Early-stage Bacterial Surface Attachment In Response To Environmental Stresses In Drinking Water Distribution Systems

Microbes can attach to and colonize surfaces as biofilms.In drinking water distribution systems(DWDSs),the formation of biofilms can block water transport,yielding severe water quality issues.Although numerous studies have been conducted on the biofilm formation and its influencing factors in DWDS in recent years,how environmental stresses to shape individual behaviors and early-stage attachment of microbes remains elusive.This study aims at exploring the impacts of nutrient and chlorine concentrations on initial surface attachment of DWDS bacteria and Pseudomonas aeruginosa(P.A.),thus revealing the mechanism of early-stage biofilms formation and offering theoretical support for biofilm control strategies.Firstly,this study experimentally examined the effects of chlorine on extracellular polymer substances(EPS)production and its impacts on early-stage biofilms formation in a model drinking water system.Results showed that low-level chlorine(?1.0 mg/L)stimulated microbial EPS(especially of proteins)excretion that favored early-stage biofilm formation.Removal of cell-attached proteins and polysaccharides diminished biofilm formation,which highlighted the critical role of EPS(especially protein components)in biofilm development.A negative correlation between chlorination-mediated microbial protein production and cell surface charge suggested that chlorine disinfection may modify cell surface properties through regulation of microbial EPS excretion and thereby mediate biofilm formation.Secondly,the attachment of motile and non-motile P.A.under various nutrient environments and chlorine dosages was investigated to further analyze the bacterial attachment mechanism in DWDSs.The results showed that the attaching ratio of motile P.A.under low-nutrition condition and low-level chlorine(0.5 mg/L)was higher than any other scenarios.For non-motile P.A.,reducing the nutrient concentration yielded a decrease in surface attachment,while the chlorine concentration had little influence on its attachment.Overall,the attaching ratio of non-motile cells was lower than that of motile ones under all scenarios.Finally,this study investigated the effects of environmental stresses on bacterial velocity and cell surface properties.Results showed that low-level nutrient and chlorine enhanced bacterial motility without obvious EPS variations for motile ones.Statistics analysis suggested that bacterial velocity was correlated significantly with the amount of surface attachment.In contrast,environmental stresses yielded higher EPS secretion and correlation between EPS contents and initial attachment for non-motile P.A.as compared to motile ones.Environmental changes affected Zeta potential of suspended cells,which was negatively correlated with surface attachment,while cell hydrophobicity did not vary significantly under various environmental stresses.