Fitness Consequences of Infection by Batrachochytrium dendrobatidis in Northern Leopard Frogs (Lithobates pipiens)

The amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), has been linked to amphibian declines and extinctions worldwide. The pathogen has been found on amphibians throughout eastern North America, but has not been associated with mass die-offs in this region. In this study, we conducted laboratory experiments on the effects of Bd infection in a putative carrier species, Lithobates pipiens, using two estimators of fitness: jumping performance and testes morphology. Over the 8-week study period, peak acceleration during jumping was not significantly different between infected and uninfected animals. Peak velocity, however, was significantly lower for infected animals after 8 weeks. Two measures of sperm production, germinal epithelium depth, and maximum spermatic cyst diameter, showed no difference between infected and uninfected animals. The width, but not length, of testes of infected animals was significantly greater than in uninfected animals. This study is the first to show effects on whole-organism performance of Bd infection in post-metamorphic amphibians, and may have important long-term, evolutionary implications for amphibian populations co-existing with Bd infection.     

Characterization of a Salmonella choleraesuis mutant that cannot multiply within epithelial cells

A mutant of Salmonella choleraesuis was identified that could invade (enter) and penetrate through polarized monolayers of Caco-2 and MDCK epithelial cells at normal levels but was defective for intracellular multiplication within these cells. It was also able to survive inside cultured J774 macrophage cells. These bacteria remained inside membrane-bound vacuoles, which coalesced at later times in the perinuclear region of the epithelial cell. This mutant exhibited slightly slower growth rates in rich or minimal media than the parental strain but was normal for iron usage, phosphate usage, and anaerobic growth and was a prototroph. The mutant was completely avirulent when administered orally or intravenously to susceptible mice. These results suggest that the ability to multiply within eukaryotic cells may contribute to S. choleraesuis virulence.     

Viral phenotypes and antibody responses in long-term survivors infected with attenuated human immunodeficiency virus type 1 containing deletions in the nef and long terminal repeat regions

The Sydney Blood Bank Cohort (SBBC) consists of eight blood transfusion recipients infected with nef-attenuated human immunodeficiency virus type 1 (HIV-1) acquired from a single donor. Here, we show that viral phenotypes and antibody responses differ considerably between individual cohort members, despite the single source of infection. Replication of isolated virus varied from barely detectable to similar to that of the wild-type virus, and virus isolated from five SBBC members showed coreceptor usage signatures unique to each individual. Higher viral loads and stronger neutralizing antibody responses were associated with better-replicating viral strains, and detectable viral replication was essential for the development of strong and sustained humoral immune responses. Despite the presence of strong neutralizing antibodies in a number of SBBC members, disease progression was not prevented, and each cohort member studied displayed a unique outcome of infection with nef-attenuated HIV-1.     

Role of calpains in diabetes mellitus: a mini review

Type 2 diabetes mellitus (T2DM) is characterized by defects in haepatic glucose production, insulin action and insulin secretion, which can also lead to a variety of secondary disorders. The disease can lead to death without treatment and it has been predicted that T2DM will affect 215 million people world-wide by 2010. T2DM is a multifactorial condition whose precise genetic causes and biochemical defects have not been fully elucidated but at both levels, calpains appear to play a role. Positional cloning studies mapped T2DM susceptibility to CAPN10, the gene encoding the intracellular cysteine protease, calpain 10. Further studies have shown a number of non-coding polymorphisms in CAPN10 to be functionally associated with T2DM whilst the identification of coding polymorphisms, suggested that mutant calpain 10 proteins may also contribute to the disease. The presence of both calpain 10 and its mRNA have been demonstrated in tissues from several mammalian species whilst calpain 10 appears to be associated with pathways involved in glucose metabolism, insulin secretion and insulin action. It appears that other calpains may also participate in these pathways and here we present an overview of recent studies on calpains and their putative role in T2DM.     

What Drives the Occurrence of the Melioidosis Bacterium Burkholderia pseudomallei in Domestic Gardens?

Melioidosis is an often fatal infectious disease affecting humans and animals in tropical regions and is caused by the saprophytic environmental bacterium Burkholderia pseudomallei. Domestic gardens are not only a common source of exposure to soil and thus to B. pseudomallei, but they also have been found to contain more B. pseudomallei than other environments. In this study we addressed whether anthropogenic manipulations common to gardens such as irrigation or fertilizers change the occurrence of B. pseudomallei. We conducted a soil microcosm experiment with a range of fertilizers and soil types as well as a longitudinal interventional study over three years on an experimental fertilized field site in an area naturally positive for B. pseudomallei. Irrigation was the only consistent treatment to increase B. pseudomallei occurrence over time. The effects of fertilizers upon these bacteria depended on soil texture, physicochemical soil properties and biotic factors. Nitrates and urea increased B. pseudomallei load in sand while phosphates had a positive effect in clay. The high buffering and cation exchange capacities of organic material found in a commercial potting mix led to a marked increase in soil salinity with no survival of B. pseudomallei after four weeks in the potting mix sampled. Imported grasses were also associated with B. pseudomallei occurrence in a multivariate model. With increasing population density in endemic areas these findings inform the identification of areas in the anthropogenic environment with increased risk of exposure to B. pseudomallei.     

DNA primase of plasmid ColIb is involved in conjugal DnA synthesis in donor and recipient bacteria.

The sog gene of the IncI alpha group plasmid ColIb is known to encode a DNA primase that can substitute for defective host primase in dnaG mutants of Escherichia coli during discontinuous DNA replication. The biological significance of this enzyme was investigated by using sog mutants, constructed from a derivative of ColIb by in vivo recombination of previously defined mutations in a cloned sog gene. The resultant Sog- plasmids failed to specify detectable primase activity and were unable to suppress a dnaG lesion. These mutants were maintained stably in E. coli, implying that the enzyme is not involved in vegetative replication of ColIb. However, the Sog- plasmids were partially transfer deficient in E. coli and Salmonella typhimurium matings, consistent with the hypothesis that the normal physiological role of this enzyme is in conjugation. This was confirmed by measurements of conjugal DNA synthesis. Studies of recipient cells have indicated that plasmid primase is required to initiate efficient synthesis of DNA complementary to the transferred strand, with the protein being supplied by the donor parent and probably transmitted between the mating cells. Primase specified by the dnaG gene of the recipient can substitute partially for the mutant enzyme, thus providing an explanation for the partial transfer proficiency of the mutant plasmids. Conjugal DNA synthesis in dnaB donor cells was deficient in the absence of plasmid primase, implying that the enzyme also initiates synthesis of DNA to replace the transferred material.     

The Amphibian Chytrid Fungus, Batrachochytrium dendrobatidis, in Fully Aquatic Salamanders from Southeastern North America

Little is known about the impact that the pathogenic amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), has on fully aquatic salamander species of the eastern United States. As a first step in determining the impacts of Bd on these species, we aimed to determine the prevalence of Bd in wild populations of fully aquatic salamanders in the genera Amphiuma, Necturus, Pseudobranchus, and Siren. We sampled a total of 98 salamanders, representing nine species from sites in Florida, Mississippi, and Louisiana. Overall, infection prevalence was found to be 0.34, with significant differences among genera but no clear geographic pattern. We also found evidence for seasonal variation, but additional sampling throughout the year is needed to clarify this pattern. The high rate of infection discovered in this study is consistent with studies of other amphibians from the southeastern United States. Coupled with previously published data on life histories and population densities, the results presented here suggest that fully aquatic salamanders may be serving as important vectors of Bd and the interaction between these species and Bd warrants additional research.     

Molecular cloning and characterization of the aroD gene encoding 3-dehydroquinase from Salmonella typhi

The aroD gene from Salmonella typhi, encoding 5-dehydroquinate hydrolyase (3-dehydroquinase), has been cloned into Escherichia coli and the DNA sequence determined. The aroD gene was isolated from a cosmid gene bank by complementation of an S. typhimurium aroD mutant. Analysis of the DNA sequence revealed the presence of an open reading frame capable of encoding a protein of 252 amino acids with a calculated Mr of 27706. Comparison of the deduced S. typhi 3-dehydroquinase protein sequence with that elucidated for E. coli revealed 69% homology. Alignment of the S. typhi sequence and equivalent Aspergillus nidulans and Saccharomyces cerevisiae sequences showed that homology was lower, at 24%, but still significant. Use of a minicell expression system demonstrated that a polyclonal antibody raised against E. coli 3-dehydroquinase cross-related with its S. typhi counterpart.