Nickel Ion Requirements for Autotrophic Growth of Several Marine Microalgae with Urea Serving as Nitrogen Source

Twelve marine species were tested for their competence to grow on urea as sole nitrogen source, and the influence of nickel ion on such urea utilization was determined. In those cases (six species) where good algal growth occurred in the seawater medium used without added nickel, the metal ion requirement was demonstrated by suppressing the algal growth with a chelator (citric acid) and testing for subsequent growth from addition of excess nickel. The results showed that a nickel requirement for urea utilization is of widespread occurrence among the microalgae tested. The concentrations of nickel tested in the laboratory were compared with the endogenous nickel levels reported for ocean waters, and it was concluded that these levels are generally sufficient to support an effective utilization of urea by most urease-producing algae. The value of chelation tests as a rapid, reliable method for the demonstration of the Ni2+ requirement is discussed.