Effect of light on Ralstonia solanacearum physiological features involved in host plant colonization

TANO J; PETROCELLI S; TONDO ML; CARRAU A; ORELLANO EG

Villa Carlos Paz

Congreso; XIII Encuentro Latinoamericano de Fotoquímica y Fotobiología (ELAFOT); 2017

Grupo Argentino de Fotobiología

Light perception in living organisms is achieved by photoreceptor proteins, which trigger signal transduction cascades that regulate light responses. LOV (Light, Oxygen or Voltage) photoreceptors are flavin-binding proteins using flavin mononucleotide (FMN) as chromophore [1-2]. Ralstonia solanacearum (Rso) is a soil-borne pathogen responsible for bacterial wilt, a severe disease that affects many economically important crops such as potato and tomato [3]. Analysis of the Rso GMI1000 genome sequence revealed the presence of one gene encoding a putative transmembrane LOV protein: rsp0254 [4]. The aim of this work was to study the effect of light in the Rso physiology.We evaluated the bacterial growth of Rso GMI1000 in liquid medium under white light, blue light and darkness. Several physiological parameters involved in the first stages of Rso infection of the host plant were determined in the different light conditions. Bacterial motility mechanisms, such as swimming and twitching, were evaluated, and the production of biosurfactants was analyzed. We also studied bacterial features related to colonization inside the host plant, such as the type two secretion system (TTSS) and the expression of antioxidant enzymes.The results obtained revealed that the white light decreases the bacterial growth with respect to blue light and darkness. It was observed that white light inhibits swimming and twitching motility. Regarding the production of biosurfactants, the strain presented the same emulsification capacity in all light conditions. However, the emulsification layer produced in sunflower oil by cultures grown under blue light exhibited a greater stability over time (about one month) compared with cultures grown under white light or darkness, indicating that, under blue light, the strain produces different biosurfactants than in the other light conditions. Finally, no differences were observed in the production of hydrolytic enzymes, but we have significant differences with respect to the expression of oxidative stress enzymes in white light, blue light and darkness. These results suggest that the rsp0254 gene of Rso GMI1000 is functional and would be involved in the regulation of physiological features required for host plant colonization.[1] M.A. van der Horst, K.J. Hellingwerf. Acc Chem Res. 2004, 37, 13.[2] A. Losi. Photochem. Photobiol. 2007, 83, 1283?1300.[3] S. Genin, T.P. Denny. Annu Rev Phytopathol. 2012, 50, 67-89.[4] C. Mandalari, A. Losi and W. Gärtner. Photochem. Photobiol. Sci. 2013, 12, 1144.