TITLE:
Cross-Effects of Nitrogen and Sulphur Starvation in Chlorella sorokiniana 211/8K
AUTHORS:
Simona Carfagna, Giovanna Salbitani, Claudia Bottone, Anna De Marco, Vincenza Vona
KEYWORDS:
Chlorella sorokiniana, Microalgae, Mineral Nutrition, Nitrogen Metabolism, Sulphur Metabolism
JOURNAL NAME:
Natural Resources,
Vol.6 No.4,
April
2,
2015
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.