Uptake and assimilation of nitrite in the acidophilic red alga Cyanidium caldarium Geitler

Abstract

S U M M A R YThe acidophilic red alga, Cyanidium caldarium Geitler, could use nitrite as a nitrogen source for growth, although this compound was very toxic in acidic media. Growth could be sustained when nitrite was added continuously at il rate lower than the maximum rate of nitrite assimilation for the culture. Nitrite assimilation was derepressed in cells growing on nitrate or nitrite, under nitrogen liinitation and by nitrogen starvation. Ammonium-grown cells showed a limited capacity for nitrite reduction in the light, even if nitrite reductase was not detectable in cell extracts. In acidic media nitrite was taken up mainly through HNO^ influx. Nitrite assimilation, in vivo, was restricted by a saturable step under conditions in which nitrite uptake was not limiting. The pH of the cell suspension affected nitrite assimilation by changing the Ki over the pH range tested but not the I-^,,,,^. The K^_ was inversely proportional to the concentration of H* in the medium. The apparent AT, , value for nitrite of nitrite reductase, in vitro, and its expected apparent K^^^ value, in vivo, estimated from the K^ of nitrite assimilation, suggested that the activity of this enzyme may not be the limiting step of nitrite assiinilation.

Nitrite assimilation by the yeast Candida nitratophila

“…Se\'eral yeasts are able to assimilate tiitrate as a nitrogen source, and the physiology and enzytnology of nitrate assimilation of some species, in genera such as Candida, Hansenula and Rhodotorula, is well understood (see reviews by Hipkin, 1989Hipkin, , 1990. Nitrite, an intermediate in the reductive assimilation of nitratc-nitrogen into ammonium-nitrogen, is also a potential source of nitrogen for these organisms and appears to play an important role in the regulation of nitrate assimilation (Gonzalez et al, 1994). However, although nitrite uptake has been studied in cyanobacteria and algae (Cresswell &: Syrett, 1982;Flores, Herrero & Guerrero.…”