This study demonstrated the improved polyhydroxybutyrate (PHB) production via high cell density cultivation of Bacillus megaterium BA-019 with balanced initial total sugar concentration and carbon to nitrogen (C/N) weight ratio. In the 10 L stirred fermentor operated at 30 °C, pH 7.0, 600 rpm, and 1.0 vvm air, with the initial total sugar concentration of 60 g/L and urea at the C/N weight ratio of 10:1, 32.48 g/L cell biomass with the corresponding PHB weight content of 26.94 % and volumetric productivity of 0.73 g/L h were obtained from batch cultivation. Continuing cultivation by intermittent feeding of the sugarcane molasses along with urea at the C/N weight ratio of 12.5:1 gave much improved biomass and PHB production (90.71 g/L biomass with 45.84 % PHB content and 1.73 g/L h PHB productivity). Similar biomass and PHB yields were obtained in the 90 L stirred fermentor when using the impeller tip speed as the scale-up criterion.

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Cassava starch production waste (cassava pulp) has been proposed as a high potential ethanolic fermentation substrate due to its high residual starch level and the small particle size of the lignocellulosic fibers. Saccharification of the residual starch from a 3% (w/v) dry weight basis (DS) of cassava pulp by α-amylase (100°C, 10 min) and glucoamylase (60°C, 2 h) resulted in a glucose yield of 22.6 g/l [67.8% (w/w) DS of cassava pulp] and in lignocellulosic fibers at 0.5 g/g DS cassava pulp. Pretreatment of the lignocellulosic fiber with dilute sulfuric acid and calcium hydroxide at 121°C, 15 lb/in 2 for 30 min increased and decreased, respectively, its susceptibility to cellulase hydrolysis. Under the optimal conditions found, pretreatment of 6% (w/v) DS lignocellulosic fiber by 2% (w/v) H 2 SO 4 for 30 min, followed by saccharification by cellulase (40°C, 9 h), yielded a glucose level of 26.6 g/l [79.8% (w/w) DS of the cassava pulp]. The starch and lignocellulosic fiber hydrolysates obtained from 30 g cassava pulp and 60 g H 2 SO 4 pretreated lignocellulosic fiber were fermented by Saccharomyces cerevisiae, without the need for (NH 4 ) 2 SO 4 supplementation, to yield ethanol levels of 9.9 and 11.9 g/l, respectively, after 48 h.

The aim of this study was to prove that Terrilactibacillus laevilacticus SK5-6, a novel D-lactate producer, exhibited a good fermentation performance comparing to the reference D-lactate producer Sporolactobacillus sp. Methods Glucose bioconversion for D-lactate production and the activity of five key enzymes including phosphofructokinase (PFK), pyruvate kinase (PYK), D-lactate dehydrogenase (D-LDH), L-lactate dehydrogenase (L-LDH), and lactate isomerase (LI) were investigated in the cultivation of T. laevilacticus SK5-6 and S. laevolacticus 0361 T. Results T. laevilacticus SK5-6 produced D-lactate at higher yield, productivity, and optical purity compared with S. laevolacticus 0361 T. T. laevilacticus SK5-6, the catalase-positive isolate, simultaneously grew and produced D-lactate without lag phase while delayed growth and D-lactate production were observed in the culture of S. laevolacticus 0361 T. The higher production of Dlactate in T. laevilacticus SK5-6 was due to the higher growth rate and the higher specific activities of the key enzymes observed at the early stage of the fermentation. The low isomerization activity was responsible for the high optical purity of D-lactate in the cultivation of T. laevilacticus SK5-6. Conclusion The lowest specific activity of PFK following by PYK and D/L-LDHs, respectively, indicated that the conversion of fructose-6-phosphate was the rate limiting step. Under the well-optimized conditions, the activation of D/L-LDHs by fructose-1,6-phosphate and ATP regeneration by PYK drove glucose bioconversion toward D-lactate. The optical purity of D-lactate was controlled by D/L-LDHs and the activation of isomerases. High D-LDH with limited isomerase activity was preferable during the fermentation as it assured the high optical purity.

Bacillus sp. BC-001 was first reported as a potent thermotolerant and homofermentative strain for an industrial-scale L-lactate production. In a flask culture, this isolate fermented both glucose and sucrose to lactate with high yield (0.96 and 0.87 g/g) and productivity (2.8 and 2.6 g/L h), respectively. The higher lactate production performance was obtained in the simultaneous saccharification and fermentation of liquefied starch (150.1 g/L final titer, 0.98 g/g yield, 3.2 g/L h productivity) and the fed-batch glucose fermentation (139.9 g/L final titer, 0.96 g/g yield, 2.9 g/L h productivity). Significant increase in lactate productivity (5.5-6.1 g/L h) was obtained from the high/heavy-inoculum seed in the stirred tank fermentor. Both calcium bases and monovalent bases were successfully employed for pH control during lactate fermentation by this isolate resulting in a versatile and simple operation. By the two-phase fermentation using the high/heavy-inoculum seed of BC-001, the fermentation reproducibility was acquired toward the pilot-scale fermentors.