The effect of Maltose release on growth and Nitrogen metabolism of symbioticChlorella

Indicators of nitrogen limitation were compared in cultured, ex-symbiotic, maltose-releasing Chlorella and in Chlorella freshly isolated from symbiosis with green hydra. Culture of Chlorella at low pH (which stimulates maltose release) caused a reduction in amino acid pool size but no change in the nitrogen to carbon ratio (N:C). In nitrogen-starved cells, both amino acid pool size and N:C decreased. Chlorophyll and protein content, and glutamine to glutamate ratios, indicated that freshly isolated symbiotic Chlorella were more similar to symbionts cultured at low pH than those cultured without nitrogen, while N:C values were intermediate. Low growth rates of Chlorella in symbiosis may be due to release of high levels of photosynthate, and consequent carbon-starvation and inability to assimilate nitrogen, rather than direct limitation of nitrogen supply.