Effects Of Bacterial Motility On Biofilm Formation Under Environmental Stresses

When confronted with environmental stress,bacteria commonly emerge in sessile ecological communities in the form of aggregation and biofilm to resist adverse environmental effects,potentially threatening safety of public health and industrial production.Bacterial motility plays a vital role in their physiological behavior in an aqueous environment,contributing to increasing their foraging opportunities and avoiding the intrusions of toxic and harmful factors.Nevertheless,effects of bacterial motility on growth,extracellular polymeric substances(EPS),surface attachment and aggregation behaviors,especially stress response bahaviors remain elusive.In this thesis,the wild-type Pseudomonas aeruginosa and its mutant strain were used as the models,with the aim of investigating the role of motility in bacterial attachment and biofilm formation,and the behaviorial responses to environmental stresses,which would provide theoretical guidance for the effective control of biofilm growth.Firstly,under different nutritional conditions,the effects of bacterial motility on growth,reproduction,extracellular polymer secretion,surface attachment and aggregation were studied.The results showed the promoting effect of flagellar motility on the biofilm initialization,rather than on biofilm development process.Moderate nutrient limitation(1/50 LB culture)increased the swimming velocity of wild-type Pseudomonas aeruginosa and surface attachment,highlighting the crucial role of flagellar motility on initial attachment.In contrast,the absence of flagellum promoted proliferation and EPS(especially extracellular proteins)release rates of the mutant strain,thus promoting the biofilm development process.Moderate nutrient-limitted condition accelerated the formation of extracellular polymers and biofilms for both strains.Secondly,the effects of disinfectant concentration on bacterial motility,growth,reproduction,extracellular polymer formation,surface attachment and aggregation were investigated.The results indicated that flagellular motility encouraged biofilm initialization,while the absence of flagellum contributed to its aggregation and biofilm formation.Moderate disinfection concentration(1.0 mg/L chlorine)accelerated flagellular motility and thus surface attachment.At the later stage,moderate disinfection concentration accelerated the EPS production and biofilm development.The disinfectant would inhibite the bacterial velocity,extracellular polymer formation during the initial attached stage and bacteria aggregation stage with a further increase in disinfectant concentration.Finally,this study investigated the biofilm formation process stressed by both nutrient limitation and disinfection stress.Similar results were found when compared with those under nutrient-rich condition.However,nutrient-limitted condition(1/50 LB)enhanced biofilm initialization and development processes accompanying with biofilm viability increasing,suggesting bacterial aggregation contributed to resistance capability to environmental stresses.Analysis of swimming velocity and EPS production indicated the nutrient-limitted condition accelerated bacterial motility and EPS formation at later stages,highlighting different roles of flagellular motility and EPS secretion during biofilm initialization and development processes.