Fermentative production of acetic acid from various pure and natural cellulosic materials by Clostridium lentocellum SG6

Abstract

Clostridium lentocellum SG6 fermented various pure crystalline cellulosic materials efficiently with maximum acetic acid yield (gram acetic acid/gram substrate) of 0.67, at low substrate (8 g l−1) concentration. The strain grew poorly on crude biopolymers but fermented them easily after alkali treatment, when grown with 8 g substrate l−1 concentration of alkali-extracted cotton straw (AECS), paddy straw (AEPS) and sorghum stover (AESS) etc. The acetic acid to substrate (A/S) ratios were similar to those obtained with pure cellulosic materials. An increase in substrate concentration led to a decreased A/S ratio and a decreased percentage of substrate degraded. At high substrate concentration of 75 g filter paper l−1, the strain SG6 converted 63.2 g filter paper into 31.28 g acetic acid l−1. At 100 g l−1 concentrations, AECS and AEPS served as the best substrates for acetic acid production when compared with other biopolymers. A maximum amount of 30.98 and 30.86 g acetic acid was produced from 70.6 g AEPS and 70.1 g AESS l−1 of medium by strain SG6, respectively. Acetic acid production of 0.67 g g−1 pure cellulose (Whatman No. 1 filter paper), 0.63 g g−1 of alkali-treated cotton straw (AECS) are the highest among the cellulolytic bacteria reported so far in mono culture fermentations with pure and native cellulosic materials.