Nitrogenase gene expression in the Chesapeake Bay Estuary

Area of Science:

• Estuarine microbiology
• Molecular ecology
• Nitrogen cycling

Background:

• Chesapeake Bay exhibits significant salinity and nutrient gradients.
• Previous research indicated high diversity and specific distributions of nitrogenase (nifH) genes in the estuary.
• Limited information existed on the active expression of nifH genes and the specific organisms responsible in this environment.

Purpose of the Study:

• To investigate the expression of nitrogenase (nifH) genes in the Chesapeake Bay.
• To identify the specific phylotypes of nitrogen-fixing microorganisms actively expressing nifH genes.
• To determine the spatial distribution and ecological significance of active nitrogen fixation.

Main Methods:

• Analysis of nifH gene expression using molecular techniques.
• Phylogenetic analysis to identify detected nifH gene sequences.
• Spatial sampling across the Chesapeake Bay to map gene expression patterns.

Main Results:

• Only two nifH phylotypes were detected expressing genes, both related to cyanobacteria.
• One phylotype, similar to Anabaena cylindrica, was found at the estuary's head.
• Another phylotype, related to Group A unicellular cyanobacteria, was detected near the mouth, a novel finding for estuarine environments.

Conclusions:

• This study provides the first evidence of active nifH gene expression in the Chesapeake Bay.
• Distinct spatial expression patterns were observed for the two detected cyanobacterial phylotypes.
• Results suggest diazotrophic unicellular cyanobacteria are more broadly distributed and active in estuaries than previously recognized.