N-Acylhomoserine lactone-mediated quorum sensing regulates biofilm structure in Methylobacterium populi P-1M, an isolate from a pink-pigmented household biofilm

Numerous gram-negative bacteria have quorum-sensing systems and produce AHL as a quorum-sensing signal molecule. In this study, we demonstrated that Methylobacterium populi P-1M, an isolate from a pink-pigmented household biofilm, produced two AHLs, C14:1-HSL as a predominant product and 3OHC14-HSL as a minor product. The complete genome sequence of M. populi P-1M revealed the presence of genes that are predicted to encode an AHL synthase (mpoI) and AHL receptor (mpoR). M. populi P-1M formed a pellicle-like biofilm, which had a flat surface and was easily removable. In contrast, biofilms formed by mpoI and/or mpoR deletion mutants had a wavy surface structure and strongly adhered to the glass tube. When C14:1-HSL was added to the mpoI mutant culture, the biofilm structure resembled that of the wild-type strain. These results demonstrated that the structure and adhesion strength of M. populi P-1M biofilms are determined in part by AHL-mediated quorum sensing. Abbreviations: AHL: N-acyl-l-homoserine lactone; C14:1-HSL: N-tetradecenoyl-l-homoserine lactone; 3OHC14-HSL: N-(3-hydroxytetradecanoyl)-l-homoserine lactone; SAM: S-adenosyl-l-methionine; ACP: acyl-acyl carrier protein; EPS: extracellular polysaccharide; DMSO: dimethyl sulfoxide Biofilm formation on the culture surface in glass tubes by M. populi P-1M and quorum-sensing mutants, P-1MΔI, P-1MΔR, and P-1MΔI with C14:1-HSL