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Non-sterilized fermentative production of polymer-grade L-lactic acid by a newly isolated thermophilic strain Bacillus sp. 2-6.

ABSTRACT: The demand for lactic acid has been increasing considerably because of its use as a monomer for the synthesis of polylactic acid (PLA), which is a promising and environment-friendly alternative to plastics derived from petrochemicals. Optically pure L-lactic acid is essential for polymerization of PLA. The high fermentation cost of L-lactic acid is another limitation for PLA polymers to compete with conventional plastics.A Bacillus sp. strain 2-6 for production of L-lactic acid was isolated at 55 degrees C from soil samples. Its thermophilic characteristic made it a good lactic acid producer because optically pure L-lactic acid could be produced by this strain under open condition without sterilization. In 5-liter batch fermentation of Bacillus sp. 2-6, 118.0 g/liter of L-lactic acid with an optical purity of 99.4% was obtained from 121.3 g/liter of glucose. The yield was 97.3% and the average productivity was 4.37 g/liter/h. The maximum L-lactic acid concentration of 182.0 g/liter was obtained from 30-liter fed-batch fermentation with an average productivity of 3.03 g/liter/h and product optical purity of 99.4%.With the newly isolated Bacillus sp. strain 2-6, high concentration of optically pure L-lactic acid could be produced efficiently in open fermentation without sterilization, which would lead to a new cost-effective method for polymer-grade L-lactic acid production from renewable resources.

SUBMITTER: Qin J

PROVIDER: S-EPMC2632756 | biostudies-literature | 2009

REPOSITORIES: biostudies-literature

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Non-sterilized fermentative production of polymer-grade L-lactic acid by a newly isolated thermophilic strain Bacillus sp. 2-6.

Qin Jiayang J Zhao Bo B Wang Xiuwen X Wang Limin L Yu Bo B Ma Yanhe Y Ma Cuiqing C Tang Hongzhi H Sun Jibin J Xu Ping P

PloS one 20090204 2

<h4>Background</h4>The demand for lactic acid has been increasing considerably because of its use as a monomer for the synthesis of polylactic acid (PLA), which is a promising and environment-friendly alternative to plastics derived from petrochemicals. Optically pure L-lactic acid is essential for polymerization of PLA. The high fermentation cost of L-lactic acid is another limitation for PLA polymers to compete with conventional plastics.<h4>Methodology/principal findings</h4>A Bacillus sp. st ...[more]

PMID: 19194504

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Project description:Polylactic acid (PLA) is one important chemical building block that is well known as a biodegradable and a biocompatible plastic. The traditional lactate fermentation processes need CaCO3 as neutralizer to maintain the desired pH, which results in an amount of insoluble CaSO4 waste during the purification process. To overcome such environmental issue, alkaliphilic organisms have the great potential to be used as an organic acid producer under NaOH-neutralizing agent based fermentation. Additionally, high optical purity property in D-lactic acid is now attracting more attention from both scientific and industrial communities because it can improve mechanical properties of PLA by blending L- or D-polymer together. However, the use of low-price nitrogen source for D-lactate fermentation by alkaliphilic organisms combined with NaOH-neutralizing agent based process has not been studied. Therefore, our goal was the demonstrations of newly simplify high-optical-purity D-lactate production by using low-priced peanut meal combined with non-sterile NaOH-neutralizing agent based fermentation.In this study, we developed a process for high-optical-purity D-lactate production using an engineered alkaliphilic Bacillus strain. First, the native L-lactate dehydrogenase gene (ldh) was knocked out, and the D-lactate dehydrogenase gene from Lactobacillus delbrueckii was introduced to construct a D-lactate producer. The key gene responsible for exopolysaccharide biosynthesis (epsD) was subsequently disrupted to increase the yield and simplify the downstream process. Finally, a fed-batch fermentation under non-sterile conditions was conducted using low-priced peanut meal as a nitrogen source and NaOH as a green neutralizer. The D-lactate titer reached 143.99 g/l, with a yield of 96.09 %, an overall productivity of 1.674 g/l/h including with the highest productivity at 16 h of 3.04 g/l/h, which was even higher than that of a sterile fermentation. Moreover, high optical purities (approximately 99.85 %) of D-lactate were obtained under both conditions.Given the use of a cheap nitrogen source and a non-sterile green fermentation process, this study provides a more valuable and favorable fermentation process for future polymer-grade D-lactate production.

Dataset Information

Non-sterilized fermentative production of polymer-grade L-lactic acid by a newly isolated thermophilic strain Bacillus sp. 2-6.

Publications

Non-sterilized fermentative production of polymer-grade L-lactic acid by a newly isolated thermophilic strain Bacillus sp. 2-6.

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