Effect of Mn2+ and Fe2+ on the Aerobic Growth of a Lactobacillus delbrueckii Strain Isolated from Buffalo Curd

Lactic acid bacteria (LAB) exhibit limited tolerance to oxygen, and metal ions such as Mn²⁺ and Fe²⁺ have been suggested to play roles in oxidative stress responses. This study investigated whether supplementation with Mn²⁺ or Fe²⁺ enhances the aerobic growth of a Lactobacillus delbrueckii strain isolated from traditionally fermented buffalo milk (curd) in Sri Lanka. The isolate was pre-treated with Mn²⁺ or Fe²⁺ under anaerobic conditions and subsequently grown under aerobic conditions. Growth was assessed by measuring acid production (pH reduction) and colony-forming units (CFUs). No statistically significant differences (p>0.05) were observed in either acid production or CFU counts between metal-treated and untreated cultures. These results indicate that supplementation with Mn²⁺ or Fe²⁺ did not confer a measurable growth advantage under the conditions tested. However, as antioxidant mechanisms were not directly assessed, further studies incorporating enzymatic assays and varying metal concentrations are required to clarify the role of these ions in oxidative stress tolerance in LAB.