DNA Restriction Patterns andDNA-DNA Solution Hybridization Studies ofFrankia Isolates fromMyricapensylvanica (Bayberry)t

Sixteen Frankia strains were isolated fromMyrica pensylvanica (bayberry) rootnodules collected atdiverse sites inNewJersey. Restriction pattern analysis oftotal genomic DNA was usedtogroup theisolates intogel groups,andthegenetic relatedness among theisolates was evaluated byDNA-DNAsolution hybridization studies. Restriction pattern analysis provided adistinctive reproducible fingerprint foreachisolate. Isolates fell into nineseparate groups(strain types). Morethanone strain typewas isolated frommostsites. Isolates from twodifferent gelgroups were foundin3 of10nodules examined. Of the16isolates, 10contained extrachromosomal DNA.Sixdifferent extrachromosomal DNA banding patterns were found. Genomically similar isolates carried related, butdifferent, banding patterns. DNA hybridization studies indicated that isolates froma single plantspecies can beminimally related as determined bytotal genome homology. Homology ranged from12to99%.Highly divergent strains were isolated fromthesame plant andfoundto cohabit thesame nodule. Thus,this study demonstrated thatFrankia strains whichinfect thesame hostplant arenotonlyphenotypically different butalsogenetically diverse. Actinomycetes ofthegenus Frankia formnitrogen-fixing nodules on adiverse group ofplants. Todate, plant species from23generahavebeenreported todevelop nodules, and hundreds ofFrankia isolates havebeencultured (11). Such actinorhizal plants are important as pioneers ofnitrogendeficient soils anddisturbed sites andare usedinland reclamation andagroforestry projects. One suchplant, Myricapensylvanica or common bayberry, isfoundfrom NorthCarolina toNovaScotia, including various sites inthe stateofNew Jersey. Thesesites areoften characterized by soils oflownitrogen andplant nutrient statussuchas sand dunesandsalt marshes, whereM.pensylvanica plants are important contributors offixed nitrogen. Little isknownaboutthevariety ofFrankia endophytes whichinfect M. pensylvanica. Fromstudies withother Frankia strains (13a), itisapparentthatthereisa large degreeofmorphological andchemical uniformity among isolates andthatmost can beassigned to one oftwo physiological groups on thebasis ofserology, physiology, andcross-inoculation studies. Although thegenusFrankia is easily differentiated fromothergenera on thebasisof infectivity andmorphological characteristics, atpresent no species delineations can berecommended (13a). Itisnot possible touseclassical actinomycete taxonomic criteria for membersofthegenus Frankia since there appeartobefew morphological differences among isolates other thanpigmentation andhyphalsizeandphysiological differentiation is unsatisfactory. Sincesuchcriteria provide insufficient resolution todistinguish betweenclosely related strains, additional methods areneeded. Sodiumdodecyl sulfate-polyacrylamide gelelectrophoresisofcellproteins (3,8)andrestriction pattern analysis of DNA (1,7)haveprovided thehighest degree ofresolution in