Fine-Scale Temperature-Dependent Shifts in Lactic Acid Bacterial Communities Under Precise Peltier Control

Temperature is a key factor shaping microbial growth and community structure, but the effects of fine-scale temperature differences remain insufficiently characterized. A Peltier-based PCR thermocycler was used as a precise micro-incubation platform (±0.1 °C) to evaluate responses of a commercial lactic acid bacterial starter culture at 1 °C intervals. Starter suspensions were incubated at 3, 4, 5, 36, 37, and 38 °C for 48 h, and species-level community composition was assessed by V3–V4 16S rRNA gene sequencing. Low-temperature conditions produced stable communities, whereas high-temperature conditions induced significant species-level differences among 36–38 °C groups, particularly for Limosilactobacillus reuteri, Limosilactobacillus fermentum, Lactobacillus helveticus, and Lactiplantibacillus plantarum (FDR < 0.01). At 37 °C versus 38 °C, the relative abundance of Limosilactobacillus reuteri increased from 4.56% to 9.31% (a 2.04-fold change), while the relative abundance of Limosilactobacillus fermentum decreased from 64.00% to 48.58%. These results highlight condition-dependent temperature sensitivity in lactic acid bacterial communities, with compositional responses differing markedly between the cold (3–5 °C) and warm (36–38 °C) ranges tested.