Rhodococcus erythropolis NI86/21, isolated from maize rhizosphere in Hungary, possesses one of the largest genomes (8.046 Mb) within the species. The genome comprises a 6.83 Mb chromosome and 1.22 Mb of extrachromosomal elements, including three circular and two fragmented linear plasmids. Comparative analysis identified five horizontally acquired genomic islands (HGTi), totaling 0.64 Mb with mosaic-like architecture derived from plasmids, phages, and chromosomal segments of other Nocardiaceae . Liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based proteomic analysis revealed a lower expression of genes located in HGT elements (53%) compared to core chromosomal genes (73%), indicating regulatory silencing of foreign DNA. Nevertheless, an inducible cytochrome P450 monooxygenase (CYP116) responsible for thiocarbamate and atrazine degradation is encoded on HGTi_V and actively expressed upon herbicide exposure. Strikingly, an identical CYP450 locus is present on a conjugative plasmid in Rhodococcus sp. TE1 isolated from thiocarbamate-treated soil in Canada, demonstrating independent acquisition of the same catabolic module from a high GC% content Rhodococcus , under similar selective pressure. Frequent recombination between chromosomal and mobile elements generates the observed mosaic-like HGT structures, which we found common for R. erythropolis strains. These results highlight extraordinary genomic plasticity and rapid adaptive evolution in Rhodococci , enabling efficient colonization of herbicide-contaminated agro-ecosystems. IMPORTANCE: Rhodococcus erythropolis NI86/21 exemplifies how bacterial genomes evolve through horizontal gene transfer and mobile elements. Its unusually large, plastic genome contains extensive HGT islands and a high load of active transposons, which shape mosaic genomic architectures and hinder complete genome assembly. These horizontally acquired regions, although partially silenced, encode key adaptive functions such as an inducible CYP116 monooxygenase enabling thiocarbamate and atrazine degradation. Remarkably, an identical CYP116 module is present in Rhodococcus sp. TE1 from thiocarbamate-treated Canadian soil, demonstrating that similar environmental pressures can drive independent acquisition of the same biodegradation trait. Together, the dynamic transposon activity, mosaic HGT structure, and geographically convergent gene recruitment highlight the extraordinary genomic plasticity of R. erythropolis and underscore its rapid adaptive potential in agro-ecosystems, with implications for microbial evolution and bioremediation strategies.

The gut microbiota plays a central role in poultry health and production performance, yet its response to intensive fattening protocols and postbiotic supplementation in geese remains poorly characterized. This study used 16S rRNA gene amplicon sequencing to profile ileal and caecal microbial communities from geese raised under two fattening protocols, with or without postbiotic supplementation, and assessed the effect of 24 h post-mortem chilling on apparent community composition. Fattening protocol was associated with the largest differences in gut microbial structure, producing significant shifts in beta diversity in both the ileum and the caecum (although protocol, age at slaughter, and duration of postbiotic exposure co-varied between cohorts and cannot be fully disentangled), accompanied by extensive taxon-level differences identified by LEfSe. Postbiotic supplementation did not significantly alter overall community structure under force-feeding conditions but produced a taxon-specific, trend-level shift in the caecum under restricted feeding, suggesting that its effect depends on the continuity of supplementation relative to slaughter. Alpha diversity did not differ significantly in the ileum, but caecal richness differed significantly between the G2 and G5 postbiotic-supplemented groups (Conover–Iman test, adjusted p < 0.05). The warm- and chilled-dissection groups differed in ileal but not caecal community composition (individual-animal variation cannot be separated from the effect of chilling in this comparison, as the two groups consisted of different birds), indicating that dissection timing is an important methodological variable in goose microbiome research. These findings highlight cohort- and protocol-related differences as key correlates of gut microbial composition in geese and provide a framework for optimizing postbiotic supplementation strategies and sampling standardization in waterfowl production.

Background: The global emergence of antibiotic resistance highlights the urgent need for novel therapeutic strategies, including adjuvants and potentiating compounds, against multidrug-resistant bacteria. Pseudomonas aeruginosa is classified by the World Health Organization (WHO) as a critical priority pathogen due to its high resistance potential and its ability to cause severe nosocomial infections. Beauvericin (BEA), a frequently detected mycotoxin, has been reported to exhibit various bioactive properties, including potential antibacterial and potentiating effects. Methods: The interaction between BEA and a last-resort antibiotic, colistin (COL), was evaluated in seven multidrug-resistant P. aeruginosa isolates using a microplate-based growth assay after preliminary MIC tests. Results: BEA at non-inhibitory concentrations (2.5–10 µg/mL) significantly enhanced the antibacterial activity of COL (1 and 2 µg/mL) in six out of seven isolates, resulting in a marked reduction in residual bacterial growth. Conclusions: BEA exhibited no measurable antibacterial activity at the concentrations used in the combination experiments but acted as a strain-dependent potentiator of colistin activity against multidrug-resistant P. aeruginosa. The observed enhancement of colistin-mediated growth inhibition supports the potential of BEA as an antibiotic adjuvant at clinically relevant colistin concentrations and provides a basis for further mechanistic investigation.