Allochthonous Bacteria Research Articles

English

The gastrointestinal (GI) tract of fish reacts to stress, sometimes with severe cell damage to intestinal enterocytes and modulation of the gut bacterial community. The effect of dominance hierarchy formation, acute - and handling stress on the intestinal bacterial community have been reported in three salmonids; Arctic charr (Salvelinus alpinus L.), Atlantic salmon (Salmo salar L.) and rainbow trout (Oncorhynchus mykiss Walbaum), and Atlantic cod (Gadus morhua L.). In Arctic charr, hierarchy formation reduced cultivable autochthonous (adherent) bacteria level in proximal intestine of subordinate fish compared to dominant fish, but this effect was not noticed in the distal intestine (DI). Furthermore, hierarchy formation modulates the gut microbiota. When Atlantic salmon and rainbow trout were exposed to acute stress the population level of adherent bacteria decrease in DI with concomitant increase in faeces, but this effect was not observed in Atlantic cod. The reason for the effect in Atlantic salmon is probably a peel-off effect of mucus and transporting autochthonous gut bacteria out of the fish. This will in turn allow allochthonous bacteria (present in the lumen or associated to digesta) to adhere and colonise the mucus layer. The elimination of the existing beneficial adherent gut microbiota and the lack of protecting mucus during acute stress might have relevance in pathogenesis. The present study reveals that stress eliminates certain protecting bacteria in the GI tract making the gut more prone to pathogen infections. Key words: Fish, stress, intestinal microbiota.

Alternative dietary protein sources for Atlantic salmon (Salmo salarL.) effect on intestinal microbiota, intestinal and liver histology and growth

The present study has addressed the issue of dietary alterations on gut microbiota in fish by investigating modulation of the allochthonous and autochthonous bacterial gut community of Atlantic salmon following feeding with pea protein concentrate, soy protein concentrate, extracted sunflower, poultry by-product and feather meal. The results revealed that total allochthonous and total autochthonous bacteria isolated from the distal intestine (DI) were affected by dietary modulations. Total autochthonous bacteria in proximal intestine remained unaffected. Corynebacteriaceae dominated the allochthonous bacteria and Lactobacillaceae dominated the autochthonous bacteria community in proximal and DI indicating that the most abundant groups are not shifted by alternative proteins. Some variations were observed between the bacterial communities as result of dietary manipulations. Alternative protein sources resulted in no severe signs of enteritis. Vacuolization of the liver was unaffected by diet. Furthermore, addition of plant materials significantly affected production of acetic acid. Weight of pyloric-, proximal- and DI was influenced by diet, especially feather meal. Growth performance was significantly affected by inclusion of feather meal to the diet. In conclusion the results showed that pea protein concentrate and poultry by-products are suitable protein replacements for Atlantic salmon and that soy protein concentrate is a potential candidate.

Microbial communities and symbionts in the hard tick Haemaphysalis longicornis (Acari: Ixodidae) from north China

BackgroundClose relationships between ticks and microbial communities are important for tick fitness and pathogen colonization and transmission. Haemaphysalis longicornis, distributed widely in China, can carry and transmit various pathogens and pose serious damages to public health and economics. However, little is known about the broader array of microbial communities and symbionts in H. longicornis under natural conditions. In the present study, we investigated the composition of bacterial communities associated with H. longicornis and evaluated the putative symbionts.MethodsThe eubacterial 16S rRNA gene clone libraries of H. longicornis were constructed and analyzed by restriction fragment length polymorphism (RFLP) and DNA sequencing. In addition, diagnostic PCR was performed to assess the prevalence, vertical transmission and infection sites of the symbionts in H. longicornis.ResultsVertically-transmitted symbionts, potential pathogens and allochthonous nonpathogenic bacteria were identified from the field-collected H. longicornis. Three types of symbionts (Coxiella-like, Arsenophonus-like and Rickettsia-like symbionts) were identified in a single host simultaneously. A series of analyses revealed the vertical transmission, prevalence, and infection sites of these symbionts. However, only Coxiella-like bacteria were transmitted stably in the laboratory-reared ticks. In addition, we identified a novel Coxiella-like agent with 95.31% sequence similarity to the taxon described previously.ConclusionsThe present study demonstrated that natural H. longicornis harboured a diverse array of microbial communities. Three types of symbionts were identified in a single host simultaneously. Moreover, high prevalence, vertical transmission and the infection sites supported an obligate symbiotic association between Coxiella symbiont and its host. The role of Coxiella symbiont in the host fitness and the interaction among microbial communities remained to be elucidated. Our investigation of microbial communities in the ticks revealed the complexity of ecological interactions between host and microbe and provided insight for the biological control of ticks.

Effects of a dietary β-(1,3)(1,6)-D-glucan supplementation on intestinal microbial communities and intestinal ultrastructure of mirror carp (Cyprinus carpio L.)

To assess the effects of dietary Saccharomyces cerevisiae β-(1,3)(1,6)-D-glucan supplementation (MacroGard(®)) on mirror carp (Cyprinus carpio L.) intestinal microbiota and ultrastructure of the enterocyte apical brush border. Carp were fed either a control diet or diets supplemented with 0.1, 1 or 2% w/w MacroGard(®). Culture-dependent microbiology revealed that aerobic heterotrophic bacterial levels were unaffected by dietary MacroGard(®) after 2 and 4 weeks. No effects were observed on the allochthonous lactic acid bacteria (LAB) populations at either time point; however, reduced autochthonous LAB populations were observed at week 4. PCR-DGGE confirmed these findings through a reduction in the abundance of autochthonous Lactococcus sp. and Vagococcus sp. in MacroGard(®)--fed fish compared with the control-fed fish. Overall, sequence analysis detected microbiota belonging to the phyla Proteobacteria, Firmicutes, Fusobacteria and unidentified uncultured bacteria. DGGE analyses also revealed that dietary MacroGard(®) reduced the number of observed taxonomical units (OTUs) and the species richness of the allochthonous microbiota after 2 weeks, but not after 4 weeks. In contrast, dietary MacroGard(®) reduced the number of OTUs, the species richness and diversity of the autochthonous microbiota after 2 weeks, and those parameters remained reduced after 4 weeks. Transmission electron microscopy revealed that intestinal microvilli length and density were significantly increased after 4 weeks in fish fed diets supplemented with 1% MacroGard(®). This study indicates that dietary MacroGard(®) supplementation modulates intestinal microbial communities of mirror carp and influences the morphology of the apical brush border. To the authors' knowledge, this is the first study to investigate the effects of β-(1,3)(1,6)-D-glucans on fish gut microbial communities, using culture-independent methods, and the ultrastructure of the apical brush border of the enterocytes in fish. This prebiotic-type effect may help to explain the mechanisms in which β-glucans provide benefits when fed to fish.

Indigenous Microbiota and Habitat Influence Escherichia coli Survival More than Sunlight in Simulated Aquatic Environments

The reported fate of Escherichia coli in the environment ranges from extended persistence to rapid decline. Incomplete understanding of factors that influence survival hinders risk assessment and modeling of the fate of fecal indicator bacteria (FIB) and pathogens. FIB persistence in subtropical aquatic environments was explored in outdoor mesocosms inoculated with five E. coli strains. The manipulated environmental factors were (i) presence or absence of indigenous microbiota (attained by natural, disinfected, and cycloheximide treatments), (ii) freshwater versus seawater, and (iii) water column versus sediment matrices. When indigenous microbes were removed (disinfected), E. coli concentrations decreased little despite exposure to sunlight. Conversely, under conditions that included the indigenous microbiota (natural), significantly greater declines in E. coli occurred regardless of the habitat. The presence of indigenous microbiota and matrix significantly influenced E. coli decline, but their relative importance differed in freshwater versus seawater. Cycloheximide, which inhibits protein synthesis in eukaryotes, significantly diminished the magnitude of E. coli decline in water but not in sediments. The inactivation of protozoa and bacterial competitors (disinfected) caused a greater decline in E. coli than cycloheximide alone in water and sediments. These results indicate that the autochthonous microbiota are an important contributor to the decline of E. coli in fresh and seawater subtropical systems, but their relative contribution is habitat dependent. This work advances our understanding of how interactions with autochthonous microbiota influence the fate of E. coli in aquatic environments and provides the framework for studies of the ecology of enteric pathogens and other allochthonous bacteria in similar environments.

Persistence and degrading activity of free and immobilised allochthonous bacteria during bioremediation of hydrocarbon-contaminated soils

Rhodococcus sp. and Pseudomonas sp. bioremediation experiments were carried out using free and immobilized cells on natural carrier material (corncob powder) in order to evaluate the feasibility of its use in the bioremediation of hydrocarbon-contaminated soils. Terminal restriction fragment length polymorphism analysis was performed on the 16S rRNA gene as molecular fingerprinting method in order to assess the persistence of inoculated strains in the soil over time. Immobilized Pseudomonas cells degraded hydrocarbons more efficiently in the short term compared to the free ones. Immobilization seemed also to increase cell growth and stability in the soil. Free and immobilized Rhodococcus cells showed comparable degradation percentages, probably due to the peculiarity of Rhodococcus cells to aggregate into irregular clusters in the presence of hydrocarbons as sole carbon source. It is likely that the cells were not properly adsorbed on the porous matrix as a result of the small size of its pores. When Rhodococcus and Pseudomonas cells were co-immobilized on the matrix, a competition established between the two strains, that probably ended in the exclusion of Pseudomonas cells from the pores. The organic matrix might act as protective agent, but it also possibly limited cell density. Nevertheless, when the cells were properly adsorbed on the porous matrix, the immobilization became a suitable bioremediation strategy.

Do stocking densities affect the gut microbiota of gibel carp Carassius auratus gibelio cultured in ponds?

The aim of the present study was to evaluate the intestinal microbial communities of gibel carp (Carassius auratus gibelio) cultivated in two beach ponds at different stocking densities. The two ponds were both ~3.33 hm 2 in acreage and ~1.5 m in depth. The stocking densities included one intensive with 2 fish m –3 while the other treated as semi-intensive with 1 fish m –3 . The gut microbiota (both allochthonous and autochthonous) were sampled after 135 days of feeding. Denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA gene segments was used to evaluate the bacterial community. Actinobacteria, Cyanobacteria, Firmicutes, Fusobacteria, Proteobacteria and some unclassified_bacteria taxa were identified in gut samples and feed. Similar bacterial communities (C s=0.83) were observed with respect to the autochthonous and allochthonous gut microbiota of gibel carp cultured in the intensive culture pond. In contrast to these results, some difference (C s =0.61) was observed in the gut microbiota of fish reared in the semi-intensive culture pond. Our results indicated that the difference in the bacterial communities between allochthonous bacteria and gut associated bacteria of gibel carp was not constant and was modulated by the stocking density.

Improvement of Bioremediation Performance for the Degradation of Petroleum Hydrocarbons in Contaminated Sediments

Microcosm bioremediation strategies were applied to sediments contaminated with hydrocarbons. Experiments were performed in aerobic conditions in a single-step treatment and in a two-step anaerobic-aerobic treatment. In aerobic conditions, either inorganic nutrients or composts were added to the microcosms, while, in the first anaerobic phase of the two-step experiment, acetate and/or allochthonous sulfate-reducing bacteria were used. After the treatment under anaerobic conditions, samples were exposed to aerobic conditions in the presence of compost. In the aerobic treatments, 81% hydrocarbon biodegradation was observed after 43 days in the presence of inorganic nutrients. In aerobic conditions in the presence of mature compost, hydrocarbon biodegradation was 51% after 43 days of treatment, whereas it was 47% after 21 days with fresh compost. The two-step experiment allowed us to obtain a hydrocarbon degradation of 91%, after a first anaerobic step with an inoculum of sulfate-reducing prokaryotes.

Effect of temperature and starvation upon survival strategies of Pseudomonas fluorescens CHA0: comparison with Escherichia coli

Microorganisms in aquatic systems are exposed to continuous modifications in their environmental conditions. In these systems, both autochthonous and allochthonous bacteria respond to adverse conditions by expressing viable but nonculturable phenotype. On the basis of this common response, the behaviour of a few species is extrapolated to others. We compared the survival strategies of Escherichia coli (allochthonous, mesophile bacterium) and Pseudomonas fluorescens CHA0 (ubiquitous, psychrotrophic bacteria) under nonoptimal temperature and nutrient deprivation. In the absence of nutrients, the effect of temperature on the loss of culturability did not show a common pattern. Whereas the survival of E. coli had an inverse relationship with temperature, whereas for P. fluorescens a direct relationship between temperature and T₉₀ values was only established in the range 5-15°C, with an inverse relationship at higher temperatures. When the subproteome of the outer membrane of P. fluorescens was comparatively analysed, starvation was not the main source of change. The most relevant modifications were due to variations in temperature. OprF, the major surface protein of the genus Pseudomonas, showed a high expression in nonculturable as well as culturable populations under all the adverse situations analysed. We therefore propose OprF as a suitable marker for Pseudomonas detection in the environment.

Induction of heat tolerance in autochthonous and allochthonous thermotolerant probiotics for application to white shrimp feed

The main aim of this work was to produce autochthonous (host origin) thermotolerant probiotic feeds to have sufficient numbers of viable cells on extended storage and application into commercial shrimp ponds. Thermotolerant lactic acid bacteria and Bacillus sp. preliminarily identified as Lactobacillus plantarum ssp1 (ID1L), Leuconostoc mesenteroides ssp mesenteroides/dextranicum2 (ID2L), Bacillus licheniformis (ID3B) and Bacillus subtilis (ID4B) were isolated under high temperature from healthy white shrimp ( Litopenaeus vannamei) grown in natural farming and research ponds, Thailand. These bacteria and introduced allochthonous (external source) L. brevis 860 showed antagonistic effects on Vibrio sp. and some food pathogens tested. Autochthonous and allochthonous lactic acid bacteria (ID1L and L. brevis 860) were further selected to study heat adaptation characteristics under different condition of pH, physiological growth state, temperature and time of heat pretreatment and growth media‏. Cultures at pH 7 and in stationary growth phase when exposed to heat adaptation temperature profile (preheated at 45 °C, 20 min) were found to improve decimal reduction time (D 70 value) and survived better than those suspended at pH 3 and in log growth phase. In order to retain 50% cell survival, ID1L could be preheated to 50 °C for a maximum of 15 min and L. brevis 860 to 45 °C for a maximum of 15 to 20 min. Cross protection (treating with 0.3 M NaCl for 30 min) also led to good cell recovery. Preheated and cross protected ID1L and L. brevis 860 were then manually sprayed (top-dressed) on hot white shrimp pellets received from the commercial pellet mill after it had cooled to 60 and 50 °C, respectively from an outlet temperature of 95 °C and then stored in refrigeration for 4 weeks. Lactobacillus plantarum ssp1 (ID1L) grown in De Man, Rogosa, Sharp media with cross protection showed the highest survival percentage (47.8%) while L. brevis 860 had the highest survival of 41.7% for those grown in skim milk. Similar tests were also conducted with heat tolerant mesophilic Bacillus sp., B. licheniformis (ID3B) and B. subtilis (ID4B) without heat adaptation by spraying (top-dressed) at 80 and 70 °C, respectively. Fresh pellets sprayed with organisms at ambient temperature were used as control. While the initial cell count was lower for those sprayed at high temperatures, the cell count was found to decrease rapidly on 4-week refrigerated storage in the case of those sprayed at ambient temperature. Overall spraying probiotics at high temperature is recommended as it also prevents the growth of fungi on the pellets which is a problem for feed storage based on all other characteristics studied.

Heterogeneity of Heterotrophic Bacteria Dominating in Brackish Lake Shira (Republic of Khakasia, Russia) Subjected to Anthropogenic Impact

In this work data on heterogeneity in halotolerance and the resistance to antibiotics of heterotrophic bacteria dominating in Lake Shira (Republic of Khakasia, Russia) were presented. It was established that halotoler-ance of the bacteria is determined by genetic and epigenetic mechanisms. Influence of anthropogenic factor (entering the ecosystem allochthonous bacteria) on the appearance of multiple antibiotic resistance appear-ance by dominating bacterial species is discussed.

Dynamics of organic‐aggregate‐associated bacterial communities and related environmental factors in Lake Taihu, a large eutrophic shallow lake in China

To investigate the spatial and temporal variations of organic‐aggregate‐associated bacterial communities (OABC), a 25‐month observation was conducted at two contrasting sites (Meiliang Bay and the lake center) in Lake Taihu, China. The structures and dynamics of the OABC were determined by partially sequencing cloned 16S rRNA genes, and by terminal restriction fragment length polymorphism (T‐RFLP) analysis. One hundred ninety‐two T‐RFs were detected from the two sites, but only 17 T‐RFs were dominant, suggesting that specific microbial populations were adapted to the unique niche provided by the organic aggregates (OA). Phylogenetically, Beta‐ and Alphaproteobacteria constituted the numerically most important heterotrophic bacterial group. Analysis of similarity revealed significant intra‐lake heterogeneity, and significant temporal shifts in OABC. Canonical correspondence analysis demonstrated that site‐specific differences in sediment resuspension and nutrient enrichment (namely nitrate and total phosphorus) were the forces driving the intra‐lake differences in OABC. Water temperature and dissolved oxygen were related to the seasonal dynamics of OABC. The annual succession in OABC was significant in Meiliang Bay, but not in the lake center. In addition, nearly 35% of the bacterial sequences from OA related to bacteria from soils, activated sludge, sediments, and other habitats, indicating the potential importance of allochthonous bacteria in OABC.

Preliminary assessment of dietary supplementation of Sangrovit® on red tilapia (Oreochromis niloticus) growth performance and health

A preliminary study was conducted to evaluate the effect of graded dietary supplementation of Sangrovit®, a commercial product containing the isoquinoline alkaloid sanguinarine, on red tilapia (Oreochromis niloticus) growth performance, feed utilisation, hepatic function, haematological parameters and gut microbiota. Compared to the control group (1.03 g fish−1 day−1), significant elevations in mean daily feed intake (1.19–1.25) were observed in fish fed Sangrovit® diets during the 60-day feeding period. Consequently, the specific growth rate (3.94–4.05% day−1) and weight gain (66.80–71.85 g fish−1) were significantly higher in the Sangrovit®-fed groups. With the exception of total leukocyte levels, which were elevated in fish fed Sangrovit®-supplemented diets, haematological and immunological parameters remained unaffected. Hepatic alanine aminotransferase activity and hepatosomatic index also remained unaffected in all fish groups. Compared to the control group, the allochthonous lactic acid bacteria (LAB) populations were lower in fish fed diets containing Sangrovit® at 75 and 100 mg kg−1. The present study demonstrates that Sangrovit® had a positive effect on tilapia growth performance with no apparent effects on carcass composition, hepatic function and health status.

Effects of dietary potassium diformate (KDF) on growth performance, feed conversion and intestinal bacterial community of hybrid tilapia ( Oreochromis niloticus ♀ × O. aureus ♂)

The aim of the present study was to investigate the effect of dietary inclusion of potassium diformate (KDF), a possible non-antibiotic growth promoter, and two widely-used antibiotics, flavomycin and quinocetone, on growth performance, feed conversion ratio and gut microbiota of hybrid tilapia. An 8 week feeding trial was conducted with five levels of KDF: 0 (C), 3.0 (KDF3), 6.0 (KDF6), 9.0 (KDF9), and 12.0 (KDF12) g kg − 1 diet and three antibiotic treatments: flavomycin (8 mg kg − 1, AF), quinocetone (100 mg kg − 1, AQ), and flavomycin (4 mg kg − 1) + quinocetone (50 mg kg − 1) (AFQ). At the end of the experiment, fish were starved for one day and bulk weighed. Pooled gut contents sampled from four replicate tanks were analyzed for bacterial community by 16 S rDNA PCR, denaturing gradient gel electrophoresis (DGGE) and Bio-1D++ software. The results indicate that the addition of dietary KDF and antibiotics had no significant effect on tilapia growth performance, feed conversion ratio or survival compared to the control group. Among the experimental groups, however, fish fed the KDF3 and KDF6 diets showed improved growth performance and feed conversion ratio with higher final body weight and specific growth rate and lower feed conversion ratio compared to those fed the AFQ diet. Dietary KDF and antibiotics showed effects on the gut microbiota. Dietary KDF3 and KDF6 improved the relative richness of some intestinal allochthonous bacteria such as Mycobacterium sp. partial MHSD12-like, Mycobacterium peregrinum-like, Pseudomonas sp. HMPB4-like and six uncultured bacterium-like species. However, alpha Proteobacterium IMCC1702-like, Rhodococcus sp. P14-like, and three uncultured bacterium-like species were depressed in the gut. Based on these results, the possible beneficial effects of KDF on gut bacteria will be discussed.

Use of 16S rRNA gene sequencing analysis to characterize culturable intestinal bacteria in Atlantic salmon (Salmo salar) fed diets with cellulose or non-starch polysaccharides from soy

Duplicate groups of Atlantic salmon (Salmo salar L.), kept in seawater, were fed fish meal-based cold-pelleted diets. Diets with non-starch polysaccharides (NSP), either cellulose, purified soybean NSP or extruded purified soybean NSP at a dietary level of 100 g kg−1, were compared with a diet without supplemental NSP and a diet with soybean meal in a 28-day feeding trial. Isolation and characterizations were limited to culturable bacteria and population levels of aerobic and facultative aerobic heterotrophic autochthonous (adherent) and allochthonous (transient) bacteria present in the mid and distal intestines of Atlantic salmon fed the five different diets estimated using traditional bacteriological techniques. The presence of an autochthonous microbiota was demonstrated using transmission electron microscopy. No significant effects of diet composition were observed on total population levels of culturable bacteria present in the digestive tract, but the study showed that the composition of the gut microbiota (autochthonous or allochthonous) was sensitive to dietary changes. A total of 752 culturable isolates from the intestines were characterized by biochemical and physiological properties. Of these, 188 isolates were further characterized by partial sequencing the 16S rRNA genes. Among these, 146 isolates belonged to 31 phylotypes that were >94% identical to previously described species. However, 42 isolates showed similarity <94% to species available at the National Center of Biotechnology Information. Several of the phylotypes identified in the present study have not been reported previously in the gastrointestinal (GI) tract of fish, including the Gram-negative bacteria Gelidibacter salicanalis, Pseudoalteromonas elyakovii, Psychrobacter aquimaris, Psychrobacter cibarius, Psychrobacter fozii, Psychrobacter maritimus, Psychrobacter okhotskensis and Psychrobacter psychrophilus. Among the Gram-positive bacteria identified were Arthrobacter bergeri, Arthrobacter psychrolactophilus, Arthrobacter rhombi, Bacillus pumilus, Bacillus subtilis, Exiguobacterium spp., Microbacterium oxydans, Planococcus maritimus, Sporosarcina ginsengisoli and several bacteria that have been described as unculturable previously. In addition, we identified Carnobacterium inhibens, a lactic acid bacterium that is not frequently isolated from the GI tract of fish. Psychrobacter cibarius was the dominant bacterial species and was isolated from the digestive tract of all fish investigated.

Effect of intraperitoneal injection of immunostimulatory substances on allochthonous gut microbiota of Atlantic salmon (Salmo salar L.) determined using denaturing gradient gel electrophoresis

The allochthonous microbiota in the proximal and distal intestine was investigated in three groups of Atlantic salmon (Salmo salar L.) fed a commercial diet and intraperitoneally injected with (a) phosphate-buffered saline (control), (b) lipopolysaccharide (LPS) from the fish pathogenic bacteria, Aeromonas salmonicida ssp. salmonicida, and (c) laminaran [β-(1,3)-d-glucan]. Denaturing gradient gel electrophoresis (DGGE) of the hyper variable V3 region was used to present the microbiota in different experimental groups. Sequencing and phylogenetic analysis of excised DGGE bands suggested that an intraperitoneal injection of LPS from A. salmonicida affects the allochthonous gut bacteria of Atlantic salmon to some extent, as Aeromonas enteropelogenes, Aeromonas veroni, Psychrobacter, Lactobacillus letvazi, Lactobacillus satsumensis, Pantoea, swine manure bacterium and several uncultured bacteria were unique for this group. On the other hand, the bacterial diversity of the allochthonous microbiota did not seem to be affected by injection of β-(1,3)-d-glucan. Sequences of this experimental group were most closely related to A. enteropelogenes, uncultured Escherichia and Lactobacillus aviarius ssp. aviarius.

Sediment–water exchange of Vibrio sp. and fecal indicator bacteria: Implications for persistence and transport in the Neuse River Estuary, North Carolina, USA

In estuaries, frequent resuspension and deposition of sediment complicate bacterial transport model development by transporting particle-attached bacteria and possibly inducing bacterial responses, such as growth, degradation, or changes in attachment. In order to better characterize these dynamics, observations were made in the Neuse River Estuary (NRE) using the combination of an in situ sampler to monitor the water column and sediment cores to monitor sediment concentrations. Two allochthonous bacteria, Escherichia coli (EC) and Enterococcus sp. (ENT), were selected as proxies for fecal contamination from stormwater runoff. Vibrio sp. (VIB), native to the NRE, was also observed as an autochthonous bacterial group that includes potentially pathogenic species. Two sampling periods were identified as dominated by different suspension types: runoff and resuspension. Despite this difference, several bacterial measures remained comparable between sampling periods. In bottom water, VIB concentration was correlated with salinity and ENT concentration was correlated with turbidity. Differences were observed for EC, where higher concentrations were found in hypoxic waters and sediment during the resuspension period. In the sediment, EC and VIB concentrations significantly increased following the passage of Hurricane Ophelia in September 2005. Throughout this study, all bacterial groups showed evidence of persistence in sediment, suggesting that sediment resuspension represents a significant source of bacteria to the water column.

Assessing the anthropogenic impact on Lake Shira from antibiotic resistance of heterotrophic bacteria by neural networks methods

A general approach to assessing the anthropogenic impact on lake ecosystems is proposed and exemplified for the case of Lake Shira (Republic of Khakasia, Russia). The impact strength is estimated by applying neural network-based methods to samples of data on interdependent marking features of autochthonous and allochthonous bacteria isolated from the lake in 1997-2001. The proposed combination of analysis methods makes it possible to determine the state of an ecosystem from both small- and large-size samples of data having complex interrelations.

Determining the domestic specific loads of two wastewater plants of the Paris conurbation (France) with contrasted treatments: A step for exploring the effects of the application of the European Directive

The effluents of wastewater treatment plants (WTTP) discharged into the rivers considerably affect the biogeochemical functioning of the system. In this paper, we characterize both raw and treated domestic wastewater from two WTTPs of Parisian agglomeration using different process treatments (Achères WWTP with a secondary treatment and Colombes WWTP with a tertiary one). In addition to the classical variables, we analyse the input of bacteria, both the heterotrophs and the nitrifyers. Tertiary treatment leads to significantly decrease ammonium-specific load (<2 g KjN inhab equ. −1 instead of 9 g KjN inhab equ. −1 for secondary treatment) and notably reduces the one of organic matter (∼2.5 g biological oxygen demand (BOD) inhab equ. −1 instead of ∼7.5 g BOD inhab equ. −1 for secondary treatment); it is therefore promising to improve oxygen status of both the Seine river and its estuary. In terms of total bacterial biomass abatement (the heterotrophs mostly), bioreactors (at Colombes WWTP) eliminate 12% more bacterial biomass than the activated sludge treatment (at Achères WWTP). Regarding the nitrifying bacteria, a tertiary treatment in bioreactors eliminates ⋍90% of both nitrifying bacteria and nitrogen pollution of wastewater. Bacterial populations are characterized by large size bacteria (>1 μm) with a higher growth rate, that represent in the treatment plant effluents 70% of the biomass. These large size bacteria have therefore a strong impact in the organic matter degradation and oxygen consumption. Relationships between classical physical–chemical variables routinely analysed in WWTPs laboratory and bacterial biomass (heterotrophic and nitrifying) are established, in order to quantify the ecological role of the allochthonous bacteria brought into the river system. In addition, domestic specific loads are calculated for both raw and treated effluents of the two types of WWTPs. As the application of the European Water Directive requires to upgrade the wastewater treatment at Achères WWTP as soon as 2007 for 90% nitrification and 30% denitrification and in 2015 for further denitrification (up to 70%), the results of this study can be taken as point-source constraints into the modelling approach already developed for the Seine basin, and chosen to test the implementation of the Water Frame Directive.

Multiple antibiotic resistance of heterotrophic bacteria in the littoral zone of Lake Shira as an indicator of human impact on the ecosystem

Resistance to Ampicillin and Kanamycin displayed by heterotrophic bacteria isolated in Summer and in Spring from the littoral and the central parts of Lake Shira (a therapeutic lake in the Khakasia Republic, Russia) has been investigated. It has been found that in Summer, human and animal microflora featuring multiple antibiotic resistance (to Ampicillin and Kanamycin) predominates in all the studied stations of the littoral zone of the lake. In Spring, concentrations of bacteria featuring multiple antibiotic resistance decrease significantly and bacteria sensitive to antibiotics predominate in the lake. Emergence of multiple antibiotic resistance in bacteria of Lake Shira is caused by the input of allochthonous bacteria into the lake; this feature of heterotrophic bacteria of Lake Shira can be used to monitor the impact on the ecosystem made by health resorts.