Most bacterial traits involved in colonization of plant roots are yet to be defined. Studies were initiated to identify genes in Pseudomonas which play significant roles in this process. The general approach is to use transposons to construct collections of insertion mutants, each of which is then screened for alterations in its interactions with the host plant. In one study a Tn5 derivative containing a constitutively expressed /3-galactosidase (lacZ) gene was used to generate a collection of insertion mutants which could be distinguished from the wild-type parent on X-gal plates. Each mutant was examined for its ability to colonize wheat seedlings in the presence of the wild-type parent. Mutants which gave wild-type:mutant ratio of 20:1 or greater were obtained. In a second study a Tn5 derivative which carries a promoterless lacZ gene located near one end of the transposon was constructed. Expression of the lacZ gene depends on the presence of an active promoter outside of the transposon in the correct orientation. Insertion mutants generated with this transposon were examined for changes in /3-galactosidase expression in the presence and absence of plant root exudate. A number of mutants which showed differential lacZ expression have been identified.

The cohesive single-stranded ends of temperate Bacillus subtilis phage +105 were analyzed with the exonuclease activities of the Kienow fragment of DNA polymerase I and with exonuclease III and were found to be 3' extensions. Chemical sequencing of 3'-end-labeled fragments showed that the ends are 7-base extended 3' single strands and have the sequence: 5'-GCGCTCC-3'. 3'-CGCGAGG-5'

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Chromosomal DNAs of lysogens of 4105 and +105 DI:lt were digested with restriction enzymes EcoRI and HpaI and were probed with nick-translated mature +105 DNA. Altered bacteriophage-specific bands in the lysogens were detected, indicating that the phage integrates into the host chromosome at a single site, probably via a Campbell-type circular intermediate. The phage attachment site is centrally located in the phage genome and lies between the phage immunity region and the nonessential deletable region of 4105.