Rapid Colonisation of Plastic Surfaces by Marine <i>Alcanivorax</i> Bacteria Is Flagellum‐Dependent and Influenced by Polymer Type and Photo‐Weathering State

Marine plastic debris provides stable surfaces for microbial colonisation, forming a unique ecosystem known as the plastisphere. Among the early colonisers are Alcanivorax bacteria, hydrocarbon degraders commonly found in oil-polluted seawater and on marine plastic surfaces. This study examined factors influencing the adhesion and colonisation dynamics of six Alcanivorax species. Flagellated species-A. balearicus, A. dieselolei and A. xenomutans-rapidly colonised plastics, particularly polyethylene and polypropylene, while non-flagellated species did not. Notably, plastic photo-weathering treatments led to the elongation of A. dieselolei cells, secretion of extracellular polymeric substance in some cases, and increased colonisation on UVB-treated polyethylene terephthalate. These changes may be linked to the reduced plastic surface hydrophobicity recorded following photo-weathering. To confirm the role of flagella in Alcanivorax adhesion, we disrupted flagellar activity using sub-concentrations of polymyxin B sulfate, resulting in inhibition of swarming motility and complete disruption of colonisation. These results contribute to our understanding of the interactions between hydrocarbon-degrading Alcanivorax bacteria and their plastic substrate, which in turn contributes to the understanding of the ecological impact of plastic pollution in marine environments.