Shedding light on biofilm formation of Halobacterium salinarum R1 by SWATH-LC/MS/MS analysis of planktonic and sessile cells.

Early and mature biofilm formation in the extremely halophilic euryarchaeon Halobacterium salinarum strain R1 was characterized by SWATH-LC/MS/MS. Using a simple surfactant-assisted protein solubilization protocol and one-dimensional ultra-high performance nanoflow chromatography on the front end, 63.2 and 58.6% of the predicted H. salinarum R1 proteome could be detected and quantified, respectively. Analysis of biophysical protein properties, functional analysis and pathway mapping indicated comprehensive characterization of the proteome. Sixty point eight percent of the quantified proteins (or 34.5% of the predicted proteome) exhibited significant abundance changes between planktonic and sessile states, demonstrating that haloarchaeal biofilm formation represents a profound "lifestyle change" on the molecular level. Our results and analysis constitute the first comprehensive study to track molecular changes from planktonic cultures to initial and mature archaeal biofilms on the proteome level. Data are available via ProteomeXchange, identifier PXD003667. Proteins exemplifying different protein expression level profiles were selected, and their corresponding gene transcripts targeted by qRT-PCR to test the feasibility of establishing rapid PCR-based assays for archaeal biofilm formation.