"INFLUENCE OF OSMOTIC STRESS ON THE PROFILE AND GENE EXPRESSION OF SURFACE LAYER PROTEINS IN LACTOBACILLUS ACIDOPHILUS ATCC 4356"

P. OJEDA; M. PRADO ACOSTA,; S. M RUZAL; P. M. WAEHNER,; L. MALONE; M. C. ALLIEVI,; J. FINA MARTIN; C. SÁNCHEZ RIVAS,; M. M. PALOMINO

San Miguel de Tucumán

Simposio; V Simposio Internacional de Bacterias Lácticas; 2016

CERELA

Surface layer (S-layer) proteins are present in some Lactobacillus species that are normal inhabitants of the oral and genital cavities and the gastrointestinal tract (GIT) of humans and animals and that are generally recognized as safe (GRAS). We have previously shown that the S-layer SlpA of Lactobacillus acidophilus has antibacterial and antiviral functions. In our laboratory, we have studied the response to osmotic stress of several gram-positive strains and species and observed several cell envelope modifications when Bacillus or Lactobacillus strains were exposed to high salt conditions. Growth under high salt conditions is of industrial importance, because NaCl concentration is 0.3 M in the gut when lactobacilli are used as a probiotic and about 0.35 M (2 % w/v) and up to 0.6 M (about 3.5 % w/v) in cheeses.In this work, we studied the influence of the growth phase and osmotic stress on the profile and gene expression of S-layer proteins in the adaptation of L. acidophilus ATCC 4356 to the osmotic stress generated by high salt. The amounts of the predominant and the auxiliary S-layer proteins SlpA and SlpX were strongly influenced by the growth phase and high salt conditions (0.6M NaCl) verified by SDS-PAGE and western blot. Changes in gene expression were also observed as the mRNAs of the slpA and slpX genes increased related to the growth phase and presence of high salt when quantified by qPCR. A growth stage-dependent modification on the S-layer protein profile in response to NaCl was observed: while in control conditions the auxiliary SlpX protein represented less than 10 % of the total S-layer protein, in high salt conditions it increased to almost 40 % in the stationary phase. The increase in S-layer protein synthesis in the stress condition could be a consequence of or a way to counteract the fragility of the cell wall, since a decrease in the cell-wall thickness and envelope components (peptidoglycan layer and lipoteichoic acid content) was observed in L. acidophilus when compared to a non-S-layer-producing species such as L. casei. Also, the stationary phase and growth in high salt medium resulted in increased release of S-layer proteins to the supernatant medium. Overall, these findings suggest that pre-growth in high salt conditions would result in an advantage for the probiotic nature of L. acidophilus ATCC 4356 as the increased amount and release of the S-layer might be appropriate for its antimicrobial capacity.