(421l) Simultaneous Saccharification and Fermentation of Cellulose by Microalgae Schizochytrium Limacinum for Lipid Production

Simultaneous Saccharification and
Fermentation of Cellulose by Microalgae Schizochytrium limacinum for
Lipid Production

Yubin Zheng, Xiaochen Yu, Jijiao
Zeng, Zhanyou Chi, Shulin Chen

Department of Biological Systems
Engineering,

Washington State University,
Pullman, WA 99164

Abstract

Due to the limitation of the agricultural oil resources, the
accumulation of lipids from microalgae has received tremendous attention
recently. Heterotrophic microalgae culture to produce
biodiesel showed the advantages of fast growth, high production rate,
convenience for harvesting and scaling up. However, the
fatal limiting factor for biodiesel production is the availability and
cost of feedstock in the heterotrophic process.
The cellulosic material is the potential candidate because of its
sustainability, abundance and low value. In this study, we investigated the
feasibility for lipid production via simultaneous saccharification
and fermentation (SSF) of Avicel, an insoluble crystalline cellulose polymer, by
microalgae Schizochytrium limacinum which was reported to produce more than 50% lipid
as well as high-value by-product docosahexaenoic acid (DHA). The effects of enzyme loading were studied
firstly. The lipid production rate was detected on 3% (w/w) Avicel
with enzyme loading from 5 to 60 FPU/g cellulose (the ratio
of cellobiase to cellulase
was fixed at 5:1). The optimal enzyme loading was 30
FPU/g cellulose
and the lipid was 46% of the theoretical value based on pure glucose as the
substrate. The lipid profile analysis showed that the enzyme loading had
significant effects on fatty acid compositions, especially the DHA, and lower enzyme loading led to higher DHA content. Then,
the ratio of cellobiase to cellulase (0-5:1) with
fixed enzyme loading of 30 FPU/g cellulose was evaluated for lipid production. Finally,
the SSF of Avicel by S. limacinum was conducted in fermentor under the optimal enzyme loading and ratio of cellobiase to cellulase. The
kinetics of glucose, cellobiose, total lipid and DHA
were investigated. These results demonstrated that the microalgae S. limacinum
had the capability to use cellulose for lipid production. This is the first
description of Avicel cellulose for biodiesel
production by microalgae. The finding is quite significant because it provides
the potential to produce biodiesel by heterotrophically
culturing microalgae on lignocellulosic biomass, such
as wheat straw, switch grass, corn stover, etc, and a
cost reduction for algal oil production can be expected by using this type of
feedstock in the future.