Yana Topalova

Survival of genetically marked Escherichia coli O157: H7 in soil as affected by soil microbial community shifts

A loamy sand soil sampled from a species-rich permanent grassland at a long-term experimental site (Wildekamp, Bennekom, The Netherlands) was used to construct soil microcosms in which the microbial community compositions had been modified by fumigation at different intensities (depths). As expected, increasing depth of fumigation was shown to result in progressively increasing effects on the microbiological soil parameters, as determined by cultivation-based as well as cultivation-independent (PCR-DGGE, PLFA) methods. Both at 7 and at 60 days after fumigation, shifts in the bacterial, fungal and protozoan communities were noted, indicating that altered community compositions had emerged following a transition phase. At the level of bacteria culturable on plates, an increase of the prevalence of bacterial r-strategists was noted at 7 days followed by a decline at 60 days, which also hinted at the effectiveness of the fumigation treatments. The survival of a non-toxigenic Escherichia coli O157:H7 derivative, strain T, was then assessed over 60 days in these microcosms, using detection via colony forming units counts as well as via PCR-DGGE. Both data sets were consistent with each other. Thus, a clear effect of fumigation depth on the survival of the invading strain T was noted, as a progressive increase of depth coincided with a progressively enhanced inoculant survival rate. As fumigation depth was presumably inversely related to community complexity, this was consistent with the hypothesis that soil systems with reduced biological complexity offer enhanced opportunities for invading microbial species to establish and persist. The significance of this finding is discussed in the light of the ongoing discussion about the complexity–invasiveness relationship within microbial communities, in particular regarding the opportunities of pathogens to persist.

ENZYME ACTIVITIES AND SHIFTS IN MICROBIAL POPULATIONS ASSOCIATED WITH ACTIVATED SLUDGE TREATMENT OF TEXTILE EFFLUENTS

ABSTRACT The enzyme studies on an activated sludge (AS) were aimed at providing information about adaptive response of microbial community during four significant alterations in textile wastewater treatment plant behavior associated with: shock loading with azo compounds; recovery after the xenobiotic shock; building up additional aerobic reactor; breakdown of facility exploitation for 5 months. The activity of several enzymes associated with target biodegradation processes was assessed. Induction of catechol 1,2—dioxygenase (C12DO), catechol 2,3—dioxygenase (C23DO), protocatechate 3,4—dioxygenase (P34DO) occurred under aerobic and notably under anoxic/microaerobic conditions, depending on the control point. Key microbial groups in the AS consortium were determined by cultivation-based-methods. The densities of bacteria from g. Pseudomonas (Ps) and Acinetobacter (Acin) were increased during the toxic shock. Aerobic heterotrophs (AH) and g. Acinetobacter decreased after pause of facility exploitation. The numbers of denitrifying bacteria (Dn) in denitrifying reactor were significantly decreased after each of the critical events.

Adaptive response of trivial activated sludge towards toxic effect of oNP, PCP and combination oNP/PCP

Abstract The reaction of the real aerobic activated sludge taken from the Sofia Waste Water Treatment Plant (SWWTP) and treated with the xenobiotics pentachlorphenol (PCP) (0.16 mMol), ortho-nitrophenol (oNP) (0.58 mMol) and with a combination of PCP (0.08 mMol), oNP (0.29 mMol) has been investigated in a model detoxification process. The adaptive changes are studied in the microbial structure level and at the level of changes in the qualitative and quantitative parameters of the macro-organisms in the activated sludge (consuments of I and II level). The presence of several different taxonomic groups has been shown by other researchers to be essential in the detoxification process. The quantitative changes in these taxonomic and physiological groups of micro-organisms are studied. The number of micro-organisms from Pseudomonas, Acinetobacter and the bacteria from the xenobiotic-catabolizing complex considerably increased with the individual and the combined effect of the xenobiotics oNP, PCP and oNP/PCP. At the same time the toxic shock leads to a remarkable reduction of NH 3 releasing, nitrifying bacteria and those from family Enterobacteriaceae . It is ascertained that the number of Ciliata, Flagellata apochromata, Oligochaeta and Rotatoria is strongly decreased in the series of samples treated with xenobiotics. The leading role of micro-organisms in the real detoxification of hazardous pollutants was experimentally confirmed by research.

Ortho—Nitrophenol Removal in two Types Activated Sludge: The Role of Microbiological and Enzymological Adaptation

ABSTRACTThe relation between the structural and functional changes in two types anaerobic activated sludge—ASt (activated sludge trivial) and ASg (activated sludge granular) from waste water treatment process with high organic load and working under presence of hazardous pollutants (oNP—ortho-nitrophenol) has been investigated. The adaptive response on the different levels—microbiological structure, effectiveness of oNP-removal, oxygenase and succinate dehydrogenase activities towards the increasing oNP-concentration has been assessed. The obtained results demonstrate that for the complete oNP-biodegradation to harmless products—the aerobic finishing treating process is applicable and needed. In these conditions the amount of microorganisms from genus Pseudomonas and oNP-degrading bacteria, an efficiency oNP-biodegradation and oxygenase activities were increased considerably.

Phenol degradation by environmental bacteria entrapped in cryogels

The aim of this study was to assess the capability of bacterial isolates immobilized on poly(ethylene oxide) (PEO) cryogels to degrade and utilize phenol as a sole source of carbon and energy. Two xenobiotic-degrading bacteria were isolated from industrial areas polluted with heavy metals and aromatics. Sequencing of their 16S rDNA classified them as Pseudomonas rhodesiae (denoted as KCM R5) and Bacillus subtilis (denoted as KCM RG5). The following operation parameters were used: sequencing batch process, 24 h cycle of feeding, increasing phenol concentrations from 300 to 1000 mg·L−1, volume of inflow – 250 mL, volume of outflow – from 212 to 7 mL and temperature of 28 °C. The PEO-KCM R5 biofilter was found to remove phenol at a concentration of 1000 mg·L−1, while the PEO-KCM RG5 system was unable to degrade phenol at a concentration of about 600 mg·L−1. After four weeks of biodegradation, the PEO biofilms remained compact, porous and elastic, while containing compact microbial biofilm as shown by scanning electron microscopy analysis of the cryogels. Taken together, our results demonstrate that our novel bacterial entrapment system in PEO cryogels is highly effective and sustainable for phenol degradation and can be relevant for application in the detoxification technologies of industrially polluted waters.

BIODEGRADATION POTENTIAL OF PHENOL-RESISTANT BACTERIA LOCALIZED IN DIFFERENT STREAM HABITATS

ABSTRACT The process of biotransformation and elimination of toxic xenobiotics in natural river ecosystems is a matter of intensive research regarding its applicability in biomonitoring and bioremediation procedures. The main objectives of this study were (1) to assess and compare the phenol-biodegradation potential among the basic river habitats using isolated mixed microbial cultures from sites, with different level of pollution, located in Iskar River; (2) to examine relationships between main parameters of the degradation process and functional structure of local microbial community using multivariate approaches. The results showed that all investigated microbial cultures were able to eliminate almost entirely (95-98%) the introduced quantities of phenol (150 mg/ml) as a sole source of carbon and energy for a period of 72 hours and that phenol was mainly degraded through the ortho ring cleavage pathways. However the extensive research revealed a significant excellence of biodegradation potential in microbial communities located in the sediment water. On the other hand the most distinct rates of phenol-degradation between sites were observed with regard to the mixed cultures, adsorbed to river sediments. Conducted principal component (PCA) and co-inertia (CIA) analyses underlined some habitat specifics in the relationships between biodegradation and microbial community characteristics. We concluded that the anthropogenic pollution leads to decrease and serious transformation of relationships mentioned above in surface water and sediments.

Long-term assessment of the self-purification potential of a technologically managed ecosystem: the Middle Iskar cascade.

The Middle Iskar cascade is situated along the middle course of the Iskar River (Bulgaria) after the capital city Sofia and has three small hydroelectric power plants that were put into operation by the end of 2012. The aim of this study was to evaluate the self-purification potential of water in the reservoirs of these plants as an important and necessary condition for their ecological functioning. The assessment was made by hydrochemical parameters (dissolved suspended solids, insoluble suspended solids, total suspended solids, nitrites, nitrates, ammonium, phosphates, chemical oxygen demand, dissolved oxygen) and microbiological parameters (aerobic heterotrophic bacteria and bacteria growing in an Endo medium) and covered a period of three years (2010, 2011 and 2012). Standard methods were applied, mainly colorimetric and microbiological cultivation methods. The obtained results showed high levels of some of the tested indicators during 2012. In the section of the Middle Iskar cascade a high self-purification potential was observed in the reservoirs which maintain good water quality.

Two Steps for Speeding up of Phenol Detoxification

ABSTRACTTwo steps of enhancement of phenol detoxification by Bacillus laterosporus BT-271 by means of increasing of the rate of aeration and adding in an apropriate moment a carrier (penopolystyrol pellets, covered with active carbon) were studied. The effectiveness of phenol biodegradation was enhanced with 42 %. Comparative study of the oxygenase activities of the freely suspended cells at the two steps of speeding up of the phenol elimination to elucidate the mechanisms of the processes was carried out.

Xenobiotic Biotransformation Potential of Pseudomonas Rhodesiae KCM-R5 and Bacillus Subtilis KCM-RG5, Tolerant to Heavy Metals and Phenol Derivatives

ABSTRACT Two environmental bacterial isolates KCM-R5 and KCM-RG5 were selected from xenobiotic-polluted environment. KCM-R5 was identified as Pseudomonas rhodesiae and KCM-RG5 as Bacillus subtilis. KCM-R5 demonstrated tolerance to heavy metals and KCM-RG5—to heavy metals and phenol derivatives. Both strains were studied for xenobiotic biotransformation in order to contribute towards bioremediation of polluted environments. Pseudomonas rhodesiae KCM-R5 and Bacillus subtilis. KCM-RG5 possess unusual ability to utilize ortho-nitrophenol (o-NP) and 2,4- dichlorophenoxyacetic acid (2,4-D). o-NP and 2,4-D were added at concentration 30 mg/l. The possible indictive/inhibiting effect of Pb cations (40mg/l) was also studied. Pseudomonas rhodesiae KCM-R5 removed 86% of o-NP and below 1% of 2,4-D. Bacillus subtilis KCM-RG5 eliminated 83% of o-NP and under 1% of 2,4-D. Biotransformation effectiveness of o-NP reached 95–100% in contrast to 2,4-D where the effectiveness was just 15–20%. Cell morphological changes were registered during the biotransformation processes. The obtained results could contribute to manage bioremediation processes in polluted with heavy metals and phenol derivatives environments.

EVOLUTION OF THE EXPERIMENTAL PLAN IN DATA COLLECTION AND VERIFICATION TACTICS IN MODELLING OF RIVER WATER QUALITY

ABSTRACT Modeling is one of the basic approaches for preventive management of the water quantity and quality, as well as for the ecological sufficiency of the river. The approach for selection of parameters and data collection, specific and unique for each model, is an important element in this aspect. This data plays a critical role for the calibration and verification of models. In this paper two years of investigations of the gradual adaptation of the experimental plan of data collection as well as the adequate development according to the HSPF (EPA) model and specificity of Iskar River (Bulgaria) have been presented. The 8—degree experimental evolution was accomplished in line with the principles of EMS, ISO-14000, WFD, ecological complexity and interdisciplinary approach. The obtained results confirmed that mathematical instruments of the model require individual experimental scenario for data collection, specific for each catchment parameter, application of variety of approaches for measurement of the real rate of the processes—opposite scaling up, physical and analogous modeling, selection of critical control points, parameters and temporal scheme.