Synthetic gene clusters

A bacterial nitrogen reduction expression system comprising nucleic acids encoding:

• at least one operon comprising a plurality of coding sequences for a set of polypeptides encoded by genes collectively associated with nitrogen fixation within a cell;
• a heterologous promoter region that directs expression of the at least one operon;
• and
• a transcriptional controller coding sequence that encodes a protein that directs expression of the at least one operon of the expression system, wherein the protein binds directly or indirectly to the heterologous promoter region.