Physiological regulation of coccolith polysaccharide production by phosphate availability in the coccolithophorid Emiliania huxleyi
2009
Kayano, K.(Tsukuba Univ., Ibaraki (Japan)) | Shiraiwa, Y.
Coccoliths of the coccolithophorid Emiliania huxleyi are calcified biomineral scales composed of calcium carbonate and coccolith polysaccharide (CPs). Coccolith production is regulated by inorganic phosphate (Psub(i)) availability, but no information currently exists on how this process occurs. In this study CP was experimentally characterized by HPLC analysis as an acid polysaccharide of mannose, galacturonic acid, xylose and rhamnose. Both calcification (estimated from sup(45)Ca uptake) and CP production (estimated from uronic acid quantification) were stimulated under Psub(i)-deficient conditions but strongly suppressed under Psub(i)-sufficient conditions. When cells were transferred from Psub(i)-sufficient to Psub(i)-deficient conditions the production of neutral polysaccharides (NP)-storage glucans-ceased rapidly after a temporary increase in the presence of Psub(i), and CP production started to increase after Psub(i) was almost depleted. Under Psub(i)-sufficient conditions NP production increased, concomitant with stimulation of cell growth. Calcification increased gradually, but photosynthetic sup(14)CO2 fixation was reduced by almost 40% for 5 d of culture during Psub(i) depletion. [sup(14)C]CP production was maintained at almost constant, high levels under Psub(i)-deficient conditions but gradually decreased under Psub(i)-sufficient conditions in conjunction with cell growth. In contrast, [sup(14)C]NP production increased about 3-fold under Psub(i)-sufficient conditions for 3d. The present study indicates that E. huxleyi switches the direction of carbon flow toward CP and NP production under psub(i)-deficient and Psub(i)-sufficient conditions, respectively.
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