Two-step production of d-lactate from mixed sugars by growing and resting cells of metabolically engineered Lactobacillus plantarum

Lactic acid production - producing microorganisms and substrates sources-state of art

Lactic acid is an organic compound produced via fermentation by different microorganisms that are able to use different carbohydrate sources. Lactic acid bacteria are the main bacteria used to produce lactic acid and among these, Lactobacillus spp. have been showing interesting fermentation capacities. The use of Bacillus spp. revealed good possibilities to reduce the fermentative costs. Interestingly, lactic acid high productivity was achieved by Corynebacterium glutamicum and E. coli, mainly after engineering genetic modification. Fungi, like Rhizopus spp. can metabolize different renewable carbon resources, with advantageously amylolytic properties to produce lactic acid. Additionally, yeasts can tolerate environmental restrictions (for example acidic conditions), being the wild-type low lactic acid producers that have been improved by genetic manipulation. Microalgae and cyanobacteria, as photosynthetic microorganisms can be an alternative lactic acid producer without carbohydrate feed costs. For lactic acid production, it is necessary to have substrates in the fermentation medium. Different carbohydrate sources can be used, from plant waste as molasses, starchy, lignocellulosic materials as agricultural and forestry residues. Dairy waste also can be used by the addition of supplementary components with a nitrogen source.

Exploring fermentation strategies for enhanced lactic acid production with polyvinyl alcohol-immobilized Lactobacillus plantarum 23 using microalgae as feedstock

Lactic acid (LA) fermentation was conducted with suspended and immobilized cells of an isolated Lactobacillus plantarum 23 strain using various fermentation strategies. Glucose and an alternative, relatively inexpensive carbon source - the hydrolysate of microalga Chlorella vulgaris ESP-31, were used as the carbon source. Batch fermentation using immobilized cells of L. plantarum 23 could enhance LA titer and yield by 43% and 39%, respectively, when compared with the suspended culture. Fed-batch culture integrated with in situ LA removal via ion exchange raised LA productivity by 72% by overcoming product inhibition. The highest LA productivity from glucose with PVA immobilized cells was 14.22 g/L/h, achieved under continuous operation at 50% w/v loading of immobilized beads and hydraulic retention time (HRT) of 2 h. PVA immobilized L. plantarum 23 could also use microalgal hydrolysate as the renewable carbon source, and the highest LA productivity was 9.93 g/L/h under continuous fermentation at 4 h HRT.

3-phenyllactic acid production by free-whole-cells of Lactobacillus crustorum in batch and continuous fermentation systems

AIM

3-Phenyllactic acid (3-PLA) has been widely used in food and material industries. Three Lactobacillus crustorum strains have shown greater 3-PLA production ability in our previous study. The objectives of this study were to further improve 3-PLA yields in batch and continuous fermentation systems using of free-whole-cells of the three L. crustorum strains.

MATERIALS AND RESULTS

The fermentation conditions of free-whole-cells of the three L. crustorum strains for 3-PLA production were optimized. Among these strains, L. crustorum NWAFU 1078 showed excellent reusability and significantly (P < 0·05) greater 3-PLA production ability than the other strains after 10th recycle. The strain possesses three l-lactate dehydrogenase and three d-lactate dehydrogenase catalysing 3-PLA production from phenylpyruvic acid (PPA). Under the optimal conditions, the strain produced 15·2 mmol l^-1 3-PLA (76% PPA conversion rate) in a batch fermentation system and 6·5 mmol l^-1  h^-1 3-PLA (55% PPA conversion rate) in a continuous fermentation system using a 0·6 dilution rate.

CONCLUSIONS

Free-whole-cells of L. crustorum NWAFU 1078 showed excellent reusability and higher 3-PLA yields under optimal biotransformation conditions in both batch and continuous fermentation systems.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides the possibility to use the free-whole-cells of L. crustorum NWAFU 1078 as a biocatalyst for effective production of 3-PLA.

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 0361T.

Results

T. laevilacticus SK5–6 produced D-lactate at higher yield, productivity, and optical purity compared with S. laevolacticus 0361T. 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 0361T. 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.

Co-culture of Lactobacillus delbrueckii and engineered Lactococcus lactis enhances stoichiometric yield of D-lactic acid from whey permeate

D-Lactic acid (D-LA) is an enantiomer of lactic acid, which has a niche application in synthesis of poly-lactic acid based (PLA) polymer owing to its contribution to the thermo-stability of stereo-complex PLA polymer. Utilization of renewable substrates such as whey permeate is pivotal to economically viable production of D-LA. In present work, we have demonstrated D-LA production from whey permeate by Lactobacillus delbrueckii and engineered Lactococcus lactis. We observed that lactose fermentation by a monoculture of L. delbrueckii yields D-LA and galactose as major products. The highest yield of D-LA obtained was 0.48 g g^-1 when initial lactose concentration was 30 g L^-1. Initial lactose concentration beyond 20 g L^-1 resulted in accumulation of glucose and galactose, and hence, reduced the stoichiometric yield of D-LA. L. lactis naturally produces L-lactic acid (L-LA), so a mutant strain of L. lactis (L. lactis Δldh ΔldhB ΔldhX) was used to prevent L-LA production and engineer it for D-LA production. Heterologous over-expression of D-lactate dehydrogenase (ldhA) in the recombinant strain L. lactis TSG1 resulted in 0.67 g g^-1 and 0.44 g g^-1 of D-LA yield from lactose and galactose, respectively. Co-expression of galactose permease (galP) and α-phosphoglucomutase (pgmA) with ldhA in the recombinant strain L. lactis TSG3 achieved a D-LA yield of 0.92 g g^-1 from galactose. A co-culture batch process of L. delbrueckii and L. lactis TSG3 achieved an enhanced stoichiometric yield of 0.90 g g^-1 and ~45 g L^-1D-LA from whey permeate (lactose). This is the highest reported yield of D-LA from lactose substrate, and the titres can be improved further by a suitably designed fed-batch co-culture process.

Biocatalytic activity of Monascus mycelia depending on physiology and high sensitivity to product concentration

Cell suspension culture using mycelia as whole cell biocatalyst for production of orange Monascus pigments has been carried out successfully in a nonionic surfactant micelle aqueous solution. Thus, selection of mycelia as whole cell biocatalyst and the corresponding enzymatic kinetics for production of orange Monascus pigments can be optimized independently. Mycelia selected from submerged culture in a nonionic surfactant micelle aqueous solution with low pH 2.5 exhibits robust bioactivity. At the same time, enzymatic kinetic study shows that the bioactivity of mycelia as whole cell biocatalyst is sensitive to high product concentration. Segregation of product from mycelia by cell suspension culture in a nonionic surfactant micelle aqueous solution or peanut oil–water two-phase system is not only necessary for studying the enzymatic kinetics but also beneficial to industrial application of mycelia as whole cell biocatalyst.

Variations in Monascus pigment characteristics and biosynthetic gene expression using resting cell culture systems combined with extractive fermentation

Monascus pigments are promising sources of natural food colorants, and their productivity can be improved by a novel extractive fermentation technology. In this study, we investigated the variations in pigment characteristics and biosynthetic gene expression levels in resting cell culture systems combined with extractive fermentation in Monascus anka GIM 3.592. Although the biomass was low at about 6 g/L DCW, high pigment titer of approximately 130 AU₄₇₀ was obtained in the resting culture with cells from extractive fermentation, illustrating that it had a good biocatalytic activity for pigment synthesis. The oxidation-reduction potential value correlated with the rate of relative content of the intracellular orange pigments to the yellow pigments (O/Y, r > 0.90, p < 0.05), indicating that the change in pigment characteristics may be responsible for the cellular redox activity. The up- or down-regulation of the pigment biosynthetic genes (MpFasA2, MpFasB2, MpPKS5, mppD, mppB, mppR1, and mppR2) in the resting culture with extractive culture cells was demonstrated by real-time quantitative polymerase chain reaction analysis. Moreover, the mppE gene associated with the yellow pigment biosynthesis was significantly (p < 0.05) down-regulated by about 18.6%, whereas the mppC gene corresponding to orange pigment biosynthesis was significantly (p < 0.05) up-regulated by approximately 21.0%. These findings indicated that extractive fermentation was beneficial for the biosynthesis of the intracellular orange pigment. The mechanism described in this study proposes a potential method for the highly efficient production of Monascus pigments.

Catalytic processes in the chemistry of lactic acid and PLLA: enzymatic stereoselective alcoholysis of rac-lactide

The preparation of the enantiomerically pure (R,R)-lactide (>99%ee) on the gram scale by alcoholysis of rac-lactide in the presence of Amano lipase PS is described. The synthesis of enantiopure lactide by this method is advantageous over traditional preparation via thermal tin-catalysed cyclisation of corresponding oligolactic acids, since the reaction temperature are much lower. That results that no meso-lactide is formed. The alcoholysis of rac-lactide with n-BuOH was studied in the presence of various enzymes in different solvent systems. The kinetic study of the alcoholysis of rac-lactide in the presence of CALB was performed.

Two-Step Production of Phenylpyruvic Acid from L-Phenylalanine by Growing and Resting Cells of Engineered Escherichia coli: Process Optimization and Kinetics Modeling

Phenylpyruvic acid (PPA) is widely used in the pharmaceutical, food, and chemical industries. Here, a two-step bioconversion process, involving growing and resting cells, was established to produce PPA from l-phenylalanine using the engineered Escherichia coli constructed previously. First, the biotransformation conditions for growing cells were optimized (l-phenylalanine concentration 20.0 g·L-1, temperature 35°C) and a two-stage temperature control strategy (keep 20°C for 12 h and increase the temperature to 35°C until the end of biotransformation) was performed. The biotransformation conditions for resting cells were then optimized in 3-L bioreactor and the optimized conditions were as follows: agitation speed 500 rpm, aeration rate 1.5 vvm, and l-phenylalanine concentration 30 g·L-1. The total maximal production (mass conversion rate) reached 29.8 ± 2.1 g·L-1 (99.3%) and 75.1 ± 2.5 g·L-1 (93.9%) in the flask and 3-L bioreactor, respectively. Finally, a kinetic model was established, and it was revealed that the substrate and product inhibition were the main limiting factors for resting cell biotransformation.

Highly efficient production of D-lactic acid from chicory-derived inulin by Lactobacillus bulgaricus

Inulin is a readily available feedstock for cost-effective production of biochemicals. To date, several studies have explored the production of bioethanol, high-fructose syrup and fructooligosaccharide, but there are no studies regarding the production of D-lactic acid using inulin as a carbon source. In the present study, chicory-derived inulin was used for D-lactic acid biosynthesis by Lactobacillus bulgaricus CGMCC 1.6970. Compared with separate hydrolysis and fermentation processes, simultaneous saccharification and fermentation (SSF) has demonstrated the best performance of D-lactic acid production. Because it prevents fructose inhibition and promotes the complete hydrolysis of inulin, the highest D-lactic acid concentration (123.6 ± 0.9 g/L) with a yield of 97.9 % was obtained from 120 g/L inulin by SSF. Moreover, SSF by L. bulgaricus CGMCC 1.6970 offered another distinct advantage with respect to the higher optical purity of D-lactic acid (>99.9 %) and reduced number of residual sugars. The excellent performance of D-lactic acid production from inulin by SSF represents a high-yield method for D-lactic acid production from non-food grains.

Biosynthesis of Monascus pigments by resting cell submerged culture in nonionic surfactant micelle aqueous solution

Growing cell submerged culture is usually applied for fermentative production of intracellular orange Monascus pigments, in which accumulation of Monascus pigments is at least partially associated to cell growth. In the present work, extractive fermentation in a nonionic surfactant micelle aqueous solution was utilized as a strategy for releasing of intracellular Monascus pigments. Those mycelia with low content of intracellular Monascus pigments were utilized as biocatalyst in resting cell submerged culture. By this means, resting cell submerged culture for production of orange Monascus pigments was carried out successfully in the nonionic surfactant micelle aqueous solution, which exhibited some advantages comparing with the corresponding conventional growing cell submerged culture, such as non-sterilization operation, high cell density (24 g/l DCW) leading to high productivity (14 AU of orange Monascus pigments at 470 nm per day), and recycling of cells as biocatalyst leading to high product yield (approximately 1 AU of orange Monascus pigments at 470 nm per gram of glucose) based on energy metabolism.

Production of d-lactic acid from hardwood pulp by mechanical milling followed by simultaneous saccharification and fermentation using metabolically engineered Lactobacillus plantarum

This study focused on the process development for the d-lactic acid production from cellulosic feedstocks using the Lactobacillus plantarum mutant, genetically modified to produce optically pure d-lactic acid from both glucose and xylose. The simultaneous saccharification and fermentation (SSF) using delignified hardwood pulp (5-15% loads) resulted in the lactic acid titers of 55.2-84.6g/L after 72h and increased productivities of 1.77-2.61g/L/h. To facilitate the enzymatic saccharification of high-load pulp at a fermentation temperature, short-term (⩽10min) pulverization of pulp was conducted, leading to a significantly improved saccharification with the suppressed formation of formic acid by-product. The short-term milling followed by SSF resulted in a lactic acid titer of 102.3g/L, an optical purity of 99.2%, and a yield of 0.879g/g-sugars without fed-batch process control. Therefore, the process presented here shows promise for the production of high-titer d-lactic acid using the L. plantarum mutant.