EVENS, TERENCE J.* and ROBBIN KOENIG. United States Department of Agriculture, Agricultural Research Service, Southern Regional Research Center, New Orleans LA 70124 USA. - Phosphatase expression by Chlorella vulgaris (Chlorophyceae) is mediated by internal phosphorus levels and external pH.
Phosphorus has been implicated as one of the causative agents of the
eutrophication of lacustrine, estuarine and coastal waters. One of the
major inputs of phosphorus into these waters comes from agricultural
non-point sources in the form of dissolved organic phosphorus (DOP).
In order to better understand how DOP may directly impact the
microalgal community structure, it is necessary to understand the
physiology of DOP uptake and utilization. To this end, cultures of
Chlorella vulgaris were grown in custom photobioreactors in
acid (pH 5.5) and alkaline (pH 7.5) media under phosphate replete and
starved conditions in order to determine the types and triggers of
phosphatase expression by this organism. Analysis of differential
phosphatase expression during phosphate stress indicates that cultures
of C. vulgaris grown under alkaline conditions derepressibly
express two alkaline phosphatases, while cultures grown under acid
conditions weakly express only one alkaline phosphatase. Analysis of
internal and external phosphorus levels, whole-cell phosphatase
activity and in-gel activity of protein extracts indicate that
alkaline phosphatase expression is further mediated by internal, as
opposed to external, phosphorus levels.
Key words: Chlorella, eutrophication, phosphatase, phosphorus