6 research outputs found
Pneumococcal Gene Complex Involved in Resistance to Extracellular Oxidative Stress
Streptococcus pneumoniae is a Gram-positive bacterium which is a member of the normal human nasopharyngeal flora but can also cause serious disease such as pneumonia, bacteremia, and meningitis. Throughout its life cycle, S. pneumoniae is exposed to significant oxidative stress derived from endogenously produced hydrogen peroxide (H2O2) and from the host through the oxidative burst. How S. pneumoniae, an aerotolerant anaerobic bacterium that lacks catalase, protects itself against hydrogen peroxide stress is still unclear. Bioinformatic analysis of its genome identified a hypothetical open reading frame belonging to the thiol-specific antioxidant (TlpA/TSA) family, located in an operon consisting of three open reading frames. For all four strains tested, deletion of the gene resulted in an approximately 10-fold reduction in survival when strains were exposed to external peroxide stress. However, no role for this gene in survival of internal superoxide stress was observed. Mutagenesis and complementation analysis demonstrated that all three genes are necessary and sufficient for protection against oxidative stress. Interestingly, in a competitive index mouse pneumonia model, deletion of the operon had no impact shortly after infection but was detrimental during the later stages of disease. Thus, we have identified a gene complex involved in the protection of S. pneumoniae against external oxidative stress, which plays an important role during invasive disease.
Complex patterns of global spread in invasive insects: eco-evolutionary and management consequences
The advent of simple and affordable tools
for molecular identification of novel insect invaders
and assessment of population diversity has changed
the face of invasion biology in recent years. The
widespread application of these tools has brought with
it an emerging understanding that patterns in biogeography,
introduction history and subsequent movement
and spread of many invasive alien insects are far more
complex than previously thought. We reviewed the
literature and found that for a number of invasive
insects, there is strong and growing evidence that
multiple introductions, complex global movement,
and population admixture in the invaded range are
commonplace. Additionally, historical paradigms
related to species and strain identities and origins of
common invaders are in many cases being challenged.
This has major consequences for our understanding of
basic biology and ecology of invasive insects and
impacts quarantine, management and biocontrol programs.
In addition, we found that founder effects
rarely limit fitness in invasive insects and may benefit
populations (by purging harmful alleles or increasing
additive genetic variance). Also, while phenotypic
plasticity appears important post-establishment,
genetic diversity in invasive insects is often higher than expected and increases over time via multiple
introductions. Further, connectivity among disjunct
regions of global invasive ranges is generally far
higher than expected and is often asymmetric, with
some populations contributing disproportionately to
global spread. We argue that the role of connectivity in
driving the ecology and evolution of introduced
species with multiple invasive ranges has been historically
underestimated and that such species are often
best understood in a global context