The evaluation of algal growth potential by cultivation on solid media

Abstract

An evaluation of algal growth potential and toxicity by cultivation on solid media has been completed. The growth rates of colonies are independent of the external strength of nutrients until 150 h of cultivation; this is due to the inner nutrient pools of cells. Thereafter, cells become more dependent on external nutrient sources and the growth rates of colonies are controlled by diffusion of nutrients from the plate to the growth zone i.e. to the perimeter of the colony. At the end of 400 h colony growth decreases at a rate proportional to the concentration of nutrients. The final size of colonies is proportional to the strength of nutrients, ranging from concentrations characteristic of oligotrophic waters to those of sewage. Yield of dense periphyton on a plate is proportional to the initial nutrient content until about 1500 mg l −1 dry weight has been achieved. Higher yields are limited by cell density or light penetration. The yield constant is inversely proportional to the solution strength. The results of a new procedure are convertible into the yields of dry weights obtained by cultivation in aerated liquid suspension. Sixty-six 9 cm diameter Petri dishes can be placed in a cultivation unit with an area of only 0.7 m 2. The use of microtitration plates for immunology, with 96 wells in a plate 9 × 13 cm, can extend the number of variants up to about 3000 colonies in the same cultivation unit. Evaluation is quick, simple and precise. The coefficient of variation is about 10%. Yield is measured by sizing under a microscope or by dry weight evaluation on filter discs.