Rapid Colonisation of Plastic Surfaces by Marine Alcanivorax 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.