Doctoral Dissertations

Scott A. Rice

Date of Award

5-1996

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Microbiology

Major Professor

Bert C. Lampson

Committee Members

David Brian, Beth Mullin, Gary Stacey

Abstract

This study presents information regarding the discovery of new retrons, their distribution in the proteobacteria, a mechanism of inheritance, and the first use of msDNA as a diagnostic probe to detect myxobacteria in soils. Approximately 10% of proteobacteria tested from the alpha and gamma groups produce msDNA. In contrast, >98% of myxobacteria strains (delta group) tested positive for msDNA production. DNA hybridization experiments revealed that myxobacteria retron elements have a clustered distribution, being found exclusively within particular myxobacteria subgroups. A retron element of the Mx162 type was cloned from Melittangium lichenicola and its DNA sequence compared with similar elements in M. xanthus and Stigmatella aurantiaca. Together, the degree of sequence diversity, the codon bias of the reverse transcriptase genes, and the clustered distribution of these retrons suggest a possible evolutionary scenario in which a common ancestor of the Myxococcus subgroup may have acquired this retroelement. It was found that some Namocystis exedens strains contain mulitple, partial copies of the msd gene and suggests that msDNA is capable of generating short repeats which may have significant effects on the evolution of these bacteria. Very few reports exist regarding the number of myxobacteria present in natural soils, or in contaminated soils. In this study, msDNAs were used as probes which indicated that DNA sequences specific to members of the Myxococcus and Namocystis subgroups were present in both the contaminated and uncontaminated soils and represented 0.01% and 0.11% of the total detectable eubacteria in these soils respectively. Members of the third subgroup, Chondromyces, were not detected in any of the soil samples used in this study. Both the total number of bacteria detected and the number of myxobacteria decreased with increasing soil depth, and no myxobacteria were detected at a depth of 60 centimeters (cm).

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