Antibiotics play a key role in the management of infectious diseases in humans, animals, livestock, and aquacultures all over the world. The release of increasing amount of antibiotics into waters and soils creates a potential threat to all microorganisms in these environments. This review addresses issues related to the fate and degradation of antibiotics in soils and the impact of antibiotics on the structural, genetic and functional diversity of microbial communities. Due to the emergence of bacterial resistance to antibiotics, which is considered a worldwide public health problem, the abundance and diversity of antibiotic resistance genes (ARGs) in soils are also discussed. When antibiotic residues enter the soil, the main processes determining their persistence are sorption to organic particles and degradation/transformation. The wide range of DT50 values for antibiotic residues in soils shows that the processes governing persistence depend on a number of different factors, e.g., physico-chemical properties of the residue, characteristics of the soil, and climatic factors (temperature, rainfall, and humidity). The results presented in this review show that antibiotics affect soil microorganisms by changing their enzyme activity and ability to metabolize different carbon sources, as well as by altering the overall microbial biomass and the relative abundance of different groups (i.e., Gram-negative bacteria, Gram-positive bacteria, and fungi) in microbial communities. Studies using methods based on analyses of nucleic acids prove that antibiotics alter the biodiversity of microbial communities and the presence of many types of ARGs in soil are affected by agricultural and human activities. It is worth emphasizing that studies on ARGs in soil have resulted in the discovery of new genes and enzymes responsible for bacterial resistance to antibiotics. However, many ambiguous results indicate that precise estimation of the impact of antibiotics on the activity and diversity of soil microbial communities is a great challenge.
The contamination of soil with aromatic compounds is of particular environmental concern as they exhibit carcinogenic and mutagenic properties. One of the methods of their removal from soil is bioaugmentation, defined as a technique for improvement of the degradative capacity of contaminated areas by introduction of specific competent strains or consortia of microorganisms. The efficiency of bioaugmentation is determined by many abiotic and biotic factors discussed in this paper. The first include chemical structure, concentration and availability of pollutants as well as physico-chemical properties of soil. In turn, among biotic factors the most important is the selection of proper microorganisms that can not only degrade contaminants but can also successfully compete with indigenous microflora. Several strategies are being developed to make augmentation a successful technology particularly in soils without degrading indigenous microorganisms. These approaches involve the use of genetically engineered microorganisms and gene bioaugmentation. The enhancement of bioaugmentation may be also achieved by delivering suitable microorganisms immobilized on various carriers or use of activated soil.
Fatty acid composition during naphthalene utilization was investigated in three strains of bacteria Pseudomonas vesicularis, Pseudomonas stutzeri and Pseudomonas sp. JS150 that expressed different naphthalene degradation abilities. All strains significantly changed their cellular fatty acid profiles as a response to naphthalene exposure. Since naphthalene was present in the medium P. stutzeri increased ratio of saturated/unsaturated fatty acids from 1.1 to 2.1 and Pseudomonas sp. JS150 from 7.5 to 12.0, respectively. In contrast, this ratio decreased from 2.1 to 1.1 in P. vesicularis under the same growth conditions. The changes comprised also alterations in the percentage of selected groups of fatty acids: iso and anteiso, hydroxy and cyclopropane fatty acids. Our results showed that naphthalene induced in tested strains different changes in fatty acids composition. It may suggest that in the presence of naphthalene microorganisms used different adaptive mechanisms to maintain the cells in appropriate physiological state.
The effects of naphthalene on the whole cell-derived fatty acid composition of Pseudomonas putida and Pseudomonas stutzeri during naphthalene degradation were investigated. These strains differed in their abilities to degrade naphthalene and in 1,2-catechol dioxygenase activities. The cells of both strains reacted to the addition of naphthalene with an increase in the saturated/unsaturated ratio. The dynamic changes comprised also alterations in the percentage of hydroxy, cyclopropane and branched fatty acids. Upon the exposure of naphthalene, new fatty acids were detected.
Hauling landfill leachate to offsite urban wastewater treatment plants is a way to achieve pollutant removal. However, the implementation of biological methods for the treatment of landfill leachate can be extremely challenging. This study aims to investigate the effect of blending wastewater with 3.5% and 5.5% of the industrial leachate from the Kalina pond (KPL) on the performance of sequencing batch reactor (SBR) and capacity of activated sludge microorganisms. The results showed that the removal efficiency of the chemical oxygen demand declined in the contaminated SBR from 100% to 69% and, subsequently, to 41% after the cotreatment with 3.5% and 5.5% of the pollutant. In parallel, the activities of the dehydrogenases and nonspecific esterases declined by 58% and 39%, and 79% and 81% after 32 days of the exposure of the SBR to 3.5% and 5.5% of the leachate, respectively. Furthermore, the presence of the KPL in the sewage affected the sludge microorganisms through a reduction in their functional capacity as well as a decrease in the percentages of the marker fatty acids for different microbial groups. A multifactorial analysis of the parameters relevant for the wastewater treatment process confirmed unambiguously the negative impact of the leachate on the operation, activity, and structure of the activated sludge.
Iodinated X-ray contrast media (ICM) such as diatrizoate, iohexol, iomeprol, iopamidol, and iopromide are commonly used in medical imaging for radiological visualization of a variety of anatomic structures. Because of their highly persistent nature and poor removal by conventional wastewater treatment, ICM can often remain unchanged after entering the environment or they are transformed into many different by-products in complex physical, chemical, and biological processes. Large amounts of ICM and their by-products are found in natural waters, groundwater, drinking water (up to 100 µg/L), and even in soil, where they can be a potential threat to the inhabitants of these environments. Because knowledge about the fate of ICM in various environments is dispersed and it concerns specific areas, the main purpose of this review is to summarize the available information about their occurrence, chemical and biological transformation/degradation, and toxicity to living organisms. The topics discussed particularly focus on mechanisms of ICM degradation/transformation in water using advanced oxidation processes and the biotransformation/biodegradation of ICM by microorganisms under different conditions, as well as the toxicity of ICM and their transformation by-products to humans and other organisms. Although environmental risk is not expected from the parent compounds of ICM, their continuous input to the water and the formation of toxic by-products may constitute a long-term potential risk for living organisms. Therefore, monitoring the transport and fate of ICM in various environments seems necessary.
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