The Texas brown tide alga, Aureoumbra lagunensis, was reported to be able to out-grow other phytoplankton in low-phosphorus and high-salinity environments. Previous study suggests that it has low cellular phosphorus requirement, but its ability to use forms of phosphorus other than phosphate under severe phosphate deficiency remains unknown. We have studied the changes of alkaline phosphatase activity (APA) and other cellular characteristics of A. lagunensis growing in P-sufficient (+P) and P-deficient (-P) batch cultures and in a series of P-limited continuous cultures over a range of growth rates. A. lagunensis grew equally well in +P and –P media, but the intracellular phosphorus cell quota was lower and APA was significantly higher in the cells growing in –P media than those in the...[ Read more ]

The Texas brown tide alga, Aureoumbra lagunensis, was reported to be able to out-grow other phytoplankton in low-phosphorus and high-salinity environments. Previous study suggests that it has low cellular phosphorus requirement, but its ability to use forms of phosphorus other than phosphate under severe phosphate deficiency remains unknown. We have studied the changes of alkaline phosphatase activity (APA) and other cellular characteristics of A. lagunensis growing in P-sufficient (+P) and P-deficient (-P) batch cultures and in a series of P-limited continuous cultures over a range of growth rates. A. lagunensis grew equally well in +P and –P media, but the intracellular phosphorus cell quota was lower and APA was significantly higher in the cells growing in –P media than those in the +P media. The results from the continuous cultures indicated that as growth rate increased the intracellular phosphorus cell quota increased. On the other hand, APA and growth rate were negatively related. Results from both batch and continuous culture experiments all suggested that A. lagunensis was very elastic in cellular phosphorus requirement and the elevation of APA appeared to be triggered by cellular P content falling below a threshold. Moreover, the changes of APA in hypersaline conditions were also tested. The responses of APA and cellular phosphorus in high-salinity treatment were similar to that in normal salinity. Study of the APA, together with Pi-transporter of A. lagunensis in P-limited condition provided a better understanding of how A. lagunensis adapted to P-deficient and hypersaline environments. Findings from this study also provided insight about the mechanism of phosphorus utilization in marine organisms.