Relationship between nitrogen fixation and nitrate metabolism in the Nodularia strains M1 and M2

Abstract

Abstract. Nitrogen fixation and nitrate-reduction activities were determined in photoautotrophic cultures of two wild-type strains of cyanobacterium Nodularia, spp. M1 and M2. Air could support growth of the two strains at a similar rate in the presence or absence of exogenous nitrate, ammonium and/or bicarbonate. Nitrogenase activity in air-grown cultures varied with culture age, and totally disappeared after 6 h of darkness. Recovery took place upon culture re-illumination. Ammonium at a concentration of 1 mM resulted in the total disappearance of nitrogenase activity and of heterocysts. In contrast, 20 mM nitrate hardly affected nitrogenase activity and heterocyst formation after ten generations. Under the same conditions, either ammonium or nitrate completely abolished nitrogenase activity and heterocyst formation in Anabaena sp. PCC 7119, a typical heterocystous strain. The inefficiency of nitrate in inhibiting nitrogen fixation in Nodularia M1 and M2 seemed to be caused by a low nitrate-reductase activity, and not by an impairment of nitrate-uptake activity. On the other hand, the presence of nitrate was not required for uptake activity to be expressed in Nodularia.

GROWTH, PRIMARY PRODUCTIVITY, AND NITROGEN FIXATION POTENTIAL OF NODULARIA SPP. (CYANOPHYCEAE) IN WATER FROM A SUBTROPICAL ESTUARY IN THE UNITED STATES

“…The differences in N 2 fixation between stations 1 and 3 could have been because of the high NO x -N concentration at station 1 (Table 1) because dissolved inorganic N inhibits nitrogenase of many cyanobacteria. However, in another study, NO 3 Ϫ did not affect N 2 fixation of Nodularia in concentrations up to 20 mM (Sanz-Alférez and del Campo 1994). At station 1, the concentration of NO x was 63.9 M; therefore NO 3 Ϫ inhibition seems unlikely.…”

“…For Nodularia to reach bloom densities, or for akinetes (resting cells of cyanobacteria) to germinate, water temperatures should exceed 16Њ or 17Њ C (Hübel and Hübel 1980, Huber 1985, Cooper and Koch 1984, Lehtimäki et al 1994, 1997, Wasmund 1997. Laboratory studies suggest an optimal salinity of 10 PSU, but growth has been observed over a wide salinity range (0-36 PSU) (Nordin and Stein 1980, Warr et al 1984, Huber 1986, Jones et al 1994, Lehtimäki et al 1994, 1997, Sanz-Alférez and Campo 1994, Heresztyn and Nicholson 1997. Salinity higher than ~20 PSU reduced growth and germination of akinetes of N. spumigena (Huber 1985, Jones et al 1994, Lehtimäki et al 1997.…”

Production of the cyanotoxin nodularin—A multifactorial approach

“…Nitrogen fixation activity was not measured in our studies, but it has previously been shown that changes in nitrate concentrations do not affect nitrogenase activity in Nodularia spp. (Sanz-Alferez and del Campo, 1994, and references therein). Further Vintala and El-Shehawy (2007), showed that the genes involved in heterocyst differentiation and nitrogen fixation in N. spumigena strain AV1 are continuously expressed and not affected by changed concentrations of the nitrogen source.…”

Aminopeptidase and phosphatase activities in basins of Lake Hiidenvesi dominated by cyanobacteria and in laboratory grown Anabaena

“…However, the Anabaena 202 A1 strain has been grown in Z8 media without N since its isolation, and may have been adapted to fix N. In other studies, inorganic N has not affected the growth of N‐fixing species, and unnaturally high concentrations have even reduced it (Rapala et al ., 1993; Lehtimäki et al ., 1997). As in this study, the N‐fixation rate has been highest at the beginning of the exponential growth phase and decreased towards the stationary phase (Huber, 1986; Sanz‐Alférez & del Campo, 1994; Lehtimäki et al ., 1997).…”