BLUE LIGHT REGULATES VIRULENCE FACTORS IN Xanthomonas campestris pv. campestris

CONFORTE, VALERIA P.; RINALDI, JIMENA; FESTA, ARIEL E.; BONOMI, HERNÁN R.; CASTAGNARO, EMILIA; VOJNOV, ADRIÁN A.; MALAMUD, FLORENCIA

Chapalmalal

Congreso; XVIII Congreso de la Sociedad Argentina de Microbiología General; 2023

SAMIGE

Xanthomonas campestris pv. campestris (Xcc) is a non-photosynthetic phytopathogenicbacterium with a worldwide distribution that possesses the ability to live epiphytically. Xcccolonizes the plant xylem by entering through stomata or wounds. During the epiphyticstage of their life cycle, these bacteria are exposed to nutrient limitation, fluctuating wateravailability and exposure to sunlight. Consequently, Xcc is subjected to the day-night lightcycle, where the quality and intensity of light change. During the morning, twilight andsunset, red wavelengths reach the surface of the earth more easily due to the atmosphericblue light filtering. Xcc senses light quality through photosensory proteins encoded in itsgenome: a bacteriophytochrome of the bathy-like type (XccBphP) that perceives far-red/redlight, a LOV domain histidine kinase protein, and a recently discoveredcryptochrome/photolyase Cry/PHR.This study seeks to explain how blue light modulatesthe physiology of Xcc, particularly its virulence.In this research we generated a lov mutant (XccbphP) mutant whose characterizationhas been described in previous work. We evaluated different mechanisms that contributeto virulence: swimming motility, xanthan production, endoglucanase activity, in vitro and invivo adhesion. We also performed qPCR to evaluate the expression of genes related tomotility and xanthan production. All these assays were performed with both photosensorymutants in dark or under blue light illumination.Our results indicate that Xcc senses blue light not only through the XccLOV-HK proteinbut also via XccBphP. The purified recombinant XccLOV-HK displays characteristicabsorption peaks at 380-390 nm as well as at 425, 450, and 475 nm, which correspond tothe FMN chromophore bound to the LOV domain. Moreover, irradiation of the recombinantXccBphP holoprotein with blue light at 450 nm results in almost complete Prphotoconversion. This change is marked by the emergence of an absorption peak at 688nm and the simultaneous disappearance of the Pfr absorption band at 752 nm.Among the virulence factors we studied we observed that both endoglucanaseproduction and flagellum-dependent motility (swimming) seem to be modulated throughlight. Xanthan production is not modulated by blue light. We observed that all the strainsused in this work produced the same amount of xanthan, the primary virulence factor of thisorganism, 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 theXccBphP and XccLOV-HK photoreceptors, and that it can affect some infectionmechanisms.