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Genome-Scale Mutagenesis and Phenotypic Characterization of Two-Component Signal Transduction Systems in Xanthomonas campestris pv. campestris ATCC 33913

The gram-negative bacterium Xanthomonas campestris pv. campestris is the causal agent of black rot disease of cruciferous plants. Its genome encodes a large repertoire of two-component signal transduction systems (TCSTSs), which consist of histidine kinases and response regulators (RR) to monitor and respond to environmental stimuli. To investigate the biological functions of these TCSTS genes, we aimed to inactivate all 54 RR genes in X. campestris pv. campestris ATCC 33913, and successfully generated 51 viable mutants using the insertion inactivation method. Plant inoculation identified two novel response regulator genes (XCC1958 and XCC3107) that are involved in virulence of this strain. Genetic complementation demonstrated that XCC3107, designated as vgrR (virulence and growth regulator), also affects bacterial growth and activity of extracellular proteases. In addition, we assessed the survival of these mutants under various stresses, including osmotic stress, high sodium concentration, heat shock, and sodium dodecyl sulfate exposure, and identified a number of genes that may be involved in the general stress response of X. campestris pv. campestris. Mutagenesis and phenotypic characterization of RR genes in this study will facilitate future studies on signaling networks in this important phytopathogenic bacterium.