Biomedical subjects

M L Canfield

Publications and source records attributed to M L Canfield.

5 recordsLinked to original sources

PubMed1997

Diversity of opines and opine-catabolizing bacteria isolated from naturally occurring crown gall tumors.

The diversity of opines from 43 naturally occurring crown gall tumors on several plant species was analyzed for the presence of agropine, chrysopine, iminodiacid, an unidentified leucinopine-like iminodiacid (IDA-B), mannopine, octopine, nopaline, DL- and LL-succinamopine, leucinopine and heliopine. Opine utilization patterns of agrobacteria and fluorescent pseudomonads resident in a tumor were then analyzed and compared for agreement with the opine isolated from that tumor. Nopaline was the most common opine found and was detected in tumors from cherry, blackberry, grape, and plum. Octopine was not found, although octopine-catabolizing bacteria were isolated from several tumors. A new, previously undescribed iminodiacid of the succinamopine-leucinopine type (provisionally designated IDA-B) was isolated from tumors of wild blackberry. Field tumors from apple, blueberry and grape yielded no detectable opines, even though opine-utilizing bacteria were present. Bacterial isolates from plum and cherry showed the best correspondence between the opine in tumors (nopaline) and the presence of bacteria that catabolized that opine. However, several unusual opine catabolic combinations were identified, including isolates that catabolized a variety of opines but were nonpathogenic. More variability was observed among isolates from field tumors on the remaining plant species. We isolated novel mannopine-nopaline type agrobacteria from field tumors of cherry, plum and blackberry that induced tumors containing either mannopine (plus agropine) or nopaline, but not both. Epidemiologically, the galled plants from an area were not of clonal origin (same Ti plasmid), indicating that the field tumors from a small area were incited by more than one type of Ti plasmid.

Journal Article↗

PubMed1995

Genetic analysis of nonpathogenic Agrobacterium tumefaciens mutants arising in crown gall tumors.

Little is known about the effect of the host on the genetic stability of bacterial plant pathogens. Crown gall, a plant disease caused by Agrobacterium tumefaciens, may represent a useful model to study this effect. Indeed, our previous observations on the natural occurrence and origin of nonpathogenic agrobacteria suggest that the host plant might induce loss of pathogenicity in populations of A. tumefaciens. Here we report that five different A. tumefaciens strains initially isolated from apple tumors produced up to 99% nonpathogenic mutants following their reintroduction into axenic apple plants. Two of these five strains were also found to produce mutants on pear and/or blackberry plants. Generally, the mutants of the apple isolate D10B/87 were altered in the tumor-inducing plasmid, harboring either deletions in this plasmid or point mutations in the regulatory virulence gene virG. Most of the mutants originating from the same tumor appeared to be of clonal origin, implying that the host plants influenced agrobacterial populations by favoring growth of nonpathogenic mutants over that of wild-type cells. This hypothesis was confirmed by coinoculation of apple rootstocks with strain D10B/87 and a nonpathogenic mutant.

Acetophenones↗

PubMed1991

Contingency interaction analysis in psychotherapy.

This article introduces (a) a computerized coding procedure that rates words and utterances in terms of emotion, cognition, and contract and (b) a contingency method of analyzing verbal interactions. Using transcripts of sessions conducted by 3 master therapists with 1 client, the rating procedure and contingency correlation analyses supported the study's hypotheses. Therapists' utterances were characterized by significantly different amounts of emotion, cognition, and contracts, indicating that communication styles varied in the relative emphasis placed on these attributes. Differences suggest that the therapists responded differently to emotional, cognitive, and contract utterances and that the client's responses were different across the 3 therapist interviews. Split halves of the interviews within therapists and within client sessions were not different, providing further evidence of reliability of the coding and contingency procedures.

Female↗

PubMed1990

Growth of Octopine-Catabolizing Pseudomonas spp. under Octopine Limitation in Chemostats and Their Potential To Compete with Agrobacterium tumefaciens.

The growth characteristics of five octopine-catabolizing pseudomonads have been determined in batch and continuous cultures. All five strains belonged to rRNA homology group I and showed a more psychrotrophic growth pattern than did Agrobacterium tumefaciens B6 and ATCC 15955. In chemostats limited by octopine, either as the source of carbon and nitrogen or the sole source of nitrogen, maximum specific growth rates and substrate affinities were lower than those in chemostats limited by glutamate. These growth dynamics were similar to those observed for Agrobacterium strains B6 and ATCC 15955 even though the catabolic genes and pathways are believed to be different in the two genera. An analysis of the yields in octopine-limited chemostats indicated that the use of octopine as the sole source of carbon and nitrogen was grossly inefficient. Octopine and presumably lysopine and octopinic acid provided a better source of nitrogen than of carbon. One of the Pseudomonas fluorescens strains, E175D, was able to produce its highest yield on octopine as a nitrogen source. Competition models formulated on pure culture parameters indicated that two of the Pseudomonas spp. would dominate A. tumefaciens B6 and ATCC 15955 when in simple competition for octopine as a limiting substrate.

Journal Article↗

PubMed1990

Competition of Octopine-Catabolizing Pseudomonas spp. and Octopine-Type Agrobacterium tumefaciens for Octopine in Chemostats.

The ability of two octopine-catabolizing Pseudomonas spp. and two virulent octopine-type Agrobacterium tumefaciens to compete for substrates has been examined in chemostats. In dual cultures with octopine or glutamate as the limiting carbon or nitrogen source, Pseudomonas fluorescens B99A and E175D always dominated over A. tumefaciens B6 or ATCC 15955. The growth dynamics of each strain in pure culture indicated that some form of antagonism was occurring in dual culture to permit the predominance of the pseudomonads under certain conditions. Although both pseudomonads fluoresce, pyoverdine was not responsible for the observed inhibition. An unidentified antibiotic secreted by both pseudomonads is believed to be responsible. A. tumefaciens B6 grew synergistically in the presence of P. fluorescens B99A with octopine as the limiting nitrogen source. This behavior of Agrobacterium strain B6 may help overcome its grossly inefficient use of octopine as previously reported. The ability of these two pseudomonads to outcompete the agrobacteria under all conditions tested raises the possibility that under field conditions, infectious agrobacteria may be succeeded by opine-catabolizing pseudomonads around crown gall tumors and in the rhizosphere.

Journal Article↗