VANADIUM REQUIREMENT FOR GROWTH ON N2 OR NITRATE AS NITROGEN-SOURCE IN A TUNGSTEN-RESISTANT MUTANT OF THE CYANOBACTERIUM NOSTOC-MUSCORUM

A tungstate-resistant mutant of Nostoc muscorum was isolated with seve rely defective molybdate transport activity. It did not show nitrogena se activity or nitrate reductase activity in the presence or absence o f Mo, but expressed both activities in the presence of vanadyl sulphat e. V-dependent nitrate assimilation was accompanied by V-dependent nit rate reductase mediated nitrate repression of heterocyst formation and nitrogenase in a way Mo-nitrate reductase did in the parent.