Cross-Effects of Nitrogen and Sulphur Starvation in <i>Chlorella sorokiniana</i> 211/8K

Abstract

Nitrogen (N) and sulphur (S), being essential macronutrients, have important roles in microalgae metabolism. Effects of N- or S-shortage were investigated in the green microalgae Chlorella sorokiniana subjected to 24 h of starvation, by measuring the glutamine synthetase (GS) and O-ace- tylserine(thiol)lyase (OASTL) activities, proteins and amino acids levels. To test possible metabolic impact related to carbon (C) metabolism in response to N- or S-deprivation, starch and total C, N and S contents were also determined. The growth of C. sorokiniana cells was affected by N or S availability. The algae cultured for 24 h in a medium deprived of nitrogen or sulphur showed a decrease in the growth rate and changes in the average volume cell. Nitrogen starvation affected proteins level in the algae cells more than S-deprivation did. The decline in the protein levels observed under S-deficient conditions was coupled with the accumulation of the amide glutamine and with OASTL activity increase; additionally, N-deficiency promoted a decrease in cysteine (Cys) levels (50%) and an increase in GS activity. Nevertheless, S-deprivation had negligible effects on GS activity, while N-deprivation significantly affected OASTL activity. Total C was also estimated in cells N- or S-deprived; nitrogen deprivation strongly affected total C content more than S-deprivation, which in addition reduced the content of C and N, but leaves intact their ratios. Our results support the hypothesis that in Chlorella sorokiniana cells a reciprocal influence of N, S and C assimilation occurs.