Relationships of Frankia isolates among themselves and to other actinomycetes based on DNA homology studies

Author

Chung Sun An

Date of Award

12-1983

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Botany

Major Professor

B. C. Mullin

Committee Members

W. S. Riggsby, R. W. Holton, P. L. Walne

Abstract

A molecular genetical approach was used to examine the genetic relatedness of 19 Frankia isolates by measuring the base composition of their deoxyribonucleic acid(DNA), the size of their genomes, the DNA-DNA homology, and the thermal stability of the hybrid DNA molecules. The mole % of guanine plus cytosine of Frankia DNA ranged from 66.6 % to 71.4 % with an average of 68.5 % as measured by the thermal denaturation method, and 69.4% by the buoyant density method. The genome size of two Frankia strains, Arl4 and Full, was 6.2 X 10⁹ and 4.6 X 10⁹ daltons, respectively.

Frankia isolates were divided into two groups based on the results of hybridization tests. Genogroup P, consisting of isolates from Alnus, Myrica and Comptonia host plants, exhibited a high degree of homology (67.4 % - 94.1 %) with Arl4. Genogroup N, consisting of isolates from Elaeagnus, Ceanothus, Purshia, Casuarina and AirI2 from Alnus. did not exhibit significant homology (less than 39 %) with Arl4. None of the strains showed a high degree of homology with Eull (less than 33 Among genogroup N strains, subgroupings seemed to exist evidenced by a very high homology (97 %] between two isolates from Casuarina. D11 and G2, but a low homology (27 %) between other strain in genogroup N and G2 strain. Thermal stability studies of the hybrid DNAs which showed a high degree of homology revealed an average of 3 % mismatch while the low homology duplexes exhibited about 5 % mismatch. Eleven actinomycetes which share a common cell wall type with Frankia were also examined for possible genetic relationships to Frankia by measuring base composition and DNA homology with two frankiae probes, Arl^ and Eull. Although no strain showed more than 30 homology, one strain, Geodermatophilus, showed relatively higher homology with both probe strains.

Recommended Citation

An, Chung Sun, "Relationships of Frankia isolates among themselves and to other actinomycetes based on DNA homology studies. " PhD diss., University of Tennessee, 1983.
https://trace.tennessee.edu/utk_graddiss/13030