Fermentation, Volume 2, Issue 2 (June 2016) – 6 articles

Butanol, produced via traditional acetone-butanol-ethanol (ABE) fermentation, suffers from low yield and productivity. In this article, a non-ABE butanol production process is reviewed. Clostridium pasteurianum has a non-biphasic metabolism, alternatively producing 1,3-propanediol (PDO)-butanol-ethanol, referred to as PBE fermentation. This review discusses the advantages of PBE fermentation with an emphasis on applications using biodiesel-derived crude glycerol, currently an inexpensive and readily available feedstock. To address the process design challenges, various strategies have been employed and are examined and reviewed; genetic engineering and mutagenesis of C. pasteurianum, characterization and pretreatment of crude glycerol and various fermentation strategies such as bioreactor design and configuration, increasing cell density and in-situ product removal. Where research deficiencies exist for PBE fermentation, the process solutions as employed for ABE fermentation are reviewed and their suitability for PBE is discussed. Each of the obstacles against high butanol production has multiple solutions, which are reviewed with the end-goal of an integrated process for continuous high level butanol production and recovery using C. pasteurianum and biodiesel-derived crude glycerol. Full article

Hydrolysis of cellulose and hemicelluloses into fermentable sugars is the primary step for the production of fuels and chemicals from lignocellulosic biomass, and is often hindered by the high cost of cellulolytic and hemicellulolytic enzymes. In the present study co- and monocultures of Penicillium sp. AKB-24 and Aspergillus nidulans AKB-25 were used under a variety of fermentation conditions to optimize enzyme production. Wheat bran was found to be the optimal carbon source yielding maximum enzyme production under solid-state fermentation conditions due to its higher water retention value (175%) and minimum C/N ratio (22.7). Penicillium sp. AKB-24 produced maximum endoglucanase (134 IU/gds), FPase (3 FPU/gds), β-glucosidase (6 IU/gds) and xylanase (3592 IU/gds) activities when incubated for 7 days at 30 °C and pH 7 with a moisture content of 77.5%, and 1.2% yeast extract and 0.1 (w/v) sodium dodecyl sulphate supplement. Co-culturing of Penicillium sp. AKB-24 and Aspergillus nidulans AKB-25 enhanced endoglucanase, FPase, and exoglucanase activities by 34%, 18%, and 11% respectively compared to Aspergillus nidulans AKB-25 alone under optimum conditions. Enzymes produced by co-cultivation released equal amounts of reducing sugars at an enzyme dose of 15 FPU/g and reaction time 72 h, but the required quantity of enzyme was 14% less compared to enzyme released from Aspergillus nidulans AKB-25 mono-culture. In conclusion, co-cultivation of Penicillium sp. AKB-24 and Aspergillus nidulans AKB-25 to produce enzymes for the hydrolysis of pearl millet stover is more cost-effective than cultivation with Aspergillus nidulans AKB-25 alone. Full article

Different biological approaches, highlighting the use of laccases, have been developed as environmentally friendly alternatives for improving the saccharification and fermentation stages of steam-pretreated lignocellulosic biomass. This work evaluates the use of a novel bacterial laccase (MetZyme) for enhancing the hydrolysability and fermentability of steam-exploded wheat straw. When the water insoluble solids (WIS) fraction was treated with laccase or alkali alone, a modest increase of about 5% in the sugar recovery yield (glucose and xylose) was observed in both treatments. Interestingly, the combination of alkali extraction and laccase treatment boosted enzymatic hydrolysis, increasing the glucose and xylose concentration in the hydrolysate by 21% and 30%, respectively. With regards to the fermentation stage, the whole pretreated slurry was subjected to laccase treatment, lowering the phenol content by up to 21%. This reduction allowed us to improve the fermentation performance of the thermotolerant yeast Kluyveromyces marxianus CECT 10875 during a simultaneous saccharification and fermentation (SSF) process. Hence, a shorter adaptation period and an increase in the cell viability—measured in terms of colony forming units (CFU/mL)—could be observed in laccase-treated slurries. These differences were even more evident when a presaccharification step was performed prior to SSF. Novel biocatalysts such as the bacterial laccase presented in this work could play a key role in the implementation of a cost-effective technology in future biorefineries. Full article

A novel strain Rhizopus sp. C4 was isolated from compost for the production of pectinase. Cultivation of Rhizopus sp. C4 on orange peel substrate under various solid-state fermentation (SSF) conditions was evaluated for pectinase yield along with the enzyme activity profile as a potential, low-cost alternative to submerged-liquid fermentation. Response surface methodology (RSM) was employed to optimize various environmental parameters for pectinase production. Various parameters, namely temperature, moisture and incubation days, were studied statistically for a total of 20 runs using central composite design. The highest yield of the enzyme, i.e., 11.63 IU/mL, was obtained from 1:3.5 moisture ratios in 7 days at 30°C. The study demonstrated that optimization through RSM could improve the enzymatic characteristics and yield of the enzyme. Full article

Previous winery-based studies showed the strains Lalvin^® RC212 (RC212) and Lalvin^® ICV-D254 (D254), when present together during fermentation, contributed to >80% relative abundance of the Saccharomyces cerevisiae population in inoculated and spontaneous fermentations. In these studies, D254 appeared to out-compete RC212, even when RC212 was used as the inoculant. In the present study, under controlled conditions, we tested the hypotheses that D254 would out-compete RC212 during fermentation and have a greater impact on key fermentation-derived chemicals. The experiment consisted of four fermentation treatments, each conducted in triplicate: a pure culture control of RC212; a pure culture control of D254; a 1:1 co-inoculation ratio of RC212:D254; and a 4:1 co-inoculation ratio of RC212:D254. Strain abundance was monitored at four stages. Inoculation ratios remained the same throughout fermentation, indicating an absence of competitive exclusion by either strain. The chemical profile of the 1:1 treatment closely resembled pure D254 fermentations, suggesting D254, under laboratory conditions, had a greater influence on the selected sensory compounds than did RC212. Nevertheless, the chemical profile of the 4:1 treatment, in which RC212 dominated, resembled that of pure RC212 fermentations. Our results support the idea that co-inoculation of strains creates a new chemical profile not seen in the pure cultures. These findings may have implications for winemakers looking to control wine aroma and flavor profiles through strain selection. Full article

Syngas biomethanation is a potent bio-conversion route, utilizing microorganisms to assimilate intermediate gases to produce methane. However, since methanogens have a long doubling time, the reactor works best at a low dilution rate; otherwise, the cells can be washed out during the continuous fermentation process. In this study, the performance of a practical reverse membrane bioreactor (RMBR) with high cell density for rapid syngas biomethanation as well as a co-substrate of syngas and organic substances was examined in a long-term fermentation process of 154 days and compared with the reactors of the free cells (FCBR). The RMBR reached maximum capacities of H₂, CO, and CO₂ conversion of 7.0, 15.2, and 4.0 mmol/L_reactor.day, respectively, at the organic loading rate of 3.40 gCOD/L.day. The highest methane production rate from the RMBR was 186.0 mL/L_reactor.day on the 147th day, compared to the highest rate in the FCBR, 106.3 mL/L_reactor.day, on the 58th day. The RMBR had the ability to maintain a high methanation capacity by retaining the microbial cells, which were at a high risk for cell wash out. Consequently, the system was able to convert more syngas simultaneously with the organic compounds into methane compared to the FCBR. Full article