GENETIC, MORPHOLOGICAL, AND TOXICOLOGICAL VARIATION AMONG GLOBALLY DISTRIBUTED STRAINS OF NODULARIA (CYANOBACTERIA)

Abstract

Morphological, toxicological, and genetic variation was examined among 19 strains of Nodularia. The strains examined could be morphologically discriminated into four groups corresponding to N. spumigena Mertens, N. sphaerocarpa Bornet et Flahault, and two strains that did not clearly correspond to currently accepted Nodularia species. Genetic variation was examined using nucleotide sequencing of the phycocyanin intergenic spacer region (cpcBA‐IGS) and RAPD‐PCR. The PCR‐RFLP of the cpcBA‐IGS differentiated four genotypes corresponding to the four morphological groups. However, nucleotide sequencing of 598 bp of the 690‐bp fragment showed that one of the three strains corresponding to N. sphaerocarpa (PCC 7804) was genetically divergent from the other two, suggesting that it constitutes a distinct species. Nucleotide variation within the morphospecies groups was limited (<1%), and all 14 Australian strains of N. spumigena possessed identical cpcBA‐IGS sequences. The RAPD‐PCR differentiated the same groups as the cpcBA sequencing and discriminated each of the seven different Australian populations of N. spumigena. Strains from within a bloom appeared genetically identical; however, strains isolated from different blooms could be separated into either a western or a southeastern Australian cluster, with one strain from western Australia showing considerable genetic divergence. The pattern of variation suggests that individual blooms of N. spumigena are clonal but also that Australian N. spumigena populations are genetically distinct from each other. Examination of genetic distance within and between blooms and within and between morphological groups showed clear genetic dicontinuities that, in combination with the cpcBA‐IGS data, suggest that Nodularia contains genetically distinct morphospecies rather than a continuous cline of genetic variation. Furthermore, these morphospecies are genetically variable, exhibiting hierarchical patterns of genetic variation on regional and global scales. Production of the hepatotoxin nodularin was not restricted to one genetic lineage but was distributed across three of the five genotypic groups. A strain of N. spumigena from a nontoxic Australian population was found to fall within the range of genetic variation for other toxic Australian strains and appears to be a unique nontoxic strain that might have arisen by loss of toxin production capacity.

Benthic cyanobacteria of the genus Nodularia are non-toxic, without gas vacuoles, able to glide and genetically more diverse than planktonic Nodularia

“…The delineation of N. spumigena type strains PCC 73104 and PCC 73104/1 here as N. sphaerocarpa is in agreement with their morphological and genetic classification into the N. sphaerocarpa cluster in other studies (Bolch et al, 1999;Lehtimäki et al, 2000;Laamanen et al, 2001;. According to our results, and the fact that N. spumigena was already described in 1886 according to the botanical system, a new bacteriological type strain ought to be assigned to N. spumigena.…”

“…These studies revealed variation among Baltic N. spumigena strains sharing identical 16S rRNA genes. In addition, fingerprinting methods such as RAPD-PCR on Baltic Sea and Australian strains (Bolch et al, 1999), and repetitive extragenic palindromic sequence-and enterobacterial repetitive intergenic consensus-PCR on the Baltic Sea strains (Lehtimäki et al, 2000) yielded a more diverse picture of the N. spumigena cluster than that shown by STRR in this study. The benthic N. sphaerocarpa and N. harveyana were more diverse than the planktonic N. spumigena, as shown by all methods used.…”

“…Planktonic Nodularia strains produce nodularin hepatotoxin and form toxic blooms in brackish and saline water bodies around the world (Sivonen et al, 1989;Harding et al, 1995;Bolch et al, 1999;del Carmen Pérez et al, 1999).…”

Morphometric variability of the genus Nodularia (Cyanobacteria) in Baltic natural communities

“…Aquat Microb Ecol 32: [251][252][253][254][255][256][257][258][259] 2003 brackish environments of the world (Sellner 1997, Bolch et al 1999, Moisander & Pearl 2000, arousing public concern over their potential toxicity. In recent years, long-term data showed increasing trends in bloom quantity and intensity in the Baltic Basin (Finni et al 2001).…”

“…Baltic Nodularia strains have been shown to produce nodularin, a hepatotoxic cyclic pentapeptide which can act as a liver tumor promoter and direct carcinogen (Carmichael et al 1988, Sivonen et al 1989. Extensive blooms of Nodularia are globally distributed in the Morphometric variability of the genus Nodularia (Cyanobacteria) in Baltic natural communities brackish environments of the world (Sellner 1997, Bolch et al 1999, Moisander & Pearl 2000, arousing public concern over their potential toxicity. In recent years, long-term data showed increasing trends in bloom quantity and intensity in the Baltic Basin (Finni et al 2001).…”