Quorum sensing (QS) is often required for the formation of bacterial biofilms and is a popular target of biofilm control strategies. Previous studies implicate the ComQXPA quorum sensing system of Bacillus subtilis as a promoter of biofilm formation. Here, we report that ComX signaling peptide deficient mutants form thicker and more robust pellicle biofilms that contain chains of cells. We confirm that ComX positively affects the transcriptional activity of the P_epsA promoter, which controls the synthesis of the major matrix polysaccharide. In contrast, ComX negatively controls the P_tapA promoter, which drives the production of TasA, a fibrous matrix protein. Overall, the biomass of the mutant biofilm lacking ComX accumulates more monosaccharide and protein content than the wild type. We conclude that this QS phenotype might be due to extended investment into growth rather than spore development. Consistent with this, the ComX deficient mutant shows a delayed activation of the pre-spore specific promoter, P_spoIIQ, and a delayed, more synchronous commitment to sporulation. We conclude that ComX mediated early commitment to sporulation of the wild type slows down biofilm formation and modulates the coexistence of multiple biological states during the early stages of biofilm development.

Genetic competence for the uptake and integration of extracellular DNA is a key process in horizontal gene transfer (HGT), one of the most powerful forces driving the evolution of bacteria. In several species, development of genetic competence is coupled with cell lysis. Using Bacillus subtilis as a model bacterium, we studied the role of surfactin, a powerful biosurfactant and antimicrobial lipopeptide, in genetic transformation. We showed that surfactin itself promotes cell lysis and DNA release, thereby promoting HGT. These results, therefore, provide evidence for a fundamental mechanism involved in HGT and significantly increase our understanding of the spreading of antibiotic resistance genes and diversification of microbial communities in the environment.

The growing amount of plastic waste requires new ways of disposal or recycling. Research into the biodegradation of recalcitrant plastic polymers is gathering pace. Despite some progress, these efforts have not yet led to technologically and economically viable applications. In this study, we show that respirometric screening of environmental fungal isolates in combination with scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy can be used to identify new strains with the potential for the degradation of plastic polymers. We screened 146 fungal strains, 71 isolated from car repair shops, an environment rich in long-chain hydrocarbons, and 75 isolated from hypersaline water capable of growing at high concentrations of NaCl. When grown in a minimal medium with no carbon source, some strains produced significantly more CO₂ when a pure plastic polymer was added to the medium, some only at high salinity. A selection of these strains was shown by FTIR and Raman spectroscopy to alter the properties of plastic polymers: Cladosporium sp. EXF-13502 on polyamide, Rhodotorula dairenensis EXF-13500 on polypropylene, Rhodotorula sp. EXF-10630 on low-density polyethylene and Wickerhamomyces anomalus EXF-6848 on polyethylene terephthalate. Respirometry in combination with specific spectroscopic methods is an efficient method for screening microorganisms capable of at least partial plastic degradation and can be used to expand the repertoire of potential plastic degraders. This is of particular importance as our results also show that individual strains are only active against certain polymers and under certain conditions. Therefore, efficient biodegradation of plastics is likely to depend on a collection of specialized microorganisms rather than a single universal plastic degrader.

This study investigated the root cause of severe corrosion damage observed on G-X4CrNi13-4 martensitic stainless steel turbine blades at the Brežice hydroelectric power plant on the Sava River in Slovenia. The investigation employed a comprehensive analytical approach, including on-site visual inspections, non-destructive testing with a portable microscope (Struers, Ballerup, Denmark), X-ray fluorescence spectroscopy (Thermo Fisher Scientific, Waltham, MA, USA), and 3D topographical mapping (Bruker Alicona, Graz, Austria). Laboratory analyses utilized scanning electron microscopy (ZEISS, Oberkochen, Germany) and energy-dispersive X-ray spectroscopy (EDAX, Pleasanton, CA, USA) to examine surface deposits, biofilms, and corrosion products, complemented by physical and chemical water quality assessments. A visual inspection revealed a dense layer of biological deposits, approximately 0.3 mm thick, with stochastic pitting damage located beneath the biofilm. The analytical results confirmed that the blade material met the specifications; however, EDS analysis (EDAX, Pleasanton, CA, USA) revealed significant localized manganese enrichment within the pits (~1.4 wt%) and in the biofilm (>10 wt%). Although water analysis showed relatively low manganese concentrations (7–18 µg/L), these values may be sufficient to support the metabolic activity of manganese-oxidizing microorganisms. Historical hydrological data suggest that extreme drought conditions in 2022, stagnant water, and elevated temperatures facilitated the attachment of microorganisms and the formation of a corrosive biofilm. These findings highlight the impact of changing environmental conditions and low-flow periods on the integrity of stainless steel components in hydroelectric facilities.