MadSci Network: Cell Biology |
Chlorella, an algae, like most plants requires nitrogen for growth. It can use nitrogen in the form of ammonia/ammonium directly. However, it is not always available in that form. Since we live in an oxygen atmosphere, nitrogen is usually available in the form of nitrate, which must be reduced to ammonia or a similar compound for use in synthesizing amino acids and thus proteins, among other uses. Reduction is by an enzyme called nitrate reductase, which in most cells is expressed only when nitrate is present. In the presence of ammonia, the algae will grow well. In the presence of ammonia plus nitrate, the organism will use ammonia preferentially, and then, if the ammonia runs out, will induce nitrate reductase and utilize nitrate. In the absence of ammonia and presence of nitrate, the organism will induce the reductase. Once this is done, it will begin to actively grow.Below are abstracts of some papers/reviews that may be of further help.= Enzyme Microb Technol 2000 Aug 1;27(3-5):312-318Heterotrophic production of biomass and lutein by Chlorella protothecoides onvarious nitrogen sources.Shi X, Zhang X, Chen FKey Laboratory of Microbiology of Agricultural Ministry, Huazhong AgriculturalUniversity, 430070, Wuhan, China The effects of nitrate, ammonium, and urea as nitrogen sources on the heterotrophic growth of Chlorella protothecoides were investigated using flaskcultures. No appreciable inhibitory effect on the algal growth was observed overa nitrogen concentration range of 0.85-1.7 g l(-)(1). In contrast, differencesin specific growth rate and biomass production were found among the cultureswith the various nitrogen compounds. The influence of different nitrogen sourcesat a concentration equivalent to 1.7 g l(-)(1) nitrogen on the heterotrophicproduction of biomass and lutein by C. protothecoides was investigated using theculture medium containing 40 g l(-)(1) glucose as the sole carbon and energysource in fermentors. The maximum biomass concentrations in the three cultureswith nitrate, ammonium, and urea were 18.4, 18.9, and 19.6 g l(- )(1) dry cells,respectively. The maximum lutein yields in these cultures were between 68.42 and83.81 mg l(-)(1). The highest yields of both biomass and lutein were achieved inthe culture with urea. It was therefore concluded that urea was the bestnitrogen source for the production of biomass and lutein. Based on theexperimental results, a group of kinetic models describing cell growth, luteinproduction, and glucose and nitrogen consumption were proposed and asatisfactory fit was found between the experimental results and predictedvalues. Dynamic analysis of models demonstrated that enhancing initial nitrogenconcentration in fermentor cultures, which correspondingly enhances cell growthand lutein formation, may shorten the fermentation cycle by 25-46%. Plant Cell Physiol 2000 Apr;41(4):534-40Oxygen uptake, acidification of medium and nitrate uptake induced by blue lightin nitrate-starved Chlorella cells.Kamiya ALaboratory of Chemistry, Faculty of Pharmaceutical Sciences, Teikyo University,Sagamiko, Kanagawa, Japan. Blue light-induced oxygen uptake of the colorless mutant of Chlorella kessleri(No. 9.80) was 30-40% higher in the presence of exogenous glycine than in itsabsence. None of the other amino acids tested had this effect. Moreover, mutantcells in which glutamine synthetase was inhibited by methionine sulphoximine,accumulated approximately 65% more ammonium ions under blue irradiation in thepresence of exogenous glycine than in its absence. The protein kinase C inhibitors, staurosporine or K252a, reduced the enhancement of oxygen uptake byapproximately 40%. The present results indicate that blue light- dependentdeamination of endogenous glycine might be a prerequisite for enhanced oxygenuptake in Chlorella. This blue light-induced oxygen uptake was not influenced bythe inhibitors of protein phosphatase, calyculin A or okadaic acid. On thecontrary, calyculin A and okadaic acid had a marked effect on the acidificationof the suspension medium and nitrate uptake induced by blue light in Chlorellacells. The different responses to the inhibitors of protein kinase andphosphatase suggest the presence of different pathways among the blue lightsignal transduction operating on oxygen uptake, acidification of the medium andnitrate uptake in Chlorella.PMID: 10845468, UI: 203020784: Arch Biochem Biophys 1989 Nov 1;274(2):525-31Induction and synthesis of nitrate reductase in Chlorella vulgaris.Sherman TD, Funkhouser EADepartment of Biochemistry and Biophysics, Texas A&M University, College Station77843.Assimilatory nitrate reductase is an inducible, eukaryotic enzyme that respondsto a variety of environmental cues. When higher plants and green algae are grownwith ammonia as a nitrogen source, low levels of nitrate reductase activity arepresent. Transfer to nitrate-containing medium is accompanied by substantialincrease of nitrate reductase activity. Here it is shown immunologically that,in the green algae Chlorella vulgaris, nitrate reductase protein isover-produced as activity appears during induction. Immunoreactive protein isalso found in cells grown on ammonia. Low levels of translatable mRNA fornitrate reductase are present in ammonia-grown cells. These data suggest that:(i) nitrate reductase appearance is controlled primarily on a transcriptionallevel, but that transcription is not completely halted under repressingconditions; (ii) there is an overproduction of nitrate reductase protein earlyduring the induction period as previously suggested; and (iii) nascent protein,from in vitro translation, is of approximately the same molecular size as thenitrate reductase subunit and therefore little posttranslational modification isnecessary to generate the functional enzyme. Insertion of cofactors and assembly are probably the only post-translational events.
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