The interaction betweenNavicula muralisgrunow and an associated species ofFlavobacterium

Abstract

A Flavobacterium sp. isolated from cultures of Navicula muralis (previously identified as N. pelliculosa) was able to both take up radioactively labelled extracellular products produced by the diatom and to have its growth supported by a dialysable fraction of this material. Among the diatom extracellular products identified were the amino acids methionine, lysine and arginine and the vitamin biotin for which the Flavobacterium sp. was found to be auxotrophic. Six sugars including glucose were also isolated from a hydrolysed sample of exponential phase diatom filtrate. Navicula muralis was able to grow heterotrophically at a low glucose concentration (10 µm) both in the presence and absence of the Flavobacterium sp. and it is suggested that the formation of a nutritional relationship with the diatom enables the slow growing Flavobacterium to compete more effectively with more active bacteria which may even be inhibited by algal extracellular products. The relationship between the diatom and Flavobacterium sp. did not appear to be one sided since the growth rate and cell yield of the diatom in mixed culture increased under most of the conditions tested. It is therefore suggested that the association between Navicula muralis and Flavobacterium constitutes a form of symbiosis.