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Knowledge about the influence of C:N ratio on the biodegradation process of hydrocarbon compounds is of significant importance in the development of biostimulation techniques. The purpose of this study was to assess the impact of nitrogen compounds on the environmental consortium during the process of biological decomposition of hydrocarbons. The experimental variants represented low, moderate, and excessive biostimulation with nitrogen compounds. The metabolic activity of the consortium was tested using the flow cytometry technique. The efficiency of the biodegradation of hydrocarbons of the consortium, based on the gas chromatography method, and metapopulation changes, based on the analysis of V4 16srRNA sequencing data, were assessed. The results of the research confirm the positive effect of properly optimized biostimulation with nitrogen compounds on the biological decomposition of polycyclic aromatic hydrocarbons. The negative impact of excessive biostimulation on the biodegradation efficiency and metabolic activity of microorganisms is also proven. Low resistance to changes in the supply of nitrogen compounds is demonstrated among the orders Xanthomonadales, Burkholderiales, Sphingomonadales, Flavobacteriales, and Sphingobacteriales. It is proven that quantitative analysis of the order of Rhizobiales, characterized by a high-predicted potential for the decomposition of polycyclic aromatic hydrocarbons, may be helpful during biostimulation optimization processes in areas with a high nitrogen deficiency. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the influence of Trichoderma viride on the metabolic activity and the community dynamics of soil bacteria during polyaromatic hydrocarbons (PAHs) biodegradation. Sixteen PAHs were introduced into soil microcosms mimicking natural conditions to achieve an initial concentration of 2000 mg kg −1 of soil. After 12 months of treatment, the efficiency of PAH removal was of 78% for the microcosms inoculated with a PAH-degrading bacterial consortium designated S3, 64% for those inoculated with the consortium S3 + T. viride , whereas an efficiency of only 47% was achieved in the microcosms inoculated with T. viride alone. Flow cytometry analysis of the bacterial metabolic activities, expressed as the oxidation-reduction potential, allowed differentiating single cells with regard to their metabolic activities. Prior to its introduction in soil microcosms, the consortium S3 consisted of 195 bacterial species which were identified by employing next generation sequencing (MiSeq, Illumina). It has been established that significant changes in the composition of the bacterial community occurred during the biodegradation process when it was carried out in the presence of T. viride . After such treatment only 73 bacterial species were identified from the metabiome, with the dominance of Stenotrophomonas retroflexus (47.46%), Ochrobactrum intermedium (25.83%) and Citrobacter freundii (19.87%). T. viride was able to degrade PAHs; however its presence mainly contributed to modify the bacterial metabiome via antagonistic interactions with the bacteria, which notably reduced the biodegradation efficiency and biodiversity in the microcosms. [ABSTRACT FROM AUTHOR]

The study focused on assessing the influence of rhamnolipids on the phytotoxicity of diesel oil-contaminated soil samples. Tests evaluating the seed germination and growth inhibition of four terrestrial plant species (alfalfa, sorghum, mustard and cuckooflower) were carried out at different rhamnolipid concentrations (ranging from 0 to 1.200 mg/kg of wet soil). The experiments were performed in soil samples with a different diesel oil content (ranging from 0 to 25 ml/kg of wet soil). It was observed that the sole presence of rhamnolipids may be phytotoxic at various levels, which is especially notable for sorghum (the germination index decreased to 41 %). The addition of rhamnolipids to diesel oil-contaminated soil samples contributed to a significant increase of their phytotoxicity. The most toxic effect was observed after a rhamnolipid-supplemented diesel oil biodegradation, carried out with the use of a hydrocarbon-degrading bacteria consortium. The supplemention of rhamnolipids (600 mg/kg of wet soil) resulted in a decrease of seed germination of all studied plant species and an inhibition of microbial activity, which was measured by the 2,3,5-triphenyltetrazolium chloride tests. These findings indicate that the presence of rhamnolipids may considerably increase the phytotoxicity of diesel oil. Therefore, their use at high concentrations, during in situ bioremediation processes, should be avoided in a terrestrial environment. [ABSTRACT FROM AUTHOR]

Abstract: Composting of oiled bleaching earth with waste sludge and corn straw was carried out to investigate the ability of microorganisms to synthesize biosurfactants that might decrease the surface tension of composts. Analytical results and changes in the surface tension suggest that biodegradation of fatty by-products was the consequence of emulsifying properties of higher fatty acids. The surface tension for isolates from all composting phases was between 37 and 43mNm–1. No substances synthesized by microorganisms that might be able to decrease the surface tension were detected in composts. Tensammetric, TLC and HPLC-MS results and changes in surface tension suggest that biodegradation of fatty by-products results from the emulsifying properties of higher fatty acids. A decrease in fatty content from 144 to 6mgg–1 dry matter was obtained. [Copyright &y& Elsevier]

Abstract: The degradation of diesel fuel, B20 blend and biodiesel in liquid cultures by a seven-member bacterial consortium was compared under conditions with full aeration or with limited aeration with nitrate added as main electron acceptor. Community dynamics was assessed employing real-time PCR and the ddCt method for relative quantification. Biodegradation rates increased with increasing biodiesel content, but were significantly reduced under conditions with nitrate. Despite large variations in biodegradation rates, magnitude changes in population numbers were typically observed only from zero to one order, regardless the type of fuel and electron acceptor. Only Comamonadaceae and Variovorax sp. distinctly preferred aerobic conditions, and during aerobic growth showed suppression as fuel contained more biodiesel. Thus, the consortium is relatively stable and most of the degraders can shift their metabolism from hydrocarbons to biodiesel. The stability of the consortium is of interest in the context of biodiesel-mediated biodegradation of petroleum hydrocarbons. [Copyright &y& Elsevier]

Metabolites of polychlorinated biphenyls (PCBs)—hydroxylated PCBs (OH-PCBs), chlorobenzyl alcohols (CB-OHs), and chlorobenzaldehydes (CB-CHOs)—were incubated in vitro with the extracellular liquid of Pleurotus ostreatus, which contains mainly laccase and low manganese-dependent peroxidase (MnP) activity. The enzymes were able to decrease the amount of most of the tested OH-PCBs by > 80% within 1 h; the removal of more recalcitrant OH-PCBs was greatly enhanced by the addition of the laccase mediator syringaldehyde. Conversely, glutathione substantially hindered the reaction, suggesting that it acted as a laccase inhibitor. Hydroxylated dibenzofuran and chlorobenzoic acid were identified as transformation products of OH-PCBs. The extracellular enzymes also oxidized the CB-OHs to the corresponding CB-CHOs on the order of hours to days; however, the mediated and nonmediated setups exhibited only slight differences, and the participating enzymes could not be determined. When CB-CHOs were used as the substrates, only partial transformation was observed. In an additional experiment, the extracellular liquid of Irpex lacteus, which contains predominantly MnP, was able to efficiently transform CB-CHOs with the aid of glutathione; mono- and di-chloroacetophenones were detected as transformation products. These results demonstrate that extracellular enzymes of ligninolytic fungi can act on a wide range of PCB metabolites, emphasizing their potential for bioremediation. [ABSTRACT FROM AUTHOR]

Abstract: Due to high fat content the treatment of oiled bleaching earth is very challenging. The neutralization of such waste may be carried out by employing the composting process. In this study, the efficiency of the composting process conducted with 19% addition of commercial oiled bleaching earth to waste sludge was evaluated. Maize straw was used as a structural material. The activity of lipases and dehydrogenases was measured during the biodegradation process. As a result of composting, changes in C/N ratio occurred (from 31 to 15) and the efficiency of fatty acids biodegradation reached 95%. The composting process also resulted in the removal of the initial phytotoxicity of composts. The mature compost did not exhibit any form of phytotoxicity during assays with Phytotoxkit. The Ames test excluded mutagenicity of any components in the compost. These results suggest that the proposed composting method may potentially be employed for rapid and efficient remediation of industrial waste containing oiled bleaching earth and waste sludge. [Copyright &y& Elsevier]

Abstract: This study aimed to determine nicotine biodegradation and the genotoxic potential of nicotine and its degradation products during the process of tobacco waste composting. Composting was carried out using two methods, i.e. the addition of 20% (bioreactor A) or 40% tobacco wastes to sewage sludge (bioreactor B) and control – sewage sludge (bioreactor C). Wheat straw was used as a structure-forming material. As a result of composting the contents of C and N in the bioreactors changed, the C:N ratio in bioreactor A changed from 22.8 to 13.00, and that in bioreactor B changed from 23.5 to 12.00. After composting, the biodegradation rate of nicotine was 78% in bioreactor A and 80% in bioreactor B, respectively. Using the Ames test it was shown that the composts produced did not exhibit mutagenicity. [Copyright &y& Elsevier]

The aim of this study was to analyse the basic mechanisms of the interaction of surfactants anionic rhamnolipids and non-ionic polysorbate-80 on a microbial consortium during the biodegradation of diesel oil under model conditions. The analysed surfactants significantly influenced the metapopulation changes of microorganisms and caused a decrease in metabolic activity; however, they did not decrease the biodiversity of the studied system. Polysorbate-80 was relatively resistant to biological decomposition, whereas rhamnolipids were subjected to biodegradation as well as microbial transformation, as confirmed by the activity of the RhlC gene. Determination of biodegradation kinetics confirmed the positive influence of polysorbate-80 on the degradation efficiency of diesel oil hydrocarbons. The addition of this surfactant in 2-fold and 4-fold critical micelle concentration revealed a positive influence on the total petroleum hydrocarbons biodegradation by 18% and 15% respectively. Rhamnolipids exhibited an inhibiting effect in all fractions, with the exception of n-alkanes. The biodegradation efficiency of total petroleum hydrocarbons was 47% and 40% lower in samples containing biosurfactants in 2-fold and 4-fold critical micelle concentration, compare to that of the control sample. The surfactant-enhanced bioremediation method is a promising alternative to traditional methods; however, the method's efficiency is associated with the proper selection of a surfactant and its concentration and consideration of the occurrence of toxic effects as well as changes in the local soil metapopulation. Image 1 • Surfactants robustly impact on shaping microbial community structure and activity. • Polysorbate-80 increases the biodegradation rate of aromatic hydrocarbons. • High concentrations of rhamnolipids decrease the biodegradation of hydrocarbons. • Exogenous rhamnolipids can be transformed by environmental consortia. • The transformation of rhamnolipids affects the development of microbial community. [ABSTRACT FROM AUTHOR]

It is not known whether diesel-degrading bacterial communities are structurally and functionally robust when exposed to different hydrocarbon types. Here, we exposed a diesel-degrading consortium to model either alkanes, cycloalkanes or aromatic hydrocarbons as carbon sources to study its structural resistance. The structural resistance was low, with changes in relative abundances of up to four orders of magnitude, depending on hydrocarbon type and bacterial taxon. This low resistance is explained by the presence of hydrocarbon-degrading specialists in the consortium and differences in growth kinetics on individual hydrocarbons. However, despite this low resistance, structural and functional resilience were high, as verified by re-exposing the hydrocarbon-perturbed consortium to diesel fuel. The high resilience is either due to the short exposure time, insufficient for permanent changes in consortium structure and function, or the ability of some consortium members to be maintained during exposure on degradation intermediates produced by other members. Thus, the consortium is expected to cope with short-term exposures to narrow carbon feeds, while maintaining its structural and functional integrity, which remains an advantage over biodegradation approaches using single species cultures. [ABSTRACT FROM AUTHOR]

Highlights: [•] Biodegradation of diesel/biodiesel blends was studied for 578days. [•] Procedure for monitoring the aliphatic and aromatic fractions was developed. [•] Additive effect of biodiesel on mineralization of fuel blends was confirmed. [•] Biodiesel did not impact the biodegradation of aliphatic and aromatic fractions. [•] Biodiesel can affect the growth of microbial consortium members. [Copyright &y& Elsevier]

A set of studies was carried using a continuous flow biodegradation unit in order to isolate a microbial community capable of efficient and complete utilization of octylphenol ethoxylates from activated sludge. Increasing concentrations of Triton X-100 (in the range of 1–1000 mg/l) were applied over a time period of 35 days in order to select microorganisms, which exhibit high tolerance towards this surfactant. The fate of the surfactant and its primary degradation products was assessed by HPLC/MS. It was observed that even small doses of the surfactant contributed to the disruption of the activated sludge, due to adsorption of primary Triton X-100 metabolites (octylphenol and short-chained ethoxylates) on the cells, although the long-chain octylphenol ethoxylates were efficiently degraded during the isolation process. The toxicity assessment of octylphenol as well as octylphenol di- and monoethoxylates towards activated sludge allowed for determination of EC50 values (8 and 55 mg/l, respectively). The identification of the residual microorganisms revealed the presence of Acinetobacter junii, Acinetobacter calcoaceticus, Aeromonas hydrophilia, Alcaligenes spp., Pseudomonas fluorescens and Sphingomonas capsulata. The isolated community exhibited a high resistance towards Triton X-100 and was capable of growth even at 10,000 mg/l, with the highest specific growth rate (0.47 h−1) observed at 4000 mg/l. Under aerobic conditions both octylphenol and the short-chained ethoxylates were completely degraded while no toxic effect towards the isolated bacterial community was observed. [Copyright &y& Elsevier]

Abstract: Bacterial utilization of rhamnolipids during biosurfactant-supplemented biodegradation of diesel and B20 (20% biodiesel and 80% diesel v/v) fuels was evaluated under conditions with full aeration or with nitrate and nitrite as electron acceptors. Rhamnolipid-induced changes in community dynamics were assessed by employing real-time PCR and the ddCt method for relative quantification. The experiments with rhamnolipids at 150mg/l, approx. double critical micelle concentration (CMC) and diesel oil confirmed that rhamnolipids were readily degraded by a soil-isolated consortium of hydrocarbon degraders in all samples, under both aerobic and nitrate-reducing conditions. The presence of rhamnolipids increased the dissipation rates for B20 constituents under aerobic conditions, but did not influence the biodegradation rate of pure diesel. No effect was observed under nitrate-reducing conditions. The biodegradation of rhamnolipids did not favor the growth of any specific consortium member, which proved that the employed biosurfactant did not interfere with the microbial equilibrium during diesel/biodiesel biodegradation. [Copyright &y& Elsevier]

Abstract: The hypothesis regarding preferential biodegradation of surfactants applied for enhancement of microbial hydrocarbons degradation was studied. At first the microbial degradation of sole Triton X-100 by soil isolated hydrocarbon degrading bacterial consortium was confirmed under both full and limited aeration with nitrate as an electron acceptor. Triton X-100 (600mg/l) was utilized twice as fast for aerobic conditions (t 1/2 =10.3h), compared to anaerobic conditions (t 1/2 =21.8h). HPLC/ESI-MS analysis revealed the preferential biodegradation trends in both components classes of commercial Triton X-100 (alkylphenol ethoxylates) as well as polyethylene glycols. The obtained results suggest that the observed changes in the degree of ethoxylation for polyethylene glycol homologues occurred as a consequence of the ‘central fission’ mechanism during Triton X-100 biodegradation. Subsequent experiments with Triton X-100 at approx. CMC concentration (150mg/l) and diesel oil supported our initial hypothesis that the surfactant would become the preferred carbon source even for hydrocarbon degrading bacteria. Regardless of aeration regimes Triton X-100 was utilized within 48–72h. Efficiency of diesel oil degradation was decreased in the presence of surfactant for aerobic conditions by approx. 25% reaching 60 instead of 80% noted for experiments without surfactant. No surfactant influence was observed for anaerobic conditions. [Copyright &y& Elsevier]