Study of the biological role of the Toxin/Antitoxin system XF2490/2491 of Xylella fastidiosa under copper stress

Abstract

The citrus industry is an important sector of the Brazilian agribusiness, generating income and jobs directly and indirectly, being responsible for leadership in the global market for frozen concentrated and non-concentrated juice. However, numerous pests and diseases threaten this culture. Among them, stands out the CVC, the citrus variegated chlorosis, caused by the bacterium xylem inhabitant X. fastidiosa, responsible for numerous economic losses in the sector. The bacterial genome has genes responsible for coding a system called toxin/antitoxin (TA), which are normally located together in a single operon, where the toxin is a stable protein toxic to the cell and the antitoxin is an unstable molecule (which may also be a protein) responsible for neutralizing the toxicity of the toxin. In E. coli, the MqsR/MqsA TA pair has been shown as gene regulator, influencing biofilm formation, motility, formation of persister cells, among others. This regulation of gene expression appears to be related to an adaptive capacity, since, for example, persister cells may occur in cells undergoing stress, which may lead to the re-colonization of the environment after the end of stress. In the case of X. fastidiosa, it could lead to re-colonization of its host and recurrence of the disease, for example. Thus, the aim of this project is to analyze the biological role of the TA system XF2490/2491 in X. fastidiosa, considered homologous to the MqsR/MqsA TA pair in E. coli. As the X. fastidiosa TA system maintains some protein domains equal to the MqsR/MqsA pair, this may suggest a similar mode of action, with the ability to regulate the expression of other genes, modifying the phenotypic expression, as biofilm formation, cell aggregation, production of exopolysaccharides, or, furthermore, induction of persister cells. Regarding persister cells, our research group has found that the XF2490/XF2491 system was highly expressed under conditions of copper stress, and that under these conditions the bacterium induced persister cells. Possibly this system can, among others, be responsible for this phenotype in X. fastidiosa under copper stress, one of the most commonly antimicrobials used in agriculture.