Preclinical Class 1 Integron with a Complete Tn402-Like Transposition Module▿

The presence of integrons was assessed in gut bacteria isolated from wild-caught prawns. A pseudomonad was recovered that contained a Tn402-like class 1 integron with a complete transposition module and two gene cassettes. One cassette was identical to a previously described cassette from a chromosomal class 3 integron in Delftia tsuruhatensis

Recombination Activity of a Distinctive Integron-Gene Cassette System Associated with Pseudomonas stutzeri Populations in Soil

Class 1 integrons have strongly influenced the evolution of multiple antibiotic resistance. Diverse integrons have recently been detected directly in a range of natural environments. In order to characterize the properties of these environmental integrons, we sought to isolate organisms containing integrons from soils, which resulted in the isolation of Pseudomonas stutzeri strain Q. Further isolation efforts targeted at this species resulted in recovery of two other strains (P and BAM). 16S rRNA sequences and chromosome mapping showed that these three strains are very closely related clonal variants in a single genomovar of P. stutzeri. Only strains Q and BAM were found to contain an integron and an associated gene cassette array. The intI and attI components of these strains showed 99 and 90% identity, respectively. The structure of these integrons and their associated gene cassettes was similar to that reported previously for other integron classes. The two integrons contained nonoverlapping sets of cassette-associated genes. In contrast, many of the cassette-associated recombination sites in the two integrons were similar and were considered to constitute a distinct subfamily consisting of 59-base element (59-be) recombination sites (the Pseudomonas subfamily). The recombination activity of P. stutzeri integron components was tested in cointegrate assays. IntIPstQ was shown to catalyze site-specific recombination between its cognate attI site and 59-be sites from antibiotic resistance gene cassettes. While IntIPstQ did not efficiently mediate recombination between members of the Pseudomonas 59-be subfamily and other 59-be types, the former sites were functional when they were tested with IntI1. We concluded that integrons present in P. stutzeri possess recombination activity and represent a hot spot for genomic diversity in this species

Mobilization of a Tn402-Like Class 1 Integron with a Novel Cassette Array via Flanking Miniature Inverted-Repeat Transposable Element-Like Structures ▿

A Tn402-like class 1 integron was recovered from a prawn-associated bacterium. One of its cassettes included methionine sulfoxide reductase genes, the first example of such genes being captured by an integron. The integron was flanked by direct repeats that resemble miniature inverted-repeat transposable element sequences. Excision of the integron by homologous recombination through these sequences was demonstrated

Mobile gene cassettes : a fundamental resource for bacterial evolution

Horizontal gene transfer increases genetic diversity in prokaryotes to a degree not allowed by the limitations of reproduction by binary fission. The integron/gene cassette system is one of the most recently characterized examples of a system that facilitates horizontal gene transfer. This system, discovered in the context of multidrug resistance, is recognized in a clinical context for its role in allowing pathogens to adapt to the widespread use of antibiotics. Recent studies suggest that gene cassettes are common and encode functions relevant to many adaptive traits. To estimate the diversity of mobile cassettes in a natural environment, a molecular technique was developed to provide representative distributions of cassette populations at points within a sampling area. Subsequently, statistical methods analogous to those used for calculating species diversity were employed to assess the diversity of gene cassettes within the sample area in addition to gaining an estimate of cassette pool size. Results indicated that the number of cassettes within a 5x12 ‐m sample area was large and that the overall mobile cassette metagenome was likely to be orders of magnitude larger again. Accordingly, gene cassettes appear to be capable of mobilizing a significant genetic resource and consequently have a substantial impact on bacterial adaptability.12 page(s

An enhanced miniaturized assay for antimicrobial prospecting

Bioprospecting for novel antimicrobials increasingly relies on extremely small samples unsuitable for conventional bulk extraction and assay. We developed a microtitre plate assay for minimal amounts of test materials which is rapid, extremely sensitive, allows time-course analysis and reduces false negatives. Developed for the analyses of antimicrobial sensitivity and resistance, the technique is appropriate for assays where source materials are scarce

Differential antimicrobial activity in response to the entomopathogenic fungus Cordyceps in six Australian bee species

Microbial pathogens were important in the evolution of insect societies and remain a major cause of colony death. The differential effects are reported of antimicrobial compounds extracted from six species of Australian native bees on the spores and hyphae of the entomopathogenic fungus Cordyceps bassiana. The bee species were: Amegilla bombiformis, A. asserta, Exoneura robusta, E. nigrescens, Exoneurella tridentata and Trigona carbonaria. The fungus was isolated from E. robusta and it was this species that showed the greatest activity against both Cordyceps spore germination and hyphal growth. One explanation is that anti-Cordyceps activity may have been under greatest selection in this bee species, but its congener, E. nigrescens, showed only slightly weaker activity against the pathogen. In contrast, A. bombiformis, A. asserta, E. tridentata and T. carbonaria showed considerable variation in anti-Cordyceps activity. Nevertheless, there was a trend of greater activity against Cordyceps spore germination than hyphal growth. On the basis of this result, a mechanism whereby fungal pathogens may have been important drivers of social evolution is suggested