This study aimed to evaluate the influence of nitrogen compounds on the protein concentration of the cyanobacterium Aphanothece microscopica Nägeli cultivated in BG11 medium and fish processing effluent. The experimental conditions were 200 mg L-1 inoculum, 30 °C, pH 7.6, and C/N ratio 20. Each culture was harvested during the early, mid-log, and late logarithmic growth phase and during the stationary phase and analyzed in terms of total nitrogen, non-protein nitrogen, ammonium nitrogen, nitrate, nitrite, and nucleic acid. It can be said that in all cultures the ammonium ion and the nucleic acids account for great portion of the non-protein nitrogen in the biomass. The results show that the culture medium influences the nitrogen content, and that the Kjeldahl method overestimates the real protein concentration in cyanobacteria.
culture medium; nitrogen; cyanobacteria
