The adaptive mechanisms of Bacillus velezensis C5 for survival on polyethylene microplastics

Abstract

Polyethylene (PE) plastics pose a severe environmental challenge due to their recalcitrance, which also creates an extremely nutrient-limited environment for microbial colonizers. Understanding the initial adaptive mechanisms is crucial for developing effective bioremediation strategies. In this study, comparative transcriptomics was employed to analyze the specific adaptive response of Bacillus velezensis C5 to PE microplastics by comparing it with responses to a non-polymeric hydrocarbon, n-docosane (C22), and a nutrient-free medium. The results revealed a robust, PE-specific transcriptional program distinct from general starvation or surface-contact responses. Exposure to PE, but not C22, triggered massive upregulation of genes involved in biofilm formation (e.g., the epsA-O operon, including a 185-fold increase in epsL) and sporulation (e.g., a 22-fold increase in yicZ), indicating a polymer-induced strategy for surface colonization and long-term persistence. Although genes associated with canonical PE degradation were not induced, several LLM-class monooxygenases were upregulated, suggesting an auxiliary role in stress mitigation. Phenotypic analyses confirmed that strain C5 remained viable without growth on PE, formed a dense biofilm that increased surface hydrophilicity, and induced only subtle physicochemical changes to the plastic. This study demonstrates that the initial interaction is dominated by a sophisticated, polymer-specific survival program rather than direct metabolic degradation. This insight is fundamental for designing future strategies capable of overcoming this adaptive phase to promote efficient plastic biodegradation.

Graphical abstract

Keywords

transcriptomics / biofilm / nutrient limitation / biodegradation / adaptation

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