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Carotenoids content of Botryococcus braunii displayed low nitrate demand; the concentration of 3.2 mM nitrate (50% of Chu 13 medium) resulted in most of the growth magnitude whereas carotenoids increments were highest at 25% (1.6 mM) nitrate. P (net photosynthetic oxygen evolution) and carotenoids content responded opposite to each other at supplemental bicarbonate; carotenoids have been enhanced at low concentrations (0, 1 or 5 mM), being highest at 100% nitrate (6.4 mM) while P N was significantly enhanced at higher concentrations (10, 15 and 20 mM) and vice versa. Enhanced P N N at high carbon and nitrogen may have shifted the metabolism to amino acid synthesis thus inhibiting hydrocarbons synthesis. NaCl (0.15 or 0.2 M) increased carotenoids content 5 times that of the control (zero NaCl) whereas higher salinity concentrations (0.25 and 0.3 M NaCl) were relatively inhibitory. Salinity, in addition, abolished the usual preferential effect of nitrate concentrations on carotenoids accumulation since their level was only slightly less at 6.4 mM than at 50% this concentration (3.2 mM). Collectively, NaCl (0.1-0.2 M) induced highest carotenoids and chlorophyll contents, highest P N and lowest R in 50% nitrate whereas does not have such effect in 100% nitrate. Botryococcus braunii proved strong capability of adjusting the pH of the medium, whether acidic or alkaline, back close to the start. Carotenoids content was not responsive to a wide range of pH values (4-12), exhibiting their highest level at pH 6. D

Carotenoids content of Botryococcus braunii displayed low nitrate demand; the concentration of 3.2 mM nitrate (50% of Chu 13 medium) resulted in most of the growth magnitude whereas carotenoids increments were highest at 25% (1.6 mM) nitrate. P (net photosynthetic oxygen evolution) and carotenoids content responded opposite to each other at supplemental bicarbonate; carotenoids have been enhanced at low concentrations (0, 1 or 5 mM), being highest at 100% nitrate (6.4 mM) while P N was significantly enhanced at higher concentrations (10, 15 and 20 mM) and vice versa. Enhanced P N N at high carbon and nitrogen may have shifted the metabolism to amino acid synthesis thus inhibiting hydrocarbons synthesis. NaCl (0.15 or 0.2 M) increased carotenoids content 5 times that of the control (zero NaCl) whereas higher salinity concentrations (0.25 and 0.3 M NaCl) were relatively inhibitory. Salinity, in addition, abolished the usual preferential effect of nitrate concentrations on carotenoids accumulation since their level was only slightly less at 6.4 mM than at 50% this concentration (3.2 mM). Collectively, NaCl (0.1-0.2 M) induced highest carotenoids and chlorophyll contents, highest P N and lowest R in 50% nitrate whereas does not have such effect in 100% nitrate. Botryococcus braunii proved strong capability of adjusting the pH of the medium, whether acidic or alkaline, back close to the start. Carotenoids content was not responsive to a wide range of pH values (4-12), exhibiting their highest level at pH 6. D

The exudates of three fungal species (Aspergillus niger, Fusarium sambucinum and Penicillium canescens) have been tested for their effect on the algal population and diversity of El-Ibrahemia Canal. It has been found that the exudates of F. sambucinum was stimulatory for the algal population, whereas that of A. niger was inhibitory. Penicillium canscens exudate, in comparison, displayed the weakest effect. The results imply a great variation in the effectiveness of different types of fungal exudates on the different algal taxa. Chlorella fusca has been studied intensively, because it was the only chlorophycean species that survived and tolerated all applied concentration of the exudates of the three studied fungi. The growth of C. fusca has been enhanced by F. sambucinum exudates, but not by that of A. niger. The effect of fungal exudates on some metabolic components of C. fusca is discussed.

To learn more about the adaptive response of Synechococcus elongatus PCC 7942 to iron starvation and the role of DpsA, presumably a protein protecting chromosomal DNA against oxidative damage, we performed a comparative analysis of S. elongatus PCC 7942 wild-type and a DpsA-free mutant, called K11. Relative to wild-type, the DpsAfree mutant had significantly higher amounts of phycocyanin and allophycocyanin, even upon iron limitation. While the Photosystem I activity in mutant K11 remained high under iron deficiency, the Photosystem II activity dropped severely with respect to wild-type. The DpsA content in wild-type was already fairly high under regular growth conditions and did not significantly increase under iron deficiency nor in the presence of 0.3 mM 2 dipyridyl in iron-sufficient BG11 medium. Nevertheless, the absence of DpsA in K11 resulted in a significantly altered transcriptional/translational activity of genes known to be involved in adaptation to iron starvation. The amount of isiA/B transcript was about two-fold lower than in wild-type, resulting in a lower 77 K chlorophyll a fluorescence at 685 nm, implying a lower concentration of Photosystem I-IsiA supercomplexes. While in wildtype idiA, idiB,andirpA transcripts were highly up-regulated, hardly any were detectable in mutant K11 under iron limitation. The concentration of mapA transcript, however, was greatly increased in K11 compared to wild-type. Measurements of acridine yellow fluorescence with intact wild-type and K11 cells revealed that iron deficiency caused an increased contribution of cyclic electron transport to membrane energisation and ATP synthesis being in agreement with the formation of the Photosystem I-IsiA supercomplex. In addition, mutant K11 had a much higher respiratory activity compared to wild-type under iron limitation.  2