One step open fermentation for lactic acid production from inedible starchy biomass by thermophilic Bacillus coagulans IPE22

Strain engineering of Bacillus coagulans with high osmotic pressure tolerance for effective L-lactic acid production from sweet sorghum juice under unsterile conditions

Open unsterile fermentation of the low-cost non-food crop, sweet sorghum, is an economically feasible lactic acid biosynthesis process. However, hyperosmotic stress inhibits microbial metabolism and lactic acid biosynthesis, and engineering strains with high osmotic tolerance is challenging. Herein, heavy ion mutagenesis combined with osmotic pressure enrichment was used to engineer a hyperosmotic-tolerant Bacillus coagulans for L-lactic acid production. The engineered strain had higher osmotic pressure tolerance, when compared with the parental strain, primarily owing to its improved properties such as cell viability, cellular antioxidant capacity, and NADH supply. In a pilot-scale open unsterile fermentation using sweet sorghum juice as a feedstock, the engineered strain produced 94 g/L L-lactic acid with a yield of 91 % and productivity of 6.7 g/L/h, and optical purity of L-lactic acid at the end of fermentation was 99.8 %. In short, this study provided effective and low-cost approach to produce polymer-grade L-lactic acid.

Exploitation of microbial activities at low pH to enhance planetary health

Awareness is growing that human health cannot be considered in isolation but is inextricably woven with the health of the environment in which we live. It is, however, under-recognized that the sustainability of human activities strongly relies on preserving the equilibrium of the microbial communities living in/on/around us. Microbial metabolic activities are instrumental for production, functionalization, processing, and preservation of food. For circular economy, microbial metabolism would be exploited to produce building blocks for the chemical industry, to achieve effective crop protection, agri-food waste revalorization, or biofuel production, as well as in bioremediation and bioaugmentation of contaminated areas. Low pH is undoubtedly a key physical-chemical parameter that needs to be considered for exploiting the powerful microbial metabolic arsenal. Deviation from optimal pH conditions has profound effects on shaping the microbial communities responsible for carrying out essential processes. Furthermore, novel strategies to combat contaminations and infections by pathogens rely on microbial-derived acidic molecules that suppress/inhibit their growth. Herein, we present the state-of-the-art of the knowledge on the impact of acidic pH in many applied areas and how this knowledge can guide us to use the immense arsenal of microbial metabolic activities for their more impactful exploitation in a Planetary Health perspective.

Enhancement effect of l-cysteine on lactic acid fermentation production

BACKGROUND

Environmental stress resistance is still a bottleneck for economical process for l-lactic acid fermentation. Chronological lifespan (CLS) extension has represented a promising strategy for improving stress resistance of microbial cell factories.

MAIN METHODS AND MAJOR RESULTS

In this study, addition of anti-aging drug cysteine, a kind of extending CLS of microbial cell factories, was systematically evaluated on cell viability and l-lactic acid production in Bacillus coagulans CICC 23843. The results revealed that 16 mm l-cysteine supplement significantly improved l-lactic acid titer in B. coagulans. The enhanced total antioxidant capacity (T-AOC) and key enzymes activities involving in glycolytic pathway as well as differentially expressed genes involved in cysteine synthesize and cysteine precursor synthesize pathways, and fatty acid degradation pathway may help to further understand the relative mechanism of l-cysteine effect on improving l-lactic acid accumulation. Finally, based on 16 mm l-cysteine supplement, a final l-lactic acid titer of 130.5 g L-1 with l-lactic acid productivity of 4.07 g L-1  h-1 and the conversion rate of 0.94 g g-1 total sugar was achieved in a 5 L bioreactor.

CONCLUSIONS AND IMPLICATIONS

This study provided a valuable option for engineering lactic acid bacteria lifespan for enhancement of lactic acid yield.

Catalytic Conversion of Sugars into Lactic Acid via a RuOx/MoS2 Catalyst

The catalytic transformation of sugars into lactic acid has shown great potential for the scalable utilization of renewable biomass. Herein, RuOx/MoS2 catalysts were synthesized with the assistance of CaO for the one-pot conversion of glucose to lactic acid. Under the reaction conditions of 120 °C and 1MPa O2, a 96.6% glucose conversion and a 54.3% lactic acid yield were realized in the one-pot catalytic reaction, with relatively high stability after four successive cycles. This catalytic system was also effective for the conversion of many other carbohydrate substrates, such as fructose, xylose and cellulose (selectivity 68.9%, 78.2% and 50.6%, respectively). According to catalyst characterizations and conditional experiments, the highly dispersed RuOx species on the surface of MoS2, together with OH−, promoted isomerization, retro-aldol condensation, dehydration and hydration reactions, resulting in a relatively high lactic acid yield for sugar conversions.

An Overview on Wood Waste Valorization as Biopolymers and Biocomposites: Definition, Classification, Production, Properties and Applications

Bio-based polymers, obtained from natural biomass, are nowadays considered good candidates for the replacement of traditional fossil-derived plastics. The need for substituting traditional synthetic plastics is mainly driven by many concerns about their detrimental effects on the environment and human health. The most innovative way to produce bioplastics involves the use of raw materials derived from wastes. Raw materials are of vital importance for human and animal health and due to their economic and environmental benefits. Among these, wood waste is gaining popularity as an innovative raw material for biopolymer manufacturing. On the other hand, the use of wastes as a source to produce biopolymers and biocomposites is still under development and the processing methods are currently being studied in order to reach a high reproducibility and thus increase the yield of production. This study therefore aimed to cover the current developments in the classification, manufacturing, performances and fields of application of bio-based polymers, especially focusing on wood waste sources. The work was carried out using both a descriptive and an analytical methodology: first, a description of the state of art as it exists at present was reported, then the available information was analyzed to make a critical evaluation of the results. A second way to employ wood scraps involves their use as bio-reinforcements for composites; therefore, the increase in the mechanical response obtained by the addition of wood waste in different bio-based matrices was explored in this work. Results showed an increase in Young's modulus up to 9 GPa for wood-reinforced PLA and up to 6 GPa for wood-reinforced PHA.

In Vitro Evaluation of Weizmannia coagulans Strain LMG S-31876 Isolated from Fermented Rice for Potential Probiotic Properties, Safety Assessment and Technological Properties

Simple Summary

Weizmanniacoagulans strain LMG S-31876, isolated from fermented rice, is Gram-positive bacilli, a spore-forming, motile, and facultative anaerobe, with an optimum temperature requirement of 40 °C. The strain is able to tolerate acidic gastric juice, bile, and pancreatin. It is non-virulent and exhibits sensitivity to most of the tested antibiotics. The strain shows antagonistic activity against pathogenic bacteria. The 16S rDNA gene sequence of W.coagulans strain LMG S-31876 has been submitted to NCBI–GenBank, archiving accession number MZ687045. The strain has also been deposited to BCCM/LMG and MTCC-IDA with reference numbers LMG S-31876 and MTCC 25396, respectively.

Abstract

Bacillus coagulans, which has been taxonomically reclassified as Weizmannia coagulans, has been the focus of research due to its wide distribution in fermented foods, probiotic properties, and tolerance to extreme environments. The purpose of this study was to characterise putative probiotic bacteria in a fermented rice sample, followed by an in vitro screening of presumptive probiotic properties and a safety assessment to ensure their safety for human consumption. The predominant isolate was Gram-positive, rod-shaped, catalase-positive, spore-forming, motile, and facultatively anaerobic. The biochemical test and 16S rDNA sequencing identify the isolate as Weizmannia coagulans strain LMG S-31876. The strain showed significant viability in acidic gastric juice, pancreatin, and bile. The strain showed tolerance to 5% NaCl, and a low-to-moderate percentage of hydrophobicity and auto-aggregation was recorded. It met all safety criteria, including haemolytic activity, DNase activity, antibiotic sensitivity, and growth inhibition of other bacteria. Evaluation of its technological properties showed positive results for amylolytic and lipolytic activities; however, negative results were obtained for proteolytic activity. It could be concluded from the gathered data that W. coagulans strain LMG S-31876 isolated from fermented rice, might serve as a potential functional probiotic food. However, extended follow-up durations and larger-scale trials by assessing the therapeutic effects in managing various clinical gastrointestinal conditions are required to warranty such effects.

Poly(3-hydroxybutyrate) biosynthesis under non-sterile conditions: Piperazine as nitrogen substrate control switch

Poly(3-hydroxybutyrate) (PHB), as a kind of bioplastics for sustainable development, can be synthesized by various microorganisms, however, the high cost of its microbial fermentation is a challenge for its large-scale application. In this study, piperazine degrading strain, Paracoccus sp. TOH, was developed as an excellent chassis for open PHB fermentation with piperazine as controlling element. Whole-genome analysis showed that TOH possesses multi-substrate metabolic pathways to synthesize PHB. Next, TOH could achieve a maximum PHB concentration of 2.42 g L^-1, representing a yield of 0.36 g-PHB g^-1-glycerol when C/N ratio was set as 60:1 with 10 g L^-1 glycerol as substrate. Furthermore, TOH could even synthesize 0.39 g-PHB g^-1-glycerol under non-sterile conditions when piperazine was fed with a suitable rate of 1 mg L^-1 h^-1. 16S rRNA gene sequencing analysis showed that microbial contamination could be effectively inhibited through the regulation of piperazine under non-sterile conditions and TOH dominated the microbial community with a relative abundance of 72.3% at the end of the operational period. This study offers an inspired open PHB fermentation system with piperazine as the control switch, which will realize the goal of efficient industrial biotechnology as well as industrial wastewater treatment.

D-Lactic acid production from agricultural residues by membrane integrated continuous fermentation coupled with B vitamin supplementation

Background

d-Lactic acid played an important role in the establishment of PLA as a substitute for petrochemical plastics. But, so far, the d-lactic acid production was limited in only pilot scale, which was definitely unable to meet the fast growing market demand. To achieve industrial scale d-lactic acid production, the cost-associated problems such as high-cost feedstock, expensive nutrient sources and fermentation technology need to be resolved to establish an economical fermentation process.

Results

In the present study, the combined effect of B vitamin supplementation and membrane integrated continuous fermentation on d-lactic acid production from agricultural lignocellulosic biomass by Lactobacillus delbrueckii was investigated. The results indicated the specific addition of vitamins B₁, B₂, B₃ and B₅ (VB₁, VB₂, VB₃ and VB₅) could reduce the yeast extract (YE) addition from 10 to 3 g/l without obvious influence on fermentation efficiency. By employing cell recycling system in 350 h continuous fermentation with B vitamin supplementation, YE addition was further reduced to 0.5 g/l, which resulted in nutrient source cost reduction of 86%. A maximum d-lactate productivity of 18.56 g/l/h and optical purity of 99.5% were achieved and higher than most recent reports.

Conclusion

These findings suggested the novel fermentation strategy proposed could effectively reduce the production cost and improve fermentation efficiency, thus exhibiting great potential in promoting industrial scale d-lactic acid production from lignocellulosic biomass.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13068-022-02124-y.

High d-lactic acid productivity is achieved by L. delbrueckii from rice straw.

B vitamins are satisfied substitute of yeast extract for d-lactic acid fermentation.

A process of membrane-integrated continuous fermentation with B vitamin is developed.

High fermentation efficiency is achieved by the novel fermentation process.

High-efficient L-lactic acid production from inedible starchy biomass by one-step open fermentation using thermotolerant Lactobacillus rhamnosus DUT1908

The purpose of this study was to establish a simplified operational process for lactic acid (LA) production from inedible starchy biomass by open fermentation using thermotolerant Lactobacillus rhamnosus DUT1908. One step simultaneous liquefaction, saccharification and fermentation (SLSF) was proposed to produce LA using aging paddy rice with hull (APRH) as feedstock. First, a robust microbial strain was obtained by adaptive laboratory evolution under high temperature stress. As a result, L. rhamnosus DUT1908 showed high thermotolerance up to 50 °C and high efficiency of substrate utilization. Then, the performance of this thermotolerant L-lactic acid producing strain was demonstrated. Finally, various fermentation strategies were compared for LA production from APRH, including simultaneous saccharification and fermentation (SSF) and SLSF. In one-step open SLSF process, 107.8 g/L lactic acid was obtained with a productivity of 3.4 g/(L.h) and a yield to theoretical glucose of 0.89 g/g. This is the highest yield and productivity of lactic acid reported on starchy residues, and provides an efficient route for the development of high value-added products.

Metabolic engineering coupled with adaptive evolution strategies for the efficient production of high-quality L-lactic acid by Lactobacillus paracasei

The main indicators for industrial production of high-quality lactic acid at elevated temperatures are high titer, productivity, yield, and optical purity. However, no such strains have been reported to meet all these requirements simultaneously. In this study, a high optical purity L-lactic acid producing strain is developed through the CRISPR-Cas9 gene editing platform. Further, adaptive evolution was used to breed and select a high-performance strain (NCBIO01-M2-ldhL1-HT) that could efficiently produce L-lactic acid at a high temperature of 45℃. This strain produced 221.0 g/L of L-lactic acid in open fermentation with high initial glucose concentration. Also, L-lactic acid productivity and yield was above 7.5 g/L/h and 0.96 g/g respectively, as well as the optical purity of L-lactic acid in the fermentation broth exceeded 99.1%. In short, this breeding strain possess high potential to be considered for the commercial production of polymer-grade L-lactic acid.

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.