The first cloning and characterization of the gene katA, encoding the major catalase (KatA), from Xanthomonas is reported. A reverse genetic approach using a synthesized katA-specific DNA probe to screen a X. campestris pv. phaseoli genomic library was employed. A positively hybridizing clone designated pKat29 that contained a full-length katA was isolated. Analysis of the nucleotide sequence revealed an open reading frame of 1,521 bp encoding a 507-amino acid protein with a theoretical molecular mass of 56 kDa. The deduced amino acid sequence of KatA revealed 84% and 78% identity to CatF of Pseudomonas syringae and KatB of P. aeruginosa, respectively. Phylogenetic analysis places Xanthomonas katA in the clade I group of bacterial catalases. Unexpectedly, expression of katA in a heterologous Escherichia coli host resulted in a temperature-sensitive expression. The KatA enzyme was purified from an overproducing mutant of X. campestris and was characterized. It has apparent K-m and V-max values of 75 mm [H2O2] and 2.55 X 10(5) mumol H2O2 mumol heme(-1) s(-1), respectively. The enzyme is highly sensitive to 3-amino-1,2,4-triazole and NaN3, has a narrower optimal pH range than other catalases, and is more sensitive to heat inactivation.
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