Greener L-lactic acid production through in situ extractive fermentation by an acid-tolerant Lactobacillus strain
Lactic acid (LA) fermentation requires a neutralizer for a physiologically acceptable range. However, a neutralizer generates a large amount of gypsum, an environmental pollutant. Furthermore, the downstream processing is complicated and expensive, comprising 50–70% of the total cost. We previously developed a Lactobacillus delbrueckii FM1, which can produce undissociated LA without neutralizer. Here, we improved FM1 by adaptive evolution at pH 4.5, which generated Adp FM1 showing an ~ 1.80-fold increase in LA production compared to FM1. The LA production via fed-batch fermentation yielded 36.2 g/L of LA, with a productivity of 0.500 g/L/h. However, cell viability was reduced due to the acidic pH and/or end-product inhibition. Therefore, an in situ LA recovery process using an extractive solvent was employed to maintain cell viability. Adp FM1 produced 49.2 g/L of LA via in situ LA-extractive fed-batch fermentation, which was ~ 1.4-fold higher than that without LA extraction. Adp FM1 provided a total LA productivity of 0.512 g/L/h in 96 h. Among the tested strains, Adp FM1 exhibited the highest H+-ATPase activity and a 415-fold increase in H+-ATPase gene expression compared to the parent strain. These results suggest that the in situ LA extractive fermentation process will ease downstream processing and prove to be a more economical and environmentally friendly option compared to the present fermentation. To our knowledge, this is the first report on the production of undissociated L-LA by Lactobacillus using an in situ recovery process, with high LA production levels and productivity.
Keywordsl-lactic acid Lactobacillus delbrueckii H+-ATPase In situ extractive fermentation
Mamata Singhvi was supported by a fellowship (no. P16100) from the Japan Society for the Promotion of Science (JSPS).
This work was partially supported by a Research Fellow JSPS grant (no. 16F16100) and a grant from JSPS KAKENHI (grant no. JP16F1610).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
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