N2 fixation rates and associated diversity (nifH) of microbialite and mat-forming consortia from different aquatic environments in Mexico

The present study describes patterns and rates of N-2 fixation and associated diversity (based on the nifH gene) of microbialite and mat-forming bacterial consortia from different aquatic environments in Mexico. All of the communities shared a diurnal pattern of N-2 fixation with peak activity during the day while showing a unique genetic composition. Our study suggests the importance of heterocystous cyanobacteria as the main diazotrophic organisms, although nifH sequences were also affiliated to Oscillatoriales, Chroococcales, and several Proteobacteria. Genetic composition did not relate to the environmental variables analysed, although rates of nitrogenase activity associated to microbial C and N explained 11% of the variation among consortia.