Strategies for biofilm optimization of plastic-degrading microorganisms and isolating biofilm formers from plastic-contaminated environments

The perpetual disposal of plastic waste, combined with ineffective waste management strategies, has resulted in widespread environmental plastic pollution. Microbial plastic biodegradation represents an emerging solution to this problem. However, biodegradation studies tend to overlook the fundamental prerequisite of initial surface colonization via biofilm formation. This study had two independent but connected aims relating to plastic surface colonization by microorganisms: to enhance biofilm formation by known plastic degraders, with translational potential for improved plastic degradation, and to isolate microorganisms from microplastic contaminated environments with the ability to colonize plastic surfaces. Planktonic and biofilm responses to diverse carbon and energy sources were investigated over 7 days, using Bacillus subtilis 168, Fusarium solani (Martius) Saccardo, Ideonella sakaiensis 201-F6, Pseudomonas putida KT2440, and Rhodococcus ruber C208. This enabled optimal conditions for biofilm formation by each strain to be determined. In parallel, environmental samples containing synthetic or natural polymeric substances (anaerobic digestate, landfill leachate, and microplastic contaminated compost) were incubated with polyethylene and polyethylene terephthalate films, to isolate microorganisms capable of colonizing their surfaces. This yielded eight bacterial isolates from three genera: Bacillus, Lysinibacillus, and Proteus. These genera contain species that have been shown to degrade plastics and other recalcitrant synthetic polymers, demonstrating the success of our approach. This study also suggests that discrete plastic types may create different ecological niches which can be exploited by unique bacterial colonizers. Our findings underscore the importance of considering plastic colonization by microbial biofilms in the context of their biodegradation.