Open AccessEpilithic Cyanobacterial Communities of a Marine Tropical Beach Rock (Heron Island, Great Barrier Reef): Diversity and Diazotrophy
Author(s) -
Beatriz Dı́ez,
Karolina Bauer,
Birgitta Bergman
Publication year - 2007
Publication title -
applied and environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.552
H-Index - 324
eISSN - 1070-6291
pISSN - 0099-2240
DOI - 10.1128/aem.02067-06
Subject(s) - biology , phylotype , cyanobacteria , gammaproteobacteria , temperature gradient gel electrophoresis , botany , ecology , lyngbya , nitrogenase , flavobacterium , nitrogen fixation , 16s ribosomal rna , bacteria , paleontology , pseudomonas
The diversity and nitrogenase activity of epilithic marine microbes in a Holocene beach rock (Heron Island, Great Barrier Reef, Australia) with a proposed biological calcification “microbialite” origin were examined. Partial 16S rRNA gene sequences from the dominant mat (a coherent and layered pink-pigmented community spread over the beach rock) and biofilms (nonstratified, differently pigmented microbial communities of small shallow depressions) were retrieved using denaturing gradient gel electrophoresis (DGGE), and a clone library was retrieved from the dominant mat. The 16S rRNA gene sequences and morphological analyses revealed heterogeneity in the cyanobacterial distribution patterns. The nonheterocystous filamentous genusBlennothrix sp., phylogenetically related toLyngbya , dominated the mat together with unidentified nonheterocystous filaments of members of thePseudanabaenaceae and the unicellular genusChroococcidiopsis . The dominance and three-dimensional intertwined distribution of these organisms were confirmed by nonintrusive scanning microscopy. In contrast, the less pronounced biofilms were dominated by the heterocystous cyanobacterial genusCalothrix , two unicellularEntophysalis morphotypes,Lyngbya spp., and members of thePseudanabaenaceae family.Cytophaga -Flavobacterium -Bacteroides andAlphaproteobacteria phylotypes were also retrieved from the beach rock. The microbial diversity of the dominant mat was accompanied by high nocturnal nitrogenase activities (as determined by in situ acetylene reduction assays). A new DGGEnifH gene optimization approach for cyanobacterial nitrogen fixers showed that the sequences retrieved from the dominant mat were related to nonheterocystous uncultured cyanobacterial phylotypes, only distantly related to sequences of nitrogen-fixing cultured cyanobacteria. These data stress the occurrence and importance of nonheterocystous epilithic cyanobacteria, and it is hypothesized that such epilithic cyanobacteria are the principal nitrogen fixers of the Heron Island beach rock.