Inactivation of guanylate kinase in Bacillus sp. TL7-3 cultivated under an optimized ratio of carbon and nitrogen sources influenced GTP regeneration capability and sporulation.

Bacillus sp. TL7-3 has potential as a dietary supplement to promote human and animal health. It produces spores that can survive in harsh environments. Thus, when supplemented with nutrients, these spores can withstand the acidic pH of the stomach and resume vegetative development in the gut when exposed to growth-promoting conditions. Spores are formed as a cellular defense mechanism when a culture experiences stress and process optimization to achieve high spore production in a typical batch process remains challenging. Existing literature on the manipulation of gene expression and enzyme activity during batch cultivation is limited. Studies on the growth patterns, morphological changes, and relevant gene expression have aided in enhancing spore production. The present study used the response surface methodology for medium optimization. The model suggested that yeast extract and NH4Cl were significant factors controlling spore production. A comparison between the high weight ratio of carbon and nitrogen (C:N) substrates (8.57:1) in the optimized and basal media (0.52:1) showed an 8.76-fold increase in the final spore concentration. The expression of major genes, including codY, spo0A, kinA, and spo0F, involved in the sporulation was compared when cultivating Bacillus sp. TL7-3 in media with varying C:N ratios. At high C:N ratios, spo0A, kinA, and spo0F were upregulated, whereas codY was downregulated. This led to decreased guanylate kinase activity, resulting in a low guanosine triphosphate concentration and inactivation of CodY, thereby reducing the repression of spo0A and CodY-repressed genes and stimulating sporulation.

Isolation, screening, and characterization of the newly isolated osmotolerant yeast Wickerhamomyces anomalus BKK11-4 for the coproduction of glycerol and arabitol.

This study explored the isolation and screening of an osmotolerant yeast, Wickerhamomyces anomalus BKK11-4, which is proficient in utilizing renewable feedstocks for sugar alcohol production. In batch fermentation with high initial glucose concentrations, W. anomalus BKK11-4 exhibited notable production of glycerol and arabitol. The results of the medium optimization experiments revealed that trace elements, such as H3BO3, CuSO4, FeCl3, MnSO4, KI, H4MoNa2O4, and ZnSO4, did not increase glucose consumption or sugar alcohol production but substantially increased cell biomass. Osmotic stress, which was manipulated by varying initial glucose concentrations, influenced metabolic outcomes. Elevated glucose levels promoted glycerol and arabitol production while decreasing citric acid production. Agitation rates significantly impacted the kinetics, enhancing glucose utilization and metabolite production rates, particularly for glycerol, arabitol, and citric acid. The operational pH dictated the distribution of the end metabolites, with glycerol production slightly reduced at pH 6, while arabitol production remained unaffected. Citric acid production was observed at pH 6 and 7, and acetic acid production was observed at pH 7. Metabolomic analysis using GC/MS identified 29 metabolites, emphasizing the abundance of sugar/sugar alcohols. Heatmaps were generated to depict the variations in metabolite levels under different osmotic stress conditions, highlighting the intricate metabolic dynamics occurring post-glucose uptake, affecting pathways such as the pentose phosphate pathway and glycerolipid metabolism. These insights contribute to the optimization of W. anomalus BKK11-4 as a whole-cell factory for desirable products, demonstrating its potential applicability in sustainable sugar alcohol production from renewable feedstocks.

The outlooks and key challenges in renewable biomass feedstock utilization for value-added platform chemical via bioprocesses.

The conversion of renewable biomass feedstock into value-added products via bioprocessing platforms has become attractive because of environmental and health concerns. Process performance and cost competitiveness are major factors in the bioprocess design to produce desirable products from biomass feedstock. Proper pretreatment allows delignification and hemicellulose removal from the liquid fraction, allowing cellulose to be readily hydrolyzed to monomeric sugars. Several industrial products are produced via sugar fermentation using either naturally isolated or genetically modified microbes. Microbial platforms play an important role in the synthesis of several products, including drop-in chemicals, as-in products, and novel compounds. The key elements in developing a fermentation platform are medium formulation, sterilization, and active cells for inoculation. Downstream bioproduct recovery may seem like a straightforward chemical process, but is more complex, wherein cost competitiveness versus recovery performance becomes a challenge. This review summarizes the prospects for utilizing renewable biomass for bioprocessing.

Association between organic nitrogen substrates and the optical purity of D-lactic acid during the fermentation by Sporolactobacillus terrae SBT-1.

The development of biotechnological lactic acid production has attracted attention to the potential production of an optically pure isomer of lactic acid, although the relationship between fermentation and the biosynthesis of highly optically pure D-lactic acid remains poorly understood. Sporolactobacillus terrae SBT-1 is an excellent D-lactic acid producer that depends on cultivation conditions. Herein, three enzymes responsible for synthesizing optically pure D-lactic acid, including D-lactate dehydrogenase (D-LDH; encoded by ldhDs), L-lactate dehydrogenase (L-LDH; encoded by ldhLs), and lactate racemase (Lar; encoded by larA), were quantified under different organic nitrogen sources and concentration to study the relationship between fermentation conditions and synthesis pathway of optically pure lactic acid. Different organic nitrogen sources and concentrations significantly affected the quantity and quality of D-lactic acid produced by strain SBT-1 as well as the synthetic optically pure lactic acid pathway. Yeast extract is a preferred organic nitrogen source for achieving high catalytic efficiency of D-lactate dehydrogenase and increasing the transcription level of ldhA2, indicating that this enzyme plays a major role in D-lactic acid formation in S. terrae SBT-1. Furthermore, lactate racemization activity could be regulated by the presence of D-lactic acid. The results of this study suggest that specific nutrient requirements are necessary to achieve a stable and highly productive fermentation process for the D-lactic acid of an individual strain.

Sulfated polysaccharides from Caulerpa lentillifera: Optimizing the process of extraction, structural characteristics, antioxidant capabilities, and anti-glycation properties.

The polysaccharides found in Caulerpa lentillifera (sea grape algae) are potentially an important bioactive resource. This study makes use of RSM (response surface methodology) to determine the optimal conditions for the extraction of valuable SGP (sea grape polysaccharides). The findings indicated that a water/raw material ratio of 10:1 mL/g, temperature of 90 °C, and extraction time of 45 min would maximize the yield, with experimentation achieving a yield of 21.576 %. After undergoing purification through DEAE-52 cellulose and Sephacryl S-100 column chromatography, three distinct fractions were obtained, namely SGP11, SGP21, and SGP31, each possessing average molecular weights of 38.24 kDa, 30.13 kDa, and 30.65 kDa, respectively. Following characterization, the fractions were shown to comprise glucose, galacturonic acid, xylose, and mannose, while the sulfate content was in the range of 12.2-21.8 %. Using Fourier transform infrared spectroscopy (FT-IR) it was possible to confirm with absolute certainty the sulfate polysaccharide attributes of SGP11, SGP21, and SGP31. NMR (nuclear magnetic resonance) findings made it clear that SGP11 exhibited α-glycosidic configurations, while the configurations of SGP21 and SGP31 were instead ß-glycosidic. The in vitro antioxidant assays which were conducted revealed that each of the fractions was able to demonstrate detectable scavenging activity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cations. All fractions were also found to exhibit the capacity to scavenge NO radicals in a dose-dependent manner. SGP11, SGP21, and SGP31 were also able to display cellular antioxidant activity (CAA) against the human adenocarcinoma colon (Caco-2) cell line when oxidative damage was induced. The concentration levels were found to govern the extent of such activity. Moreover, purified SGP were found to exert strong inhibitory effects upon glycation, with the responses dependent upon dosage, thus confirming the potential for SGP to find a role as a natural resource for the production of polysaccharide-based antioxidant drugs, or products to promote improved health.

Sporolactobacillus mangiferae sp. nov., a spore-forming lactic acid bacterium isolated from tree bark in Thailand.

A Gram-stain-positive, facultatively anaerobic and endospore-forming rod-shaped bacterium, designed strain CPB3-1T, was isolated from tree bark. This homofermentative strain produced dl-lactic acid from glucose. It grew at 20-45 °C, pH 4.0-9.5 and in 0-3.0 % (w/v) NaCl. It contained meso-diaminopimelic acid in cell-wall peptidoglycan and had menaquinone with seven isoprene units (MK-7) as the predominant component. The major fatty acid was anteiso-C17 : 0. The polar lipids were phosphatidylglycerol, diphosphatidylglycerol, an unknown phospholipid and an unknown lipid. Based on the results of 16S rRNA gene sequence analysis, strain CPB3-1T belonged to the genus Sporolactobacillus and was closely related to Sporolactobacillus kofuensis DSM 11701T and Sporolactobacillus spathodeae BK117-1T (both 96.7 % similarity), Sporolactobacillus inulinus NRIC 1133T and Sporolactobacillus terrae DSM 11697T (both 96.6 % similarity), and Sporolactobacillus shoreicorticis MK21-7T, Sporolactobacillus laevolacticus DSM 442T, Sporolactobacillus shoreae BK92T and Sporolactobacillus pectinivorans GD201205T (all 95.8-96.5 % similarity). The draft genome of strain CPB3-1T contained 2 930 919 bps with 3117 coding genes. The DNA G+C content was 45.1 mol%. The digital DNA-DNA hybridization values between strain CPB3-1T and closely related type strains were 19.2-24.0 %. The average nucleotide identity (84.0-87.6 %) and average amino acid identity (66.5-76.3 %) values were lower than the cut-off values for species delineation. Strain CPB3-1T was clearly distinguished from related Sporolactobacillus species based on its phenotypic and chemotaxonomic characteristics, 16S rRNA gene sequence similarity and the results of draft genome analysis. Therefore, the strain represents a novel species of the genus Sporolactobacillus, for which the name Sporolactobacillus mangiferae sp. nov. is proposed. The type strain is CPB3-1T (=JCM 35082T=TISTR 10004T).

Weizmannia acidilactici sp. nov., a lactic acid producing bacterium isolated from soils.

The strains designed PP-18T, JC-4 and JC-7 isolated from soils, were Gram-stain-positive rods, facultative anaerobe, endospore-forming bacteria. The strains produced l-lactic acid from glucose. They showed positive for catalase but negative for oxidase, nitrate reduction and arginine hydrolysis. Strains P-18T, JC-4 and JC-7 were closely related to Weizmannia coagulans LMG 6326T (97.27-97.64%) and W. acidiproducens KCTC 13078T (96.46-96.74%) based on 16S rRNA gene sequence similarity, respectively. They contained meso-diaminopimelic acid in cell wall peptidoglycan and had seven isoprene units (MK-7) as the predominant menaquinone. The major cellular fatty acids of strain PP-18T were iso-C15:0, anteiso-C17:0, iso-C16:0 and anteiso-C15:0. The ANIb and ANIm values among the genomes of strains PP-18T, JC-4 and JC-7 are above 99.4% while their ANIb and ANIm values among them and W. coagulans LMG 6326T and W. acidiproducens KCTC 13078T were ranged from 76.61 to 79.59%. These 3 strains showed the digital DNA-DNA hybridization (dDDH) values of 20.7-23.6% when compared with W. coagulans LMG 6326T and W. acidiproducens DSM 23148T. The DNA G + C contents of strains PP-18T, JC-4 and JC-7 were 45.82%, 45.86% and 45.86%, respectively. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol and phosphoglycolipids. The results of phenotypic and chemotaxonomic characteristics and whole-genome analysis indicated that the strains PP-18T, JC-4 and JC-7 should be represented as a novel species within the genus Weizmannia for which the name Weizmannia acidilactici sp. nov. is proposed. The type strain is PP-18T (=KCTC 33974T = NBRC 113028T = TISTR 2515T).

Metal ion removal using a low-cost coconut shell activated carbon bioadsorbent in the recovery of lactic acid from the fermentation broth.

Downstream recovery and purification of lactic acid from the fermentation broth using locally available, low-cost materials derived from agricultural residues was demonstrated herein. Surface modification of coconut shell activated carbon (CSAC) was performed by grafting with carboxymethyl cellulose (CMC) using citric acid (CA) as the crosslinking agent. A proper ratio of CMC and CA to CSAC and grafting time improved the surface functionalization of grafted nanostructured CMC-CSAC while the specific surface area and porosity remained unchanged. Lactic acid was partially purified (78%) with the recovery percentage of lactic acid at 96% in single-stage adsorption at room temperature and pH 6 with a 10:1 ratio of cell-free broth to CMC-CSAC bioadsorbent. A thermodynamic study revealed that the adsorption was exothermic and non-spontaneous while the Langmuir isotherm model explained the adsorption phenomena. The results in this study represented the potential of waste utilization as solid adsorbents in green and low-cost adsorption technology.

Mathematical Modeling for Evaluating Inherent Parameters Affecting UVC Decontamination of Indicator Bacteria.

UV light is a tool associated with the denaturation of cellular components, DNA damage, and cell disruption. UV treatment is widely used in the decontamination process; however, predicting a sufficient UV dose by using traditional methods is doubtful. In this study, an in-house UVC apparatus was designed to investigate the process of the inactivation of five indicator bacteria when the initial cell concentrations and irradiation intensities varied. Both linear and nonlinear mathematical models were applied to predict the inactivation kinetics. In comparison with the Weibull and modified Chick-Watson models, the Chick-Watson model provided a good fit of the experimental data for five bacteria, Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus, Streptococcus faecalis, and Bacillus subtilis. The specific death rate (kd) significantly increased when the irradiation intensity (I) increased from 1.41 W/m2 to 3.02 W/m2 and 4.83 W/m2 (P < 0.05). Statistical analysis revealed no significant difference in the kd values among the groups of tested Gram-positive bacteria, Gram-negative bacteria, and B. subtilis spores, but the kd values differed among groups (P < 0.05). The death rate coefficient (k) varied from species to species. The k values of the tested Gram-positive bacteria were higher than those of the Gram-negative bacteria. The thick peptidoglycan layer in the Gram-positive membrane was responsible for UVC resistance. The high guanine-cytosine (GC) content in bacteria also contributed to UV resistance due to the less photoreactive sites on the nucleotides. This investigation provides a good understanding of bacterial inactivation induced by UVC treatment. IMPORTANCE Prevention and control measures for microbial pathogens have attracted worldwide attention due to the recent coronavirus disease 2019 pandemic. UV treatments are used as a commercial control to prevent microbial contamination in diverse applications. Microorganisms exhibit different UV sensitivities, which are often measured by the UV doses required for decreasing the number of microbial contaminants in the logarithmic order. The maximum efficacy of UV is usually observed at 254 nm (residing in the UVC range of the light spectrum). UV technology is a nonthermal physical decontamination measure that does not require any chemicals and consumes low levels of energy while leaving insignificant amounts of chemical residues or toxic compounds. Therefore, obtaining the microbial death kinetics and their intrinsic parameters provided in this study together with the UV photoreaction rate enables advancement in the design of UV treatment systems.

A modified approach for high-quality RNA extraction of spore-forming Bacillus subtilis at varied physiological stages.

BACKGROUND: High quality RNA is required for the molecular study. Sample preparation of the spore-forming, Gram-positive bacteria like Bacillus sp., remains challenging although several methods have been proposed. Those techniques were simply developed using cell samples at certain growth stages despite some molecular studies like transcriptomic analyses require RNA samples from different physiological stages. METHODS AND RESULTS: We developed the rapid, simple yet effective cell-lysis technique with limit use of harsh reagents by modifying the kit-based protocols. Appropriate lysozyme loading (20 mg/mL), incubation time (30 min), and temperature (37 °C) enabled cell lysis and enhanced RNA extraction from both vegetative cells and endospores of Bacillus subtilis TL7-3. High RNA Integrity Numbers and ratios of A260/A280 and A260/A230 of all RNA products collected during the batch cultivation confirmed that invert mixing with absolute ethanol prevented RNA damage during protein denaturation. With the process modification of the major steps in cell lysis and RNA extraction compared with the kit-based protocols that are typically used in laboratory work, interestingly, our modified protocol, simple-yet-effective, yielded higher concentration, purity, and integrity of RNA products from all cell samples collected at different physiological stages. While the kit-based protocols either failed to provide high RNA concentration or RNA purity and integrity for all cell samples particularly during the late-log, stationary, or sporulation. CONCLUSIONS: Therefore, we can claim the significance of this modified protocol to be applicable for RNA extraction to those spore-forming Gram-positive bacteria not limited to B. subtilis growing at varied physiological stages.

Draft genome sequencing of Sporolactobacillus terrae SBT-1, an efficient bacterium to ferment concentrated sugar to D-lactic acid.

Recently, the industrial-scale development of microbial D-lactic acid production has been discussed. In this study, the efficiency of the new isolate Sporolactobacillus terrae SBT-1 for producing D-lactic acid under challenge conditions was investigated. The isolate SBT-1 exhibited superior activity in fermenting a very high glucose or sucrose concentration to D-lactic acid compared to the other S. terrae isolates previously reported in the literature; therefore, SBT-1 could overcome the limitations of effective lactic acid production. In batch cultivation using 360 g/L glucose, SBT-1 produced 290.30 g/L D-lactate with a sufficiently high glucose conversion yield of 86%, volumetric productivity of 3.02 g/L h, and optical purity of 96.80% enantiomer excess. SBT-1 could also effectively utilize 440 g/L sucrose as a sole carbon source to produce 276.50 g/L lactic acid with a conversion yield of 90%, a production rate of 2.88 g/L h, and an optical purity of 98%. D-Lactic acid fermentation by two other related producers, S. inulinus NRIC1133T and S. terrae NRIC0357T, was compared with fermentation by isolate SBT-1. The experimental data revealed that SBT-1 possessed the ability to ferment relatively high glucose or sucrose concentrations to D-lactic acid without obvious catabolite repression and byproduct formation compared to the two reference strains. In draft genome sequencing of S. terrae SBT-1, the results provided here can promote further study to overcome the current limitations for the industrial-scale production of D-lactic acid.

Terrilactibacillus tamarindi sp. nov., isolated from bark of Tamarindus indica.

A Gram-stain-positive, catalase-positive, facultatively anaerobic, terminal-spore-forming rod, designated strain BCM23-1T, was isolated from bark of Tamarindus indica collected from Chiang Mai Province, Thailand. This strain produced d-lactic acid from glucose. It grew at 20-45 °C (optimum, 30 °C), pH 3.5-9 (optimum, pH 7.0) and in the presence of 1-4 % (w/v) NaCl. The cell-wall peptidoglycan contained meso-diaminopimelic acid (A1γ). The major isoprenoid quinone was menaquinone 7 (MK-7). Polar lipids analysis revealed the presence of diphosphatidylglycerol, phosphatidylglycerol, an unidentified aminophospholipid, an unidentified phospholipid and an unidentified lipid. The predominant cellular fatty acids were anteiso-C17 : 0, anteiso-C15:0, and iso-C16 : 0 when cultivated on GYP agar plates. The 16S rRNA gene sequence similarity between strain BCM23-1T and Terrilactibacillus laevilacticus NK26-11T was 98.3 %. The draft genome of BCM23-1T was 3.24 Mb in size and contained 3088 coding sequences with an in silico DNA G+C content of 37.1 mol%. The values of ANIb, ANIm and digital DNA-DNA hybridization between strain BCM23-1T and T. laevilacticus NK26-11T were 89.9, 90.8 and 40.4 %, respectively. The results of phenotypic and chemotaxonomic, 16S rRNA gene sequence similarity, and whole genome analyses support strain BCM23-1T as representing a novel species of Terrilactibacillus for which the name Terrilactibacillus tamarindi sp. nov. is proposed. The type strain is BCM23-1T (=LMG 31662T=JCM 33748T=TISTR 2841T).

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

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.

Regulating Pyruvate Carboxylase in the Living Culture of Aspergillus Terreus Nrrl 1960 by L-Aspartate for Enhanced Itaconic Acid Production.

Aspergillus terreus was reported as the promising fungal strain for itaconic acid; however, the commercial production suffers from the low yield. Low production yield was claimed as the result of completing the tricarboxylic acid (TCA) cycle towards biomass synthesis while under limiting phosphate and nitrogen; TCA cycle was somewhat shunted and consequently, the metabolite fluxes move towards itaconic acid production route. By regulating enzymes in TCA cycle, it is believed that itaconic acid production can be improved. One of the key responsible enzymes involved in itaconic acid production was triggered in this study. Pyruvate carboxylase was allosterically inhibited by L-aspartate. The presence of 10 mM L-aspartate in the production medium directly repressed PC expression in the living A. terreus while the limited malate flux regulated the malate/citrate antiporters resulting in the increasing cis-aconitate decarboxylase activity to simultaneously convert cis-aconitate, citrate isomer, into itaconic acid. The transport of cis-aconitate via the antiporters induced citrate synthase and 6-phosphofructo-1-kinase activities in response to balance the fluxes of TCA intermediates. Successively, itaconic acid production yield and final concentration could be improved by 8.33 and 60.32 %, respectively, compared to those obtained from the control fermentation with the shortened lag time to produce itaconic acid during the production phase.

Manipulating pyruvate decarboxylase by addition of enzyme regulators during fermentation of Rhizopus oryzae to enhance lactic acid production.

Ethanol was found as the major by-product in lactate fermentation by Rhizopus oryzae. Several methods have been conducted in order to limit ethanol formation, thus increasing the lactate yield. The direct way to suppress ethanol production can be done by inhibition of the responsible enzymes in the related pathway. Pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) are responsible for ethanol production in R. oryzae. Shunting the ethanol production pathway by targeting at PDC was attempted in this study. Three compounds including 4-methylpyrazole, glyoxylic acid, and 3-hydroxypyruvate with the in vitro reversible inhibitory effect on PDC were selected from the literature and were used to regulate the living cell of R. oryzae during the fermentation. The results show that 0.1 mM 4-methylpyrazole of which the structure resembled a thiazolium ring in thiamine diphosphate, PDC cofactor, and 1.0 µm 3-hydroxypyruvate, pyruvate analog, effectively hampered ethanol production. Further observation on the enzyme expression indicated that these two regulators not only targeted PDC but also caused changes in ADH and lactate dehydrogenase (LDH) activities. This was perhaps due to the living cell of R. oryzae that responded to the presence of the regulators to balance the pyruvate flux and subsequently maintain its metabolic activities.

1,2-diazole and 2,2,2-trifluoroethanol and their regulatory effects on ethanol and lactic acid formation in the living culture of Rhizopus oryzae.

In heterofermentation of Rhizopus oryzae, ethanol is the major byproduct which reduces the production of a desired product, an optically pure L-lactic acid. To improve lactic acid production, regulating the alcohol fermentative pathway to limit ethanol production has been done by various techniques. In vitro study on alcohol dehydrogenase (ADH) inhibition in several organisms showed that 1,2-diazole and 2,2,2-trifluoroethanol were competitively bound at the active sites that eventually limited ethanol production. In this study, 1,2-diazole and 2,2,2-trifluoroethanol were present during fermentation of R. oryzae. It was found that both 1,2-diazole and 2,2,2-trifluoroethanol not only strongly affected ethanol formation but they also indirectly regulated lactate production as observed by the decreasing affinity for glucose flux toward lactate and ethanol production. The increase in both ethanol and lactate formation rates revealed 1,2-diazole and 2,2,2-trifluoroethanol not only regulated the reversible redox reaction by ADH, but they also caused the dynamic change in the conversion of all metabolites in the living R. oryzae in order to maintain the balanced flux for cellular growth and maintenance.

In vivo regulation of alcohol dehydrogenase and lactate dehydrogenase in Rhizopus oryzae to improve L-lactic acid fermentation.

Rhizopus oryzae is becoming more important due to its ability to produce an optically pure L: -lactic acid. However, fermentation by Rhizopus usually suffers from low yield because of production of ethanol as a byproduct. Limiting ethanol production in living immobilized R. oryzae by inhibition of alcohol dehydrogenase (ADH) was observed in shake flask fermentation. The effects of ADH inhibitors added into the medium on the regulation of ADH and lactate dehydrogenase (LDH) as well as the production of cell biomass, lactic acid, and ethanol were elucidated. 1,2-diazole and 2,2,2-trifluroethanol were found to be the effective inhibitors used in this study. The highest lactic acid yield of 0.47 g/g glucose was obtained when 0.01 mM 2,2,2-trifluoroethanol was present during the production phase of the pregrown R. oryzae. This represents about 38% increase in yield as compared with that from the simple glucose fermentation. Fungal metabolism was suppressed when iodoacetic acid, N-ethylmaleimide, 4,4'-dithiodipyridine, or 4-hydroxymercury benzoic acid were present. Dramatic increase in ADH and LDH activities but slight change in product yields might be explained by the inhibitors controlling enzyme activities at the pyruvate branch point. This showed that in living R. oryzae, the inhibitors regulated the flux through the related pathways.

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.