Research on resistivities of Lactobacillus delbrueckii ssp. bulgaricus ve Streptococcus thermophilus strains against heavy metal and on their exopolysaccharide (EPS) productions

In this study, it is aimed to determine the cellular developments and EPS productions of the Lactobacıllus delbrueckii ssp. bulgaricus ATCC 11842 and Streptococcus thermophilus ATCC 14425 strains which are used as the starter culture in the diary industry, and impacts of the various heavy metal salts [Co(NO3)2.6H2O, ZnSO4.7H2O, Cr(NO3)3.9H2O, Pb(CH3COO)2.3H2O, NiCl2, K2Cr2O7, CuSO4.5H2O, AgNO3, CdCl2] on the total protein amount. The minimal inhibition concentration (MIC) levels of the metal salts against the strains are determined by using the different concentrations between (0,005 - 80 mM). As those values in the streptococcus thermophilus ATCC 14425 strain are determined as 1 mM for Co(NO3)2.6H2O; 0,1 mM for ZnSO4.7H2O; 10 mM for Cr(NO3)3.9H2O; 1 mM for Pb(CH3COO)2.3H2O; 0,1 mM for NiCl2; 1 mM for K2Cr2O7; 2,5 mM for CuSO4.5H2O; 0,5 mM for AgNO3; 0,005 mM for CdCl2 respectively; they are determined as 10 mM for Co(NO3)2.6H2O; 5 mM for ZnSO4.7H2O; 10 mM for Cr(NO3)3.9H2O; 0,5 mM for Pb(CH3COO)2.3H2O; 10 mM for NiCl2; 0,5 mM for K2Cr2O7; 5 mM for CuSO4.5H2O; 0,5 mM for AgNO3; and 0.005 mM for CdCl2 in the Lactobacillus delbrueckii ssp. bulgaricus ATCC 11842 strain. In general, it is observed that the metal resistance of Lactobacillus delbrueckii ssp. vii bulgaricus ATCC 11842 strain is higher than of the Streptococcus thermophilus ATCC 14425 strain. As the highest EPS production (505 mg/L) is determined in the Lactobacillus delbrueckii ssp bulgaricus ATCC 11842 strain (0,005 mM) in the CuSO4.5H2O concentration, it is determined that the highest EPS (255 mg/L) is produced in the Streptococcus thermophilus ATCC 14425 strain (0,005 mM) in the NiCl2 concentration EPS. Those values are found as 127 and 157 (mg/L) in the controlled feeding environment respectively. As the highest protein production (0,052 mg/mL) is determined in the Lactobacillus delbrueckii ssp. bulgaricus ATCC 11842 strain (0,005 mM) in the Cr(NO3)3.9H2O concentration, the protein amount in the Streptococcus thermophilus ATCC 14425 strain (0,005 mM) is determined as (0,058 mg/mL) in the Co(NO3)2.6H2O concentration. In the study, it is found that EPS production and protein amounts of the bacteria decrease depending on the increasing of heavy metal concentration. Keywords : Lactic acid bacteria, Heavy Metal, Exopolysaccharide, Protein.