Meat-derived Escherichia coli and Pseudomonas fragi manage to co-exist in dual-species biofilms by adjusting gene-regulated competitive strength

Pseudomonas fragi and Escherichia coli are considered as common colonizers of fresh and spoilage meat, where they tend to live in the proximity. In this study, we primarily tested interplay patterns between different isolates of these two species in two-by-two combinations grown on stainless steel surfaces as dual-species biofilms. Results showed that these two species presented competition as major observed interplay patterns as biofilms progressed independent of bacterial strains and growth temperatures (15 °C and 25 °C). One dual-species combination was proposed as a representative to further explore dynamic patterns of interaction strength between these two species, with species colonization order taken into consideration as a biological effector. We firstly reported that prior colonization of one species significantly decreased the initiatively colonized cell counts of counterpart species by one to three orders of magnitude when competing for limited adhesion surface, under which E. coli was observed to be more aggressive in surface colonization as compared to P. fragi. However, the spatial structure and microbial composition of mature dual-species biofilms were not observed to be significantly affected. Our findings also shed new light on the evidence that E. coli and P. fragi, respectively, enhanced their biofilm formation capabilities by upregulating expression level of genes that encoded Type 1 fimbriae and phosphate response regulator as dual-species consortia progressed, which could serve as a crucial factor that improved the difficulty of food biocontrol.