Genetic Variance in the Composition of Two Functional Groups (Diazotrophs and Cyanobacteria) from a Hypersaline Microbial Mat

Abstract

Examination of variation in ecological communities can lead to an understanding of the forces that structure communities, the consequences of change at the ecosystem level, and the relevant scales involved. This study details spatial and seasonal variability in the composition of nitrogen-fixing and cyanobacterial (i.e., oxygenic photosynthetic) functional groups of a benthic, hypersaline microbial mat from Salt Pond, San Salvador Island, Bahamas. This system shows extreme annual variability in the salinity of the overlying water and the extent of water coverage. Analysis of molecular variance and F ST tests of genetic differentiation of nifH and cyanobacterial 16S rRNA gene clone libraries allowed for changes at multiple taxonomic levels (i.e., above, below, and at the species level) to inform the conclusions regarding these functional groups. Composition of the nitrogen-fixing community showed significant seasonal changes related to salinity, while cyanobacterial composition showed no consistent seasonal pattern. Both functional groups exhibited significant spatial variation, changing with depth in the mat and horizontally with distance from the shoreline. The patterns of change suggest that cyanobacterial composition was more insensitive to water stress, and consequently, cyanobacteria dominated the nitrogen-fixing community during dry months but gave way to a more diverse community of diazotrophs in wet months. This seasonal pattern may allow the mat community to respond quickly to water-freshening events after prolonged dry conditions (system recovery) and maintain ecosystem function in the face of disturbance during the wet season (system resilience).

Diversity of Ammonia-Oxidizing Archaea and Bacteria in the Sediments of a Hypernutrified Subtropical Estuary: Bahía del Tóbari, Mexico

“…These observed variations in community composition were statistically compared using ͐-Libshuff (41), an approach that has been applied to 16S rRNA gene libraries (11) and was recently shown to be effective for comparison of N-cycling microbial communities based on functional genes, including nitrous oxide reductase (nosZ), nitrite reductase (nirS and nirK), and nitrogenase (nifH) gene libraries (19,37,51). ͐-Libshuff compares the coverage of clone libraries to a hypothetical coverage generated from multiple randomizations of sequences and calculates a population P value.…”

Epilithic Cyanobacterial Communities of a Marine Tropical Beach Rock (Heron Island, Great Barrier Reef): Diversity and Diazotrophy

“…The dominant stratified microbial community on the beach rock, referred to here as the dominant mat, was investigated further by constructing a 16S rRNA genetic library and by using scanning microscopy (confocal laser scanning microscopy [CLSM] and scanning electron microscopy [SEM]) to obtain the three-dimensional distribution of the microbial community. As beach rocks are often hostile and nutrient-poor environments (54), we expected the presence of nitrogen fixers. This was investigated by cyanobacterial nifH gene characterization and diurnal acetylene reduction (nitrogenase activity) assays in order to estimate the potential ecophysiological importance.…”

Evaporite Microbial Films, Mats, Microbialites and Stromatolites

“…The current chemical and detrital sedimentary deposits within the lake are usually less than one meter thick and composed of finely laminated organic-rich carbonate mud and evaporite similar to Salt Pond that is adjacent to Storrs Lake (Yannarell et al 2007). The nitrogen-fixing microbial community in Salt Pond has been shown to change spatially with seasonal salinity changes (Yannarell et al 2006). …”