Affordable Access

deepdyve-link deepdyve-link
Publisher Website

Improvement of multiple-stress tolerance and lactic acid production in Lactococcus lactis NZ9000 under conditions of thermal stress by heterologous expression of Escherichia coli DnaK.

Authors
Type
Published Article
Journal
Applied and Environmental Microbiology
1098-5336
Publisher
American Society for Microbiology
Publication Date
Volume
76
Issue
13
Pages
4277–4285
Identifiers
DOI: 10.1128/AEM.02878-09
PMID: 20453133
Source
Medline
License
Unknown

Abstract

The effects of nisin-induced dnaK expression in Lactococcus lactis were examined, and this expression was shown to improve stress tolerance and lactic acid fermentation efficiency. Using a nisin-inducible expression system, DnaK proteins from L. lactis (DnaK(Lla)) and Escherichia coli (DnaK(Eco)) were produced in L. lactis NZ9000. In comparison to a strain harboring the empty vector pNZ8048 (designated NZ-Vector) and one expressing dnaK(Lla) (designated NZ-LDnaK), the dnaK(Eco)-expressing strain, named NZ-EDnaK, exhibited more tolerance to heat stress at 40 degrees C in GM17 liquid medium. The cell viability of NZ-Vector was reduced 4.6-fold after 6 h of heat treatment. However, NZ-EDnaK showed 13.5-fold increased viability under these conditions, with a very low concentration of DnaK(Eco) production. Although the heterologous expression of dnaK(Eco) did not effect DnaK(Lla) production, heat treatment increased the DnaK(Lla) level 3.5- and 3.6-fold in NZ-Vector and NZ-EDnaK, respectively. Moreover, NZ-EDnaK showed tolerance to multiple stresses, including 3% NaCl, 5% ethanol, and 0.5% lactic acid (pH 5.47). In CMG medium, the lactate yield and the maximum lactate productivity of NZ-EDnaK were higher than the corresponding values for NZ-Vector at 30 degrees C. Interestingly, at 40 degrees C, these values of NZ-EDnaK were not significantly different from the corresponding values for the control strain at 30 degrees C. Lactate dehydrogenase (LDH) activity was also found to be stable at 40 degrees C in the presence of DnaK(Eco). These findings suggest that the heterologous expression of dnaK(Eco) enhances the quality control of proteins and enzymes, resulting in improved growth and lactic acid fermentation at high temperature.

Statistics

Seen <100 times