The Marine Bacterium Pseudoalteromonas Tunicata Alters its Proteome Upon Adhesion to Extracellular Matrix

Abstract

The marine bacterium Pseudoalteromonas tunicata is commonly found associated with eukaryotic hosts and produces anti-fouling activity. The genome of P. tunicata contains several genes with high sequence similarity to those encoding outer membrane proteins of human pathogens from the genus Leptospira. One of these proteins, PTD2-05920, was recently shown to bind mammalian extracellular matrix (ECM) similar to that seen with LipL32, the major outer membrane protein of Leptospira. Since these organisms share a functional ECM binding protein, we set out to determine whether P. tunicata could adhere to mammalian ECM. Once this adhesion was established, a systematic study of the proteomic changes associated with the transition from planktonic to ECMadherent states was performed for P. tunicata. Using Blue Native PAGE coupled with second dimension SDS PAGE, more than 50 well-resolved protein spots were seen, one of which changed upon adhesion. One third of the identified proteins were annotated as TonB-dependent receptors reflecting the great number of TonB genes in the genome. This technique also revealed two protein complexes, each consisting of two proteins. Interestingly, both of the individual complexes arise from consecutive genes suggesting the coordinate regulation, co-transcription, and co-translation of two proteins that are assembled into a complex. Secondly, immobilized pH gradient separation coupled with SDSPAGE was used to identify additional protein changes upon adhesion. This study is the first to examine the interaction of a marine bacterium with a mammalian extracellular matrix and suggests a general mechanism by which P. tunicata regulates protein complex formation.