Structural Properties and Features of Parasitic Bdellovibrio bacteriovorus

The structure of five parasitic strains of Bdellovibrio bacteriovorus was studied by electron microscope after negative staining and in shadow-case and etched freeze-fractured preparations. Special attention was paid to the cell wall and the flagellar sheath which is continuous with the wall or part of it. These structural components reveal distinct features which are induced by certain staining substances; they are exceedingly susceptible to disruption by physical treatments, and in old cells often appear impaired. In freeze-fractured cells the wall shows characteristic fracturing tendencies not known in other microorganisms. These structural properties and features are distinct to Bdellovibrio wall and flagellar sheath, the structural integrity of which is a fundamental requirement for the infectivity and survival of this organism. The anterior end of Bdellovibrio is differentiated: 6 to 12 ring-like structures (9 to 12 nm, outer diameter) are built into its wall and several fibers (7 to 10 nm wide, up to 1.5 μm long) emerge from it. Intracellular structures, which are revealed as compact oval bodies bulging from the cell border and have internal laminated organization, are characteristic of Bdellovibrio after negative staining with certain compounds. These findings on the structure of parasitic Bdellovibrio substantiate previous observations indicating the uniqueness of this organism and add criteria for the identification of this genus.     

How propagule size and environmental suitability jointly determine establishment success: a test using dung beetle introductions

Both the size of founding populations (propagule size) and environmental suitability are known to influence whether a species newly introduced to a location will establish a self-sustaining population. However, these two factors do not operate independently: it is the interaction between propagule size and environmental suitability that determines the probability an introduced population will establish. Here I use the example of dung beetle introductions to Australia to illustrate the importance of this interaction. I first describe equations that model establishment success jointly as a function of propagule size and environmental suitability. I then show how these equations provide insight into the different outcomes observed in two dung beetle species widely introduced to Australia. In one species, variation in propagule size had relatively little influence on establishment success due to large variation in environmental suitability, leading to an essentially bimodal outcome: sites were either very suitable for establishment and introductions succeeded, or sites were unsuitable and introductions failed regardless of propagule size. For the second species, there was much less variation among locations in environmental suitability, leading to propagule size having a strong influence on establishment success. These examples highlight how the interplay between environmental suitability and founding population size is central to determining the probability an introduced species will establish.     

Complement Factor H-Related Protein 3 Serum Levels Are Low Compared to Factor H and Mainly Determined by Gene Copy Number Variation in CFHR3

The major human complement regulator in blood, complement factor H (FH), has several closely related proteins, called FH-related (FHR) proteins. As all FHRs lack relevant complement regulatory activity, their physiological role is not well understood. FHR protein 3 (FHR-3) has been suggested to compete with FH for binding to Neisseria meningitidis, thereby affecting complement-mediated clearance. Clearly, the in vivo outcome of such competition greatly depends on the FH and FHR-3 concentrations. While FH levels have been established, accurate FHR-3 levels were never unequivocally reported to date. Moreover, CFHR3 gene copy numbers commonly vary, which may impact the FHR-3 concentration. Hence, we generated five anti-FHR-3 mAbs to specifically measure FHR-3 in human healthy donors of which we determined the gene copy number variation at the CFH/CFHR locus. Finally, we examined the acute-phase response characteristics of FHR-3 in a small sepsis cohort. We determined FHR-3 levels to have a mean of 19 nM and that under normal conditions the copy number of CFHR3 correlates to a very large extent with the FHR-3 serum levels. On average, FHR-3 was 132-fold lower compared to the FH concentration in the same serum samples and FHR-3 did not behave as a major acute phase response protein.