Assessing the effect of temperature on metabolite production.

Rare actinomycetes are increasingly recognised as a valuable yet underexplored source of bioactive compounds with significant biomedical potential. While it is well established that bacteria have evolved adaptive mechanisms to withstand environmental stressors, such as variations in temperature, salinity or pH, our understanding of how these abiotic parameters influence bacterial metabolism remains limited. This has important implications not only for laboratory cultivation but also for predicting microbial behaviour in natural ecosystems. In this study, we investigated the effect of temperature on specialized metabolite production by the genus . Seven strains isolated from marine sediments in three regions - Scotland, the sub-Arctic and Antarctica - were cultured at 20, 25 and 30 °C. Strain-specific growth curves were generated to normalize metabolite extraction at equivalent growth stages, resulting in a total of 54 metabolite extracts. Liquid chromatography-high-resolution mass spectrometry analysis combined with molecular networking revealed that lower cultivation temperatures reduced bacterial biomass and delayed the onset of the stationary phase, and strain KRD197 exhibited temperature shifts in metabolism that were associated with alterations in carbohydrate and fatty acid metabolism, potentially linked to osmotic regulation and cell membrane adaptation. These findings highlight the impact of temperature on -specialized metabolism and support the potential of rare actinomycetes from extreme environments for expanding chemistry from these understudied genera.