Transport and Assimilation of Nitrogen by Stichococcus bacillaris Grown in the Presence of Methionine Sulfoximine

Abstract

Stichococcus bacillaris Naeg., a green soil alga, can grow in the presence of methionine sulfoximine (MSX) Recently, using MSX2 as a specific inhibitor of GS, we have demonstrated the ability of Chlorella autotrophica to maintain a normal rate ofNH44 assimilation via the NADPH-GDH pathway (1,2). This contrasts with the report of a direct inhibition of NH4+ transport system by MSX in Anabaenaflos-aquae (12). It has recently been pointed out (3) that methylammonium is metabolized to methylglutamine in cyanobacteria. Therefore, the observed inhibition of methylammonium uptake appears to be attributable to MSX inhibition of methylammonium assimilation via GS. The metabolism of methylammonium in cyanobacteria and bacteria (7) raises serious questions about its usefulness as an analog for NH4+ transport in prokaryotes. Eukaryotic microalgae do not appear to be able to metabolize methylammonium (13,14). We have recently studied the transport of nitrogenous compounds by the green alga Stichococcus bacillaris. As this alga contains NADPH-GDH with sufficiently high affinity for ammonium (6), it provides a useful system to investigate the effect of MSX on the transport of inorganic nitrogen without the undesirable effects of a buildup of an internal NH4+ pool. MATERIAIS AND METHODSOrganism and Culture Conditions. Stichococcus bacillaris (UTEX No. 314) was grown axenically as described (5). The culture nitrogen source was either 2 mM NaNO3 or 2 mM NH4CI. Preparation of MSX-containing media was as described (1, 2).Enzyme Activities. Preparation of cell-free extracts and determination of synthetase activities of GS and amination reactions of NAD(P)H-GDH were as described (1, 2).

ESTABLISHMENT OF MINIMAL AND MAXIMAL TRANSCRIPT LEVELS FOR NITRATE TRANSPORTER GENES FOR DETECTING NITROGEN DEFICIENCY IN THE MARINE PHYTOPLANKTON ISOCHRYSIS GALBANA (PRYMNESIOPHYCEAE) AND THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE)1

“…2005), eukaryotic algae can also assimilate ammonium through other pathways. According to results obtained in two green algae, Stichococcus bacillaris and Chlorella autotrophica , when GS was blocked by MSX, ammonium could be assimilated via the glutamate dehydrogenase (GDH) pathway (Ahmad and Hellebust 1985a,b). It remains unclear if the same mechanism occurs in diatoms, but MSX is apparently unsuitable as a universal chemical to generate maximal Nrt2 transcript levels in eukaryotic algae.…”

Phosphinothricin resistance in Aspergillus niger and its utility as a selectable transformation marker

“…Increased NADP-GDH expression can provide additional mechanisms for PPT resistance by raising the intracellular glutamate levels (Ahmad et al, 1995) and/or by increasing the rate of ammonium assimilation (Ahmad and Hellebust, 1985;Nolte et al, 2004). All the enzyme specific activities are presented as nmol min À1 mg protein À1 .…”

Bioprocessing of Stichococcus bacillaris strain siva2011

“…In addition, this alga has adapted to low temperatures and is found in ice-free areas of Antarctica [ 13 ]. Moreover, it also contains high NADPH-GDH activity [ 14 ], low CO 2 resistance [ 15 ] and has unique microtubule organization in prophase [ 16 ]. The NADPH-GDH plays an important role in photosynthetic microalgae, which is associated with photoregulation and the incorporation of ammonia into amino acids.…”