Adenosine kinase (ADK) catalyses phosphorylation of adenosine (Ado) and generates adenosine monophosphate (AMP). ADK gene (adksli, an ortholog of SCO2158) was disrupted in Streptomyces lividans by single crossover-mediated vector integration. The adksli disruption mutant (Delta adk(Sli)) was devoid of sporulation and a plasmid copy of adksli restored sporulation ability in Delta adk(Sli), thus indicating that loss of adksli abolishes sporulation in S. lividans. Ado supplementation strongly suppressed sporulation ability in S. lividans wildtype (wt), supporting that disruption of adksli resulted in Ado accumulation, which in turn suppressed sporulation. Cell-free experiments demonstrated that Delta adk(Sli) lacked ADK activity and in vitro characterization confirms that adksli encodes ADK. The intracellular level of Ado was highly elevated while the AMP level was significantly reduced after loss of adksli while Delta adk(Sli) displayed no significant derivation from wt in the levels of S-adenosylhomocysteine (SAH) and S-adenosylmethionine (SAM). Notably, Ado supplementation to wt lowered AMP content, albeit not to the level of Delta adk(Sli), implying that the reduction of AMP level is partially forced by Ado accumulation in Delta adk(Sli). In Delta adk(sli), actinorhodin (ACT) production was suppressed and undecylprodigiosin (RED) production was dramatically enhanced; however, Ado supplementation failed to exert this differential control. A promoter-probe assay verified repression of actII-orf4 and induction of redD in Delta adk(Sli), substantiating that unknown metabolic shift(s) of ADK-deficiency evokes differential genetic control on secondary metabolism in S. lividans. The present study is the first report revealing the suppressive role of Ado in Streptomyces development and the differential regulatory function of ADK activity in Streptomyces secondary metabolism, although the underlying mechanism has yet to be elucidated. (C) 2007 Elsevier Inc. All rights reserved.