Abstract
Outer membrane (OM) proteins play a significant role in bacterial pathogenesis. In this work, we examined and compared the expression of the OM proteins of the rice pathogen Acidovorax avenae subsp. avenae strain RS-1, a Gram-negative bacterium, both in an in vitro culture medium and in vivo rice plants. Global proteomic profiling of A. avenae subsp. avenae strain RS-1 comparing in vivo and in vitro conditions revealed the differential expression of proteins affecting the survival and pathogenicity of the rice pathogen in host plants. The shotgun proteomics analysis of OM proteins resulted in the identification of 97 proteins in vitro and 62 proteins in vivo by mass spectrometry. Among these OM proteins, there is a high number of porins, TonB-dependent receptors, lipoproteins of the NodT family, ABC transporters, flagellins, and proteins of unknown function expressed under both conditions. However, the major proteins such as phospholipase and OmpA domain containing proteins were expressed in vitro, while the proteins such as the surface anchored protein F, ATP-dependent Clp protease, OmpA and MotB domain containing proteins were expressed in vivo. This may indicate that these in vivo OM proteins have roles in the pathogenicity of A. avenae subsp. avenae strain RS-1. In addition, the LC-MS/MS identification of OmpA and MotB validated the in silico prediction of the existance of Type VI secretion system core components. To the best of our knowledge, this is the first study to reveal the in vitro and in vivo protein profiles, in combination with LC-MS/MS mass spectra, in silico OM proteome and in silico genome wide analysis, of pathogenicity or plant host required proteins of a plant pathogenic bacterium.
Highlights
Acidovorax avenae subsp. avenae is a phytobacterium that can cause diseases in many economically important plants, including rice, corn, oats, sugarcane, millet, and foxtail [1]
We developed a method to collect the in vivo bacteria from rice plants, which makes it possible to analyze in vivo Outer membrane (OM) proteome and the T6SS of A. avenae subsp. avenae strain RS-1
Results of this study clearly revealed the differential expression of OM proteins in A. avenae subsp. avenae strain RS-1 between in vivo and in vitro
Summary
Acidovorax avenae subsp. avenae is a phytobacterium that can cause diseases in many economically important plants, including rice, corn, oats, sugarcane, millet, and foxtail [1]. Some OM proteins from different Gram-negative bacteria have been recognized as important virulence factors and targets for host immune recognition [5], and have recently been proposed to be required for the bacterial Type VI secretion system (T6SS). This represents a new paradigm of protein secretion that is critical for the pathogenesis of many Gram-negative bacteria [6]
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