Catabolite regulation of enzymatic activities in a white pox pathogen and commensal bacteria during growth on mucus polymers from the coral Acropora palmata

Colonization of host mucus surfaces is one of the first steps in the establishment of coral-associated microbial communities. Coral mucus contains a sulfated glycoprotein (in which oligosaccharide decorations are connected to the polypeptide backbone by a mannose residue) and molecules that result from its degradation. Mucus is utilized as a growth substrate by commensal and pathogenic organisms. Two representative coral commensals, Photobacterium mandapamensis and Halomonas meridiana, differed from a white pox pathogen Serratia marcescens PDL100 in the pattern with which they utilized mucus polymers of Acropora palmata. Incubation with the mucus polymer increased mannopyranosidase activity in S. marcescens, suggestive of its ability to cleave off oligosaccharide side chains. With the exception of glucosidase and N-acetyl galactosaminidase, glycosidases in S. marcescens were subject to catabolite regulation by galactose, glucose, arabinose, mannose and N-acetyl-glucosamine. In commensal P. mandapamensis, at least 10 glycosidases were modestly induced during incubation on coral mucus. Galactose, arabinose, mannose, but not glucose or N-acetyl-glucosamine had a repressive effect on glycosidases in P. mandapamensis. Incubation with the mucus polymers upregulated 3 enzymatic activities in H. meridiana; glucose and galactose appear to be the preferred carbon source in this bacterium. Although all these bacteria were capable of producing the same glycosidases, the differences in the preferred carbon sources and patterns of enzymatic activities induced during growth on the mucus polymer in the presence of these carbon sources suggest that to establish themselves within the coral mucus surface layer commensals and pathogens rely on different enzymatic activities.