TWO DISTINCT COLONIAL MORPHOTYPES OF AMPHORA COFFEAEFORMIS (BACILLARIOPHYCEAE) CULTURED ON SOLID MEDIA1

Abstract

ABSTRACTWhen cultured on different types of solid media, the marine‐fouling diatom Amphora coffeaeformis (Ag.) Kütz. consistently formed two distinct colonial morphotypes named tight and fuzzy. Tight colonies were comprised mainly of small, morphologically distorted, nonmotile cells, whereas morphologically normal and highly motile cells formed the fuzzy colonies. Cells from tight colonies were less adherent to glass, grew more slowly in liquid media, and had a slightly decreased viability on plates with copper than cells from fuzzy colonies. Whereas the protein profiles of the two types of cells were nearly identical in polyacrylamide gels stained with Coomassie blue, cells from tight colonies produced a significantly lower amount of a protease‐resistant, low Mr polysaccharide or glycoconjugate as detected in silver‐stained gels. The frequency of appearance of the fuzzy and tight morphotypes was not influenced by the mode of nutrition or the type of substratum to which the algal cells adhered. However, certain formulations of solid medium and the presence of growth‐inhibitory concentrations of copper in agar plates favored the formation of tight colonies. Due to their frequencies and patterns of appearance, it was clear that the two naturally formed morphotypes were not the consequence of spontaneous mutations, genetic rearrangement, or selection of stable natural variants, and we have hypothesized that they were linked to a normal physiological behavior. The tight colonial morphotype was used as a valuable marker to screen for true motility/adhesion mutants within an ultraviolet‐mutagenized population of A. coffeaeformis. Seven mutants were isolated that were non‐motile on agar plates, poorly adherent to glass, and distinguished from naturally formed cells from tight colonies by their inability to form fuzzy colonies upon subculture on solid media.