Identification of lactic acid bacteria in suancai,a traditional Northeastern Chinese fermented food,and salt response of Lactobacillus paracasei LN-1

Suancai is a traditional fermented food that is still popular in northeastern China. Twenty-four bacterial isolates, obtained from 10 samples of naturally fermented suancai broth via screened cultivation, were found to be lactic acid bacteria by physiological and biochemical testing and 16S rDNA-sequence analysis. Among the isolates, 21 rod-shaped strains were classified as Lactobacillus plantarum (eight strains), Lactobacillus sakei (six strains), Lactobacillus curvatus (five strains), or Lactobacillus paracasei (two strains), while three cocci-shaped isolates were identified as Leuconostoc mesenteroides. These lactic acid bacteria are subjected to salt stress during the fermentation of suancai. In the present study, we examined Lactobacillus paracasei LN-1’s display of salt tolerance. To understand the mechanism involved, a proteomics-based, two-dimensional electrophoresis analysis was undertaken to reveal the response of LN-1 during growth in medium with or without NaCl. Out of 23 protein spots that showed differential changes in expression, seven were identified by matrix-assisted laser desorption and ionization time-of-flight mass spectrometry. Further analysis showed that chaperone proteins (Hsp 60 and Hsp 70) and a fatty acid biosynthesis enzyme (Fab G) possibly play important roles in the ability of Lactobacillus paracasei LN-1 to resist salt stress.