2 DISTINCT COLONIAL MORPHOTYPES OF AMPHORA-COFFEAEFORMIS (BACILLARIOPHYCEAE) CULTURED ON SOLID MEDIA

When cultured on different types of solid media, the marine-fouling di atom Amphora coffeaeformis (Ag.) Kutz. consistently formed two distinc t colonial morphotypes named tight and fuzzy. Tight colonies were comp rised mainly of small, morphologically distorted, nonmotile cells, whe reas morphologically normal and highly motile cells formed the fuzzy c olonies. Cells from tight colonies were less adherent to glass, grew m ore 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 polyacryl amide gels stained with Coomassie blue, cells from tight colonies prod uced a significantly lower amount of a protease-resistant, low M(r) po lysaccharide or glycoconjugate as detected in silver-stained gels. The frequency of appearance of the fuzzy and tight morphotypes was not in fluenced by the mode of nutrition or the type of substratum to which t he 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 frequenc ies and patterns of appearance, it was clear that the two naturally fo rmed morphotypes were not the consequence of spontaneous mutations, ge netic rearrangement, or selection of stable natural variants, and we h ave hypothesized that they were linked to a normal physiological behav ior. The tight colonial morphotype was used as a valuable marker to sc reen for true motility/adhesion mutants within an ultraviolet-mutageni zed population of A. coffeaeformis. Seven mutants were isolated that w ere non-motile on agar plates, poorly adherent to glass, and distingui shed from naturally formed cells from tight colonies by their inabilit y to form fuzzy colonies upon subculture on solid media.