Degradation of Levan by Actinomyces viscosus

Abstract

Actinomyces viscosus ATCC 15987 was examined for its ability to hydrolyze its own levan. Washed whole cells and an ammonium sulfate fraction from cell-free culture fluids were shown to possess levan hydrolase activity. Analyses of reaction mixtures by gel filtration and thin-layer chromatography demonstrated that the product of levan hydrolysis was free fructose. The cell-associated and extracellular enzyme preparations also hydrolyzed inulin and the levans synthesized by Aerobacter levanicum and Bacillus subtilis. Growth of A. viscosus in media supplemented with 0.1% A. viscosus levan resulted in a 33-fold increase and a 7-fold increase in the specific activities of the respective extracellular and cell-associated enzymes when compared with those from 55 mM glucose cultures. Growth in the presence of 29.2 mM sucrose resulted in a 28-fold increase and a 5-fold increase in the specific activities of the respective enzymes when compared with those from the glucose cultures. The extracellular enzyme exhibited high activity over a wide pH range, with 87 and 89% of its pH 6.0 optimum activity at pH 5.0 and 7.0, respectively. The cell-associated enzyme also exhibited optimum activity at pH 6.0, but this was decreased to 10 and 20% at pH 5.0 and 7.0, respectively. Analysis for the presence of extracellular levan during growth of A. viscosus in sucrose broths demonstrated that peak levan concentrations occurred during the mid-exponential to late-exponential phase of growth followed by a rapid decline in extracellular levan as a result of levan hydrolase activity.

Isolation and properties of levanase from Streptococcus salivarius KTA-19

“…The presence of fructan in dental plaque has been demonstrated by several authors (19,23,24). Fructan in dental plaque is synthesized extracellularly by many oral bacteria such as Streptococcus salivarius (11,12,14,16,27,31), Streptococcus mutans (3,4,5,8,11), Actinomyces viscosus (19,20,25,26,28,29,36,39), and Rothia dentocariosa (21). However, the fructan produced in dental plaque is not homogeneous.…”

“…On the other hand, several studies have shown that fructans synthesized in dental plaque are degraded or metabolized by some of the dental plaque organisms (7,15,18,23,37,41). Several streptococcal strains in human dental plaque have been reported to hydrolyze levan produced by S. salivarius, S. mutans, and A. viscosus (7,23,25,37,41). The latter strain degraded its own levan (25).…”

“…Several streptococcal strains in human dental plaque have been reported to hydrolyze levan produced by S. salivarius, S. mutans, and A. viscosus (7,23,25,37,41). The latter strain degraded its own levan (25). However, there have been few reports on the characteristics of the fructan-hydrolyzing enzymes of bacteria.…”

“…Avigad and Bauer (1) isolated and purified a levanase preparation from an Arthrobacter species derived from soil origin. A levan-hydrolyzing enzyme of A. viscosus was partially purified by Miller and Somers (25). The fructan-hydro-lyzing microorganisms in dental plaque have been studied and it has been found that approximately 37% of the plaque bacteria degrade fructans, including levan and inulin (35).…”

Roles of Fructosyltransferase and Levanase-Sucrase of Actinomyces naeslundii in Fructan and Sucrose Metabolism

“…Bacteria that produce fructans also produce enzymes that degrade these polymers (11). Previous studies have indicated that oral Actinomyces have the capacity to hydrolyze a variety of fructans via enzymes that specifically break down (i) only levans, (ii) only inulins, sucrose, and raffinose, but not levans; or (iii) levans, inulins, sucrose, and raffinose (40,62). Enzymes that can attack levans, regardless of whether they attack multiple other fructosides, are often referred to as levanases.…”