Identification and analysis of a large gene cluster involved in floc formation of activated sludge bacterium Mitsuaria chitosanitabida

Abstract:

[Background] The activated sludge (AS) process has been widely applied for municipal sewage and industrial wastewater treatment. The microbial floc formation is very important in gravitational sludge-effluent separation and sludge recycling. A floc-forming strain of Mitsuaria chitosanitabida XHY-A6, has been isolated from the sludge sample of Beishiqiao Sewage Treatment Plant, Xi’an. [Objective] We intended to analyze the genes and reveal the mechanism underlying the floc-forming phenotype of Mitsuaria chitosanitabida XHY-A6 strain. [Methods] Molecular genetics, including the mariner transposon mutagenesis and genetic complementation, and genomics approaches were utilized for analyzing the genes and gene cluster required for floc formation. [Results] Two floc-formation deficient mutants have been isolated and the transposon insertional sites successfully mapped to the sequenced and annotated genome of Mitsuaria chitosanitabida XHY-A6. The glycosyltransferase (termed gt3) and polysaccharide chain length determinant protein (wzz) genes are located within a large gene cluster comprising the genes for extracellular polysaccharide biosynthesis and secretion, epsB2-prsK-prsR-prsT genes, a PEP-CTERM gene and other genes. The requirement of gt3 gene, wzz gene and wzc gene for floc-formation were further confirmed by genetic complementation. [Conclusion] Our results demonstrate that bacterial floc formation mediated by both exopolysaccharides and PEP-CTERM proteins might be well-conserved between Zoogloea resiniphila and Mitsuaria chitosanitabida. The chitosan-degrading capability of Mitusaria strains could be utilized for treating the seafood processing and other chitin-containing sewage and wastewater.