سعید حاجی رضایی

Abstract Streptococcus iniae is known as a most common pathogen in rainbow trout farms, which its pathogenicity depends strongly on temperature. This study was performed to identify the metabolic responses of the Streptococcus iniae at different temperatures (22, 18, 14, 10°C). For this purpose, the samples of the bacteria were cultured at experimental temperatures in three replicates. After metabolite extraction, the metabolites were identified and quantified. The results of PLS-DA analysis showed the main metabolites responsible for the separation of the temperature treatments, including acetone, betaine, inserin, N-acetyl- ornithine, N-acetylglutamine and pyruvate. In addition, the results of analysis of variance showed a significant difference in the content of metabolome between temperature treatments. Bacteria exposed to higher temperatures showed higher concentrations of acetone and betaine than those grown at 10°C. Higher levels of N-acetyl glutamine were observed in bacteria inoculated at temperatures less than 14°C compared to those grown at 18 and 22°C. Anserin concentration increased as the temperature increased, however, a significant decrease occurred at 22°C. The rise of temperature from 10 to 22°C significantly decreased the levels concentrations of N-acetylcysteine, N-acetyl tyrosine, 5-hydroxy- indole- 3- acetate. In conclusion, the results of the present study revealed that temperature alters the metabolome content Streptococcus iniae, which may be linked to its pathogenicity. Temperature may affect fermentation, homeostasis, energy status and amino acid metabolism in the Streptococcus iniae.