High-yield actinorhodin production in fed-batch culture by a Streptomyces lividans strain overexpressing the pathway-specific activator gene actll-ORF4.
Streptomyces lividans 1,326 usually does not produce the red/blue colored polyketide actinorhodin in liquid culture even though it carries the entire actinorhodin biosynthesis gene cluster. The bacterium can be forced to produce this secondary metabolite by introducing actII-ORF4, the actinorhodin pathway-specific activator gene from Streptomyces coelicolor, on a multicopy plasmid. The production of actinorhodin by such a strain has been optimized by medium and process manipulations in fed-batch cultures. With high-yield cultivation conditions, 5 g actinorhodin/l are produced during 7 days of cultivation; or approximately 0.1 g actinorhodin/g dry weight (DW)/day in the production phase. The yield in this phase is 0.15 Cmol actinorhodin/Cmol glucose, which is in the range of 25% to 40% of the maximum theoretical yield. This high-level production mineral medium is phosphate limited. In contrast, nitrogen limitation resulted in low-level production of actinorhodin and high production of a-ketoglutaric acid. Ammonium as nitrogen source was superior to nitrate supporting an almost three times higher actinorhodin yield as well as a two times higher specific production rate. The wild-type strain lacking the multicopy plasmid did not produce actinorhodin when cultivated under any of these conditions. This work examines the actinorhodin-producing potential of the strain, as well as the necessity to improve the culture conditions to fully utilize this potential. The overexpression of biosynthetic pathway-specific activator genes seems to be a rational first step in the design of secondary metabolite overproducing strains prior to alteration of primary metabolic pathways for redirection of metabolic fluxes.
Bruheim
P
P
Department of Biotechnology, Norwegian University of Science and Technology, Trondheim.
Sletta
H
H
Bibb
M J
MJ
White
J
J
Levine
D W
DW
D000880:Anthraquinones / Q000378:metabolism*; D000900:Anti-Bacterial Agents / Q000096:biosynthesis*; D003470:Culture Media; D005798:Genes, Bacterial; D009584:Nitrogen / Q000378:metabolism; D010957:Plasmids; D013302:Streptomyces / Q000235:genetics / Q000378:metabolism*; D000095622:Benzoisochromanequinones
D000880:Anthraquinones; D000900:Anti-Bacterial Agents; D003470:Culture Media; D009584:Nitrogen; C013390:actinorhodin; D000095622:Benzoisochromanequinones