Tolerance of lactic acid bacteria isolated from kefir to heavy metals

E. GERBINO, P. MOBILI, E.E. TYMCZYSZYN, A. GÓMEZ-ZAVAGLIA.

Villa Carlos Paz

Congreso; Sociedad Argentina de Microbiología General (SAMIGE); 2009

SAMIGE

Interaction of different organisms with metal ions can be beneficial or harmful according to the metals concentration to which the organisms are exposed. In this sense, some metals as Zn are trace elements essential to carry out many biological processes but they are toxic at high concentrations. On the other hand, there are metals that are not essential to biological processes and can accumulate into the organisms becoming toxic even at low concentration. According to USA Environmental Protection Agency, Pb, Cd, Zn, Ni and Al are the most toxic heavy metals. These metals can be often found in high concentrations in different aquatic environments or in soils, representing a potential hazard to health. Some bacteria are able to grow in the presence of heavy metals producing at the same time its bioaccumulation or bioadsortion. This capacity transforms these microorganisms in potential bioremediation agents. The objective of this work is to evaluate the capacity of strains of Lactobacillus kefir to grow in the presence of different environmentally relevant metal ions (Pb+2, Cd+2, Al+3, Zn+2 y Ni+2). L. kefir strains CIDCA 8348 (aggregating) and JCM 5818 (non-aggregating) were used. Bacteria were activated in LAPTg broth and then grown in the same medium in the presence of different concentrations of metal ions at 30ºC for 48 h. The bacterial growth was determined by measuring the absorbance at 550 nm. Both L. kefir strains were able to grow in the presence of all the metal ions assayed, although the tolerated levels were different for each one. The tolerated concentrations were: 5 mM Zn+2 and Pb+2 and 1 mM Al+3 and Ni+2. Cd+2 was the most toxic metal. Microorganisms tolerated it in concentrations within the 0.01-0.5 mM range only if they had been previously pre-adapted and further incubated 20-days. Microscopic observation of the Gram stained microorganisms allowed us to detect morphological changes induced by Pb+2 or Al+3. The aggregating strain CIDCA 8348 lost the capacity to agglutinate when grown in presence of Pb and Al. On the other hand, the non-aggregating strain JCM 5818 appeared wider in the presence of these metals. In this work the capacity of two strains of L. kefir to grow in the presence of heavy metals was demonstrated even at high concentrations. This capacity is of great importance for the utilization of these bacteria in processes of bioadsortion or bioremediation.