Slime molds is a term commonly used to describe a group of soil amoebas that have the ability to use bacteria as a source of food. They are neither a mold nor a fungus, but rather organisms that share many basic biochemical and genetic mechanisms with higher eukaryotic cells. They can be readily cultivated in the laboratory, and a considerable array of techniques have been developed to manipulate them on a biochemical, genetic, and cellular level. To the molecular biologist, these organisms can present opportunities to examine the details of the regulation and function of systems common to higher organisms, but in a less complicated and more accessible setting.
The two species most studied in the laboratory are Dictyostelium discoideum (see Dictyostelium) and Physarum polycephalum (see Physarum). They both have the ability to change their basic cellular architecture in a programmed, developmental pathway to optimize their growth and survival. They differ in that Physarum has a number of vegetative forms, including a flagellated swimming form, a migrating amoeboid form, and a unique single large cell form containing many nuclei, called a plasmodium. When starved, it can develop into a variety of environmentally resistant forms, including spores. The Dictyostelium developmental program differs from that of Physarum in that the cells aggregate when starved and develop into a multicellular organism, called a slug. The cell walls do not fuse, and cells differentiate into unique types that perform different functions. If this faster moving slug fails to find better conditions, it can develop into a terminal fruiting structure containing resistant spores. The vegetative form of Dictyostelium is a single cell that uses amoeboid motility to find food.
Slime molds have been classified in the Mycetozoa phylum. There are three recognized subclasses: acellular (myxogastrid), cellular (dictyostelid), and protostelid. It has been proposed that slime molds are related to the multicellular eukaryotes, more closely to fungal and animal cells than to plants (1). Outside the laboratory, they can be found in forest detritus, where they occupy a unique niche, eating bacteria. In the laboratory, by combining genetic, biochemical, and cell biological techniques, these organisms have given investigators multifaceted approaches to problems that are intractable elsewhere.
