Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)




The taxonomy of the anaerobic bacteria known as diphtheroids is a subject of study by the Subgroup on Taxonomy of Microaerophilic Actinomycetes, an authorized Subgroup of the Subcommittee on Taxonomy of the Actinomycetales of the International Committee on Nomenclature of Bacteria, International Association of Microbiological Societies. Dr. Gordon Robertstad, a member of this committee, has stimulated a series of studies on these organisms. At present, the species differentiation coupled with genus differentiation among anaerobic diphtheroids is in a state of flux. Tests which were previously thought to be indisputable are now not entirely reliable. Fermentation reactions, catalase tests, serology, and cell wall analyses not sufficient in themselves as criteria for identification. If it is necessary to perform every known biochemical, serological, metabolic, and nutritional test to identify any isolate, then the practical identification with a minimum of time and materials is not feasible. Ideally, differentiation via one or two tests only is the goal of the taxonomist and diagnostician, as well as· the researcher. As an approach to the above problem, deoxyribonucleic acid (DNA) base ratios are now becoming a promising tool in separating organisms; that is, DNA base ratios along with DNA homologies. D_IA base ratios are expressed as mole-percent guanine + cytosine (the four DNA bases are adenine, thymine, guanine, and cytosine) obtained directly by chemical means or indirectly by physical means. DNA homologies are assessed by measuring hybrid formation between single-stranded DNA's of diverse origin. Taxonomy based on properties of the DNA molecule offers a more direct mode of classification. The phenotypic properties of an organism may be more apparent to the observer, but more subject to environmental changes. For example, cell wall analyses may change with the media used to cultivate the organisms. The genotype of the cell, as present in its DNA genome, is not affected thus; rather, it is stable until the factors of mutation and base analogs enter the picture.

Library of Congress Subject Headings

Botany -- Classification
Anaerobic bacteria



Number of Pages



South Dakota State University