Dual-calibration RT-qPCR reveals distinct dnaK1/2/3 and groEL1/2 expression dynamics under heat and acid stress in the sinefungin producer Streptomyces incarnatus.

Streptomyces incarnatus NRRL8089 produces sinefungin, a nucleoside antibiotic whose yield is enhanced under defined environmental stresses. Here, dual-calibration RT-qPCR was used to resolve paralogue-specific expression dynamics of the dnaK and groE chaperone systems under heat and acid stress conditions that increase sinefungin titres. The canonical dnaK1–dnaJ1 and groES–groEL1 operons exhibited moderate induction, whereas monocistronic paralogues (dnaK2, dnaK3 and groEL2) showed markedly higher inducibility, with up to ~ 125-fold increases relative to baseline expression. Promoter analyses revealed conserved inverted repeats and differences in predicted secondary-structure stability, suggesting that promoter architecture contributes to paralogue-specific responsiveness. Structural modelling indicated divergence among DnaK paralogues in regions associated with substrate interaction, whereas GroEL paralogues retained a conserved overall scaffold, consistent with kinetic rather than structural differentiation. Together, these findings indicate that duplicated paralogues are not functionally redundant but are differentially regulated to partition proteostasis capacity under stress. This paralogue-specific regulation may provide a framework linking environmental perturbation to secondary-metabolite production in actinomycetes.