title: Regulation of CO on heterocyst differentiation and nitrate uptake in the cyanobacterium Anabaena sp. PCC 7120.
abstract: OBJECTIVE
  The aim of the present investigation was to study the effects of different inorganic carbon and nitrogen sources on nitrate uptake and heterocyst differentiation in the culture of cyanobacterium Anabaena sp. PCC 7120.
  
  
  RESULTS
  Anabaena was cultivated in media BG11 containing combined nitrogen and supplementary NaHCO3 or CO2. Cell growth, heterocyst differentiation, nitrate reductase (NR, EC 1.7.7.2), glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49) and NO uptake were analysed. The cells cultivated in BG11(0) medium with aeration were taken as reference. Experimental results showed that the differentiation frequency of heterocysts when the cells were cultivated with elevated CO2 was higher than that of the cells grown with air or bicarbonate. Heterocysts appeared unexpectedly when CO2 was introduced into the medium containing nitrate. However, no heterocysts emerged when CO2 was added to medium containing NH or urea, or when NaHCO3 was supplied to the medium with nitrate. Both nitrate uptake rate and nitrate reduction enzyme activity were depressed by the supplement of CO2 to the culture. The activity of G6PDH was enhanced with the increase in heterocyst differentiation frequency.
  
  
  CONCLUSIONS
  CO2 might compete with NO for energy and electrons in the uptake process and CO2 appears favoured. This led to a high intracellular C/N ratio and a relative N limitation. So the process of heterocyst differentiation was activated to supplement nitrogen uptake.
  
  
  CONCLUSIONS
  This study provided an attractive possibility to form more heterocysts by rapid growth of Anabaena cells cultivated in the medium containing nitrate in order to increase nitrogen fixation and hydrogen production.
authors.affiliation: State Key Laboratory of Biochemical Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, China. rjkang@home.ipe.ac.cn
authors.forename: R-J
authors.initials: RJ
authors.lastname: Kang
authors.forename: D-J
authors.initials: DJ
authors.lastname: Shi
authors.forename: W
authors.initials: W
authors.lastname: Cong
authors.forename: Z-L
authors.initials: ZL
authors.lastname: Cai
authors.forename: F
authors.initials: F
authors.lastname: Ouyang
mesh_terms: D017033:Anabaena / Q000254:growth & development / Q000378:metabolism*; D001431:Bacteriological Techniques; D002245:Carbon Dioxide / Q000378:metabolism / Q000494:pharmacology*; D005954:Glucosephosphate Dehydrogenase / Q000378:metabolism; D007218:Industrial Microbiology; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism; D009586:Nitrogen Fixation
chemical_list: D009566:Nitrates; D002245:Carbon Dioxide; D005954:Glucosephosphate Dehydrogenase; D009565:Nitrate Reductases; D050901:Nitrate Reductase