BLUE LIGHT REGULATES VIRULENCE FACTORS IN Xanthomonas campestris pv campestris.

CONFORTE, VALERIA; RINALDI JIMENA; FESTA ARIEL ; BONOMI, HERNÁN RUY; CASTAGNARO EMILIA; VOJNOV ADRIAN A; MALAMUD FLORENCIA

Congreso; SAMIGE; 2023

Xanthomonas campestris pv. campestris (Xcc) is a non-photosynthetic phytopathogenic bacterium with a worldwide distribution that possesses the ability to live epiphytically. Xcc colonizes the plant xylem by entering through stomata or wounds. During the epiphytic stage of their life cycle, these bacteria are exposed to nutrient limitation, fluctuating water availability and exposure to sunlight. Consequently, Xcc is subjected to the day-night light cycle, where the quality and intensity of light change. During the morning, twilight and sunset, red wavelengths reach the surface of the earth more easily due to the atmospheric blue light filtering. Xcc senses light quality through photosensory proteins encoded in its genome: a bacteriophytochrome of the bathy-like type (XccBphP) that perceives far-red/red light, a LOV domain histidine kinase protein, and a recently discovered cryptochrome/photolyase Cry/PHR.This study seeks to explain how blue light modulates the physiology of Xcc, particularly its virulence.In this research we generated a lov mutant (Xcc∆lov) and we worked with the Xccbphp mutant whose characterization has been described in previous work. We evaluated different mechanisms that contribute to virulence: swimming motility, xanthan production, endoglucanase activity, in vitro and in vivo adhesion. We also performed qPCR to evaluate the expression of genes related to motility and xanthan production. All these assays were performed with both photosensory mutants in dark or under blue light illumination.Our results indicate that Xcc senses blue light not only through the XccLOV-HK protein but also via XccBphP. The purified recombinant XccLOV-HK displays characteristic absorption peaks at 380-390 nm as well as at 425, 450, and 475 nm, which correspond to the FMN chromophore bound to the LOV domain. Moreover, irradiation of the recombinant XccBphP holoprotein with blue light at 450 nm results in almost complete Pr photoconversion. This change is marked by the emergence of an absorption peak at 688 nm and the simultaneous disappearance of the Pfr absorption band at 752 nm.Among the virulence factors we studied we observed that both endoglucanase production and flagellum-dependent motility (swimming) seem to be modulated through light. Xanthan production is not modulated by blue light. We observed that all the strains used in this work produced the same amount of xanthan, the primary virulence factor of this organism, if they were grown under blue light or in complete darkness. From this, we can conclude that Xcc has the ability to sense blue light through the XccBphP and XccLOV-HK photoreceptors, and that it can affect some infection mechanisms.