Strength of a “single-tube” protocol for protein isolation from multiple cell fractions shown for the plant pathogen Xanthomonas campestris pv. campestris B100 with a focus on proteins involved in the biosynthesis of the exopolysaccharide xanthan

Xanthomonas campestris pv. campestris (Xcc) B100 is a phytopathogenic bacterium, which uses xanthan, a secreted heterogeneous exopolysaccharide in both stages of infection of Brassicaceae. Until now, proteome analysis of Xcc lacking a detailed view on the proteins involved in xanthan biosynthesis. Proteins involved in the biosynthesis of this polysaccharide are located near, in or at the cell membrane. This study aims to establish a robust and rapid protocol for a comprehensive proteome analysis of Xcc strains, without the need to isolate different cell fractions. Therefore, a method for the analysis of the whole cell proteome was compared to the isolation of specific fractions regarding the total number of identified proteins, the overlap as well as the differences between the approaches. The whole cell proteome analysis using the “single-tube” preparation protocol resulted in more than 2,000 identified proteins with a coverage of 95.11% of the cell fraction specific identifications. To prove the usability of the protocol to study natural product formation at the envelope with proteins distributed over various cell fractions, Gum proteins of Xcc B100 were identified and quantified by a label free quantification (LFQ) approach. Thus, expression profiles of 9 out of 12 Gum proteins comparing stationary phase and growth phase were measured and showed differential expression levels within the operon structure. Five out of ten identified Gum proteins show a differential regulation indicating regulatory mechanisms beyond transcription level.