Production of d-lactate from sugarcane bagasse and corn stover hydrolysates using metabolic engineered Escherichia coli strains

Simultaneous and rate-coordinated conversion of lignocellulose derived glucose, xylose, arabinose, mannose, and galactose into D-lactic acid production facilitates D-lactide synthesis

D-lactide is the precursor of poly(D-lactide) (PDLA) or stereo-complex with poly(L-lactide) (PLLA). Lignocellulosic biomass provides the essential feedstock option to synthesize D-lactic acid and D-lactide. The residual sugars in D-lactic acid fermentation broth significantly blocks the D-lactide synthesis. This study showed a simultaneous and rate-coordinated conversion of lignocellulose derived glucose, xylose, arabinose, mannose, and galactose into D-lactic acid by adaptively evolved Pediococcus acidilactici ZY271 by simultaneous saccharification and co-fermentation (SSCF) of wheat straw. The produced D-lactic acid achieved minimum residual sugars (∼1.7 g/L), high chirality (∼99.1%) and high titer (∼128 g/L). A dry acid pretreatment eliminated the wastewater stream generation and the biodetoxification by fungus Amorphotheca resinae ZN1 removed the inhibitors from the pretreatment. The removal of the sugar residues and inhibitor impurities in D-lactic acid production from lignocellulose strongly facilitated the D-lactide synthesis. This study filled the gap in cellulosic D-lactide production from lignocellulose-derived D-lactic acid.

Sustainable valorization of sugarcane residues: Efficient deconstruction strategies for fuels and chemicals production

The global climate crisis and the ongoing increase in fossil-based fuels have led to an alternative solution of using biomass for fuel production. Sugarcane bagasse (SCB) is an agricultural residue with a global production of more than 100 million metric tons and it has various applications in a biorefinery concept. This review brings forth the composition, life cycle assessment, and various pretreatments for the deconstruction techniques of SCB for the production of valuable products. The ongoing research in the production of biofuels, biogas, and electricity utilizing the bagasse was elucidated. SCB is used in the production of carboxymethyl cellulose, pigment, lactic acid, levulinic acid, and xylooligosaccharides and it has prospective in meeting the demand for global energy and environmental sustainability.

Fermentative Lactic Acid Production From Lignocellulosic Feedstocks: From Source to Purified Product

The second (lignocellulosic biomass and industrial wastes) and third (algal biomass) generation feedstocks gained substantial interest as a source of various value-added chemicals, produced by fermentation. Lactic acid is a valuable platform chemical with both traditional and newer applications in many industries. The successful fractionation, separation, and hydrolysis of lignocellulosic biomass result in sugars' rich raw material for lactic acid fermentation. This review paper aims to summarize the investigations and progress in the last 5 years in lactic acid production from inexpensive and renewable resources. Different aspects are discussed-the type of raw materials, pretreatment and detoxification methods, lactic acid-producers (bacteria, fungi, and yeasts), use of genetically manipulated microorganisms, separation techniques, different approaches of process organization, as well as main challenges, and possible solutions for process optimization.

Limited oxygen conditions as an approach to scale-up and improve D and L-lactic acid production in mineral media and avocado seed hydrolysates with metabolically engineered Escherichia coli

The effectiveness of micro-aeration on lactate (LA) production by metabolically engineered Escherichia coli was evaluated in 1 L bioreactors containing mineral media and glucose (70 g/L). Volumetric oxygen transfer coefficients (k_La) between 12.6 and 28.7 h^-1 increased the specific growth rate (µ) and volumetric productivity (Q_LA) by 300 and 400%, respectively, without a significant decrease in lactate yield (Y_LA), when compared with non-aerated fermentations. A k_La of 12.6 h^-1 was successfully used as a criterion to scale-up the production of L and D-lactate from 1 to 11 and 130 L. Approximately constant Q_LA and Y_LA values were obtained throughout the fermentation scale-up process. Furthermore, a D-lactogenic fermentation was carried out in 1 L bioreactors using avocado seed hydrolysate as a culture medium under the same k_La value, displaying high Q_LA and Y_LA.

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

Although biological upgrading of lignocellulosic sugars represents a promising and sustainable route to bioplastics, diverse and variable feedstock compositions (e.g., glucose from the cellulose fraction and xylose from the hemicellulose fraction) present several complex challenges. Specifically, sugar mixtures are often incompletely metabolized due to carbon catabolite repression while composition variability further complicates the optimization of co-utilization rates. Benefiting from several unique features including division of labor, increased metabolic diversity, and modularity, synthetic microbial communities represent a promising platform with the potential to address persistent bioconversion challenges. In this work, two unique and catabolically orthogonal Escherichia coli co-cultures systems were developed and used to enhance the production of D-lactate and succinate (two bioplastic monomers) from glucose-xylose mixtures (100 g L-1 total sugars, 2:1 by mass). In both cases, glucose specialist strains were engineered by deleting xylR (encoding the xylose-specific transcriptional activator, XylR) to disable xylose catabolism, whereas xylose specialist strains were engineered by deleting several key components involved with glucose transport and phosphorylation systems (i.e., ptsI, ptsG, galP, glk) while also increasing xylose utilization by introducing specific xylR mutations. Optimization of initial population ratios between complementary sugar specialists proved a key design variable for each pair of strains. In both cases, ∼91% utilization of total sugars was achieved in mineral salt media by simple batch fermentation. High product titer (88 g L-1 D-lactate, 84 g L-1 succinate) and maximum productivity (2.5 g L-1 h-1 D-lactate, 1.3 g L-1 h-1 succinate) and product yield (0.97 g g-total sugar-1 for D-lactate, 0.95 g g-total sugar-1 for succinate) were also achieved.

Electrolyzing lactic acid in situ in fermentation broth to produce pyruvic acid in electrolysis cell

Pyruvic acid is an important chemical in the carboxylate platform. Obstacles for its implementation are the need for high energy in chemical synthesis and additives in fermentation leading to increased production costs. Here, pyruvic acid generation from direct conversion of lactic acid in fermentation broth by electrolysis method is presented. It was found that lactic acid could be converted to pyruvic acid in the electrolysis cell under alkaline conditions. Using 12.53 g/L lactic acid fermentation broth as anolyte, 7.01 g/L pyruvic acid could be produced and productivity to lactic acid was 57.66% at initial pH 11.74 and 5.0 V applied a voltage in the electrolysis cell. Meanwhile, 0.472 mol hydrogen was produced at the cathode. The electric energy efficiency was 76.18%. Lactic acid fermentation is relatively cheap and can be performed on many kinds of wastes and biomasses. The results suggest that pyruvic acid production from direct electrolysis of lactic acid fermentation broth can be economically feasible.

Production of d-Lactate from Avocado Seed Hydrolysates by Metabolically Engineered Escherichia coli JU15

Agroindustry residues can be used to produce valuable chemicals such as lactic acid, which is a primary chemical platform with many industrial applications. Biotechnological processes are the main approach of lactic acid production; however, culture media has an important impact on their costs. As a result, researchers are exploring various methods of production that use residual or waste biomass as raw materials, most of which are rich in lignocellulose. Nevertheless, starch and micronutrients such as those contained in avocado seeds stand out as promising feedstock for the bioprocess as well. In this study, the lactogenic Escherichia coli strain JU15 was evaluated for producing d-lactate using an avocado seed hydrolysate medium in a controlled stirred-tank bioreactor. The highest lactic acid concentration achieved was 37.8 g L−1 using 120 g L−1 as the content of initial reducing sugars. The results showed that d-lactate can be produced from avocado seed, which hydrolysates to 0.52 g L−1 h−1 using the engineered E. coli JU15. This study may serve as a starting point to further develop bioprocesses for producing metabolites using avocado seed hydrolysates.

Lactic acid production from glucose and xylose using the lactogenic Escherichia coli strain JU15: Experiments and techno-economic results

In this work, d-lactic acid production was evaluated from a simulated hydrolysate of corn stover (32 g/L xylose, 42 g/L glucose) with the metabolically engineered Escherichia coli strain JU15. Based on the experimental results, a technical and economic analysis of the entire process was performed using the Aspen Plus software. As a result, it was possible to show that the strain can efficiently produce lactic acid from both sugars, reaching a final concentration of 40 g/L and a yield of 0.6 g lactic acid/g sugars. The process is economically viable at higher scales of 1000 tons/day. The cost distribution is influenced by the scale of the process; on a larger scale, the cost of raw materials represents a higher percentage of total cost than it does on smaller scales. The use of a metabolically engineered strain allows a better use of the sugars obtained from agroindustrial residues.

Improving xylose utilization of defatted rice bran for nisin production by overexpression of a xylose transcriptional regulator in Lactococcus lactis

Present investigation explores the potential of defatted rice bran (DRB) serving as sole carbon source and partial nitrogen source to support Lactococcus lactis growth and nisin production. To retain the nutrients in DRB, especially protein fractions, thermal pretreatment followed by enzymatic hydrolysis without washing step was applied for saccharification. A maximum of 45.64g reducing sugar mainly containing 30.26g glucose and 5.66g xylose from 100g DRB was attained in hydrolysates of DRB (HD). A novel strategy of xylR (xylose transcriptional regulator) overexpression followed by evolutionary engineering was proposed, which significantly increased the capacity of L. lactis to metabolize xylose. Subsequently, RT-PCR results indicated that xylR overexpression stimulated expression of xylose assimilation genes synergistically with exposure to xylose. In HD medium, the highest nisin titer of the engineered strain FEXR was 3824.53IU/mL, which was 1.37 times of that in sucrose medium by the original strain F44.