Metabolic Engineering of Lactobacillus plantarum for Direct l-Lactic Acid Production From Raw Corn Starch

Advances and new horizons in metabolic engineering of heterotrophic bacteria and cyanobacteria for enhanced lactic acid production

Bacteria species such as E.Coli, Lactobacilli, and pediococci play an important role as starter strains in fermentation food or polysaccharides into lactic acid. These bacteria were metabolically engineered using multiple proven genome editing methods to enhance relevant phenotypes. The efficacy of these procedures varies depending on the editing tool used and researchers' ability to pick suitable recombinants, which significantly increased genome engineering throughput. Cyanobacteria produce oxygenic photosynthesis and play an important role in carbon dioxide fixing. The fixed carbon dioxide is then retained as polysaccharides in cells and metabolised into various low carbon molecules such as lactate, succinate, and ethanol. Lactate is used as a building ingredient in various bioplastics, food additives, and medicines. This review covers the recent advances in lactic acid production through metabolic and genetic engineering in bacteria and cyanobacteria.

Omics analysis of key pathway in flavour formation and B vitamins synthesis during chickpea milk fermentation by Lactiplantibacillus plantarum

Chickpea milk is a nutrient-rich plant-based milk, but its pronounced beany flavour limits consumer acceptance. To address this issue, chickpea milk was fermented using two strains of Lactiplantibacillus plantarum, FMBL L23251 and L23252, which efficiently utilize chickpea milk. L. plantarum FMBL L23251 demonstrated superior fermentation characteristics. Fermentation with L. plantarum FMBL L23251 resulted in a 1.90-fold increase in vitamin B3 (271.66 ng/ml to 516.15 ng/ml) and a 1.58-fold increase in vitamin B6 (91.24 ng/ml to 144.16 ng/ml) through the L-aspartic acid pathway and the 1-deoxy-D-xylulose-5-phosphate (DXP)-independent pathway, respectively. Furthermore, L. plantarum FMBL L23251 effectively removed beany flavours due to its enhanced pathway for pyruvate metabolism. The main aldehydes are converted into corresponding alcohols or acids, resulting in 87.74 % and 96.99 % reductions in hexanal and 2-pentyl-furan, respectively. In summary, the fermentation of L. plantarum FMBL L23251 generated fermented chickpea milk that is rich in B vitamins and provides a better flavour.

Innovative Lactic Acid Production Techniques Driving Advances in Silage Fermentation

Lactic acid (LA) plays a crucial role in the silage process, which occurs through LA fermentation. Consequently, there is a strong correlation between lactic acid production and the efficiency of the silage. However, traditional methods face challenges like long fermentation times, low acid production, and unstable quality, limiting agricultural preservation. This paper aims to explore innovations in lactic acid production technologies and show how these technologies have driven the development of silage fermentation for agricultural conservation. First, the important role of LA in agricultural preservation and the limitations of traditional silage techniques are presented. Next, advancements in LA production methods are thoroughly examined, covering the selection of microbial strains and the substitution of fermentation substrates. Following this, new technologies for silage fermentation are explored, drawing from innovations in LA production. These include the selection of LA strains, optimization of fermentation conditions, and improvements in fermentation techniques. These innovations have proven effective in increasing LA production, improving feed quality, extending shelf life, and providing new solutions to enhance agricultural production and sustainability.

The lactate dehydrogenase gene is involved in the growth and metabolism of Lacticaseibacillus paracasei and the production of fermented milk flavor substances

Objective

Lactate dehydrogenase (ldh) in lactic acid bacteria is an important enzyme that is involved in the process of milk fermentation. This study aimed to explore the changes and effects of fermented milk metabolites in mutant strains after knocking out the ldh gene of Lacticaseibacillus paracasei.

Methods

The ldh mutant ΔAF91_07315 was obtained from L. paracasei using clustered regularly interspaced short palindromic repeats technology, and we determined fermented milk pH, titratable acidity, viable count, and differential metabolites in the different stages of milk fermentation that were identified using metabolomic analysis.

Results

The results showed that the growth rate and acidification ability of the mutant strain were lower than those of the wild-type strain before the end of fermentation, and analysis of the differential metabolites showed that lactate, L-cysteine, proline, and intermediate metabolites of phenylalanine, tryptophan, and methionine were downregulated (P < 0.05), which affected the growth initiation rate and acidification ability of the strain. At the end of fermentation (pH 4.5), the fermentation time of the mutant strain was prolonged and all differential metabolites were upregulated (P < 0.05), including amino acids and precursors, acetyl coenzyme A, and other metabolites involved in amino acid and fatty acid synthesis, which are associated with the regulation of fermented milk flavors. In addition, riboflavin was upregulated to promote the growth of the strain and compensate for the growth defects caused by the mutation.

Conclusion

Our data established a link between the AF91_07315 gene and strain growth and metabolism and provided a target for the regulation of fermented milk flavor substances.

Essential characteristics improvement of metallic nanoparticles loaded carbohydrate polymeric films - A review

Petroleum-based films have contributed immensely to various environmental issues. Developing green-based films from carbohydrate polymers is crucial for addressing the harms encountered. However, some limitations exist on their property, processibility, and applicability that prohibit their processing for further developments. This review discusses the potential carbohydrate polymers and their sources, film preparation methods, such as solvent-casting, tape-casting, extrusion, and thermo-mechanical compressions for green-based films using various biological polymers with their merits and demerits. Research outcomes revealed that the essential characteristics improvement achieved by incorporating different metallic nanoparticles has significantly reformed the properties of biofilms, including crystallization, mechanical stability, thermal stability, barrier function, and antimicrobial activity. The property-enhanced bio-based films made with nanoparticles are potentially interested in replacing fossil-based films in various areas, including food-packaging applications. The review paves a new way for the commercial use of numerous carbohydrate polymers to help maintain a sustainable green environment.

Sustainable Vegetable Oil-Based Biomaterials: Synthesis and Biomedical Applications

One of the main criteria for ecological sustainability is that the materials produced for common use are green. This can include the use of biomaterials and materials that are environmentally friendly, biodegradable and produced at low cost. The exploration of natural resources as sustainable precursors leads to the production of biopolymers that are useful for 3D printing technology. Recently, waste vegetable oils have been found to be a good alternative source for the production of biopolymers in various applications from the engineering to the biomedicine. In this review, the processes for the synthesis of vegetable oil-based biomaterials are described in detail. Moreover, the functionalization strategies to improve the mechanical properties of these materials and the cell-material interaction for their potential use as micro-structured scaffolds in regenerative medicine are discussed.

Engineered Microbial Cell Factories for Sustainable Production of L-Lactic Acid: A Critical Review

With the increasing demand for the biodegradable polymer material polylactic acid and its advantage of being metabolized by the human body, L-lactic acid (L-LA) is becoming increasingly attractive in environmental protection and food industry applications. However, the supply of L-LA is not satisfied, and the price is still high. Compared to enzymatic and chemical synthesis methods, L-LA production by microbial fermentation has the advantages of low cost, large yield, simple operation, and environmental protection. This review summarizes the advances in engineering microbial cell factories to produce L-LA. First, the synthetic pathways and microorganisms for L-LA production are outlined. Then, the metabolic engineering strategies for constructing cell factories to overproduce L-LA are summarized and fermentation modes for L-LA production are also given. Finally, the challenges and prospects of the microbial production of L-LA are discussed. This review provides theoretical guidance for researchers engaged in L-LA production.

State of the Art on the Microbial Production of Industrially Relevant Organic Acids

The industrial relevance of organic acids is high; because of their chemical properties, they can be used as building blocks as well as single-molecule agents with a huge annual market. Organic acid chemical platforms can derive from fossil sources by petrochemical refining processes, but most of them also represent natural metabolites produced by many cells. They are the products, by-products or co-products of many primary metabolic processes of microbial cells. Thanks to the potential of microbial cell factories and to the development of industrial biotechnology, from the last decades of the previous century, the microbial-based production of these molecules has started to approach the market. This was possible because of a joint effort of microbial biotechnologists and biochemical and process engineers that boosted natural production up to the titer, yield and productivity needed to be industrially competitive. More recently, the possibility to utilize renewable residual biomasses as feedstock not only for biofuels, but also for organic acids production is further augmenting the sustainability of their production, in a logic of circular bioeconomy. In this review, we briefly present the latest updates regarding the production of some industrially relevant organic acids (citric fumaric, itaconic, lactic and succinic acid), discussing the challenges and possible future developments of successful production.

L-Lactate oxidase-mediated removal of L-lactic acid derived from fermentation medium for the production of optically pure D-lactic acid

BACKGROUND

There has been an increasing demand for optically pure D-lactic and L-lactic acid for the production of stereocomplex-type polylactic acid. The D-lactic acid production from lignocellulosic biomass is important owing to its great abundance in nature. Corn steep liquor (CSL) is a cheap nitrogen source used for industrial fermentation, though it contains a significant amount of L-lactic acid, which decreases the optical purity of D-lactic acid produced.

METHOD AND RESULTS

To remove L-lactic acid derived from the CSL-based medium, L-lactate oxidase (LoxL) from Enterococcus sp. NBRC 3427 was expressed in an engineered Lactiplantibacillus plantarum (formally called Lactobacillus plantarum) strain KOLP7, which exclusively produces D-lactic acid from both hexose and pentose sugars. When the resulting strain was applied for D-lactic acid fermentation from the mixed sugars consisting of the major constituent sugars of lignocellulose (35 g/L glucose, 10 g/L xylose, and 5 g/L arabinose) using the medium containing 10 g/L CSL, it completely removed L-lactic acid derived from CSL (0.52 g/L) and produced 41.7 g/L of D-lactic acid. The L-lactic acid concentration was below the detection limit, and improvement in the optical purity of D-lactic acid was observed (from 98.2% to > 99.99%) by the overexpression of LoxL.

CONCLUSION AND IMPLICATIONS

The LoxL-mediated consumption of L-lactic acid would enable the production of optically pure D-lactic acid in any medium contaminated by L-lactic acid. This article is protected by copyright. All rights reserved.

A Review of the Recent Developments in the Bioproduction of Polylactic Acid and Its Precursors Optically Pure Lactic Acids

Lactic acid (LA) is an important organic acid with broad industrial applications. Considered as an environmentally friendly alternative to petroleum-based plastic with a wide range of applications, polylactic acid has generated a great deal of interest and therefore the demand for optically pure l- or d-lactic acid has increased accordingly. Microbial fermentation is the industrial route for LA production. LA bacteria and certain genetic engineering bacteria are widely used for LA production. Although some fungi, such as Saccharomyces cerevisiae, are not natural LA producers, they have recently received increased attention for LA production because of their acid tolerance. The main challenge for LA bioproduction is the high cost of substrates. The development of LA production from cost-effective biomasses is a potential solution to reduce the cost of LA production. This review examined and discussed recent progress in optically pure l-lactic acid and optically pure d-lactic acid fermentation. The utilization of inexpensive substrates is also focused on. Additionally, for PLA production, a complete biological process by one-step fermentation from renewable resources is also currently being developed by metabolically engineered bacteria. We also summarize the strategies and procedures for metabolically engineering microorganisms producing PLA. In addition, there exists some challenges to efficiently produce PLA, therefore strategies to overcome these challenges through metabolic engineering combined with enzyme engineering are also discussed.

Recent Advances in Lactic Acid Production by Lactic Acid Bacteria

Lactic acid can synthesize high value-added chemicals such as poly lactic acid. In order to further minimize the cost of lactic acid production, some effective strategies (e.g., effective mutagenesis and metabolic engineering) have been applied to increase productive capacity of lactic acid bacteria. In addition, low-cost cheap raw materials (e.g., cheap carbon source and cheap nitrogen source) are also used to reduce the cost of lactic acid production. In this review, we summarized the recent developments in lactic acid production, including efficient strain modification technology (high-efficiency mutagenesis means, adaptive laboratory evolution, and metabolic engineering), the use of low-cost cheap raw materials, and also discussed the future prospects of this field, which could promote the development of lactic acid industry.

Enzymes, In Vivo Biocatalysis, and Metabolic Engineering for Enabling a Circular Economy and Sustainability

Since the industrial revolution, the rapid growth and development of global industries have depended largely upon the utilization of coal-derived chemicals, and more recently, the utilization of petroleum-based chemicals. These developments have followed a linear economy model (produce, consume, and dispose). As the world is facing a serious threat from the climate change crisis, a more sustainable solution for manufacturing, i.e., circular economy in which waste from the same or different industries can be used as feedstocks or resources for production offers an attractive industrial/business model. In nature, biological systems, i.e., microorganisms routinely use their enzymes and metabolic pathways to convert organic and inorganic wastes to synthesize biochemicals and energy required for their growth. Therefore, an understanding of how selected enzymes convert biobased feedstocks into special (bio)chemicals serves as an important basis from which to build on for applications in biocatalysis, metabolic engineering, and synthetic biology to enable biobased processes that are greener and cleaner for the environment. This review article highlights the current state of knowledge regarding the enzymatic reactions used in converting biobased wastes (lignocellulosic biomass, sugar, phenolic acid, triglyceride, fatty acid, and glycerol) and greenhouse gases (CO₂ and CH₄) into value-added products and discusses the current progress made in their metabolic engineering. The commercial aspects and life cycle assessment of products from enzymatic and metabolic engineering are also discussed. Continued development in the field of metabolic engineering would offer diversified solutions which are sustainable and renewable for manufacturing valuable chemicals.

Application of raw starch degrading enzyme from Laceyella sacchari LP175 for development of bacterial cellulose fermentation using colored rice as substrate

Brown and black rice substrates were applied for sugar syrup production by the hydrolysis of raw starch degrading enzyme (RSDE) from Laceyella sacchari LP175 (300 U/mL) and commercial glucoamylase (GA, 2.0 U/mL) at 50 °C for 12 h using a simplex centroid mixture design. Results indicated that 300 g/L of substrates, consisting of 255 g/L Leum Pua glutinous rice and 45 g/L Black Jasmine rice, gave the highest sugar syrup production at 124.6 ± 2.52 g/L with 2.00 ± 0.05 mg GAE/mL of total phenolic content (TPC), equivalent to 0.42 ± 0.01 g/g rice sample and 6.67 ± 0.15 mg GAE/g rice sample, respectively. The obtained sugar syrup was used as the substrate for production of bacterial cellulose (Nata) by Komagataeibacter xylinus AGR 60 in a plastic tray at room temperature for 9 days. The fermentation medium containing 200 mL of rice syrup (25 g/L), 2.0 g of ammonium sulfate [(NH₄)₂SO₄] and 0.4 mL glacial acetic acid yielded 1.1 ± 0.08 cm thickness with 8.15 ± 0.12 g of dry weight. The obtained bacterial cellulose from colored rice was characterized compared with bacterial cellulose from the conventional coconut juice by scanning electron microscope (SEM) and Fourier-transform infrared spectroscopy (FTIR) which demonstrated that the sugar syrup from colored rice could use as substrate for a novel bacterial cellulose as a healthy product in the future through microbial enzyme technological process.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02673-3.

Improvement of Polymer Grade L-Lactic Acid Production Using Lactobacillus rhamnosus SCJ9 from Low-Grade Cassava Chips by Simultaneous Saccharification and Fermentation

The present study aims to examine the process for L-lactic acid production from low-grade cassava chips (LGC) using a two-step fermentation approach (TSF) and simultaneous saccharification and fermentation (SSF) by proficient, newly isolated Lactobacillus rhamnosus strain SCJ9. The optimized medium composition revealed by response surface methodology for TSF was 166 g/L LGC hydrolysate and 20 g/L yeast extract (YE), while other medium components were fixed (g/L) as follows: tween80 (2.0), (NH4)2HPO4 (2.0), CH3COONa∙3H2O (6.0), (NH4)2HC6H5O7 (2.0), MgSO4∙7H2O (0.5), and MnSO4∙H2O (0.3). Based on the optimization conditions, the maximum experimental L-lactic acid of 134.6 g/L was achieved at 60 h fermentation time with a production efficiency of 89.73%, 0.95 g/g yield and 2.24 g/L/h productivity. In contrast, L-lactic acid production by SSF under optimized concentrations of thermostable-α-amylase (AA) and glucoamylase (GA) gave maximum L-lactic acid of 125.79 g/L at only 36 h fermentation time which calculated to the production efficiency, yield and productivity of 83.86%, 0.93 g/g and 3.49 g/L/h, respectively. The L-lactic acid production obtained from SSF was significantly improved when compared to TSF based on lower enzyme loading usage, shorter hydrolysis time and increase in production efficiency and productivity. Furthermore, there were no significant differences in the production by SSF between experiments conducted in laboratory bottle and 10-L fermenter. The results indicated the success of up-scaling for L-lactic acid production by SSF which could be developed for a further pilot-scale production of L-lactic acid.

Metabolically engineered Lactobacillus gasseri JCM 1131 as a novel producer of optically pure L- and D-lactate

High-quality environmentally-friendly bioplastics can be produced by mixing poly-L-lactate with poly-D-lactate. On an industrial scale, this process simultaneously consumes large amounts of both optically pure lactate stereoisomers. However, because optimal growth conditions of L-lactate producers often differ from those of D-lactate producers, each stereoisomer is produced in a specialised facility, which raises cost and lowers sustainability. To address this challenge, we metabolically engineered Lactobacillus gasseri JCM 1131^T, a bioprocess-friendly and genetically malleable strain of homofermentative lactic acid bacterium, to efficiently produce either pure L- or pure D-lactate under the same bioprocess conditions. Transformation of L. gasseri with plasmids carrying additional genes for L- or D-lactate dehydrogenases failed to affect the ratio of produced stereoisomers, but inactivation of the endogenous genes created strains which yielded 0.96 g of either L- or D-lactate per gram of glucose. In this study, the plasmid pHBintE, routinely used for gene disruption in Bacillus megaterium, was used for the first time to inactivate genes in lactobacilli. Strains with inactivated genes for endogenous lactate dehydrogenases efficiently fermented sugars released by enzymatic hydrolysis of alkali pre-treated wheat straw, an abundant lignocellulose-containing raw material, producing 0.37-0.42 g of lactate per gram of solid part of alkali-treated wheat straw. Thus, the constructed strains are primed to serve as producers of both optically pure L-lactate and D-lactate in the next-generation biorefineries.

Organic acids as antimicrobial food agents: applications and microbial productions

Food safety is a global health and socioeconomic concern since many people still suffer from various acute and life-long diseases, which are caused by consumption of unsafe food. Therefore, ensuring safety of the food is one of the most essential issues in the food industry, which needs to be considered during not only food composition formulation but also handling and storage. For safety purpose, various chemical preservatives have been used so far in the foods. Recently, there has been renewed interest in replacing chemically originated food safety compounds with natural ones in the industry, which can also serve as antimicrobial agents. Among these natural compounds, organic acids possess the major portion. Therefore, in this paper, it is aimed to review and compile the applications, effectiveness, and microbial productions of various widely used organic acids as antimicrobial agents in the food industry.

Inducible Plasmid Self-Destruction (IPSD) Assisted Genome Engineering in Lactobacilli and Bifidobacteria

Genome engineering is essential for application of synthetic biology in probiotics including lactobacilli and bifidobacteria. Several homologous recombination system-based mutagenesis tools have been developed for these bacteria, but still have many limitations in different species or strains. Here we developed a genome engineering method based on an inducible self-destruction plasmid delivering homologous DNA into bacteria. Excision of the replicon by induced recombinase facilitates selection of homologous recombination events. This new genome editing tool called inducible plasmid self-destruction (IPSD) was successfully used to perform gene knockout and knock-in in lactobacilli and bifidobacteria. Due to its simplicity and universality, the IPSD strategy may provide a general approach for genetic engineering of various bacterial species.

Steps Toward High-Performance PLA: Economical Production of d-Lactate Enabled by a Newly Isolated Sporolactobacillus terrae Strain

Optically pure d-lactate production has received much attention for its critical role in high-performance polylactic acid production. However, the current technology can hardly meet the comprehensive demand of industrialization on final titer, productivity, optical purity, and raw material costs. Here, an efficient d-lactate producer strain, Sporolactobacillus terrae (S. terrae) HKM-1, is isolated for d-lactate production. The strain HKM-1 shows extremely high d-lactate fermentative capability by using peanut meal, soybean meal, or corn steep liquor powder as a sole nitrogen source; the final titers (205.7 g L-1 , 218.9 g L-1 , and 193.9 g L-1 , respectively) and productivities (5.56 g L-1  h-1 , 5.34 g L-1  h-1 , and 3.73 g L-1  h-1 , respectively) of d-lactate reached the highest level ever reported. A comparative genomic analysis between S. terrae HKM-1 and previously reported d-lactate high-producing Sporolactobacillus inulinus (S. inulinus) CASD is conducted. The results show that many unrelated genetic features may contribute to the superior performance in d-lactate production of S. terrae HKM-1. This d-lactate producer HKM-1, along with its fermentation process, is promising for sustainable d-lactate production by using agro-industrial wastes.