Improved oxygen transfer and increased l-lactic acid production by morphology control of Rhizopus oryzae in a static bed bioreactor

Rhizopus oryzae was immobilized on a cotton matrix in a static bed bioreactor. Compared with free cells in a stirred tank bioreactor, immobilized R. oryzae in this bioreactor gave higher lactic acid production but lower ethanol production. The highest lactic acid production rate (2.09 g/L h) with the final concentration of 37.83 g/L from 70 g/L glucose was achieved when operating the bioreactor at 700 rpm and 0.5 vvm air. To better understand the relationship between shear effects (agitation and aeration) and R. oryzae morphology and metabolism, oxygen transfer rate, fermentation kinetics, and lactate dehydrogenase activity were determined. In immobilized cell culture, higher oxygen transfer rate and lactic acid production were achieved but lower lactate dehydrogenase activity was found as compared with those in free cell culture operated at the same conditions. These results clearly imply that mass transport was the rate controlling step in lactic acid fermentation by R. oryzae.     

D-Lactic acid fermentation performance and the enzyme activity of a novel bacterium Terrilactibacillus laevilacticus SK5–6

Purpose

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 D-lactate 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.

     

Enhancing polyhydroxybutyrate production from high cell density fed-batch fermentation of Bacillus megaterium BA-019

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.     

Characterisation of lactic acid producing <Emphasis Type="Italic">Sporolactobacillus</Emphasis> strains from tree barks in Thailand

Eight spore-forming lactic acid producing bacteria were isolated from tree barks in Thailand. They were identified as Sporolactobacillus nakayamae (Group I, three isolates), S. terrae (Group II, two isolates), S. kofuensis (Group III, one isolate) and S. inulinus (Group IV, two isolates) based on their phenotypic characteristics and 16S rRNA gene sequence analyses. Four isolates in Groups I and II produced DL lactic acid (89.60–114.61 g/L), while three isolates in Groups III and IV produced D-lactic acid (88.01–113.78 g/L). Isolate BK65-3 identified as S. inulinus produced the highest D-lactic acid concentrations (101.42 g/L), productivity (1.41 g/L/h), yields (84.52%) and optical purity of D-lactic acid (100%).     

Co-fermentation of cassava waste pulp hydrolysate with molasses to ethanol for economic optimization

Cassava waste pulp (CWP)–enzymatic hydrolysate was co-fermented with molasses (CWP-EH/molasses mixture) with the aim to optimize ethanol production by Saccharomyces cerevisiae TISTR 5606 (SC 90). The optimal fermentation conditions for ethanol production using this mixture were 245 g/L initial total sugar supplemented with KH₂PO₄ (8 g/L), at 30 °C for 48 h of fermentation under an oxygen-limited condition with agitation at 100 rpm, producing an ethanol concentration of 70.60 g/L (0.31 g ethanol/g total sugar). The addition of cassava tuber fiber (solid residue of CWP after enzymatic hydrolysis) at 30 g/L dry weight to the CWP-EH/molasses mixture increased ethanol production to 74.36 g/L (0.32 g ethanol/g total sugar). Co-fermentation of CWP-EH with molasses had the advantage of not requiring any supplementation of the fermentation mixture with reduced nitrogen.     

Characterization of<Emphasis Type="SmallCaps"> D</Emphasis>-lactic acid,spore-forming bacteria and <Emphasis Type="Italic">Terrilactibacillus laevilacticus</Emphasis> SK5-6 as potential industrial strains

In this study, we screened and isolated D-lactic acid-producing bacteria from soil and tree barks collected in Thailand. Among the isolates obtained, Terrilactibacillus laevilacticus SK5-6 exhibited good D-lactate production in the primary screening fermentation (99.27 g/L final lactate titer with 0.90 g/g yield, 1.38 g/L?h, and 99.00% D-enantiomer equivalent). Terrilactibacillus laevilacticus SK5-6 is a Gram-positive, endospore-forming, homofermentative D-lactate producer that can ferment a wide range of sugars to produce D-lactate. Unlike the typical D-lactate producers, such as catalase-negative Sporolactobacillus sp., T. laevilacticus SK5-6 possesses catalase activity; therefore, a two-phase fermentation was employed for D-lactate production. During an aerobic preculture stage, a high-density cell mass was rapidly obtained due to aerobic respiration. When transferred to the fermentation stage at the correct physiological stage (inoculum age) and proper concentration of cell mass (inoculum size), T. laevilacticus rapidly converted glucose into D-lactate under anaerobic conditions, resulting in a high final lactate titer (102.22 g/L), high yield (0.84 g/g), and high productivity (2.13 g/L?h). When the process conditions were shifted from an aerobic to an anaerobic environment, unlike other lactate-producing bacteria, the mixed acid fermentation route was not activated in the culture of T. laevilacticus SK5-6 during the fermentation stage when some trace oxygen still remained. Our study demonstrates the excellent characteristics of this isolate for D-lactate production; in particular, a high product yield was obtained without byproduct formation. Based on these key characteristics of T. laevilacticus SK5-6, we suggest that this isolate is a novel D-lactate producer for use in industrial fermentation.     

A homofermentative Bacillus sp. BC-001 and its performance as a potential l-lactate industrial strain

Bioprocess and Biosystems Engineering - Bacillus sp. BC-001 was first reported as a potent thermotolerant and homofermentative strain for an industrial-scale l-lactate production. In a flask...