In Vivo Regulation of Alcohol Dehydrogenase and Lactate Dehydrogenase in Rhizopus Oryzae to Improve l-Lactic Acid Fermentation

Cationic polyelectrolytes prevent the aggregation of l-lactate dehydrogenase under unstable conditions

Unstructured biological macromolecules have attracted attention as protein aggregation inhibitors in living cells. Some are characterized by their free structural configuration, highly charged, and water-soluble. However, the importance of these properties in inhibiting protein aggregation remains unclear. In this study, we investigated the effect of charged poly (amino acids), which mimic these properties, on aggregation of l-lactate dehydrogenase (LDH) and compared their effects to monomeric amino acids and folded proteins. LDH was stable and active at a neutral pH (~7) but formed inactive aggregates at acidic pH (< 6). Adding cationic polyelectrolytes of poly-l-lysine and poly-l-arginine suppressed the acid-induced aggregation and inactivation of LDH under acidic pH values. Adding monomeric amino acids and cationic folded proteins also prevented LDH aggregation but with lower efficacy than cationic polyelectrolytes. These results indicate that unstructured polyelectrolytes effectively stabilize unstable enzymes because they interact flexibly and multivalently with them. Our findings provide a simple method for stabilizing enzymes under unstable conditions.

Inhibitory and Stimulatory Effects of Fruit Bioactive Compounds on Edible Filamentous Fungi: Potential for Innovative Food Applications

The fermentation of fruit processing residuals (FPRs) with filamentous fungi can provide protein-rich food products. However, FPRs that contain bioactive compounds with antimicrobial properties present a major challenge. In this work, the resistance of two edible filamentous fungi, Rhizopus oligosporus and Neurospora intermedia, to 10 typically inhibiting bioactive compounds available in FPRs (epicatechin, quercetin, ellagic acid, betanin, octanol, hexanal, D-limonene, myrcene, car-3-ene, and ascorbic acid) was examined. These compounds’ inhibitory and stimulatory effects on fungal growth were examined individually. Three different concentrations (2.4, 24, and 240 mg/L) within the natural concentration range of these compounds in FPRs were tested. These bioactive compounds stimulated the growth yield and glucose consumption rate of R. oligosporus, while there was no increase in the biomass yield of N. intermedia. Ellagic acid caused an up to four-fold increase in the biomass yield of R. oligosporus. In addition, octanol and D-limonene showed antifungal effects against N. intermedia. These results may be helpful in the development of fungus-based novel fermented foods.

The anaerobic survival mechanism of Schizophyllum commune 20R-7-F01, isolated from deep sediment 2 km below the seafloor

Fungi dominated the eukaryotic group in the anaerobic sedimentary environment below the ocean floor where they play an essential ecological role. However, the adaptive mechanism of fungi to these anaerobic environments is still unclear. Here, we reported the anaerobic adaptive mechanism of Schizophyllum commune 20R-7-F01, isolated from deep coal-bearing sediment down to ~2 km below the seafloor, through biochemical, metabolomic and transcriptome analyses. The fungus grows well, but the morphology changes obviously and the fruit body develops incompletely under complete hypoxia. Compared with aerobic conditions, the fungus has enhanced branched-chain amino acid biosynthesis and ethanol fermentation under anaerobic conditions, and genes related to these metabolisms have been significantly up-regulated. Additionally, the fungus shows novel strategies for synthesizing ethanol by utilizing both glycolysis and ethanol fermentation pathways. These findings suggest that the subseafloor fungi may adopt multiple mechanisms to cope with lack of oxygen.

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.

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.

Impacts of lignocellulose-derived inhibitors on L-lactic acid fermentation by Rhizopus oryzae

Inhibitors generated in the pretreatment and hydrolysis of corn stover and corn cob were identified. In general, they inhibited cell growth, lactate dehydrogenase, and lactic acid production but with less or no adverse effect on alcohol dehydrogenase and ethanol production in batch fermentation by Rhizopus oryzae. Furfural and 5-hydroxymethyl furfural (HMF) were highly toxic at 0.5-1 g L(-1), while formic and acetic acids at less than 4 g L(-1) and levulinic acid at 10 g L(-1) were not toxic. Among the phenolic compounds at 1 g L(-1), trans-cinnamic acid and syringaldehyde had the highest toxicity while syringic, ferulic and p-coumaric acids were not toxic. Although these inhibitors were present at concentrations much lower than their separately identified toxic levels, lactic acid fermentation with the hydrolysates showed much inferior performance compared to the control without inhibitor, suggesting synergistic or compounded effects of the lignocellulose-degraded compounds on inhibiting lactic acid fermentation.

Influence of Altered NADH Metabolic Pathway on the Respiratory-deficient Mutant of Rhizopus oryzae and its L-lactate Production

Respiratory-deficient mutants of Rhizopus oryzae (R. oryzae) AS 3.3461 were acquired by ultraviolet (UV) irradiation to investigate changes in intracellular NADH metabolic pathway and its influence on the fermentation characteristics of the strain. Compared with R. oryzae AS 3.3461, the intracellular ATP level of the respiratory-deficient strain UV-1 decreased by 52.7 % and the glucose utilization rate rose by 8.9 %; When incubated for 36 h, the activities of phosphofructokinase (PFK), hexokinase (HK), and pyruvate kinase (PK) in the mutant rose by 74.2, 7.2, and 12.0 %, respectively; when incubated for 48 h, the intracellular NADH/NAD(+) ratio of the mutant rose by 14.6 %; when a mixed carbon source with a glucose/gluconic acid ratio of 1:1 was substituted to culture the mutant, the NADH/NAD(+) ratio decreased by 4.6 %; the ATP content dropped by 27.6 %; the lactate dehydrogenase (LDH) activity rose by 22.7 %; and the lactate yield rose by 11.6 %. These results indicated that changes to the NADH metabolic pathway under a low-energy charge level can effectively increase the glycolytic rate and further improve the yield of L-lactate of R. oryzae.

L-lactic acid production from starch by simultaneous saccharification and fermentation in a genetically engineered Aspergillus oryzae pure culture

Lactic acid is a commodity chemical that can be produced biologically. Lactic acid-producing Aspergillus oryzae strains were constructed by genetic engineering. The A. oryzae LDH strain with the bovine L-lactate dehydrogenase gene produced 38 g/L of lactate from 100g/L of glucose. Disruption of the wild-type lactate dehydrogenase gene in A. oryzae LDH improved lactate production. The resulting strain A. oryzae LDHΔ871 produced 49 g/L of lactate from 100g/L of glucose. Because A. oryzae strains innately secrete amylases, A. oryzae LDHΔ871 produced approximately 30 g/L of lactate from various starches, dextrin, or maltose (all at 100 g/L). To our knowledge, this is the first report describing the simultaneous saccharification and fermentation of lactate from starch using a pure culture of transgenic A. oryzae. Our results indicate that A. oryzae could be a promising host for the bioproduction of useful compounds such as lactic acid.