Downloaded from www.microbiologyresearch.org by IP: 23.22.50.124 On: Sat, 09 Apr 2016 16:43:35 International Journal of Systematic and Evolutionary Microbiology (2000), 50, 1833–1847 Printed in Great Britain Prochlorococcus marinus Chisholm et al. 1992 subsp. pastoris subsp. nov. strain PCC 9511, the first axenic chlorophyll a 2 /b 2 -containing cyanobacterium (Oxyphotobacteria) Rosmarie Rippka, 1 The  re  se Coursin, 1 Wolfgang Hess, 2 Christiane Lichtle  , 3 David J. Scanlan, 4 Katarzyna A. Palinska, 1 Isabelle Iteman, 1 Fre  de  ric Partensky, 5 Jean Houmard 1 † and Michael Herdman 1 Author for correspondence : Rosmarie Rippka. Tel : 33 1 45 68 84 16. Fax: 33 1 40 61 30 42. e-mail : rrippkapasteur.fr 1 Unite  de Physiologie Microbienne (CNRS URA 1129), De  partement de Biochimie et Ge  ne  tique Mole  culaire, Institut Pasteur, 28 Rue du Dr Roux, 75724 Paris Cedex 15, France 2 Department of Biology, Humboldt-University, Chausseestrasse 117, D-10115 Berlin, Germany 3 Laboratoire de Photore  gulation et Dynamique des Membranes Ve  ge  tales, Ecole Normale Supe  rieure (CNRS URA 1810), 46 Rue d’Ulm, 75230 Paris Cedex 05, France 4 Department of Biological Sciences, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK 5 Station Biologique de Roscoff (CNRS UPR 9042) et Universite  Paris VI, BP 74, 29682 Roscoff Cedex, France The formal description of Prochlorococcus marinus Chisholm et al. 1992, 299 was based on the non-axenic nomenclatural type, strain CCMP 1375 T . The purification and properties of the axenic strain PCC 9511, derived from the same primary culture (SARG) as the type species, are reported here. Prochlorococcus PCC 9511 differs from the latter in possessing horseshoe- shaped thylakoids, exhibiting a low chlorophyll b 2 content and lacking phycoerythrin, but shares these phenotypic properties with Prochlorococcus strain CCMP 1378. This relationship was confirmed by 16S rRNA sequence analyses, which clearly demonstrated that the axenic isolate is not co-identic with the nomenclatural type. Strain PCC 9511 has a low mean DNA base composition (32 mol % GMC) and harbours the smallest genome of all known oxyphotobacteria (genome complexity 13 GDa  2 Mbp). Urea and ammonia are the preferred sources of nitrogen for growth, whereas nitrate is not utilized. Several different organic phosphorus compounds efficiently replace phosphate in the culture medium, indicative of ecto-phosphohydrolase activity. In order to distinguish strain PCC 9511 from the nomenclatural type, a new subspecies is proposed, Prochlorococcus marinus Chisholm et al. 1992 subsp. pastoris subsp. nov. Keywords : Prochlorales, cyanobacteria, nitrogen assimilation, phosphohydrolases, 16S rRNA ................................................................................................................................................. This paper is dedicated in gratitude to Professor Germaine Cohen-Bazire on the occasion of her 80th birthday. Together with her late husband, Professor R. Y. Stanier, Germaine gave the members of the Physiologie Microbienne (Institute Pasteur, Paris) generous scientific guidance and spiritual support over many years (1971–1988). † Present address : Laboratoire de Photore  gulation et Dynamique des Membranes Ve  ge  tales, Ecole Normale Supe  rieure (CNRS URA 1810), 46 Rue d’Ulm, 75230 Paris Cedex 05, France. Abbreviations : chl, chlorophyll ; HL, high light ; LL, low light ; PPFD, photosynthetic photon flux density ; PE, phycoerythrin ; T m , temperature mid-point of denaturation. The GenBank accession numbers for the 16S rRNA sequences of PCC 9511, CCMP 1426 and NATL1 are AF180967, AF133833 and AF133834, respect- ively. INTRODUCTION In the last edition of Bergey’s Manual of Systematic Bacteriology, the class Oxyphotobacteria was sub- divided into the Cyanobacteria, whose ordinal rec- ognition still awaits validation, and the order Pro- chlorales Lewin 1977 (Castenholz & Waterbury, 1989). In the light, like algae and plants, these photosynthetic prokaryotes use H  O for the generation of chemical energy and reducing power and liberate molecular O  as a by-product. The demand for cellular carbon is met by CO  fixation. Cyanobacteria synthesize monovinyl chlorophyll a (chl a  ) and harvest light by aid of water- soluble multimeric complexes, the phycobilisomes, composed of biliproteins and linker polypeptides 01355  2000 IUMS 1833