Cyanobacteria associated with the phyllosphere of the seagrass Cymodocea rotundata: Diversity, diel nifH expression and nitrogenase activity: Diversity, nifH expression and activity in seagrass
(English)Manuscript (preprint) (Other academic)
Tropical seagrass ecosystems are highly productive and extremely important for sustaining marine life. As seagrasses are associated with complex assemblages of poorly examined epiphytic microbes, we proposed that nitrogen-fixing microorganisms may contribute to the productivity. The morphological and genetic diversity (based on the 16S rRNA and nifH genes) of cyanobacteria and diel variations in nifH gene expression, NifH protein levels and nitrogenase (nitrogen-fixing) activity were examined in the phyllosphere of Cymodocea rotundata of coastal areas of the western Indian Ocean (Tanzania). The 16S rRNA and nifH gene analyses during two consecutive years (October-November, 2007 and 2008) revealed the dominance of a mixed cyanobacterial community. Most sequences represented free-living uncultured cyanobacteria previously reported as benthic in the region, clearly separated from marine planktonic phylotypes, while a few sequences clustered with cyanobacterial symbionts of diatoms. Appreciable, but varying nitrogenase activities were found on a diel as well as monthly basis, with the highest activity encountered, 358 ± 232 and 258 ± 139 nmol C2H4 g-1 h-1, in November. On a diel basis, nifH gene expression coincided with the NifH protein level (Oct 2008) and nitrogenase activity. At day time, nifH gene expression primarily originated from heterocystous phylotypes, while from non-heterocystous filamentous phylotypes (mainly Oscillatoriales) at night. The data suggest that a variety of diazotrophic cyanobacteria are common among the epiphytes on Cymodocea and we propose that these may represent a valuable source of ‘new’ nitrogen in the often oligotrophic, but ecologically important seagrass ecosystems.
Cymodocea rotundata, diazotrophs, diversity, nifH, nitrogenase activity, seagras phyllosphere
Cell and Molecular Biology Botany Ecology
Research subject Marine Ecology; Plant Physiology; Molecular Biology
IdentifiersURN: urn:nbn:se:su:diva-38267OAI: oai:DiVA.org:su-38267DiVA: diva2:308491
ProjectsSida/SAREC Bilateral Marine Science Programme