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Mutagenesis of β-1,3-Glucanase Genes in Lysobacter enzymogenes Strain C3 Results in Reduced Biological Control Activity Toward Bipolaris Leaf Spot of Tall Fescue and Pythium Damping-Off of Sugar Beet

June 2005 , Volume 95 , Number  6
Pages  701 - 707

Jeffrey D. Palumbo , Gary Y. Yuen , C. Christine Jochum , Kristin Tatum , and Donald Y. Kobayashi

First, fourth, and fifth authors: Department of Plant Biology and Pathology, Rutgers, The State University of New Jersey, New Brunswick 08901; and second and third authors: Department of Plant Pathology, University of Nebraska, Lincoln 68583

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Accepted for publication 3 February 2005.

Lysobacter enzymogenes produces extracellular lytic enzymes capable of degrading the cell walls of fungi and oomycetes. Many of these enzymes, including β-1,3-glucanases, are thought to contribute to the biological control activity expressed by several strains of the species. L. enzymogenes strain C3 produces multiple extracellular β-1,3-glucanases encoded by the gluA, gluB, and gluC genes. Analysis of the genes indicates they are homologous to previously characterized genes in the related strain N4-7, each sharing >95% amino acid sequence identity to their respective counterparts. The gluA and gluC gene products encode enzymes belonging to family 16 glycosyl hydrolases, whereas gluB encodes an enzyme belonging to family 64. Mutational analysis indicated that the three genes accounted for the total β-1,3-glucanase activity detected in culture. Strain G123, mutated in all three glucanase genes, was reduced in its ability to grow in a minimal medium containing laminarin as a sole carbon source. Although strain G123 was not affected in antimicrobial activity toward Bipolaris sorokiniana or Pythium ultimum var. ultimum using in vitro assays, it was significantly reduced in biological control activity against Bipolaris leaf spot of tall fescue and Pythium damping-off of sugar beet. These results provide direct supportive evidence for the role of β-1,3-glucanases in biocontrol activity of L. enzymogenes strain C3.

© 2005 The American Phytopathological Society