Ultrastructure of the Marine Cryptomonad Chroomonas salina Cultured under Conditions of Photoautotrophy and Glycerol‐Heterotrophy*

Abstract

SYNOPSIS. Chroomonas salina was cultured in seawater medium enriched with nitrate, phosphate, silicate, trace‐metal ions, and vitamins, under 3 conditions: (A) light without other organic additions (photoautotrophic); (B) light and added glycerol (photoheterotrophic); (C) in darkness but with added glycerol (chemoheterotrophic). The heterotrophic cultures were initiated from a stock maintained on glycerol in continuous darkness for 41/4 years. The autotrophic culture was initiated from a corresponding stock maintained under continuous illumination without any organic growth substrate. The fine structure of organisms from simultaneously initiated cultures was compared after 1, 2, 3, and 4 weeks of growth.“Young'’cells from the autotrophic and heterotrophic cultures of comparable maturity had no recognizable ultrastructural difference. In organisms from both the photoautotrophic and photoheterotrophic cultures there was a progressive accumulation of starch and lipid with aging, but whereas in cells from the former the production of starch was arrested after early growth and lipid was concentrated thereafter, in those from the latter both metabolites continued to be produced with consequent rapid degeneration of the cytoplasm followed by autolysis. By contrast, flagellates grown in the chemoheterotrophic culture accumulated only starch, with vacuole formation replacing the lipid stores. In all cases, the lipid bodies appeared to differ from the membrane‐bound droplets normally observed, which actually diminished with aging. Starch accumulation appeared to cause more rapid cytopathologic changes and autolysis. No evidence of chloroplastic phycobilisome‐type aggregations was noted in organisms from any culture at any age.