Towards efficient production of highly optically pure d-lactic acid from lignocellulosic hydrolysates using newly isolated lactic acid bacteria

Converting a D-/L lactic acid bacteria to its d-type counterpart via a combined chemical mutagenesis and biosensor screening method, and its application in lignocellulosic biorefinery

Optically pure lactic acid is essential for poly(lactic acid) manufacturing, nonetheless, most wild-type lactic acid bacteria inherently produce D-/L- mixed lactic acid. In this study, an elaborate system was designed for developing d-lactic acid producing mutants from a wild-type D-/L- lactic acid producingLactobacillus by combining chemical mutagenesis with ethyl methane sulfonate as the mutagen and high throughput screening with a l-lactate dehydrogenase based biosensor. Mechanistic analysis revealed that the loss of l-lactate dehydrogenase activity via C → T transitions in the corresponding gene is responsible for generation of d-lactic acid producing mutants. The obtained d-lactic acid producing mutant exhibited excellent performance in different types of lignocellulosic hydrolysates and produced 128.3 g/L d-lactic acid from corn stover hydrolysate in 3-L bioreactor fermentation, with optical purity higher than 98 %. In conclusion, this study provided a practical framework for obtaining optically pure lactic acid producers without genetic engineering operations, advancing the sustainable production of cellulosic bioplastics.

Non-targeted metabolomics reveals the effects of fermented methods on the flavor, quality, and metabolites of whipping cream

Flavored fermented whipping cream has received particular attention. However, the effects of different fermentation methods on the quality and flavor of whipping cream remain elusive. This study characterized the flavor, quality, and metabolites of whipping cream produced by different fermentation methods based on non-targeted metabolomics. The results showed that the quality, color, and flavor of fermented whipping cream were significantly improved. Notably, the GMF fermentation group had the highest variety and content of flavoring substances. A total of 729 shared metabolites were identified, mainly including glycerophospholipids (151, 20.71 %), fatty acyls (114, 15.64 %), organoacyls (89, 12.21 %). Whipping cream by the mixed bacteria fermentation contained lower lipids and higher flavor amino acids, while the contents of bitter peptides and some organic acids and their derivatives were significantly lower. The results of this study provide a valuable reference for enhancing the quality, flavor, flavor of whipping cream using mixed bacteria fermentation methods.

Advances in L-Lactic Acid Production from Lignocellulose Using Genetically Modified Microbial Systems

Lactic acid is a vital organic acid with a wide range of industrial applications, particularly in the food, pharmaceutical, cosmetic, and biomedical sectors. The conventional production of lactic acid from refined sugars poses high costs and significant environmental impacts, leading to the exploration of alternative raw materials and more sustainable processes. Lignocellulosic biomass, particularly agro-industrial residues such as agave bagasse, represents a promising substrate for lactic acid production. Agave bagasse, a by-product of the tequila and mezcal industries, is rich in fermentable carbohydrates, making it an ideal raw material for biotechnological processes. The use of lactic acid bacteria (LAB), particularly genetically modified microorganisms (GMMs), has been shown to enhance fermentation efficiency and lactic acid yield. This review explores the potential of lignocellulosic biomass as a substrate for microbial fermentation to produce lactic acid and other high-value products. It covers the composition and pretreatment of some agricultural residues, the selection of suitable microorganisms, and the optimization of fermentation conditions. The paper highlights the promising future of agro-industrial residue valorization through biotechnological processes and the sustainable production of lactic acid as an alternative to conventional methods.

Adaptive Evolution for the Efficient Production of High-Quality d-Lactic Acid Using Engineered Klebsiella pneumoniae

d-Lactic acid serves as a pivotal platform chemical in the production of poly d-lactic acid (PDLA) and other value-added products. This compound can be synthesized by certain bacteria, including Klebsiella pneumoniae. However, industrial-scale lactic acid production in Klebsiella pneumoniae faces challenges due to growth inhibition caused by lactic acid stress, which acts as a bottleneck in commercial microbial fermentation processes. To address this, we employed a combination of evolutionary and genetic engineering approaches to create an improved Klebsiella pneumoniae strain with enhanced lactic acid tolerance and production. In flask fermentation experiments, the engineered strain achieved an impressive accumulation of 19.56 g/L d-lactic acid, representing the highest production yield observed in Klebsiella pneumoniae to date. Consequently, this strain holds significant promise for applications in industrial bioprocessing. Notably, our genome sequencing and experimental analyses revealed a novel correlation between UTP-glucose-1-phosphate uridylyltransferase GalU and lactic acid resistance in Klebsiella pneumoniae. Further research is warranted to explore the potential of targeting GalU for enhancing d-lactic acid production.

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.

New Genomic Techniques applied to food cultures: a powerful contribution to innovative, safe, and sustainable food products

Nontransgenic New Genomic Techniques (NGTs) have emerged as a promising tool for food industries, allowing food cultures to contribute to an innovative, safe, and more sustainable food system. NGTs have the potential to be applied to microorganisms, delivering on challenging performance traits like texture, flavour, and an increase of nutritional value. This paper brings insights on how nontransgenic NGTs applied to food cultures could be beneficial to the sector, enabling food industries to generate innovative, safe, and sustainable products for European consumers. Microorganisms derived from NGTs have the potentials of becoming an important contribution to achieve the ambitious targets set by the European 'Green Deal' and 'Farm to Fork' policies. To encourage the development of NGT-derived microorganisms, the current EU regulatory framework should be adapted. These technologies allow the introduction of a precise, minimal DNA modification in microbial genomes resulting in optimized products carrying features that could also be achieved by spontaneous natural genetic evolution. The possibility to use NGTs as a tool to improve food safety, sustainability, and quality is the bottleneck in food culture developments, as it currently relies on lengthy natural evolution strategies or on untargeted random mutagenesis.

Saccharina latissima, candy-factory waste, and digestate from full-scale biogas plant as alternative carbohydrate and nutrient sources for lactic acid production

To substitute petroleum-based materials with bio-based alternatives, microbial fermentation combined with inexpensive biomass is suggested. In this study Saccharina latissima hydrolysate, candy-factory waste, and digestate from full-scale biogas plant were explored as substrates for lactic acid production. The lactic acid bacteria Enterococcus faecium, Lactobacillus plantarum, and Pediococcus pentosaceus were tested as starter cultures. Sugars released from seaweed hydrolysate and candy-waste were successfully utilized by the studied bacterial strains. Additionally, seaweed hydrolysate and digestate served as nutrient supplements supporting microbial fermentation. According to the highest achieved relative lactic acid production, a scaled-up co-fermentation of candy-waste and digestate was performed. Lactic acid reached a concentration of 65.65 g/L, with 61.69% relative lactic acid production, and 1.37 g/L/hour productivity. The findings indicate that lactic acid can be successfully produced from low-cost industrial residues.