Biodegradation of polysaccharide in brown seaweeds, Laminaran by isolated microorganisms

Abstract

Microorganisms with the ability to produce an enzyme capable of degrading polysaccharide in brown seaweeds, particularly laminaran (β-(1,3)-glucan) were newly isolated from soil by enrichment culture contained brown seaweeds as a sole carbon source. A total six microorganisms were isolated and were studied for enzyme activities. The cellular growth of six microorganisms was monitored using spectrophotometer at OD375 and their ability to degrade laminaran was deduced from the increase in the amount of reducing sugars measured by dinitrosalicylic acid (DNS) method at OD570. The results showed that mixed six isolated microorganisms were able to grow in the culture medium containing laminaran (5 g L-1) as a sole carbon source. Compared to single isolated microorganism, mixed six isolated microorganisms also showed the higher reducing sugars amount with decreasing of pH during reaction. Biodegradation of laminaran by mixed six isolated microorganisms was more investigated under batch conditions at 37oC and 180 rpm. The experiment was performed in 15-mL cotton-plugged tube using culture medium containing laminaran (5 g L-1), initial pH 6.8. Effects of pH changes and mixed cells composition were studied and the pattern of biodegradation product was analyzed by High Performance Liquid Chromatography (HPLC). The pH changes affected to the microorganism activity when it was adjusted with NaOH solution during reaction by decreasing of reducing sugars amount. The HPLC analysis showed that the biodegradation product formed from laminaran was not only glucose but amounts of oligosaccharides were also produced. It is indicating that the enzyme degraded linear 1,3-β-glucan laminaran in an endo splitting manner. Glucose was detected by HPLC about 1516 mgㆍL-1 with 30.33% yield after 3 days. Based on these results, we successfully found the microorganisms which can utilize polysaccharide in brown seaweeds, laminaran. It would be important from the viewpoint of production of renewable fuels and promising for either seaweed industry or bioethanol industry.