FEMS Microbiology Letters 17 (1983) 221-225 221 Published by Elsevier Biomedical Press Cyclic adenosine 3',5'-monophosphate in Rhodopseudomonas capsulata R. Guerrero, J. Barbe, E. Montesinos and J. Mas Department of Microbiology and Institute for Fundamental Biology, Autonomous University of Barcelona, Bellaterra (Barcelona), Spain Received 14 October 1982 Accepted 29 October 1982 1. INTRODUCTION Cyclic adenosine 3',5'-monophosphate (cAMP) has been shown to be present in a high number of bacterial species and other microorganisms. In ad- dition to the well-known role of cAMP in the control of initiation of transcription of inducible catabolic operons [1,2], this molecule appears to affect many other functions [3], among them, lysogeny by bacteriophage, replication of plas- mids, a variety of envelope properties including regulation of synthesis of flagella and pili, antibio- tic susceptibility and regulation of different mem- brane-associated enzymes. However, the presence and/or effect of this nucleotide in photosynthetic bacteria has never been reported. For this reason we have studied in the present work the possible existence of cAMP as well as the effect of addi- tions of this compound to cultures of Rhodopseu- domonas capsulata growing both under aerobic (heterotrophic) and phototrophic (anaerobic) con- ditions. The data obtained show that R. capsulata grow- ing aerobically in organic rich medium has an intracellular cAMP concentration of the same order as Escherichia coli and Salmonella typhimurium under the same growth conditions, whereas under phototrophic conditions we have been unable to detect cAMP in R. capsulata. In addition, we also show that cAMP does not control the synthesis of photopigments (bacteriochlorophyll a) in R. capsulata. Although exogenous 5 mM cAMP pro- duces an important decrease in the rate of growth of R. capsulata under phototrophic conditions, the specific concentration of photopigments is not af- fected by the addition of this nucleotide. 2. MATERIAL AND METHODS 2.1. Bacterial strains R. capsulata was isolated from natural samples of Ciso lake (Banyoles, Girona, Spain) [4] and it conformed to the typical biotype of the species. Wild-type S. typhimurium and E. coli were ob- tained from the collection of the Department of Bacteriology of the University of California in Davis, CA. 2.2. Media and growth conditions Aerobic dark growth was carried out at 37°C in LB-rich medium [5]. Photosynthetic growth was performed at 25°C in minimal Pfennig medium [6] supplemented with yeast extract at 0.1% (w/v) and acetate at 0.2% (w/v) (PAE medium). Cultures were grown anaerobically in com- pletely filled screw-cap tubes (20 ml) or bottles (100 ml), using a 1.5% (v/v) inoculum. The cul- tures were exposed to fluorescent illumination from Excel 15 W lamps providing a constant light inten- 0378-1097/83/0000-0000/$03.00 © 1983 Federation of European Microbiological Societies