Outer membrane protein of OmpF contributes to swimming motility, biofilm formation, osmotic response as well as the transcription of maltose metabolic genes in Citrobacter werkmanii

Abstract Background Bacterial outer membrane proteins (Omps) play crucial roles in environmental senses, stress responses and substance transportation. Our previous study has found that OmpA contributes to planktonic growth, biocide resistance, biofilm formation and swimming motility in Citrobacter werkmanii, whereas molecular functions of OmpF in this strain remain largely unknown. Hence, in this work, the ompF was firstly knocked out from the genome of C. werkmanii using a homologous recombination method and its phenotypical alternations of ∆ompF were then thoroughly characterized with the parental wild type (WT) and complementary (∆ompF-com) strains using biochemical and molecular approaches. Results The results demonstrated that the swimming ability of ∆ompF was reduced on semi-solid plates compared to WT due to down-regulation of flgC, flgH, fliK and fliF. Meanwhile, the deletion of ompF leads to a decrease of biofilm formation on both glass and polystyrene surfaces because of the reduced cell aggregation. Additionally, the inactivation of ompF also induced different osmotic stress (carbon sources and mental ions) responses of its biofilms comparing with that of WT and ∆ompF-com. Finally, a total of 6 maltose metabolic genes of lamB, malE, malK, malG, malM and malF were all up-regulated in ∆ompF. Gene knockout and HPLC results further revealed that MalEFGK2 cluster mainly contributed to maltose transportation in C. werkmanii. What’s more, for the first time, we have found that the upstream promoter of OmpF and its transcription can be combined with and regulated by MalT. Conclusions Overall, OmpF contributes to a variety of biochemical processes and molecular functions in C. werkmanii and even may be acted as a targeted site to restrain biofilm formation.