TITLE:
Switchgrass (Panicum virgatum) Fermentation by Clostridium thermocellum and Clostridium beijerinckii Sequential Culture: Effect of Feedstock Particle Size on Gas Production
AUTHORS:
Michael D. Flythe, Noelia M. Elía, Micah B. Schmal, Sue E. Nokes
KEYWORDS:
Bioenergy, Cellulosic Butanol, Co-Culture, Consolidated Bioprocessing
JOURNAL NAME:
Advances in Microbiology,
Vol.5 No.5,
May
14,
2015
ABSTRACT: Fermentation
of cellulosic biomass can be done in a single step with cellulolytic, solventogenic
bacteria, such as Clostridium thermocellum.
However, the suite of products is limited in consolidated bioprocessing. Fortunately,
the thermophilic nature of C. thermocellum can be exploited in sequential culture. Experiments were conducted to determine
the effect of feedstock particle size on fermentation by sequential cultures and
to demonstrate this effect could be shown by gas production. Dual-temperature sequential
cultures were conducted by first culturing with C. thermocellum (63°C, 48 h) before culturing with C. beijerinckii (35°C, 24 h). Switchgrass
(2, 5 or 15 mm particle size) was the feedstock in submerged substrate (10% w/v)
fermentation. The extent of fermentation was evaluated by gas production and compared
by analysis of variance with Tukey’s test post
hoc. C. thermocellum alone produced
78 kPa cumulative pressure (approx. 680 mL gas) when the particle size was 2 or
5 mm. The C. thermocellum cultures with
15 mm feedstock particles had a mean cumulative pressure of 15 kPa after 48 h, which
was less than the 2 and 5 mm treatments (P °C) and inoculated with C. beijerinckii, and the cumulative pressures
were reset to ambient, cumulative pressure values as great as 70 kPa (equivalent
to an additional 670 mL gas) were produced in 24 h. Again, the longer (15 mm) particle
size produced less gas (P C.
beijerinckii without previous fermentation by C. thermocellum, the mean cumulative pressures were approximately 10
kPa. These results indicate that biological pretreatment with C. thermocellum increased the availability
of switchgrass carbohydrates to C. beijerinckii,
and that gas production is suitable method to show the effectiveness of a pretreatment.