THE GENE ENCODING THE BETA-1,4-ENDOGLUCANASE (CELA) FROM MYXOCOCCUS-XANTHUS - EVIDENCE FOR INDEPENDENT ACQUISITION BY HORIZONTAL TRANSFER OF BINDING AND CATALYTIC DOMAINS FROM ACTINOMYCETES

The celA gene encoding a beta-1,4 endoglucanase (CelA) from Myxococcus xanthus has been cloned in Escherichia coli and sequenced. The C-term inal region of CelA displayed a high level of similarity with the cata lytic domain of several Egl belonging to the glycosyl hydrolases famil y 6 (CenA from Cellulomonas fimi, CelA from Microbispora bispora, E2 f rom Thermonospora fusca, CasA from Streptomyces KSM9 and CelA1 from St reptomyces halstedii) and less similarity to the cellobiohydrolases of the fungi Trichoderma reesei and Agar icus bisporus. Using PCR amplif ication we found in another myxobacterium, Stigmatella aurantiaca, a p art of a glycosyl hydrolase belonging to the same family. The N-termin al part of CelA displayed significant similarities with the cellulose- binding domain of other cellulases belonging to a rare subset of famil y II, such as the avicelase I from Streptomyces reticuli, both tandem repeats N1 and N2 of the cellulase CenC from Cellulomonas fimi, and th e N-terminal part of the Egl E1 from Thermonospora fusca. Analyses of the multiple alignments and reconstruction of phylogenetic trees stron gly suggest that both domains of CelA were acquired by independent hor izontal transfers between Gram(+) soil bacteria and scavenging myxobac teria followed by domain shuffling.