Mannosidase production by viridans group streptococci

The production of mannosidase activity by all currently recognized species of human viridans group streptococci was determined using an assay in which bacterial growth was dependent on the degradation of the high-mannose-type glycans of RNase B and subsequent utilization of released mannose. RNase B is an excellent substrate for the demonstration of mannosidase activity si nce it is a glycoprotein with a single glycosylation site which is occupied by high-mannose-type glycoforms containing five to nine mannose residues. Mannosidase activity was produced only by some members of the mitis group ( Streptococcus mitis, Streptococcus oralis, Streptococcus gordonii, Streptoc occus cristatus, Streptococcus infantis, Streptococcus parasanguinis, and S treptococcus pneumoniae) and Streptococcus intermedius of the anginosus gro up. None of the other species within the salivarius and mutans groups or St reptococcus peroris and Streptococcus sanguinis produced mannosidase activi ty. Using matrix-assisted laser desorption ionization time-of-flight mass s pectrometry, it was demonstrated that the Man, glycan alone was degraded wh ile Man(6) to Man(9), which contain terminal alpha (1-->2) mannose residues in addition to the (alpha (1-->3), (alpha (1-->6), and beta (1-->4) residu es present in Man,, remained intact. Investigations on mannosidase producti on using synthetic (4-methylumbelliferone- or p-nitrophenol-linked) (alpha- P-mannosides as substrates indicated that there was no correlation between degradation of these substrates and degradation of the Man, glycan of RNas e B. No species degraded these oc-linked mannosides, while degradation of t he P-linked synthetic substrates was restricted to strains within the Strep tococcus anginosus, S. gordonii, and S. intermedius species. The data gener ated using a native glycoprotein as the substrate demonstrate that mannosid ase production within the viridans group streptococci is more widely distri buted than had preiously been considered.