Epiphytic cyanobacteria of the seagrass Cymodocea rotundata: Diversity, diel nifH expression and nitrogenase activity


Seagrasses are photoautotrophic, ecologically important components of many globally widespread coastal ecosystems, in which combined nitrogen may limit their production. We examined the biodiversity and diazotrophic capacity of microbial epiphytes associated with the phyllosphere of the seagrass Cymodocea rotundata of the Western Indian Ocean. Light microscopy, 16S rRNA and nifH gene analysis revealed the dominance of cyanobacteria in the epiphytic microbial community. Most phylotypes were related to free-living uncultured benthic cyanobacteria, while some to cyanobacterial endosymbionts of marine diatoms. Novel and potentially diazotrophic species, some of known pantropical distribution, were also discovered. Significant diel nitrogenase activities (acetylene reduction assay) were recorded (up to 358±232nmolC2H4g-1 of seagrass FWh-1). The nifH gene expression patterns showed that heterocystous phylotypes may be the dominant diazotrophs during the day and non-heterocystous at night. These data show that C.rotundata is colonized by diverse diazotrophic cyanobacteria species and suggest that these may be beneficial partners of seagrasses in nitrogen-depleted waters. {\textcopyright} 2013 John Wiley & Sons Ltd and Society for Applied Microbiology.

Environmental Microbiology Reports
Beatriz Díez Moreno
Beatriz Díez Moreno
Associate Professor.
P. Universidad Católica de Chile.
School of Biological Sciences,
Department of Molecular
Genetics and Microbiology,
Santiago, Chile.