Thermotolerance of the immunobiotic Lactobacillus rhamnosus crl 1505: effect of intracellular polyphosphate inclusions

CORREA DEZA M.A. ; GRILLO-PUERTAS M., ; SALVA S., ; MARTOS G.I., ; RAPISARDA V.A., ; CARLA L. GEREZ,; FONT DE VALDEZ G. A

San Miguel deTucumán

Congreso; XII Congreso Argentino de Microbiología General.; 2017

SAMIGE. Tucumán

The immunobiotic Lactobacillus rhamnosus CRL 1505 (CRL-1505) is produced as dehydrated powder by spray drying for subsequent addition into different food matrix to improve transportation and storage. The success for having a high survival rate depends on the thermotolerance of the strain during the drying process.Previous studies put in evidence the accumulation of inorganic polyphosphate (polyP) as cytoplasmic inclusions by the cells when CRL-1505 was grown in a culture medium with high inorganic phosphate. The accumulation of these inclusions, reported in other lactic acid bacteria, depends on the concentration of inorganic phosphate in the culture medium and its presence could be related to osmotic, oxidative and acid stress response mechanisms. The aim of this work was to evaluate the effect of cytoplasmic polyP inclusions on the thermotolerance of the strain CRL-1505. Fermentations were performed at 37°C under free pH in MCM medium with and without addition of inorganic phosphate. A DAPI-based fluorescence technique was used as a measuring of intracellular polyP accumulation. Cells from both culture media were harvested at the stationary phase, suspended in phosphate buffer, and exposed to heat shock (60°C, 5 min). The cell viability before and after heat shock was determined by plate count and flow citometry using the BD? Cell Viability Kit.No significant differences (p ≥ 0.05) in cell growth were observed but the polyP level was lower (ca. 40%) in cells grown without inorganic phosphate addition. The subsequent exposure of these cells to heat shock resulted in a greater loss of cell viability (3.0 ± 0.5 Δlog CFU/mL) compared to those of high polyP content (2.0 ± 0.2 Δlog CFU/mL). These results were confirmed by flow cytometry. The strain CRL-1505 with low polyP content displayed 85.9 % dead cells after heat shock while it was 50.4% in cells with high level of polyP. From these results, we conclude that the thermotolerance of CRL-1505 strain was dependent on the phosphate concentration in the culture media and, consequently, on the levels of polyP in the cells.