Ultrastructure and taxonomic position of two species of the cyanobacterial genus Schizothrix

The cyanobacterial genus Schizothrix is traditionally classified in the special family Schizotrichaceae (order Oscillatoriales) according to the structure of the filaments and thallus: one, two, or more ensheathed and fasciculated trichomes are enveloped by common sheaths. The fine Structure of cells and filaments of two natural populations of typical Schizothrix-species (S. facilis, S lacustris) were investigated in our Study. The ultrastructure of trichomes was found to be similar to the pseudartabaenacean types (thylakoid arrangement, inclusions, cell wall), and indicates the close relationship to this group of simple filamentous cyanobacteria. The special life form, which was considered as the most important phenotypic intergeneric (and interfamilial) differentiating character was proven: Fasciculated trichomes are enveloped by their own sheaths, and form (usually heteropolar) filaments enveloped by mother common sheath. However, in spite of the fact that the ultrastructure and morphology of trichomes were found to be similar to other pseudanabacnacean types, the relationship to Pseudanabaenaceae must await detailed molecular studies to be more completely evaluated. The first molecular results concerning a few Schizothrix-like strains from Antarctica show that most belong to a cluster, which is separated from the other oscillatorian clusters. This could support the genetic basis of the Schizothrix genus.MICROMA

Bacterial succession in a glacier foreland of the high arctic

Succession is defined as changes in biological communities over time. It has been extensively studied in plant communities, but little is known about bacterial succession, in particular in environments such as High Arctic glacier forelands. Bacteria carry out key processes in the development of soil, biogeochemical cycling and facilitating plant colonization. In this study we sampled two roughly parallel chronosequences in the foreland of Midre Love´n glacier on Svalbard, Norway and tested whether any of several factors were associated with changes in the structure of bacterial communities, including time after glacier retreat, horizontal variation caused by the distance between chronosequences and vertical variation at two soil depths. The structures of soil bacterial communities at different locations were compared using terminal restriction fragment length polymorphisms of 16S rRNA genes, and the data were analyzed by sequential analysis of loglinear statistical models. Although no significant differences in community structure were detected between the two chronosequences, statistically significant differences between sampling locations in the surface and mineral soils could be demonstrated even though glacier forelands are patchy and dynamic environments. These findings suggest that bacterial succession occurs in High Arctic glacier forelands but may differ in different soil depths.Ursel M E Schütte, Zaid Abdo, Stephen J Bent, Christopher J Williams, G Maria Schneider, Bjørn Solheim and Larry J Forne

Contrasts between the cryoconite and ice-marginal bacterial communities of Svalbard glaciers

Cryoconite holes are foci of unusually high microbial diversity and activity on glacier surfaces worldwide, comprising melt-holes formed by the darkening of ice by biogenic granular debris. Despite recent studies linking cryoconite microbial community structure to the functionality of cryoconite habitats, little is known of the processes shaping the cryoconite bacterial community. In particular, the assertions that the community is strongly influenced by aeolian transfer of biota from ice-marginal habitats and the potential for cryoconite microbes to inoculate proglacial habitats are poorly quantified despite their longevity in the literature. Therefore, the bacterial community structures of cryoconite holes on three High-Arctic glaciers were compared to bacterial communities in adjacent moraines and tundra using terminal-restriction fragment length polymorphism. Distinct community structures for cryoconite and ice-marginal communities were observed. Only a minority of phylotypes are present in both habitat types, implying that cryoconite habitats comprise distinctive niches for bacterial taxa when compared to ice-marginal habitats. Curiously, phylotype abundance distributions for both cryoconite and ice-marginal sites best fit models relating to succession. Our analyses demonstrate clearly that cryoconites have their own, distinct functional microbial communities despite significant inputs of cells from other habitats