CHARACTERIZATION OF THE 16S rRNA GENE AND ASSOCIATED 16S‐23S ITS REGION IN MICROCOLEUS (CYANOPHYTA)

Abstract

Boyer, S. L., Johansen, J. R., & Flechtner, V. R.Department of Biology, John Carroll University, University Heights, OH 44118 USAThirty‐one strains of Microcoleus were isolated from diverse arid regions in the western United States. The 16S rRNA gene of all these strains was characterized. The 16S‐23S internal transcribed spacer (ITS) region of many of the strains was sequenced as well. Detailed morphological characterization of strains was carried out on a subset of the strains when molecular data indicated that more than one species was represented. Combined molecular and morphological data reveal the presence of two morphologically similar taxa in our collections, Microcoleus vaginatus (Vaucher) Gomont and Microcoleus steenstrupii Boye‐Petersen. These taxa are sufficiently dissimilar in their 16S rRNA sequence that we suspect the two taxa belong in separate genera. M. vaginatus is phylogenetically closest to Trichodesmium and Arthrospira. M. steenstrupii as defined in this paper includes M. chtonoplastes, and may have closest relatives among several genera in the Phormidiaceae. Configurations within the 16S‐23S ITS regions are variable between the two taxa. M. vaginatus has both tRNAIle and tRNAAla genes in the ITS, just the tRNAIle gene, a fragment of the tRNAIle gene, or no tRNA genes. M. steenstrupii has rRNA operons with both tRNAIle and tRNAAla genes, the tRNAIle gene only, or no tRNA genes in their associated ITS regions. It appears that M. vaginatus shows no subspecific level or population level variation within the combined morphological and molecular characterizations. M. steenstrupii did show considerable genetic variability, and so we suspect that our strains represent several cryptic genospecies. However, the genetic variability was not congruent with geography.