ABSTRACT

The different forms of cell aggregation may be classified into "hornotypic" and "heterotypic" systems. A homotypic system is made up of similar units, whereas a heterotypic system is made up of dissimilar units. Flocculation of brewers' yeast during fermentation is homotypic. CO-flocculation of yeast with bacteria is heterotypic. Microbial aggregation systems are distributed among many microbial taxa. They are found in both prokaryotes and eukaryotes. Sexual agglutination reactions in yeasts tend to become more intense as species evolve from haploid to a higher ploidy, L. J. Wickerham surmises that haploid species developing strong agglutination reactions could hardly remain haploid for long. Microbial aggregation systems make good models for cell aggregation of higher forms, for just the reasons that make microbes the organisms of choice for working out more complicated biological problems.