FIG 2.

Descriptions of various strains constructed for this work. Shown above are simple representations of modifications made to various regions of the A. vinelandii genome to construct the nitrogen biosensor A. vinelandii AZBB063, which results in minimal growth in the absence of extraneously provided nitrogen and yields a blue phenotype when grown in the presence of X-Gal. Additional constructs A. vinelandii AZBB030 and AZBB035 contain ΔureABC::Str^r, resulting in the accumulation of minor amounts of urea (Fig. 1). A. vinelandii AZBB035 also contains a deregulated nitrogenase by first removing the nifLA genes and then replacing them with nifA behind the nifL promoter, resulting in a rescued nitrogen fixing phenotype. The bottom left shows the urea cycle and urease enzyme (3.5.1.5) as it has been annotated in A. vinelandii. A known gene for arginase (3.5.3.1) has not been identified in A. vinelandii. The bottom right illustration indicates how urea as a terminal product could potentially support the growth of the nitrogen biosensor A. vinelandii AZBB063 if quantities of urea increased to a level sufficient to meet the nitrogen requirements of this strain. Additional metabolites produced by A. vinelandii AZBB030 and AZBB035 following transposon mutagenesis experiments could also substitute for the urea in this representation, as was found in these studies.