Effect of light on growth, pigmentation and N2 fixation of cultured Trichodesmium sp. from the Great Barrier Reef lagoon

The influence of light intensity and light quality on the growth, N2 fixation and pigmentation of cultures of the cyanobacterium Trichodesmium GBRTRLI101 were investigated under defined laboratory conditions. Both growth rate and N2 fixation rate were strongly dependent on light intensity. The N2 fixation rate increased with light intensity over the whole range tested (PAR 10–160 μmol quanta m−2 s−1) but the growth rate passed through a maximum in the range 45–75 μmol quanta m−2 s−1. Growth rates were the highest under white and yellow light and were significantly reduced under red light. The results also showed that the cellular concentrations of chlorophyll a and phycobiliproteins (PBPs) increased under low light conditions and were affected by light quality. Overall the results suggest that the availability of light and the quality of that light play an important role in the growth and distribution of Trichodesmium in coastal and oceanic waters.