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The glyceraldehyde-3-phosphate dehydrogenase of Xanthomonas campestris pathovar campestris is required for extracellular polysaccharide production and full virulence

Guangxi Key Laboratory of Subtropical Bioresources Conservation and Utilization, The Key Laboratory

ABSTRACT

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) plays an important role in glucose catabolism, converting glyceraldehyde-3-phosphates to 1, 3-bisphosphoglycerates. The open reading frame (ORF) XC_0972 in the genome of the Xanthomonas campestris pathovar campestris (Xcc) strain 8004 is the only ORF annotated to encode a GAPDH. In this work, we have demonstrated genetically that this ORF encodes a unique GAPDH in the Xcc strain 8004, which seems to be constitutively expressed. The GAPDH-deficient mutant could still grow in the medium with glucose or other sugars as the sole carbon source and no phosphofructokinase activity was detectable in the strain 8004. These suggest that Xcc may employ the Entner-Doudoroff pathway but not glycolysis to utilize glucose. The mutant could not utilize pyruvate as sole carbon source while the wild type could, implying that the GAPDH of Xcc is involved in gluconeogenesis. Furthermore, inactivation of the Xcc GAPDH resulted in impairment of bacterial growth and virulence in host plant, and reduction of intracellular ATP and extracellular polysaccharide (EPS). These reveal that the GAPDH is required for EPS production and full pathogenicity of Xcc.

¹ E-mail: jltang{at}gxu.edu.cn