Optimization of carrageenase fermentation conditions of Antarctic bacterium Alteromonas sp. R11-5

Abstract:

[Background] Cold-adapted enzymes from Antarctic and Arctic microorganisms offer several advantages over their mesophilic and thermophilic counterparts, and their properties make them valuable alternatives with industrial and biotechnological applications. Recent studies have shown that these cold environments represent an important reservoir of cold-adapted, complex polysaccharide-degrading marine bacteria that are a major source of novel polysaccharidases and diverse biological active compounds. In general, screening medium is not the best fermentation condition for producing enzyme bacteria, in order to improve enzyme production for research and application, the culture conditions of enzyme producing bacteria need to be optimized. [Objective] To identify a producing carrageenase Antarctic bacterium and optimize the fermentation conditions for carrageenase production. [Methods] The producing carrageenase Antarctic bacterium R11-5 was identified by 16S rRNA gene sequence and the fermentation conditions for carrageenase production of R11-5 was optimized using the method of response surface methodology. [Results] The 16S rRNA gene sequence analysis results showed that the Antarctic bacterium belonged to Alteromonas sp. and was named as Alteromonas sp. R11-5. In order to optimize the fermentation conditions of Alteromonas sp. R11-5, 7 single factors (inoculation amount, temperature, pH, carbon source, nitrogen source, carrageenan concentration and metal ions) were selected by single test. Four important factors (temperature, beef extract, carrageenan and calcium ion) influencing carrageenase production, which identified by initial experimental design of Plackett-Burman by Design-Expert software. Then Box-Behnken design and response surface analysis were adopted to further study the interaction among the variables and obtain optimal values that bring maximum carrageenase production. The optimal fermentation conditions were as follows: Temperature 15.0 °C, beef extract concentration 11.0 g/L, carrageenan concentration 3.0 g/L, Ca2+ concentration 5.0 mmol/L. The supernatant carrageenanse activity of optimized fermentation reached 87.193 U/mL, 1.8 times higher than that before optimization. [Conclusion] Carrageenanse production of Antarctic bacterium Alteromonas sp. R11-5 was improved after the fermentation conditions optimized using the method of response surface methodology. R11-5 was a promising candidate for industrial application.