population, humic substances and biological parameters (lignin, cellulose and hemicellulose) during the study is discussed. Moreover, the reduction in waste mass and volume is also reported.

Assessment of Chicken Carcass Microbiome Responses During Processing in the Presence of Commercial Antimicrobials Using a Next Generation Sequencing Approach

The purpose of this study was to 1) identify microbial compositional changes on chicken carcasses during processing, 2) determine the antimicrobial efficacy of peracetic acid (PAA) and Amplon (blend of sulfuric acid and sodium sulfate) at a poultry processing pilot plant scale, and 3) compare microbial communities between chicken carcass rinsates and recovered bacteria from media. Birds were collected from each processing step and rinsates were applied to estimate aerobic plate count (APC) and Campylobacter as well as Salmonella prevalence. Microbiome sequencing was utilized to identify microbial population changes over processing and antimicrobial treatments. Only the PAA treatment exhibited significant reduction of APC at the post chilling step while both Amplon and PAA yielded detectable Campylobacter reductions at all steps. Based on microbiome sequencing, Firmicutes were the predominant bacterial group at the phyla level with over 50% frequency in all steps while the relative abundance of Proteobacteria decreased as processing progressed. Overall microbiota between rinsate and APC plate microbial populations revealed generally similar patterns at the phyla level but they were different at the genus level. Both antimicrobials appeared to be effective on reducing problematic bacteria and microbiome can be utilized to identify optimal indicator microorganisms for enhancing product quality.

Impact of Different Methods of Soil Sampling and DNA Extraction on the Identification of Soil Bacterial Abundance under Elevated CO2

Elevated atmospheric CO2 (eCO2) is anticipated to have marked effects on soil microbial populations. While there is experimental evidence to support this view there are also studies where changes in microbial populations, such as the abundance of bacteria, are suggested but cannot be statistically established. We conducted this study to identify whether the sampling and sample treatment methods used could influence the results obtained using bacterial abundance as the variable of interest. We tested three different sampling methods and two different DNA extraction kits. The first because microbes are distributed heterogeneously in soil so the sampling procedure might be expected to influence the accuracy and precision of the population estimate and the second because the quantity and quality of DNA extracted influences the microbial analyses that can be performed and can introduce bias. Samples were taken from a long-running FACE experiment on grassland from under plants ofAgrostis capillaris. We found that bacterial abundance was consistently lower under eCO2 but we were only able to establish a statistical difference where a more intense sampling regime was used and bulking of the soil sample was avoided. A reduction in bacterial abundance is a consistent outcome in eCO2 field experiments but the only other occasion where this reduction has been found to be significant was also where individual soil cores were analysed rather than the samples being bulked. We conclude that while there is extra work and cost attached to more detailed sampling this approach is highly desirable if we are to make robust conclusions about the impacts of eCO2 on soil microbes.

Duodenal endoluminal barrier sleeve alters gut microbiota of ZDF rats.

Background/ObjectivesThe combination of energy dense diets and reduced energy expenditure in modern society has escalated the prevalence of obesity and obesity-related comorbidities. Among these disease-states, type-2 diabetics (T2D) are disproportionately associated with obesity, suggesting a shared etiology. In conjunction with defects in hormonal and inflammatory states, obesity and T2D are also characterized by dysbiosis.MethodsWe have recently described the beneficial effects of duodenal nutrient exclusion, as induced by the duodenal endoluminal sleeve (DES); including body weight loss, prevented fat mass accumulation, and improved glucose tolerance in the ZDF rat, a rodent model of obesity and type-2 diabetes (T2D). To assess the relative role of DES on hindgut microbiota in the context of these metabolic changes, we analyzed cecal samples from rats implanted with a duodenal endoluminal sleeve (DES), or a sham control of this procedure. A group of pair-fed (pf) sham controls was also included to account for changes induced by reduced body weight and food intake.ResultsAnalysis of hind gut microbiota following DES in the ZDF rat elucidated discrete changes in several microbial populations including a reduction in Paraprevotella family members of the Clostridiales order along with an increase in Akkermansia muciniphila and species of the Allobaculum and Bifidobacterium genera.ConclusionsTogether these observations suggest that like Roux-en Y gastric bypass (RYGB) and Metformin, regulation of gut microbiota may be a contributing factor to the therapeutic effects of DES.

Evaluation of Bacterial Contamination Sources in Meat Production Line

AbstractBacterial contamination during slaughtering process is a safety problem and concern for shelf life in meat production. We compare two different slaughter lines, sheep and cattle samples from Iranian slaughterhouse using PCR‐denaturing gradient gel electrophoresis (DGGE) analysis for evaluation the sources of bacterial contaminations.Bacterial diversity was significantly different between and within cattle and sheep slaughter lines. Samples are contaminated most frequently with Salmonella enterica (28% and 30%), Enterococcus fecalis (18% and 20%), Escherichia coli (13% and 14%) and Pseudomonas fluorescens (8% and 6%), either on equipment surfaces after general cleaning and sanitizing treatments (56%).Biodiversity of carcasses samples is increased during skinning and evisceration process and may indicate similar sources of contamination from hides and rectums of the animal to carcasses and environment.Practical Applications16S rDNA based denaturing gradient gel electrophoresis‐PCR is a method for assessment of microbial diversity, source of contaminations and changes of microbial population in slaughterhouses.

Changes of Soil Microbial Population and Structure Under Short-term Application of an Organically Enhanced Nitrogen Fertilizer

Changes of Soil Microbial Population and Structure Under Short-term Application of an Organically Enhanced Nitrogen Fertilizer

복합항균제제를 첨가한 생면의 미생물학적 및 이화학적 품질 특성

This study was conducted to investigate the effects of natural preservatives (G3, G3-1, F3, and F3-1) using Cordyceps militaris on improvement of food quality and safety of noodle during storage. Wheat flour noodle were prepared using three different concentrations of natural preservatives (0.100, 0.200, and 0.400%). Changes in microbial populations, pH value, titratable acidity, and sensory evaluation were measured during storage at 12±2℃ for 3 days. Overall, use of natural preservatives resulted in lower levels of total mesophilic bacteria, coliform, yeast and mold in noodle compared to the control. In particular, natural preservatives using 2× MIC concentrations (0.400%) of F3 and F3-1 were effective at maintaining levels of total mesophilic bacteria for noodle during storage. The pH values of noodle made with F3 and F3-1 were higher than the others. The titratable acidity of noodle with natural preservatives did not significantly change during storage. In sensory evaluation, appearance, color, and overall acceptability of noodle with F3 and F3-1 were preferred than the control. These results could provide useful information for developing an alternative preservation method to improve food quality and shelf-life of noodle using natural preservatives.

Wastewater ammonia removal using an integrated fixed-film activated sludge-sequencing batch biofilm reactor (IFAS-SBR): Comparison of suspended flocs and attached biofilm

Integrated fixed-film activated sludge (IFAS) that combines the activated sludge (suspended flocs) and attached biofilm has been applied in municipal wastewater treatment to promote nitrification. This study investigated the changes in reactor performance and bacterial community structure in response to different organic loadings (500, 250, 150 mg/L COD) in an integrated fixed-film activated sludge (IFAS) reactor operated under sequencing batch mode. Changes of bacterial population in the suspended flocs and attached biofilm were compared. Biomass in the suspended flocs and in biofilm decreased as the organic loading decreased. The specific nitrification rate was highest when COD was only 150 mg/L in the feeding, which highlighted the effects of competition between heterotrophic bacteria and autotrophic bacteria over oxygen and space. Besides, lack of carbon sources limited denitrification activities. The percentages of nitrifying related genes over total genes were higher in biofilms as compared to those in activated sludge flocs, indicating biofilm was a more favorable habitat for nitrifiers. In addition, extracellular polymeric substance (EPS) in biofilm and suspended flocs changed differently in response to the organic loading changes, which might also be related to the microbial population changes.

Salt-tolerant microorganisms treating hypersaline organic wastewater and the microbial population dynamics

ABSTRACT Halotolerant microorganism was domesticated and used for the treatment of hypersaline organic wastewater containing acetone and dichloroethane. The degradation performance and the microbial population changes of the activated sludge were investigated. The degradation performance of the domesticated activated sludge for acetone and dichloroethane (94.3% and 88.4%) was much better than the un- domesticated activated sludge (17.8% and 74.1%). The main strains in domesticated sludge were salt-tolerant strains for organics degradation, indicating that the microbial community has been effectively domesticated and cultured.