Transfer-of-Chromosomal-Genes-and-Plasmids-In - Vol. 53,No....

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Unformatted text preview: Vol. 53,No. 7 APPLIED AND ENVIRONMENTAL MICROBIOLOGY, July 1987, p. 1525-1530 0099-2240/87/071525-06$02.00/0 Copyright D1987, American Society for Microbiology TransferofChromosomal Genes and Plasmids in Bacillus thuringiensis ARTHUR I. ARONSON* AND WILLIAM BECKMAN Department ofBiologicalSciences, Purdue University, West Lafayette, Indiana 47907 Received 22 December 1986/Accepted 31 March 1987 A lowfrequencyofchromosomal gene transferfrom BacillusthuringiensistoBacilluscereus w a s detected by cellmating,with a tryptophanmarker beingthemost frequentlytransferredgene among fourthatwere tested. The process was resistant to DNase and was not mediated by cell filtrates. Among several B. thuringiensis subspeciestested,transfer was bestwitha derivativeofB. thuringiensissubsp. kurstakiHD1, which lostseveral plasmids. AlloftheB. cereus recombinants contained at leastone plasmid from the donor B. thuringiensis; frequently, it was a plasmid that encoded a protoxin gene. In matings with B. thuringiensis subsp. kurstaki HD1, a 29-megadaltonplasmid thatcontained a ca. 2.5-kilobaseregionofhomology withthechromosome was alwaystransferred.No detectabletransferofchromosomal genes was found inB. thuringiensissubsp. kurstaki HD1 strainslackingthisplasmid, suggesting thatthere may be chromosome mobilization. The most prevalent methods forgene transferamong the spore-forming bacilli are transformation and transduction. Only the latter process has been described for Bacillus thuringiensis subspecies, and several generalized trans- ducing phage have been isolated (4, 13, 18, 19, 25). In addition,asystemthatappearstoinvolvecelltocellcontact has been documented for the transfer of plasmids from certain B. thuringiensissubspecies toBacillus cereus (11), Bacillus anthracis (5), and plasmid-cured variants of B. thuringiensis (11). Among the plasmids transferred fre- quentlywere thoseencodingprotoxingenes(5,9,11,22)or those involved intheregulationofprotoxin synthesis(22). Very fewB. thuringiensissubspeciestransferplasmidsat a sufficientlyhighfrequencytobedetectablewithoutselect- ablemarkers,althoughinsome casescoloniesofderivatives thatdoordonotproduceinclusionscanbedistinguishedon certainmedia(11).Unfortunately,therearefew ifany such markers encoded by indigenousplasmids,solow-frequency transfereventsaredifficulttodetect.Insuchcases,plasmid transfercan be found by selectingforthe transferofchro- mosomal markers and then screening the recombinants for plasmids from the donor strain. In this way, ithas been possibletodemonstrate thetransfertoB. cereus ofseveral differentprotoxin-encodingplasmids(9,22). The interrelationship between chromosome and plasmid transfer has been most extensively studied inB. thuringi- ensissubsp.kurstakiHD1, andasdiscussedinthisreport,it may involve chromosome mobilization.Inaddition, further documentation ofthetransferofchromosomal markers and plasmidsbyseveralB. thuringiensissubspeciesisincluded....
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Transfer-of-Chromosomal-Genes-and-Plasmids-In - Vol. 53,No....

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