The marine cyanobacterium Synechococcus sp. WH7805 requires urease (urea amidohydrolase, EC 3.5.1.5) to utilize urea as a nitrogen source: molecular-genetic and biochemical analysis of the enzyme

Cyanobacteria assigned to the genus Synechococcus are an important componen t of oligotrophic marine ecosystems, where their growth may be constrained by low availability of fixed nitrogen. Urea appears to be a major nitrogen resource in the sea, but little molecular information exists about its util ization by marine organisms, including Synechococcus. Oligonucleotide prime rs were used to amplify a conserved fragment of the urease (urea amidohydro lase, EC 3.5.1.5) coding region from cyanobacteria. A 5.7 kbp region of the genome of the unicellular marine cyanobacterium Synechococcus sp. strain W H7805 was then cloned, and genes encoding three urease structural subunits and four urease accessory proteins were sequenced and identified by homolog y. The WH7805 urease had a predicted subunit composition typical of bacteri al ureases, but the organization of the WH7805 urease genes was unique. Bio chemical characteristics of the WH7805 urease enzyme were consistent with t he predictions of the sequence data. Physiological data and sequence analys is both suggested that the urease operon may be nitrogen-regulated by the n tcA system in WH7805. Inactivation of the large subunit of urease, ureC, pr evented WH7805 and Synechococcus WH8102 from growing on urea, demonstrating that the urease genes cloned are essential to the ability of these cyanoba cteria to utilize urea as a nitrogen source.