Quantifying Microbial Diversity Through Dilution/Extinction

A method of relatively easily, rapidly, and inexpensively quantifying the structural diversity of a multiple-species community of micro-organisms is based on the rate of extinction of phenotypic traits across a dilution gradient of a sample of the community. In this context, the concept of structural diversity encompasses the number (richness) and distribution (evenness) of separate or interacting biological entities responsible for given functions within the overall set of functions performed by the community. It is assumed that the rate of loss of character (as measured through testing for a given function) from the community upon dilution/ extinction is proportional to the diversity of biological entities in the community. This assumption should be true as long as the average metabolic versatility of individuals (the width of a nutritional niche) does not increase with structural diversity. Inasmuch as most experimental evidence suggests that the widths of nutritional niches decrease with increasing diversity, the assumption appears valid. In experiments performed to evaluate the method, the nonlinear relationship between the number of positive tests and the density of cells across a dilution series was successfully fit to a rectangular hyperbola, yielding regression variables related to the structural diversity of the samples.