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


RESULTS
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%.


CONCLUSIONS
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.
Qin
Jiayang
J
Tianjin Industrial Biotechnology R&D Center, Chinese Academy of Sciences, Tianjin, People's Republic of China.
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
D001407:Bacillus / Q000187:drug effects / Q000201:enzymology / Q000302:isolation & purification*; D019149:Bioreactors; D003470:Culture Media; D005285:Fermentation / Q000187:drug effects; D005947:Glucose / Q000494:pharmacology; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D019344:Lactic Acid / Q000096:biosynthesis*; D009243:NAD / Q000378:metabolism; D009584:Nitrogen / Q000494:pharmacology; D011108:Polymers / Q000378:metabolism*; D013242:Sterilization; D013696:Temperature
D003470:Culture Media; D011108:Polymers; D009243:NAD; D019344:Lactic Acid; D007770:L-Lactate Dehydrogenase; D005947:Glucose; D009584:Nitrogen