Composition of intracellular and extracellular pools of amino acids, and amino acid utilization of microalgae of different sizes

Abstract

15 axenic species and strains of unicellular algae of micro, nano, and pico sizes were examined. The total concentration of α-amino-N inside cells of all species declined on N deprivation but the changes in proportion of individual amino acids are generally too complex for use as a metabolic fingerprint. The only exception was that the mole ratio glutamine/glutamate was consistently high for exponentially growing cells and low for N-deprived cultures. Generally, the smaller algae showed little significant ability to use amino acids supplied at near-natural concentrations. This lack of ability contrasts with reports of amino acid uptake by diatoms. Some of these algae also release amino acids, whilst others release and use little and may play little part in amino acid cycling. The explanation for the apparent limited used of amino acids by nano- and picoalgae may lie in the tight coupling of use and regeneration of inorganic nutrients within microbial loop communities negating any competitive advantage in evolving a capability to use a wide range of amino acids.