Temporal secretion of a multicellulolytic system in Myxobacter sp. AL‐1

Abstract

The Gram‐negative soil micro‐organism Myxobacter sp. AL‐1 possesses at least five extracellular cellulases, the production of which is regulated by the growth cycle. We cloned the complete gene for one of these cellulases, termed cel 9, which encoded a 67‐kDa modular family 9 endoglycohydrolase, which was produced during the stationary phase of growth and was strongly enhanced by avicel. The predicted product of cel 9 matches the structural architecture of family 9 cellulases such as Thermonospora fusca endo/exocellulase E4. Cel9 protein was synthesized in Escherichia coli from a multicopy plasmid and in Bacillus subtilis from the isopropyl thiogalactoside‐inducible P spac promoter and was purified from the culture medium. Thermal stability, optimum pH and temperature dependence of Cel9 were similar when expressed from either source, and were indistinguishable from related cellulases produced by thermophilic bacteria. Downstream from cel 9 was found a partial ORF, designated cel 48, the deduced product of which was highly similar to bacterial exocellobiohydrolases and processive endoglucanases belonging to family 48 of the glycosyl hydrolases. The cel 9 and cel 48 genes appear to be arranged as part of an operon.