Predation by a dinoflagellate on a red microalga with a cell wall modified by sulfate and nitrate starvation

Abstract

The dlnoflagellate Crypthecodinium cohn~i was found to prey specifically on the unicellular red alga Porphyrjdum sp. and to contain enzymes that degrade its cell wall Cell wall production and conlposition of the alga are affected by nitrate and sulfate deprivation, the main changes being an increase in methylhexose and a decrease in glucose and xylose. When the dinoflagellate was fed with Porphyndium sp. having modified cell walls, fewer cells were ingested. Similarly, in chemosensory experiments it was found that the dinoflagellate was more attracted to the native polysaccharide than to polysaccharides extracted from deprived Porphyridium sp. Polysaccharide-degrading activity was higher when the dinoflagellate was fed with nondeprived algal cells than with deprived cells (82 to 86% and 45 to 53% reduction in viscosity, respectively). Although the dinoflagellate could not survive on polysaccharide alone, the induced enzymatic activity was similar irrespective of whether the polysaccharide was extracted from deprived or nondeprived cells. The results indicate that the process of predation is not linked to polysaccharide-degrading activity, which is affected by the cell-wall composition of the prey, i.e. algal cells.

N-Glycosylation of the 66-kDa Cell-Wall Glycoprotein of a Red Microalga

“…Therefore, the effects of nitrogen and sulfate starvation on N-glycosylation of the 66-kDa protein were found to be similar. These observations are in agreement with former studies [55][56][57], where it was reported that in both starvation conditions, the cells directed most of their energy toward the synthesis of cell-wall polysaccharide, an activity that is probably important for its survival. The decrease in 66-kDa protein production and in its N-glycan composition in both starvation conditions was expected, because under these conditions, the cells inhibit protein synthesis to the benefit of polysaccharide production.…”

“…For example, growing Porphyridium sp. in a medium deprived of nitrate and sulfate enhances production and solubilization of the polysaccharide [14]. Moreover, these conditions have also been shown to change polysaccharide compositions [14].…”

Nitrogen-deficient microalgae are rich in cell-surface mannose: potential implications for prey biorecognition by phagotrophic protozoa

“…Furthermore, a mannose-rich cell wall glycoprotein on the red microalga Porphyridium sp. is suspected to act as a biorecognition site for its specialist predator, a Crypthecodinuim cohnii-like protozoan (23,26,27). The possibility that lectin-carbohydrate interactions might also be implicated in prey biorecognition and/or selection is clearly feasible, but now requires further investigation.…”

“…Some 16 years ago it was proposed that certain protozoa might use 'contact chemoreceptors' to discern the profitability of different prey items on the basis of their cell-surface biochemical composition (28). However, exploration of molecular-level signalling and recognition processes between predatory and prey cells has only been pursued more recently (23,26,27,32). Of significance are the recent findings of Wootton et al (32) who identify a mannose-specific feeding receptor on the phagotrophic protozoan Oxyrrhis marina -a marine species in which selective feeding is well-documented (7,10,16,29).…”

Regenerated extracellular NH4+ affects the motile chemosensory responses of batch-cultured Oxyrrhis marina

“…species -Crypthecodinium cohnii -shows strong positive chemotaxis towards polysaccharides derived from its specialist prey species -the marine microalga Porphyridium (29). Given the specificity of S. microadriaticum and C. cohnii, it is reasonable to infer that the chemosensory apparatus and responses of both could be highly refined.…”