L-lactic acid production by Aspergillus brasiliensis overexpressing the heterologous ldha gene from Rhizopus oryzae

Abstract

BackgroundLactic acid is the building block of poly-lactic acid (PLA), a biopolymer that could be set to replace petroleum-based plastics. To make lactic acid production cost-effective, the production process should be carried out at low pH, in low-nutrient media, and with a low-cost carbon source. Yeasts have been engineered to produce high levels of lactic acid at low pH from glucose but not from carbohydrate polymers (e.g. cellulose, hemicellulose, starch). Aspergilli are versatile microbial cell factories able to naturally produce large amounts of organic acids at low pH and to metabolize cheap abundant carbon sources such as plant biomass. However, they have never been used for lactic acid production.ResultsTo investigate the feasibility of lactic acid production with Aspergillus, the NAD-dependent lactate dehydrogenase (LDH) responsible for lactic acid production by Rhizopus oryzae was produced in Aspergillus brasiliensis BRFM103. Among transformants, the best lactic acid producer, A. brasiliensis BRFM1877, integrated 6 ldhA gene copies, and intracellular LDH activity was 9.2 × 10−2 U/mg. At a final pH of 1.6, lactic acid titer reached 13.1 g/L (conversion yield: 26%, w/w) at 138 h in glucose-ammonium medium. This extreme pH drop was subsequently prevented by switching nitrogen source from ammonium sulfate to Na-nitrate, leading to a final pH of 3 and a lactic acid titer of 17.7 g/L (conversion yield: 47%, w/w) at 90 h of culture. Final titer was further improved to 32.2 g/L of lactic acid (conversion yield: 44%, w/w) by adding 20 g/L glucose to the culture medium at 96 h. This strain was ultimately able to produce lactic acid from xylose, arabinose, starch and xylan.ConclusionWe obtained the first Aspergillus strains able to produce large amounts of lactic acid by inserting recombinant ldhA genes from R. oryzae into a wild-type A. brasiliensis strain. pH regulation failed to significantly increase lactic acid production, but switching nitrogen source and changing culture feed enabled a 1.8-fold increase in conversion yields. The strain produced lactic acid from plant biomass. Our findings make A. brasiliensis a strong contender microorganism for low-pH acid production from various complex substrates, especially hemicellulose.

Assessment of the chemical and trace metal composition of dried cassava products from Nigeria

“…Starch was highest in HQCF (65.17%) and lowest in yellow kpokpo gari (53.60%). The low starch content in the Southern Guinea savannah products could be attributed to the starch content of varieties of cassava preferred in the zone and the activities of microorganisms, which might have converted the starch into organic acids (Liaud et al, 2015), resulting in the low starch content. This observation agrees with that of Ray and Sivakumar (2009).…”

Production of Lactic Acid from Seaweed Hydrolysates via Lactic Acid Bacteria Fermentation

“…For example, there has been an increasing demand of lactic acid in the manufacturing of biodegradable polylactic acid materials used as an alternative to petroleum-derived plastics [3]. It was estimated that the worldwide demand for lactic acid would reach 1,000,000 metric tons by the year 2020 [4].…”

“…Moreover, engineered microbial strains have been reported for the efficacious production of lactic acid. Liaud et al [4] indicated that Aspergillus brasiliensis could produce more lactic acid as a result of the insertion of recombinant idhA genes obtained from R. oryzae. Metabolically engineered Saccharomyces cerevisiae and A. oryzae could produce lactic acid more efficiently if a bovine L-lactate dehydrogenase gene (LDH) was integrated into their genome [15,16].…”

Separation and Purification Technologies for Lactic Acid – A Brief Review

“…In this case, gypsum is not produced. Liaud et al (2015) obtained the first Aspergillus strains able to produce large amounts of LA by inserting recombinant ldhA genes from R. oryzae into a wild-type A. brasiliensis strain. The strain produced 32.2 g/L of LA, with a yield of 0.44 g/g from glucose in fed-batch fermentation with a final pH of 3.2 (Abdel-Rahman and Sonomoto 2016).…”

“…The strain produced 32.2 g/L of LA, with a yield of 0.44 g/g from glucose in fed-batch fermentation with a final pH of 3.2 (Abdel-Rahman and Sonomoto 2016). The advantages of these strains are they can grow at low pH and utilize cheap abundant carbon sources such as plant biomass (Liaud et al 2015). Another option to overcome the pH inhibition is the in situ removal of LA to prevent microorganism inhibition using conventional electrodialysis, solvent extraction, adsorption, and membrane bioreactors (Abdel-Rahman and Sonomoto 2016).…”