Phenotypic Evolution of Therapeutic Salmonella enterica Serovar Typhimurium after Invasion of TRAMP Mouse Prostate Tumor

Salmonella has been of interest in cancer research due to its intrinsic ability to selectively target and colonize within tumors, leading to tumor cell death. Current research indicates promising use of Salmonella in regular administrations to remove tumors in mouse models while minimizing toxic side effects. However, selection of mutants during such long-term tumor colonization is a safety concern, and understanding selection of certain phenotypes within a tumor is an important consideration in predicting the long-term success of bacterium-based cancer treatment strategies. Thus, we have made an initial examination of selected phenotypes in a therapeutic Salmonella enterica serovar Typhimurium population developed from an archival wild-type LT2 strain and intraperitoneally injected into a 6-month-old TRAMP (transgenic adenocarcinoma of mouse prostate) mouse. We compared the original injected strain to isolates recovered from prostate tumors and those recovered from the spleen and liver of non-tumor-bearing TRAMP mice through phenotypic assessments of bacteriophage susceptibility, motility, growth rates, morphology, and metabolic activity. Tumor isolate traits, particularly the loss of wild-type motility and flagella, reflect the selective pressure of the tumor, while the maintenance of bacteriophage resistance indicates no active selection to remove this robust trait. We posit that the Salmonella population adopts certain strategies to minimize energy consumption and maximize survival and proliferation once within the tumor. We find these insights to be nonnegligible considerations in the development of cancer therapies involving bacteria and suggest further examinations into the evolution of therapeutic strains during passage through tumors.Center for Cancer Research (National Cancer Institute (U.S.)

Near-Ultraviolet Mutagenesis in Superoxide Dismutase-deficient Strains of Escherichia coli.

We compared mutagenic spectra induced by polychromatic near-ultraviolet radiation (near-UV; 300-400 nm) with superoxide anion (O2-) -dependent mutagenesis using a set of Escherichia coli tester strains. Near-UV radiation produced increased frequencies of G:C to A:T transitions, G:C to T:A and A:T to T:A transversions, and small increases in frameshift mutations in wild-type cells. Tester strains lacking superoxide dismutase (SOD) activity (sodAsodB double mutants) demonstrated high spontaneous mutation frequencies and increased near-UV sensitivity. The double mutants also showed increased mutations induced by near-UV compared to either isogenic wild type, sodA or sodB single mutants. Futhermore, these mutants had an unusual spontaneous mutation spectrum, with a predominance of A:T to T:A transversions, followed by G:C to T:A transversions and frameshifts generated in runs of adenines in both the +1 and -1 direction. Other frameshifts were detected to a lesser degree. The oxygen dependency and the type of mutations spontaneously induced in SOD-deficient cells indicated that this mutagenic spectrum was caused by oxidative DNA damage. However, no apparent synergistic action between near-UV radiation and an increased flux of O2- could be detected. From the frequency and types of mutations induced by the two agents, we speculate that near-UV-induced mutagenesis and O2--dependent mutagenesis involve, in part, different lesion(s) and/or mechanism(s). The nature and possible mutagenic pathways of each are discussed

Ongoing Phenotypic and Genomic Changes in Experimental Coevolution of RNA Bacteriophage Qβ and Escherichia coli

According to the Red Queen hypothesis or arms race dynamics, coevolution drives continuous adaptation and counter-adaptation. Experimental models under simplified environments consisting of bacteria and bacteriophages have been used to analyze the ongoing process of coevolution, but the analysis of both parasites and their hosts in ongoing adaptation and counter-adaptation remained to be performed at the levels of population dynamics and molecular evolution to understand how the phenotypes and genotypes of coevolving parasite–host pairs change through the arms race. Copropagation experiments with Escherichia coli and the lytic RNA bacteriophage Qβ in a spatially unstructured environment revealed coexistence for 54 days (equivalent to 163–165 replication generations of Qβ) and fitness analysis indicated that they were in an arms race. E. coli first adapted by developing partial resistance to infection and later increasing specific growth rate. The phage counter-adapted by improving release efficiency with a change in host specificity and decrease in virulence. Whole-genome analysis indicated that the phage accumulated 7.5 mutations, mainly in the A2 gene, 3.4-fold faster than in Qβ propagated alone. E. coli showed fixation of two mutations (in traQ and csdA) faster than in sole E. coli experimental evolution. These observations suggest that the virus and its host can coexist in an evolutionary arms race, despite a difference in genome mutability (i.e., mutations per genome per replication) of approximately one to three orders of magnitude

Evidence for phage-mediated gene transfer among Pseudomonas aeruginosa strains on the phylloplane

As the use of genetically engineered microorganisms for agricultural tasks becomes more frequent, the ability of bacteria to exchange genetic material in the agricultural setting must be assessed. Transduction (bacterial virus-mediated horizontal gene transfer) is a potentially important mechanism of gene transfer in natural environments. This study investigated the potential of plant leaves to act as surfaces on which transduction can take place among microorganisms. Pseudomonas aeruginosa and its generalized transducing bacteriophage F116 were used as a model system. The application of P. aeruginosa lysogens of F116 to plant leaves resulted in genetic exchange among donor and recipient organisms resident on the same plant. Transduction was also observed when these bacterial strains were inoculated onto adjacent plants and contact was made possible through high-density planting.Peer reviewedMicrobiology and Molecular Genetic

Tryptohan photoproduct as a genetic probe : effects on bacteria

Recombinationless (rec) mutants of bacteria are sensitive to visible and near-ultraviolet wavelengths of light. In addition, these mutants are sensitive to a tryptophan photoproduct that results from irradiation of this amino acid by 280-365 nm wavelengths. The physical and biological damages are different from those produced by 254 nm UV. Both the longer wavelengths and the tryptophan photoproduct are mutagenic and influence the genetic recombinational process in bacteria. Since the natural environment includes an abundance of both free tryptophan and sunlight, the relevance of the effect of these agents is provocative.A. EISENSTARK, Division of Biological Sciences, University of Missouri-Columbia Columbia, Missouri