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The DNA base compositions of 176 strains of cyanobacteria were determined by thermal denaturation or by CsCl density gradient centrifugation. A summary of all data now available for this prokaryotic group is presented and the taxonomic and evolutionary implications are discussed. et al. (1967) reported mean DNA base compositions for a limited number of strains of cyanobacteria, representative of many different sub-groups. More extensive data were published by Stanier et al. (1971) for one sub-group, the unicellular cyanobacteria. In this paper we present data for a large number of additional strains, broadly representative of this major prokaryotic taxon. I N T R O D U C T I O N Edelman METHODS Strains.The strains examined are all maintained in the Pasteur Culture Collection (PCC) and havenow been deposited in the American Type Culture Collection (ATCC). They are identified here by both PCC and ATCC strain numbers. Full strain histories, media employed for cultivation and the explanation of generic terminology are given by Rippka et al. (1979). An additional strain (Oscillatoria agardhii) was isolated by Dr F. I. Kappers from the Veluwemeer, The Netherlands, and is now in pure culture as strain PCC 7805.Extraction of DNA. DNA for use in thermal denaturation experiments was purified by a method modified from that of Britten et al. (1968). Harvested cells (approximately 5 g wet wt) were suspended in 20 ml lysis mixture containing 8 M-urea, 1 M-NaClO,, 0.01 M-EDTA (disodium salt) and 1 % (w/v) sodium dodecyl sulphate (SDS) in 0.24 M-phosphate buffer (pH 7-0), disrupted by passage through a French press at 76 MPa, and partially deproteinized by shaking with an equal volume of chloroform/3-methylbutan-l-ol (24: 1, v/v) at room temperature for 30 min. Following centrifugation at 3000 g for 15 min the upper (aqueous) phase, containing DNA, was retained. DNA-grade hydroxyapatite (HAP; 2 g; Bio-Rad) was suspended in 20 ml 0.24 M-phosphate buffer (pH 7.0), boiled for 30 min, centrifuged at low speed, and washed twice with 15 ml MUP (Britten et al., 1968) containing 8 M-urea in 0.24 M-phosphate buffer (pH 7.0), being sedimented after each wash by brief low-speed centrifugation. The deproteinized nucleic acid solution was mixed with the washed HAP and stirred (5 min) to permit binding of DNA. The bound DNA was purified by washing the mixture (by centrifugation) seven times with 15 ml MUP, to remove RNA and residual protein, and then four times with 15 ml 0.014 M-phosphate buffer (pH 7.0), to remove urea. The purified DNA was eluted Present address :

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Aims:  In order to evaluate the part played in biocorrosion by microbial groups other than sulfate‐reducing bacteria (SRB), we characterized the phylogenetic diversity of a corrosive marine biofilm attached to a harbour pile structure as well as to carbon steel surfaces (coupons) immersed in seawater for increasing time periods (1 and 8 months). We thus experimentally checked corroding abilities of defined species mixtures. Methods and Results:  Microbial community analysis was performed using both traditional cultivation techniques and polymerase chain reaction cloning–sequencing of 16S rRNA genes. Community structure of biofilms developing with time on immersed coupons tended to reach after 8 months, a steady state similar to the one observed on a harbour pile structure. Phylogenetic affiliations of isolates and cloned 16S rRNA genes (rrs) indicated that native biofilms (developing after 1‐month immersion) were mainly colonized by γ‐proteobacteria. Among these, Vibrio species were detected in majority with molecular methods while cultivation techniques revealed dominance of Enterobacteriaceae such as Citrobacter, Klebsiella and Proteus species. Conversely, in mature biofilms (8‐month immersion and pile structure), SRB, and to a lesser extent, spirochaetes were dominant. Conclusions:  Corroding activity detection assays confirmed that Enterobacteriaceae (members of the γ‐proteobacteria) were involved in biocorrosion of metallic material in marine conditions. Significance and Impact of the Study:  In marine biofilms, metal corrosion may be initiated by Enterobacteriaceae.

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