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 nutrientlimited 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 nonpolymeric hydrocarbon (ndocosane, C22) and a nutrientfree medium. The results reveal a sophisticated, polymerspecific survival program.
Transcriptomic analysis identified 253 differentially expressed genes in PEexposed cells, compared to only 109 in C22exposed 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 epsAO 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 22fold. This broad activation of the sporulation machinery suggests that strain C5 interprets the PE environment as a longterm, nonpermissive habitat requiring entry into a dormant state – a survival strategy that prioritizes persistence over energyintensive degradative processes.
Although genes encoding typical PEdegrading enzymes remained uninduced, five LLMclass flavindependent 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, survivaloriented 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 polymerspecific survival program – biofilm formation, sporulation, and membrane transport remodeling – rather than metabolic degradation. This survivalfirst paradigm represents a critical initial phase that must be overcome to unlock the longterm degradative potential of microorganisms for plastic bioremediation.
DOI
10.1007/s11705-026-2669-z