Physiological responses of salt stress and osmoprotection with proline in two strains of lactococci isolated from camel’s milk in Southern Algeria

Abstract

The response of Lactococcus sp. strains isolated from camel milk to salt stress was characterized in M17 medium. We studied the growth of 20 strains in saline M17 medium, M17 medium containing various concentrations of NaCl (1.1, 1.2, 1.4, 1.6 and 1.7 M), and determined the minimal inhibitory concentration (MIC) of NaCl. Among the 20 studied strains, 2 strains presented a considerable growth in the presence of high concentrations of NaCl: The MIC reached 1.7 and 1.6 M for the CHT1 and CHT4 respectively. We studied the growth of 2 strains when proline was added in the medium, the bacteria actively accumulates proline from saline M17 medium. The results confirm the effectiveness of proline as an osmoprotectant. The optimal osmoprotection of both strains was obtained when concentration of proline is 70 mM. Analysis of the cellular content by thin layer chromatography (TLC) showed that internal concentration of proline was higher in cells grown in presence of salt. Among the responses to stress is the production of protein that ensured correct folding of new proteins and prevents aggregation of proteins altered, the SDS PAGE analysis of the proteins contents of two strains CHT1, CHT4, indicated the appearance of high and low molecular mass new proteins.

Keywords: Salt stress, bacterial growth, osmoregulation, proline, stress protein synthesis.