Full Length Research Paper

Screening and fermentation optimization of microbial lipid-producing molds from forest soils

Gao-Qiang Liu^1,2*, Qin-Lu Lin², Xian-Chun Jin³, Xiao-Ling Wang¹and Yan Zhao¹

¹College of Life Sciences and Technology, Central South University of Forestry and Technology, Changsha 410004, P.R. China.

²National Engineering Laboratory for Grain Further Processing, Central South University of Forestry and Technology, Changsha 410004, P. R. China.

³College of Life Science, Henan Agriculture University, Zhengzhou 450002, P. R.  China.

*Corresponding author. E-mail: gaoliuedu@yahoo.com.cn. Tel/Fax: +86-731-85623498.

Accepted 22 June, 2010

Abstract

Sixty-one isolates including molds, yeasts and bacteria from the forest soils collected from Hunan Province, China were tested for their potentiality to accumulate microbial lipid as alternative sources for biodiesel production. The results showed that sixteen mold isolates were potential oleaginous microorganisms, among which, strain SCIM 3.009 was the best lipid producers, which may accumulate up to 50.4% of lipids in dry biomass. Further study showed that the components profile of the lipid from strain SCIM 3.009 had the similar characters to that of vegetable oil, abundant in low degree unsaturated long chain fatty acid (C18:1) and saturated long chain fatty acids (C16:0), suggesting the lipid is a potential source for biodiesel production. Based on the morphology and a commercial identification system, the strain SCIM 3.009 was found to be Thamnidium ctenidium. To enhance the lipid production by the strain, the fermentation parameters were optimized, the optimium conditions were as follows: glucose as carbon source with initial concentration 60 g/L, NH₄NO₃ as nitrogen source at 3.0 g/L, culture temperature was 30°C, initial pH = 6.5, culture volume was 50 mL in a 250 mL flask, agitation speed was 220 rpm. Results on verification of the optimium conditions in a 5 L stirred-tank bioreactor reveal that the strain accumulate up to 66.02% of lipids in dry biomass and the lipid yield significantly enhanced from 6.4 ± 0.39 to 13.6 ± 0.37 g/L, while biomass enhanced from 12.7 ± 0.72 to 20.6 ± 0.52 g/L.

Key words: Biodiesel, microbial lipid, oleaginous microorganism, strains screening, submerged fermentation.