Pectinolytic enzymes of oral spirochetes from humans

Abstract

Five strains of obligately anaerobic, pectin-fermenting spirochetes were isolated from the subgingival plaque of humans. The strains produced two extracellular enzymatic activities that functioned in pectin degradation. One of these enzymatic activities was pectin methylesterase (EC 3.1.1.11), and the other was pectate lyase (EC 4.2.2.2) of the endo type. The data indicate that the cumulative action of these two enzymatic activities brought about depolymerization of pectin in spirochete cultures. Pectin- or polygalacturonate-degrading hydrolases were not detected. A cell-associated lyase activity that catalyzed polygalacturonate breakdown was present in one of the spirochete strains. In addition to pectin, the isolates utilized polygalacturonic, glucuronic, or galacturonic acid as fermentable substrate but did not neutral sugars, amino acids, or other substrates tested. Although the oral spirochetes did not ferment hyaluronic acid, one of the strains grew in coculture with a hyaluronidase-producing Peptostreptococcus strain in a medium containing hyaluronic acid as fermentable substrate. Two of the isolates were identified as Treponema pectinovorum strains on the basis of their substrate utilization pattern, end products of fermentation, other phenotypic characteristics, and the guanine-plus-cytosine content of their DNA. Even though the pectinolytic isolates were specialized with respect to the fermentable substrates they utilized, they appeared to compete successfully with other microorganisms in their habitat.