Pseudomonas cellulosa expresses a single membrane-bound glycoside hydrolase family 51 arabinofuranosidase

In the accompanying paper [Beylot, McKie, Voragen, Doeswijk-Voragen and Gil bert (2001) Biochem. J. 358, 607-614] the chromosome of Pseudomonas cellulo sa was shown to contain two genes, abf51A and abf62A, that encode arabinofu ranosidases belonging to glycoside hydrolase families 51 and 62, respective ly. In this report we show that expression of Abf51A is induced by arabinos e and arabinose-containing polysaccharides. Northern-blot analysis showed t hat abf51A was efficiently transcribed, whereas no transcript derived from abf62A was detected in the presence of arabinose-containing polysaccharides . Zymogram and Western-blot analyses revealed that Abf51A was located on th e outer membrane of P. cellulosa. To investigate the importance of Abf51A i n the release of arabinose from poly- and oligosaccharides, transposon muta genesis was used to construct an abf51A-inactive mutant of P. cellulosa (De lta abf51A). The mutant did not grow on linear arabinan or sugar beet arabi nan, and utilized arabinoxylan much more slowly than the wild-type bacteriu m. Arabinofuranosidase activity in Delta abf51A against aryl-alpha -arabino furanosides, arabinan and alpha1,5-linked arabino-oligosaccharides was appr ox. 1% of the wild-type bacterium. The mutant bacterium did not exhibit ara binofuranosidase activity against arabinoxylan, supporting the view that ab f62A is not expressed in P. cellulosa. These data indicate that P. cellulos a expresses a membrane-bound glycoside hydrolase family 51 arabinofuranosid ase that plays a pivotal role in releasing arabinose from polysaccharides a nd arabino-oligosaccharides.