Bioaccessible PAH influence on distribution of antibiotic resistance genes and soil toxicity of different types of land use

For a better understanding of the dissemination of antibiotic resistance genes (ARGs) in natural microbial communities, it is necessary to study the factors influencing it. There are not enough studies showing the connection of some pollutants with the dissemination of ARGs and especially few works on the effect of polycyclic aromatic compounds (PAHs) on the spread of resistance in microbiocenosis. In this respect, the aim of the study was to determine the effect of bioaccessible PAHs on soil resistome. The toxicity and the content of bioaccessible PAHs and ARGs were studied in 64 samples of soils of different types of land use in the Rostov Region of Russia. In most soils, a close positive correlation was demonstrated between different ARGs and bioaccessible PAHs with different content of rings in the structure. Six of the seven studied ARGs correlated with the content of 2-, 3-, 4-, 5- or 6-ring PAHs. The greatest number of close correlations was found between the content of PAHs and ARGs in the soils of protected areas, for agricultural purposes, and in soils of hospitals. The diverse composition of microbial communities in these soils might greatly facilitate this process. A close correlation between various toxic effects identified with a battery of whole-cell bacterial biosensors and bioaccessible PAHs of various compositions was established. This correlation showed possible mechanisms of PAHs' influence on microorganisms (DNA damage, oxidative stress, etc.), which led to a significant increase in horizontal gene transfer and spread of some ARGs in soil microbial communities. All this information, taken together, suggests that bioaccessible PAHs can enhance the spread of antibiotic resistance genes.

Polycyclic aromatic hydrocarbons, antibiotic resistance genes, toxicity in the exposed to anthropogenic pressure soils of the Southern Russia

The influence of anthropogenic pollution, particularly with polycyclic aromatic hydrocarbons (PAHs) on soil toxicity and spread of antibiotic resistance genes (ARGs) is extremely important nowadays. We studied 20 soil samples from a technogenically polluted site, municipal solid wastes (MSW) landfills, and rural settlements in the southwestern part of the Rostov Region of Russia. A close correlation was established between the results of biosensor testing for integral toxicity, the content of genes for the biodegradation of hydrocarbons, and the concentration of PAHs in soils. The relation between the quantitative content of ARGs and the qualitative and quantitative composition of PAHs has not been registered. Soils subjected to different types of the anthropogenic pressure differed in PAHs composition. The technogenic soils are the most polluted ones. These soils are enriched with 5 ring PAHs and carry the maximum variety of assayed ARGs, despite the fact that they do not receive household or medical waste.

Evaluation of bacterial biosensors to determine chromate bioavailability and to assess ecotoxicity of soils

Chromate can be considered a potent environmental contaminant and consequently, an understanding of chromate availability and toxicity to soil biology is essential for effective ecological assessment of metal impact in soils. This study shows the response of two bacterial bioreporters, pCHRGFP1 Escherichiacoli and pCHRGFP2 Ochrobactrumtritici, to increasing concentrations of chromate in two different soils. The bioreporters, carrying the regulatory gene chrB transcriptionally fused to the gfp reporter system, exhibited different features. In both, the fluorescence signal and the chromate concentration could be linearly correlated but E. coli biosensor functioned within the range of 0.5-2 μM and O. tritici biosensor within 2-10 μM chromate. The bioreporters were validated through comparative measurements using the chemical chromate methods of diphenylcarbazide and ionic chromatography. The bacterial sensors were used for the estimation of bioavailable fraction of chromate in a natural soil and OECD artificial soil, both spiked with chromate in increasing concentrations of 0-120 mg Cr(VI) kg(-1) of soil. OECD soil showed a faster chromate decrease comparing to the natural soil. The toxicity of soils amended with chromate was also evaluated by ecotoxicological tests through collembolan reproduction tests using Folsomia candida as test organism. Significant correlations were found between collembolans reproduction and chromate concentration in soil (lower at high chromate concentrations) measured by biosensors. Data obtained showed that the biosensors tested are sensitive to chromate presence in soil and may constitute a rapid and efficient method to measure chromate availability in soils.