Abstract
The γ-proteobacterium Xanthomonas campestris pv. campestris B100 is the causal agent of black rot disease in a wide range of economically important crops. In addition, X. campestris pv. campestris is commercially relevant due to the synthesis of the exopolysaccharide xanthan. In this work, we first introduce a novel transcriptional regulator, termed Crt1, and present the effect that the deletion of the crt1 gene exerts on growth, xanthan production, virulence, and transcriptome and proteome profiles. Differential transcriptome analysis of the deletion mutant X. campestris pv. campestris B100 Δcrt1 compared to the wild type revealed the up-regulation of the pilP, pilM and pilE genes, which are relevant for the type 4 pilus assembly. Furthermore, increased xanthan production and upregulated transcription of genes within the gum cluster, which are critical for xanthan biosynthesis, were observed. Profiling of the cytosolic proteome identified increased expression of the glucosyltransferase GtrB, which is involved in LPS biosynthesis, and of a type III effector with phytase activity. Moreover, the presence of the fructose import and utilization proteins FruAB and FruK was reduced in the deletion mutant. The plant-pathogenicity assay demonstrated that the severity of the infection of the host plant tissue was higher in the case of the deletion mutant than in the wildtype strain. The regulator Crt1 modulates multiple virulence factors as well as LPS and xanthan production. In conclusion, Crt1 influences a diverse network of genes that contribute to the pathogenic lifestyle of X. campestris pv. campestris.