scholarly journals Impact of NaCl, nitrate and temperature on the microbial community of a methanol-fed, denitrifying marine biofilm

2019 ◽  
Author(s):  
Richard Villemur ◽  
Geneviève Payette ◽  
Valérie Geoffroy ◽  
Florian Mauffrey ◽  
Christine Martineau
Keyword(s):  
Microbial Community ◽  
Environmental Changes ◽  
Heterotrophic Bacteria ◽  
Denitrifying Bacteria ◽  
Metagenomic Data ◽  
Strong Impact ◽  
Anoxic Conditions ◽  
Pure Cultures ◽  
Denitrification Genes ◽  
The Impact

AbstractBackgroundThe biofilm of a continuous, methanol-fed, fluidized denitrification system that treated a marine effluent at the Montreal Biodome is composed of a multi-species microbial community, among whichHyphomicrobium nitrativoransNL23 andMethylophaga nitratireducenticrescensJAM1 are the principal bacteria involved in the denitrifying activities. To assess its resilience to environmental changes, the biofilm taken from the denitrification system was cultured at laboratory scale in artificial seawater (ASW) under anoxic conditions and exposed to a range of specific physico-chemical parameters. We previously showed that the seawater formulation and the NaCl concentrations had a strong impact on theH. nitrativoransNL23 population, with its displacement by a new denitrifier,M. nitratireducenticrescensGP59. Here, we report the impact of these cultures conditions on the dynamics of the overall microbial community of the denitrifying biofilm.MethodsThe original biofilm (OB) taken from the denitrification system was acclimated for five weeks in ASW under anoxic conditions with a range of NaCl concentrations, and with four combinations of nitrate concentrations and temperatures. The OB was also acclimated to the commercial Instant Ocean seawater medium (IO). The bacterial diversity of the biofilm cultures and the OB was determined by 16S ribosomal RNA amplicon metagenome sequencing. Culture-dependent approach was used to isolate other denitrifying bacteria from the biofilm cultures. The metatranscriptomes of some of the biofilm cultures were derived, along with the transcriptomes of planktonic pure cultures ofH. nitrativoransNL23 andM. nitratireducentricrescensGP59 cultivated under denitrifying conditions.ResultsThe 16S metagenomic data revealed very high proportions ofM. nitratireducenticrescensin the biofilm cultures.H. nitrativoransNL23 was found in high proportion in the OB, both was absent in the biofilm cultures with 2.75% NaCl in the ASW medium. It was found however in low proportions in the biofilm cultures with 0 to 1% NaCl in the ASW medium and in the IO biofilm cultures. Emergence ofMarinicellaspp. occurred in these biofilm cultures. Denitrifying bacterial isolates affiliated toMarinobacterspp. andParacoccusspp. were isolated. Up regulation of the denitrification genes in strains GP59 and NL23 occurred in the biofilm cultures compared to the planktonic pure cultures. Denitrifying bacteria affiliated to theStappiaspp. were metabolically active in the biofilm cultures.ConclusionsThese results illustrate the dynamics of the microbial community in the denitrifying biofilm cultures in adapting to different environmental conditions. The NaCl concentration is an important factor affecting the microbial community in the biofilm cultures. Up regulation of the denitrification genes in strain GP59 and strain NL23 in the biofilm cultures suggests different mechanisms of regulation of the denitrification pathway in the biofilm compared to the planktonic pure cultures. Other denitrifying heterotrophic bacteria are present in low proportions in the biofilm, suggesting that the biofilm has the potential to adapt to heterotrophic, non-methylotrophic environments.

scholarly journals Dynamics of a methanol-fed marine denitrifying biofilm: 2—impact of environmental changes on the microbial community

PeerJ ◽  
2019 ◽  
Vol 7 ◽  
pp. e7467 ◽  
Author(s):  
Richard Villemur ◽  
Geneviève Payette ◽  
Valérie Geoffroy ◽  
Florian Mauffrey ◽  
Christine Martineau
Keyword(s):  
Microbial Community ◽  
Environmental Conditions ◽  
Environmental Changes ◽  
Heterotrophic Bacteria ◽  
Denitrifying Bacteria ◽  
Anoxic Conditions ◽  
Nacl Concentration ◽  
Pure Cultures ◽  
Denitrification Genes ◽  
The Impact

Background The biofilm of a methanol-fed, marine denitrification system is composed of a multi-species microbial community, among which Hyphomicrobium nitrativorans and Methylophaga nitratireducenticrescens are the principal bacteria involved in the denitrifying activities. To assess its resilience to environmental changes, the biofilm was cultivated in artificial seawater (ASW) under anoxic conditions and exposed to a range of specific environmental conditions. We previously reported the impact of these changes on the denitrifying activities and the co-occurrence of H. nitrativorans strain NL23 and M. nitratireducenticrescens in the biofilm cultures. Here, we report the impact of these changes on the dynamics of the overall microbial community of the denitrifying biofilm. Methods The original biofilm (OB) taken from the denitrification system was cultivated in ASW under anoxic conditions with a range of NaCl concentrations, and with four combinations of nitrate/methanol concentrations and temperatures. The OB was also cultivated in the commercial Instant Ocean seawater (IO). The bacterial diversity of the biofilm cultures and the OB was determined by 16S ribosomal RNA gene sequences. Culture approach was used to isolate other denitrifying bacteria from the biofilm cultures. The metatranscriptomes of selected biofilm cultures were derived, along with the transcriptomes of planktonic pure cultures of H. nitrativorans strain NL23 and M. nitratireducenticrescens strain GP59. Results High proportions of M. nitratireducenticrescens occurred in the biofilm cultures. H. nitrativorans strain NL23 was found in high proportion in the OB, but was absent in the biofilm cultures cultivated in the ASW medium at 2.75% NaCl. It was found however in low proportions in the biofilm cultures cultivated in the ASW medium at 0–1% NaCl and in the IO biofilm cultures. Denitrifying bacterial isolates affiliated to Marinobacter spp. and Paracoccus spp. were isolated. Up regulation of the denitrification genes of strains GP59 and NL23 occurred in the biofilm cultures compared to the planktonic pure cultures. Denitrifying bacteria affiliated to the Stappia spp. were metabolically active in the biofilm cultures. Conclusions These results illustrate the dynamics of the microbial community in the denitrifying biofilm cultures in adapting to different environmental conditions. The NaCl concentration is an important factor affecting the microbial community in the biofilm cultures. Up regulation of the denitrification genes of M. nitratireducenticrescens strain GP59 and H. nitrativorans strain NL23 in the biofilm cultures suggests different mechanisms of regulation of the denitrification pathway in the biofilm. Other denitrifying heterotrophic bacteria are present in low proportions, suggesting that the biofilm has the potential to adapt to heterotrophic, non-methylotrophic environments.

scholarly journals Multi-domain probiotic consortium as an alternative to chemical remediation of oil spills at coral reefs and adjacent sites

Microbiome ◽  
2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Denise P. Silva ◽  
Helena D. M. Villela ◽  
Henrique F. Santos ◽  
Gustavo A. S. Duarte ◽  
José Roberto Ribeiro ◽  
...  
Keyword(s):  
Microbial Community ◽  
Coral Reefs ◽  
Environmental Changes ◽  
Oil Spills ◽  
Anthropogenic Activities ◽  
Oil Contamination ◽  
Negative Effects ◽  
Corexit 9500 ◽  
Coral Health ◽  
The Impact

Abstract Background Beginning in the last century, coral reefs have suffered the consequences of anthropogenic activities, including oil contamination. Chemical remediation methods, such as dispersants, can cause substantial harm to corals and reduce their resilience to stressors. To evaluate the impacts of oil contamination and find potential alternative solutions to chemical dispersants, we conducted a mesocosm experiment with the fire coral Millepora alcicornis, which is sensitive to environmental changes. We exposed M. alcicornis to a realistic oil-spill scenario in which we applied an innovative multi-domain bioremediator consortium (bacteria, filamentous fungi, and yeast) and a chemical dispersant (Corexit® 9500, one of the most widely used dispersants), to assess the effects on host health and host-associated microbial communities. Results The selected multi-domain microbial consortium helped to mitigate the impacts of the oil, substantially degrading the polycyclic aromatic and n-alkane fractions and maintaining the physiological integrity of the corals. Exposure to Corexit 9500 negatively impacted the host physiology and altered the coral-associated microbial community. After exposure, the abundances of certain bacterial genera such as Rugeria and Roseovarius increased, as previously reported in stressed or diseased corals. We also identified several bioindicators of Corexit 9500 in the microbiome. The impact of Corexit 9500 on the coral health and microbial community was far greater than oil alone, killing corals after only 4 days of exposure in the flow-through system. In the treatments with Corexit 9500, the action of the bioremediator consortium could not be observed directly because of the extreme toxicity of the dispersant to M. alcicornis and its associated microbiome. Conclusions Our results emphasize the importance of investigating the host-associated microbiome in order to detect and mitigate the effects of oil contamination on corals and the potential role of microbial mitigation and bioindicators as conservation tools. Chemical dispersants were far more damaging to corals and their associated microbiome than oil, and should not be used close to coral reefs. This study can aid in decision-making to minimize the negative effects of oil and dispersants on coral reefs.

scholarly journals Removal of tetracyclines in wastewater : accumulation and distribution of chlortetracycline in bulk water and biomass compartments in activated sludge

2021 ◽  
Author(s):  
Ruba F. Farkh
Keyword(s):  
Microbial Community ◽  
Activated Sludge ◽  
Ethylenediaminetetraacetic Acid ◽  
Divalent Cations ◽  
Bulk Water ◽  
Microbial Cells ◽  
Initial Concentration ◽  
Anoxic Conditions ◽  
Polymeric Substance ◽  
The Impact

A study was conducted to examine the removal of chlortetracycline and its distribution and accumulation in three compartments; bulk water, extracellular polymeric substance (EPS) and the microbial cells in activated sludge. Also the effect of different environmental conditions on the distribution and accumulation in the three compartments was investigated. Effluent samples collected from a municipal activated sludge treatment system were set up in bath experiments to test the distribution and accumulation of chlortetracycline under aerobic and anoxic conditions for 14 days. In addition, the impact of the activity of the microbial community on the amassing of the antibiotic in the biomass was examined. The effect of divalent cations on import and accumulation of chlortetracycline was tested. Sorption in believed to be the main removal pathway in wastewater treatment systems for tetracyclines in general and chlortetracycline in particular. In this study that notion was confirmed, and it was found that the removal via sorption under anoxic condition (43.2%) is almost double of that under aerobic conditions (27.0%). The amount of what accumulated in the cells compared to that sorbed in the EPS is twice as much in the former and triple as much in the latter. These findings suggest that changes in the structure and charge of the EPS could be the reason of higher accumulation in the polymeric substance. The impact of microbial activity on the sorption and distribution of the chlortetracycline in the three compartments showed almost a similar behaviour to that under aerobic and anoxic conditions. It was clear that the more viable the microbial community, the less the antibiotic accumulated in the [sic] both biomass compartments; the EPS and microbial cells. Biomass with inhibited respiration accrued 90% of the initial concentration; where as the active microbial community was more resistant and only 24.2% of the initial concentration accumulated within the cells. The findings suggest that the antibiotic makes its way to the cells thus bypassing the EPS, and is trapped in the EPS as it is pumped out of the cells in an energy dependent mechanism. The presence of ethylenediaminetetraacetic acid (EDTA) which is a strong chelator had no import effect. Nevertheless it did indicate that the accumulation in the EPS could be attributed to the presence of cations since there was a high negative correlation (-0.98) between the disappearance of the antibiotic from the EPS compartment and the EDTA concentration used in incubation.

scholarly journals Achieving similar root microbiota composition in neighbouring plants through airborne signalling

2020 ◽  
Author(s):  
Hyun Gi Kong ◽  
Geun Cheol Song ◽  
Hee-Jung Sim ◽  
Choong-Min Ryu
Keyword(s):  
Microbial Community ◽  
Environmental Changes ◽  
Tomato Seedling ◽  
Environmental Signals ◽  
Plant Volatile ◽  
The Status ◽  
Plant Growth Promoting ◽  
The Impact ◽  
First Time ◽  
Rhizosphere Microbial Community

Abstract The ability to recognize and respond to environmental signals is essential for plants. In response to environmental changes, the status of a plant is transmitted to other plants in the form of signals such as volatiles. Root-associated bacteria trigger the release of plant volatile organic compounds (VOCs). However, the impact of VOCs on the rhizosphere microbial community of neighbouring plants is not well understood. Here, we investigated the effect of VOCs on the rhizosphere microbial community of tomato plants inoculated with a plant growth-promoting rhizobacterium Bacillus amyloliquefaciens strain GB03 and that of their neighbouring plants. Interestingly, high similarity (up to 69%) was detected in the rhizosphere microbial communities of the inoculated and neighbouring plants. Leaves of the tomato plant treated with strain GB03-released β-caryophyllene as a signature VOC, which elicited the release of a large amount of salicylic acid (SA) in the root exudates of a neighbouring tomato seedling. The exposure of tomato leaves to β-caryophyllene resulted in the secretion of SA from the root. Our results demonstrate for the first time that the composition of the rhizosphere microbiota in surrounding plants is synchronized through aerial signals from plants.

scholarly journals The role of chronic kidney disease-associated dysbiosis in cardiovascular disease

2019 ◽  
Vol 244 (6) ◽  
pp. 514-525 ◽  
Author(s):  
Mark A Bryniarski ◽  
Fares Hamarneh ◽  
Rabi Yacoub
Keyword(s):  
Cardiovascular Disease ◽  
Chronic Kidney Disease ◽  
Microbial Community ◽  
Kidney Disease ◽  
Cardiovascular Events ◽  
Environmental Changes ◽  
Intestinal Microbiome ◽  
Intestinal Lumen ◽  
Stage Renal Disease ◽  
The Impact

Survival outcomes of patients with end stage renal disease are worse than those of many metastatic cancers. Kidney disease patients are often inflicted with higher rates of cardiovascular disease, in which nearly half of the mortalities are attributed to adverse cardiovascular events. Of the multifarious reasons for this detrimental impact, dysbiosis in the intestinal microbiome is surfacing as a potential participant. This is likely due to the numerous metabolic and inflammatory shifts found in chronic kidney disease, as well as environmental changes within the intestinal lumen. Studies are beginning to link microbiota alterations mediated by chronic kidney disease to negative cardiovascular outcomes. Here, recent findings connecting dysbiosis in chronic kidney disease and various cardiovascular insults are reviewed. Impact statement Negative alterations, or dysbiosis, in the intestinal microbial community balance in response to chronic kidney disease is emerging as a substantial and important factor in inducing and exacerbating multiple comorbid conditions. Patients with renal insufficiency experience a substantial increase in cardiovascular risk, and recent evidence is shedding light on the close interaction between microbiome dysbiosis and increased cardiovascular events in this population. Previous association and recent causality studies utilizing experimental animal models have enriched our understanding and confirmed the impact of microbial community imbalance on cardiac health in both the general population and in patients with renal impairment.

Changes in soil properties on agricultural land with the impact of water and tillage erosion in the last 60 years

2020 ◽  
Author(s):  
Anna Juřicová ◽  
Tomáš Chuman ◽  
Daniel Žížala
Keyword(s):  
Spatial Variability ◽  
Soil Properties ◽  
Large Scale ◽  
Agricultural Land ◽  
Environmental Changes ◽  
Soil Depth ◽  
Field Investigation ◽  
Strong Impact ◽  
The Impact ◽  
Tillage Erosion

<p>The decline in soil organic carbon (SOC) is generally perceived as a major threat to the sustainability of the soil due to its key role in many productive and non - productive soil functions. The aim of this research is to assess the intensity of changes and the spatial variability of SOC and soil depth in the last 60 years. Estimation of spatial variability of soil properties was performed by using digital soil mapping. A study area is located in the chernozems area in south Moravia (Czechia). This region is traditionally intensively cultivated with the strong impact of water and tillage erosion. The study is based on the analysis of historical data that comes from the Large-scale mapping of Agricultural Soils in Czechoslovakia soil database. Our dataset contained data from 120 soil profiles. A new field investigation shows significant SOC losses on steep slopes and slope shoulders with a decrease of depth of the humic horizon. As a result, there is a gradual transformation of soil units from the former Calcic Chernosems into the Haplic Calcisols. These findings are the result of ongoing environmental changes with the strong impact of historical agricultural policy and inappropriate interference in the landscape.</p>

scholarly journals Main drivers affecting the Holocene sedimentary record – implications from small lake in Latvia

Baltica ◽  
2016 ◽  
Vol 29 (1) ◽  
pp. 63-78 ◽  
Author(s):  
Jaanus Terasmaa ◽  
Liisa Puusepp ◽  
Egert Vandel ◽  
Agáta Marzecová ◽  
Tiiu Koff ◽  
...  
Keyword(s):  
Environmental Changes ◽  
Climatic Conditions ◽  
Lake Basin ◽  
Strong Impact ◽  
Sedimentary Record ◽  
The Holocene ◽  
Multiple Indicators ◽  
Sediment Mass ◽  
Ground Penetrating ◽  
The Impact

A multi-indicator paleolimnological study of sediments from Lake Ķūži (central Latvia) was used to obtain a comprehensive record of environmental changes in the Holocene. Periodicity in the changes and the main drivers (lake basin development, catchment properties, climate, human activities) of the sedimentary record was studied. In order to comprehend the whole-lake sedimentation during the Holocene, a detailed multiindicator record from the central part of the lake was integrated with records of sediment mass accumulation rates from four cores from different parts of the lake and a GPR (ground-penetrating radar) survey of the lake basin. The observed changes in the sedimentation regime that took place during the early Holocene are strongly linked with variations in climatic conditions, but the catchment and lake basin also played an important role. In the middle Holocene the water level was stable and the lake was influenced by climate mediated through changes in the catchment vegetation. Around 5 000 cal. BP sedimentation pattern changed, and three of the four main drivers made a comparably strong impact on the sedimentary signal. Since 2 000 cal. BP multiple indicators point to a major disturbance clearly related to human activity, which conceals the impact of the natural drivers.

scholarly journals Dynamics of a methanol-fed marine denitrifying biofilm: 1-Impact of environmental changes on the denitrification and the co-occurrence of Methylophaga nitratireducenticrescens and Hyphomicrobium nitrativorans

PeerJ ◽  
2019 ◽  
Vol 7 ◽  
pp. e7497
Author(s):  
Geneviève Payette ◽  
Valérie Geoffroy ◽  
Christine Martineau ◽  
Richard Villemur
Keyword(s):  
Environmental Changes ◽  
Gradual Increase ◽  
Artificial Seawater ◽  
Methanol Concentration ◽  
Anoxic Conditions ◽  
High Ph ◽  
Nacl Concentration ◽  
Biofilm Development ◽  
The Impact

Background The biofilm of a methanol-fed denitrification system that treated a marine effluent is composed of multi-species microorganisms, among which Hyphomicrobium nitrativorans strain NL23 and Methylophaga nitratireducenticrescens strain JAM1 are the principal bacteria involved in the denitrifying activities. Here, we report the capacity of the denitrifying biofilm to sustain environmental changes, and the impact of these changes on the co-occurrence of H. nitrativorans and M. nitratireducenticrescens. Methods In a first set of assays, the original biofilm (OB) was cultivated in an artificial seawater (ASW) medium under anoxic conditions to colonize new carriers. The new formed biofilm was then subjected to short exposures (1–5 days) of a range of NaCl, methanol, nitrate (NO3−) and nitrite (NO2−) concentrations, and to different pHs and temperatures. In a second set of assays, the OB was cultivated in ASW medium for five weeks with (i) a range of NaCl concentrations, (ii) four combinations of NO3−/methanol concentrations and temperatures, (iii) NO2−, and (iv) under oxic conditions. Finally, the OB was cultivated for five weeks in the commercial Instant Ocean (IO) seawater. The growth of the biofilm and the dynamics of NO3− and NO2− were determined. The levels of M. nitratireducenticrescens and H. nitrativorans were measured by qPCR. Results In the first set of assays, the biofilm cultures had the capacity to sustain denitrifying activities in most of the tested conditions. Inhibition occurred when they were exposed to high pH (10) or to high methanol concentration (1.5%). In the second set of assays, the highest specific denitrification rates occurred with the biofilm cultures cultivated at 64.3 mM NO3− and 0.45% methanol, and at 30 °C. Poor biofilm development occurred with the biofilm cultures cultivated at 5% and 8% NaCl. In all biofilm cultures cultivated in ASW at 2.75% NaCl, H. nitrativorans strain NL23 decreased by three orders of magnitude in concentrations compared to that found in OB. This decrease coincided with the increase of the same magnitude of a subpopulation of M. nitratireducenticrescens (strain GP59 as representative). In the biofilm cultures cultivated at low NaCl concentrations (0% to 1.0%), persistence of H. nitrativorans strain NL23 was observed, with the gradual increase in concentrations of M. nitratireducenticrescens strain GP59. High levels of H. nitrativorans strain NL23 were found in the IO biofilm cultures. The concentrations of M. nitratireducenticrescens strain JAM1 were lower in most of the biofilms cultures than in OB. Conclusions These results demonstrate the plasticity of the marine methylotrophic denitrifying biofilm in adapting to different environmental changes. The NaCl concentration is a crucial factor in the dynamics of H. nitrativorans strain NL23, for which growth was impaired above 1% NaCl in the ASW-based biofilm cultures in favor of M. nitratireducenticrescens strain GP59.

scholarly journals Feedback between environment and traits under selection in a seasonal environment: consequences for experimental evolution

2018 ◽  
Vol 285 (1876) ◽  
pp. 20180284 ◽  
Author(s):  
Dorian Collot ◽  
Thibault Nidelet ◽  
Johan Ramsayer ◽  
Olivier C. Martin ◽  
Sylvie Méléard ◽  
...  
Keyword(s):  
Experimental Evolution ◽  
Life History Traits ◽  
Environmental Changes ◽  
Strong Impact ◽  
Fitness Components ◽  
Batch Cultures ◽  
Seasonal Environment ◽  
Different Seasons ◽  
Using Data ◽  
The Impact

Batch cultures are frequently used in experimental evolution to study the dynamics of adaptation. Although they are generally considered to simply drive a growth rate increase, other fitness components can also be selected for. Indeed, recurrent batches form a seasonal environment where different phases repeat periodically and different traits can be under selection in the different seasons. Moreover, the system being closed, organisms may have a strong impact on the environment. Thus, the study of adaptation should take into account the environment and eco-evolutionary feedbacks. Using data from an experimental evolution on yeast Saccharomyces cerevisiae , we developed a mathematical model to understand which traits are under selection, and what is the impact of the environment for selection in a batch culture. We showed that two kinds of traits are under selection in seasonal environments: life-history traits, related to growth and mortality, but also transition traits, related to the ability to react to environmental changes. The impact of environmental conditions can be summarized by the length of the different seasons which weight selection on each trait: the longer a season is, the higher the selection on associated traits. Since phenotypes drive season length, eco-evolutionary feedbacks emerge. Our results show how evolution in successive batches can affect season lengths and strength of selection on different traits.

scholarly journals Removal of tetracyclines in wastewater : accumulation and distribution of chlortetracycline in bulk water and biomass compartments in activated sludge

2021 ◽  
Author(s):  
Ruba F. Farkh
Keyword(s):  
Microbial Community ◽  
Activated Sludge ◽  
Ethylenediaminetetraacetic Acid ◽  
Divalent Cations ◽  
Bulk Water ◽  
Microbial Cells ◽  
Initial Concentration ◽  
Anoxic Conditions ◽  
Polymeric Substance ◽  
The Impact

A study was conducted to examine the removal of chlortetracycline and its distribution and accumulation in three compartments; bulk water, extracellular polymeric substance (EPS) and the microbial cells in activated sludge. Also the effect of different environmental conditions on the distribution and accumulation in the three compartments was investigated. Effluent samples collected from a municipal activated sludge treatment system were set up in bath experiments to test the distribution and accumulation of chlortetracycline under aerobic and anoxic conditions for 14 days. In addition, the impact of the activity of the microbial community on the amassing of the antibiotic in the biomass was examined. The effect of divalent cations on import and accumulation of chlortetracycline was tested. Sorption in believed to be the main removal pathway in wastewater treatment systems for tetracyclines in general and chlortetracycline in particular. In this study that notion was confirmed, and it was found that the removal via sorption under anoxic condition (43.2%) is almost double of that under aerobic conditions (27.0%). The amount of what accumulated in the cells compared to that sorbed in the EPS is twice as much in the former and triple as much in the latter. These findings suggest that changes in the structure and charge of the EPS could be the reason of higher accumulation in the polymeric substance. The impact of microbial activity on the sorption and distribution of the chlortetracycline in the three compartments showed almost a similar behaviour to that under aerobic and anoxic conditions. It was clear that the more viable the microbial community, the less the antibiotic accumulated in the [sic] both biomass compartments; the EPS and microbial cells. Biomass with inhibited respiration accrued 90% of the initial concentration; where as the active microbial community was more resistant and only 24.2% of the initial concentration accumulated within the cells. The findings suggest that the antibiotic makes its way to the cells thus bypassing the EPS, and is trapped in the EPS as it is pumped out of the cells in an energy dependent mechanism. The presence of ethylenediaminetetraacetic acid (EDTA) which is a strong chelator had no import effect. Nevertheless it did indicate that the accumulation in the EPS could be attributed to the presence of cations since there was a high negative correlation (-0.98) between the disappearance of the antibiotic from the EPS compartment and the EDTA concentration used in incubation.

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