Metabolic engineering of Bacillus subtilis for production of D‐lactic acid

Abstract

Poly lactic acid (PLA) based plastics is renewable, bio-based, and biodegradable. Although present day PLA is composed of mainly L-LA, an L- and D- LA copolymer is expected to improve the quality of PLA and expand its use. To increase the number of thermotolerant microbial biocatalysts that produce D-LA, a derivative of Bacillus subtilis strain 168 that grows at 50°C was metabolically engineered. Since B. subtilis lacks a gene encoding D-lactate dehydrogenase (ldhA), five heterologous ldhA genes (B. coagulans ldhA and gldA101, and ldhA from three Lactobacillus delbrueckii) were evaluated. Corresponding D-LDHs were purified and biochemically characterized. Among these, D-LDH from L. delbrueckii subspecies bulgaricus supported the highest D-LA titer (about 1M) and productivity (2 g h g cells ) at 37°C (B. subtilis strain DA12). The D-LA titer at 48°C was about 0.6 M at a yield of 0.99 (g D-LA g glucose consumed). Strain DA12 also fermented glucose at 48°C in mineral salts medium to lactate at a yield of 0.89 g g glucose and the D-lactate titer was 180 ± 4.5 mM. These results demonstrate the potential of B. subtilis as a platform organism for metabolic engineering for production of chemicals at 48°C that could minimize process cost.

Lactic acid production from sugarcane bagasse hydrolysates by Lactobacillus pentosus: Integrating xylose and glucose fermentation

“…Lactic acid is a valuable chemical platform that presents extensive applications in food, cosmetics, textile, pharmaceutical, and chemical industries. Demand for lactic acid has grown substantially in recent years, owing to its great potential as a building block for the production of polylactic acid (PLA) materials, biodegradable agro‐based products that are more environmentally friendly, and alternative to petroleum‐based plastics . In 2013, global demands for lactic acids and PLA were 714.2 and 360.8 kilo tons.…”

“…Demand for lactic acid has grown substantially in recent years, owing to its great potential as a building block for the production of polylactic acid (PLA) materials, biodegradable agro-based products that are more environmentally friendly, and alternative to petroleum-based plastics. [1][2][3][4] In 2013, global demands for lactic acids and PLA were 714.2 and 360.8 kilo tons. Considering an expected annual growth of 15.5% and 18.8%, demands could reach 1,960 and 1,205 kilo tons, respectively, by 2020.…”

Evolutionary engineering of Lactobacillus bulgaricus reduces enzyme usage and enhances conversion of lignocellulosics to D-lactic acid by simultaneous saccharification and fermentation

“…The utility of D-lactate dehydrogenase (D-LDH) of L. delbrueckii subsp. bulgaricus in high temperature fermentation has been demonstrated by Awasthi et al [44]. The heterologous expression of D-LDH in an engineered Bacillus subtilis resulted in a D-LA titre of 54 g/L from glucose at a yield of 0.89 at 48 °C.…”

Catabolic Division of Labor Enhances Production of D-Lactate and Succinate From Glucose-Xylose Mixtures in Engineered Escherichia coli Co-culture Systems

“…To date, several engineered microorganisms producing LA [e.g., lactic-acid bacteria (LAB), Saccharomyces cerevisiae, E. coli] and SA (e.g., Mannheimia succiniciproducens, Corynebacterium glutamicum, Bacillus strains) have been reported using various substrates (Grabar et al, 2006;Ishida et al, 2006;Wang et al, 2011;Litsanov et al, 2012;Awasthi et al, 2018). While different strains have their own unique advantages/disadvantages (e.g., ease of genetic manipulation, product tolerance, and other physiological benefits), from a bioprocessing perspective, it is desirable that it should also be capable of rapidly and simultaneously utilizing the substrate at high initial loadings (e.g., ≥ 100 g L −1 total sugar).…”