THE EFFECT OF AGAR ON THE GROWTH OF NITZSCHIA LINEARIS

Abstract

THE DIATOM, Nitzschia linearis W. Sm., is one of the common diatoms found in the eastern United States growing in shallow water on mud in streams not adversely affected by pollution. In 1947 an effort was made to culture this diatom in the laboratory. Various types of culture media, such as aqueous solutions, silica gels, and agar were tried. The nutrient solutions used were a modification of Miquel's medium (Miquel, 1892), Chu's number 14 (Chu, 1942), and Ketchum and Redfield (1938) ,medium added to natural stream water. In a series of experiments in which the above nutrients were added to the various media, Nitzschia linearis consistently grew better on the agar medium regardless of the type of nutrient solution used for enrichment. Experiments were then conducted to see if the substance producing the stimulating effect could be pyridine extracted from the agar as described by Robbins (1939). The extract obtained from the pyridine-treated agar was added to agar enriched with Miquel's nutrients and to agar enriched with Chu 14. The agar to which the nutrients were added was purified with Chlorox (sodium hypochlorite) as described by G. W. Beadle (personal communication, 1947). This was done in order to remove any growth-promoting substances such as biotin which might be present. It was found that a stimulating effect upon the growth of Nitzschia linearis was produced when the quantity of extract per 100 ml. of medium was equivalent to that obtained from 1-5 g. of agar. However, due to the difficulty of counting diatoms on an agar medium to determine the amount of growth, no precise results were obtained. Therefore, these experiments were repeated using an aqueous medium. MATERIALS AND METHODS.-The pyridine extraction of the agar was conducted as follows: Glassware, linen, and all equipment used in the extraction were treated with a 5 per cent aqueous pyridine solution for 48 hr. before beginning the agar extraction. The equipment was then washed and rinsed with glass distilled water. The agar was put in linen bags allowing ample room for the expansion of the agar. Difco agar was extracted with a 5 per cent aqueous solution of pyridine over a period of 48 hr. The pyridine solution was changed three times during this 48-hr. period. At the end of 48 hr. the extracts were combined and vacuum distilled at 28?C. until all the pyridine was removed. The extract was then concentrated by evaporating it at 28?C. The extract was refrigerated and experiments were started as