Ever decreasing efficiency of antibiotic treatment due to growing antibiotic resistance of pathogenic bacteria is a critical issue in clinical practice. The two generally accepted major approaches to this problem are the search for new antibiotics and the development of antibiotic adjuvants to enhance the antimicrobial activity of known compounds. It was therefore the aim of the present study to test whether alkylresorcinols, a class of phenolic lipids, can be used as adjuvants to potentiate the effect of various classes of antibiotics. Alkylresorcinols were combined with 12 clinically used antibiotics. Growth-inhibiting activity against a broad range of pro- and eukaryotic microorganisms was determined. Test organisms did comprise 10 bacterial and 2 fungal collection strains, including E. coli and S. aureus, and clinical isolates of K. pneumoniae. The highest adjuvant activity was observed in the case of 4-hexylresorcinol (4-HR), a natural compound found in plants with antimicrobial activity. 50% of the minimal inhibitory concentration (MIC) of 4-HR caused an up to 50-fold decrease in the MIC of antibiotics of various classes. Application of 4-HR as an adjuvant revealed its efficiency against germination of bacterial dormant forms (spores) and prevented formation of antibiotic-tolerant persister cells. Using an in vivo mouse model of K. pneumoniae-induced sepsis, we could demonstrate that the combination of 4-HR and polymyxin was highly effective. 75% of animals were free of infection after treatment as compared to none of the animals receiving the antibiotic alone. We conclude that alkylresorcinols such as 4-HR can be used as an adjuvant to increase the efficiency of several known antibiotics. We suggest that by this approach the risk for development of genetically determined antibiotic resistance can be minimized due to the multimodal mode of action of 4-HR.

One of the adaptive strategies for the constantly changing conditions of the environment utilized in bacterial cells involves the condensation of DNA in complex with the DNA-binding protein, Dps. With the use of electron microscopy and electron tomography, we observed several morphologically different types of DNA condensation in dormant Escherichia coli cells, namely: nanocrystalline, liquid crystalline, and the folded nucleosome-like. We confirmed the presence of both Dps and DNA in all of the ordered structures using EDX analysis. The comparison of EDX spectra obtained for the three different ordered structures revealed that in nanocrystalline formation the majority of the Dps protein is tightly bound to nucleoid DNA. The dps-null cells contained only one type of condensed DNA structure, liquid crystalline, thus, differing from those with Dps. The results obtained here shed some light on the phenomenon of DNA condensation in dormant prokaryotic cells and on the general problem of developing a response to stress. We demonstrated that the population of dormant cells is structurally heterogeneous, allowing them to respond flexibly to environmental changes. It increases the ability of the whole bacterial population to survive under extreme stress conditions.

Effect of sublethal doses of physical and chemical stressors (heat shock for 2 h at 45°C and addition of C12-alkylhydroxybenzene, a microbial alarmone) on development of resistance to the subsequent l

Climate change and the increasing frequency and severity of drought events pose significant challenges for sustainable agriculture worldwide. Soil microorganisms, both beneficial and pathogenic, play a crucial role in mediating plant–environment interactions and shaping the overall functioning of agroecosystems. This review summarizes current knowledge on the adaptive mechanisms used by different groups of plant-beneficial soil microorganisms—rhizobacteria and arbuscular mycorrhizal fungi (AMF)—as well as phytopathogenic bacteria and fungi, in response to drought. The review focuses on identifying the commonalities and differences in the survival strategies of these groups of beneficial and pathogenic soil microorganisms under drought conditions. Additionally, it reviews and compares the plant defence mechanisms under drought conditions facilitated by rhizobacteria and AMF. Special attention is given to the genetic exchange between beneficial and pathogenic soil microorganisms through horizontal gene transfer (HGT), which allows them to exchange traits. It is observed that drought may favor enhanced genetic exchange and the spread of pathogenic traits in the soil microbiome. This review will be useful for a wide range of readers to better understand the dynamics of the soil microbiome under climate change and to apply this knowledge to sustainable agricultural practices.

Intensive human activity in the Arctic region leads to hydrocarbon pollution of reservoirs and soils. Isolation of bacteria capable of growing at low temperatures and degrading oil and petroleum products is of scientific and practical value. The aim of this work was to study the physiology and growth in oil at temperatures below 0 °C of four strains of bacteria of the genera Pseudomonas, Rhodococcus, Arthrobacter, and Sphingomonas—previously isolated from diesel-contaminated soils of the Franz Josef Land archipelago—as well as genomic analysis of the Sphingomonas sp. AR_OL41 strain. The studied strains grew on hydrocarbons at temperatures from −1.5 °C to 35 °C in the presence of 0–8% NaCl (w/v). Growth at a negative temperature was accompanied by visual changes in the size of cells as well as a narrowing of the spectrum of utilized n-alkanes. The studied strains were psychrotolerant, degraded natural biopolymers (xylan, chitin) and n-alkanes of petroleum, and converted phosphates into a soluble form. The ability to degrade n-alkanes is rare in members of the genus Sphingomonas. To understand how the Sphingomonas sp. AR_OL41 strain has adapted to a cold, diesel-contaminated environment, its genome was sequenced and analyzed. The Illumina HiSeq 2500 platform was used for AR_OL41 genome strain sequencing. The genome analysis of the AR_OL41 strain showed the presence of genes encoding enzymes of n-alkane oxidation, pyruvate metabolism, desaturation of membrane lipids, and the formation of exopolysaccharides, confirming the adaptation of the strain to hydrocarbon pollution and low habitat temperature. Average nucleotide identity and digital DNA–DNA hybridization values for genomes of the AR_OL41 strain with that of the phylogenetically relative Sphingomonas alpine DSM 22537^T strain were 81.9% and 20.9%, respectively, which allows the AR_OL41 strain to be assigned to a new species of the genus Sphingomonas. Phenomenological observations and genomic analysis indicate the possible participation of the studied strains in the self-purification of Arctic soils from hydrocarbons and their potential for biotechnological application in bioremediation of low-temperature environments.