Physiological and biochemical response of freshwater cryptomonads (Cryptophyceae) to Fe deficiency

Cryptomonads show strong seasonal distribution in lakes yet little is known of their nutrient requirements. In this study, we examined the role of Fe nutrition in the growth and photosynthetic properties of two freshwater cryptomonads (Cryptomonas sp. UTCC 337 and C. erosa UTCC 446). Cryptomonas sp. appeared more tolerant to Fe deprivation compared with C. erosa. Growth rates calculated for Cryptomonas sp. provided 100 nM and 1 000 nM Fe did not vary (0.55 d(-1)). Only cultures provided 10 nM Fe displayed significantly lower rates of growth (0.26 d(-1)) and lower cellular yields of chlorophyll. In contrast, cultures of C. erosa provided 10 nM Fe failed to grow, whereas cultures provided 100 nM Fe exhibited a reduced rate of growth (30% reduction) and lower yields of cellular chlorophyll (19% reduction) compared to high Fe (1 000 nM) cultures. Photochemical competency, assessed by measuring DCMU-enhanced fluorescence, was high for cells of Cryptomonas sp. regardless of the level of Fe provided (F(v)/F(m) > 0.7). In contrast, photochemical competency was considerably reduced (F(v)/F(m) = 0.46) for C. erosa provided 100 nM Fe. Consistent with this, levels of the Fe-containing electron transfer catalyst ferredoxin were reduced by 2.5 times in C. erosa provided 100 nM Fe compared to Fe-replete cells. By comparison, ferredoxin levels varied only slightly in cells of Cryptomonas sp. provided either 100 nM or 1 000 nM Fe.