The GrrA/GrrS system regulates Serratia plymuthica IC1270 surface proteins that induce expression of the host cell α5β1 integrin involved in the invasion of these bacteria.

The rhizobacteria Serratia plymuthica are considered promising antimicrobial agents. However, cases of infection of both plants and humans by these bacteria have been described. espite the various mechanisms of infection of plants and humans, cases cross-kingdom pathogenicity of bacteria are increasingly being recorded. The aim of the work was to assess the possibility of infection of human cells by S. plymuthica. Using confocal microscopy and a quantitative microbiological method, we showed for the first time that S. plymuthica IC1270 is able to penetrate M-HeLa cells. And the Quorum Sensing system and the global gene regulation system GrrA/GrrS determine the intensity of their invasion. Surprisingly, inactivation of the grrA gene reduces invasion, in contrast to inactivation of the grrS gene, which increases invasion. For penetration, these bacteria use the host cell α5β1 integrin, the intensity of expression of which increases as a result of infection. Moreover, the intensity of invasion upon gene inactivation correlate with the intensity of expression of α5 and β1 integrin subunits. The increased expression of these genes is due to contact with the Serratia surface protein OmpX, which is regulated by GrrA and GrrS. An additional factor that enhances invasion upon inactivation of the grrS gene may be the accumulation of isomerase PpiA, which mediates the folding of surface proteins. Thus, S. plymuthica penetrates M-HeLa cells using α5β1 integrin, the expression of which is regulated by the GrrA/GrrS-dependent surface protein of bacteria.