Nitrogen Cycling in Microbial Mats and Stromatolites

With funding from NASA's Exobiology Program, in collaboration with Jon Zehr's lab at the University of California, Santa Cruz, we are studying nitrogen cycling in microbial mats in Baja California.

Nitrogen is obtained by microbial mats from combined nitrogen (nitrate, ammonium and dissolved organic nitrogen) in the water, and through nitrogen fixation, in which atmospheric dinitrogen is fixed into a biologically useful form. In Baja, salt is being produced by the company Exportadora de Sal by concentrating lagoon water through a series of ponds. Microbial mats grow in ponds that have salinities intermediate between the lagoon water and the ponds where sodium chloride (salt) comes out of solution. By measuring the nutrient concentrations in the ponds where mats occur, and where mats do not, we can assess the impact of these communities on the nutrients in the ponds. In addition, we do experiments with the mats to determine the rates at which nutrients are taken up, and transformed from one form to another (and back again).

Nitrogen fixation is a very important process in some Baja mats. Using molecular methods, we are identifying nitrogen fixing micororganisms from the Baja mats using their nitrogen fixing genes (nifH). We are also looking at which organisms are expressing those genes, and at how important nitrogen fixation is in supporting mat growth.