Polyethylene (PE) is one of the most recalcitrant plastics, persistently accumulating in landfills and natural environments due to its high molecular weight, crystalline structure, and pronounced hydrophobicity. These properties create an extremely nutrient-limited environment for microbial colonizers, severely restricting biodegradation efficiency. Understanding how microorganisms initially adapt to PE is crucial for developing effective bioremediation strategies.
In a study published in ENG. Chem. Eng., researchers at Beijing University of Chemical Technology employed comparative transcriptomics to investigate the specific adaptive response of Bacillus velezensis C5 to PE microplastics, comparing it with responses to a non-polymeric hydrocarbon (n-docosane, C22) and a nutrient-free medium. The results reveal a sophisticated, polymer-specific survival program.
Transcriptomic analysis identified 253 differentially expressed genes in PE-exposed cells, compared to only 109 in C22-exposed cells, indicating a much more extensive response to the polymer. PE exposure, but not C22, triggered massive upregulation of genes involved in biofilm formation. The epsA-O operon, responsible for exopolysaccharide synthesis, showed strong induction, indicating a targeted strategy for surface colonization. Genes encoding chemotaxis proteins (MCPs, MotA, CheB) were also upregulated, consistent with the activation of a biofilm formation program.
Sporulation genes were also specifically induced by PE, with 27 genes upregulated 2- to 22-fold. This broad activation of the sporulation machinery suggests that strain C5 interprets the PE environment as a long-term, non-permissive habitat requiring entry into a dormant state – a survival strategy that prioritizes persistence over energy-intensive degradative processes.
Although genes encoding typical PE-degrading enzymes remained uninduced, five LLM-class flavin-dependent monooxygenases were upregulated. Phylogenetic analysis classified these into Class A and Class C. Based on genomic context, they may play auxiliary roles in stress mitigation – such as oxidizing aromatic additives, regulating intracellular redox state, or influencing cysteine transport – rather than functioning as primary depolymerases.
Phenotypic analyses confirmed the transcriptomic findings. Over 28 days, strain C5 showed no significant growth, while CFU counts remained stable, indicating a dormant, survival-oriented state. The water contact angle of PE films decreased significantly after 3 days, indicating increased surface hydrophilicity. SEM revealed a dense biofilm composed of bacterial cells embedded in an EPS matrix. FTIR detected a novel peak corresponding to amide groups in treated samples, providing evidence of extracellular protein secretion. HTGPC analysis revealed only subtle shifts in molecular weight distribution, confirming that extensive depolymerization did not occur.
This study demonstrates that the initial interaction between bacteria and PE is dominated by a polymer-specific survival program – biofilm formation, sporulation, and membrane transport remodeling – rather than metabolic degradation. This survival-first paradigm represents a critical initial phase that must be overcome to unlock the long-term degradative potential of microorganisms for plastic bioremediation.

DOI
10.1007/s11705-026-2669-z