Characterization of S-layer proteins produced by lactobacilli isolated from Romanian artisan fermented products

Abstract Aims To characterize S-layer proteins produced by four lactobacilli isolated from Romanian artisan fermented products. Methods and results Four lactobacilli strains have been shown to produce S-layer proteins, both under optimal and stressfull conditions. The presence of S-layer proteins was confirmed by transmission electron microscopy. Removal of S-layer proteins caused a loss of the bacterial resistance to stress conditions and of the autoaggregation ability. Liquid chromatography–mass spectrometry analysis identified peptides corresponding to Slp M sequence in case of Levilactobacillus brevis 403, and peptides corresponding to Slp A sequence in case of Lactobacillus helveticus 34.9. The analysis confirmed molecular masses of ∼51 and 48 kDa, respectively, for the two proteins, and gave information about their pI, of about 9.4–9.6. A specific PCR amplification was obtained for the genome of Lact. helveticus 34.9 with slpA primers, and the amplicon sequence was 95.31% identical to slpA gene. Conclusions Our findings indicate that certain environmental stress conditions can induce the S-layer production, which helps the producing cells to survive under unfavorable conditions.