Metagenomics reveals differences in spore-forming bacterial diversity in raw milk in different regions and seasons in China

The spore-forming bacteria in the dairy industry are notable for their spores resilience and capacity to survive heating processes, allowing them to germinate and enter the vegetative stage, potentially leading to spoilage of the milk. Additionally, these spores can form biofilms, becoming a persistent source of contamination in processing environments. In this study, we collected a total of 165 raw milk from six different parts in China in spring, summer, autumn, and winter, respectively. Metagenomics sequencing method was used to explore and compare the differences in spore-forming bacterial composition and diversity in raw milk samples. Among these samples, four genera and 207 species of spore-forming bacteria were identified, with the genus Bacillus and the species Paenibacillus darwinianus dominant. Seasonal variations had a greater impact on the composition and abundance of spore-forming bacteria in raw milk than regional differences. Notable, raw milk samples collected during the spring and summer exhibited a higher number of unique spore-forming bacterial species compared to those collected in other seasons. Moreover, different regions and seasons have their own dominant bacteria. Metabolism of cofactors and vitamins, energy metabolism, carbohydrate metabolism, and amino acid metabolism were the main metabolic pathways. Hence, specific strategies need to be adopted to prevent and control spore-forming bacteria in raw milk in different regions and seasons.