Examining the interplay between Streptococcus agalactiae, the biopolymer chitin, and its derivatives

Authors: Aksoy, Mediha; Beck, Benjamin; Zhang, Dunhua

Submitted to: MicrobiologyOpen
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/21/2018
Publication Date: 10/1/2018
Citation: Aksoy, M., Beck, B.H., Zhang, D. 2018. Examining the interplay between Streptococcus agalactiae, the biopolymer chitin, and its derivatives. MicrobiologyOpen. 8(5):1-11. https://doi.org/10.1002/mbo3.733.
DOI: https://doi.org/10.1002/mbo3.733

Interpretive Summary: Streptococcus agalactiae is a highly pathogenic bacterium of animals worldwide whereas chitin and its derivative chitosan are among the most abundant biopolymers found in nature, particularly in the aquatic environment. The present investigation assessed the capability of S. agalactiae to degrade or use these polymers for growth. The effect of chitin and degraded chitin on the growth of S. agalactiae was determined. Colloidal chitin had no effect on the growth of S. agalactiae. Degraded chitin, however, stimulated the growth of S. agalactiae cultures and their survival time increased in minimal medium. S. agalactiae cells did not produce the enzyme chitinase to degrade chitin; however, they were capable of cohabiting with a chitin degrading organism and were also found to readily utilize GlcNAc (a product of degraded chitin), which is released during chitin degradation as a sole source of nutrients for growth. Chitosan at high concentrations (0.2% or above) was found to have antibacterial activities against S. agalactiae while lower levels of chitosan stimulated the growth of the bacterium. In presence of chitosan, S. agalactiae was found to secret chitosanase to degrade chitosan, and utilized it to a limited extent to benefit growth. The interaction of S. agalactiae with chitin and chitosan could play a role in the diverse habitat distribution and pathogenicity of S. agalactiae worldwide.

Technical Abstract: Streptococcus agalactiae is a highly pathogenic gram positive bacterium of aquatic species and terrestrial animals worldwide whereas chitin and its derivative chitosan (deacetylated chitin), are among the most abundant biopolymers found in nature, including the aquatic milieu. The present investigation focused on the capability of S. agalactiae to degrade and utilize these polymers. The effect of chitin and degraded chitin on the growth of S. agalactiae was determined by colony count from the aliquot of culture sample for 4 and 6 days, respectively. Growth of S. agalactiae in minimal medium containing various concentrations of chitosan or N-acetyl-glucosamine (GlcNAc) were evaluated for 24h and 72-h incubation period, respectively. Chitosanase production was measured daily over 7 days of growth period and degraded products were evaluated with thin layer chromatography. Colloidal chitin had no effect on the growth of S. agalactiae. Degraded chitin, however, stimulated the growth of S. agalactiae cultures and their survival time increased in minimal medium. S. agalactiae cells did not produce chitinase to degrade chitin; however, they were capable of cohabiting with a chitin degrading organism and readily utilize GlcNAc (product of degraded chitin), which is released during the process of chitin degradation as sole source of carbon and nitrogen for growth. Chitosan at high concentrations (0.2% or above) had antibacterial activities against S. agalactiae while levels lower than the inhibitory level of chitosan, stimulated the growth of the bacterium. In presence of chitosan in the medium, S. agalactiae secrets chitosanase to degrade chitosan, and utilizes it to a limited extent to benefit growth. The interaction of S. agalactiae with chitin hydrolytes and chitosan could play a role in the diverse habitat distribution and pathogenicity of S. agalactiae worldwide.