DEPRESSION OF STREPTOMYCIN PRODUCTION BY STREPTOMYCES-GRISEUS AT ELEVATED GROWTH TEMPERATURE - STUDIES USING GENE FUSIONS

Streptomyces griseus ATCC 12475 fails to produce streptomycin when gro wn at 34 degrees C or above, although growth is appreciable up to at l east 37 degrees C. This depression of streptomycin production at eleva ted growth temperature is manifest equally in liquid and on solid, and with complex and minimal, media. We report studies with gene fusions of the reporter genes aph or xylE to restriction fragments containing the streptomycin biosynthesis promoter PstrB1. aph constructs were in high, and xylE constructs in low, copy number vectors. Two strB1 promo ter fragments were used, one requiring activation by the pathway-speci fic activator StrR of S. griseus, the other reportedly activator indep endent. PstrB1 expression in the aph constructs in S. griseus and in S . lividans was significantly reduced at 37 degrees C compared to 30 de grees C. Some of this reduction could be explained by lower plasmid co py number at the higher temperature, but strR-dependent expression was clearly temperature controlled. Using the xylE reporter system, the t emperature dependence of PstrB1 expression was confirmed but, surprisi ngly, the strR dependence of the two promoter fragments differed from that observed in the multicopy aph constructs. These data identify a t emperature-dependent promoter which may contribute to the depressive e ffect of elevated growth temperature on streptomycin production.