Evolving origin-of-transfer sequences on staphylococcal conjugative and mobilizable plasmids—who’s mimicking whom?

In Staphylococcus aureus, most multiresistance plasmids lack conjugation or mobilization genes for horizontal transfer. However, most are mobilizable due to carriage of origin-of-transfer (oriT) sequences mimicking those of conjugative plasmids related to pWBG749. pWBG749-family plasmids have diverged to carry five distinct oriT subtypes and non-conjugative plasmids have been identified that contain mimics of each. The relaxasome accessory factor SmpO, encoded by each conjugative plasmid, determines specificity for its cognate oriT. Here we characterized the binding of SmpO proteins to each oriT. SmpO proteins predominantly formed tetramers in solution and bound 5′-GNNNNC-3′ sites within each oriT. Four of the five SmpO proteins specifically bound their cognate oriT. An F7K substitution in pWBG749 SmpO switched oriT-binding specificity in vitro. In vivo, the F7K substitution reduced but did not abolish self-transfer of pWBG749. Notably, the substitution broadened the oriT subtypes that were mobilized. Thus, this substitution represents a potential evolutionary intermediate with promiscuous DNA-binding specificity that could facilitate a switch between oriT specificities. Phylogenetic analysis suggests pWBG749-family plasmids have switched oriT specificity more than once during evolution. We hypothesize the convergent evolution of oriT specificity in distinct branches of the pWBG749-family phylogeny reflects indirect selection pressure to mobilize plasmids carrying non-cognate oriT-mimics.     

Interspike Interval Fluctuations in the Crayfish Stretch Receptor

Trains of nerve impulses from the crayfish stretch receptor under steady conditions are found to be extremely regular with a standard deviation of S = 0.7 x 10(-2)tau when tau, the mean interval, is in the 15 to 80 msec range. Such a small fluctuation increases the problems of film recording, accurate measurement of intervals, and especially, drifts. Experimental and mathematical techniques are described to obviate these problems. Evidence is found for a serial correlation coefficient of about -0.2 in the range, tau = 35 msec to tau = 70 msec. Shot noise and Johnson noise in a long axon are evaluated in detail and are shown to be comparable in size. It is also shown that neither shot noise nor Johnson noise is large enough to explain simply the observed interval fluctuations. Other types of membrane noise are discussed.     

Iridovirus and microsporidian linked to honey bee colony decline

Background

In 2010 Colony Collapse Disorder (CCD), again devastated honey bee colonies in the USA, indicating that the problem is neither diminishing nor has it been resolved. Many CCD investigations, using sensitive genome-based methods, have found small RNA bee viruses and the microsporidia, Nosema apis and N. ceranae in healthy and collapsing colonies alike with no single pathogen firmly linked to honey bee losses.

Methodology/Principal Findings

We used Mass spectrometry-based proteomics (MSP) to identify and quantify thousands of proteins from healthy and collapsing bee colonies. MSP revealed two unreported RNA viruses in North American honey bees, Varroa destructor-1 virus and Kakugo virus, and identified an invertebrate iridescent virus (IIV) (Iridoviridae) associated with CCD colonies. Prevalence of IIV significantly discriminated among strong, failing, and collapsed colonies. In addition, bees in failing colonies contained not only IIV, but also Nosema. Co-occurrence of these microbes consistently marked CCD in (1) bees from commercial apiaries sampled across the U.S. in 2006–2007, (2) bees sequentially sampled as the disorder progressed in an observation hive colony in 2008, and (3) bees from a recurrence of CCD in Florida in 2009. The pathogen pairing was not observed in samples from colonies with no history of CCD, namely bees from Australia and a large, non-migratory beekeeping business in Montana. Laboratory cage trials with a strain of IIV type 6 and Nosema ceranae confirmed that co-infection with these two pathogens was more lethal to bees than either pathogen alone.

Conclusions/Significance

These findings implicate co-infection by IIV and Nosema with honey bee colony decline, giving credence to older research pointing to IIV, interacting with Nosema and mites, as probable cause of bee losses in the USA, Europe, and Asia. We next need to characterize the IIV and Nosema that we detected and develop management practices to reduce honey bee losses.     

Congestive heart failure. New frontiers.

Congestive heart failure is a common syndrome with high mortality in its advanced stages. Current therapy includes the use of vasodilator drugs, which have been shown to prolong life. Despite current therapy, mortality remains high in patients with severe heart failure. Potent new inotropic vasodilators have improved ventricular performance but have not prolonged life in patients with end-stage heart failure. Serious arrhythmias are implicated in the sudden deaths of 30% to 40% of patients with severe heart failure, but the benefits of antiarrhythmic therapy have not been established. Upcoming trials will address this question. Ventricular remodeling and progressive dilatation after myocardial infarction commonly lead to congestive heart failure; early unloading of the ventricle with an angiotensin-converting enzyme inhibitor may attenuate these events. These findings support the concept that angiotensin-converting enzyme inhibitors may be useful in managing heart failure of all degrees of severity, including left ventricular dysfunction and end-stage heart failure. Part of the damage that may occur with acute myocardial infarction, particularly in this era of thrombolysis therapy, is reperfusion injury, which may be mediated by oxygen-derived free radicals. Better knowledge of the mechanisms and treatment of myocardial infarction, the leading cause of congestive heart failure, may help prevent or attenuate the development of this syndrome.     

Identification of novel Th2-associated genes in T memory responses to allergens

Atopic diseases are associated with hyperexpression of Th2 cytokines by allergen-specific T memory cells. However, clinical trials with recently developed Th2 inhibitors in atopics have proven disappointing, suggesting underlying complexities in atopy pathogenesis which are not satisfactorily explained via the classical Th1/Th2 paradigm. One likely possibility is that additional Th2-associated genes which are central to disease pathogenesis remain unidentified. The aim of the present study was to identify such novel Th2-associated genes in recall responses to the inhalant allergen house dust mite. In contrast to earlier human microarray studies in atopy which focused on mitogen-activated T cell lines and clones, we concentrated on PBMC-derived primary T cells stimulated under more physiological conditions of low dose allergen exposure. We screened initially for allergen-induced gene activation by microarray, and validated novel genes in independent panels of subjects by quantitative RT-PCR. Kinetic analysis of allergen responses in PBMC revealed an early wave of novel atopy-associated genes involved in signaling which were coexpressed with IL-4 and IL-4R, followed by a later wave of genes encoding the classical Th2 effector cytokines. We further demonstrate that these novel activation-associated Th2 genes up-regulate in response to another atopy-associated physiological stimulus bacterial superantigen, but remain quiescent in nonphysiological responses in primary T cells or cell lines driven by potent mitogens, which may account for their failure to be detected in earlier microarray studies.     

Detection of a fourth orbivirus non-structural protein

The genus Orbivirus includes both insect and tick-borne viruses. The orbivirus genome, composed of 10 segments of dsRNA, encodes 7 structural proteins (VP1-VP7) and 3 non-structural proteins (NS1-NS3). An open reading frame (ORF) that spans almost the entire length of genome segment-9 (Seg-9) encodes VP6 (the viral helicase). However, bioinformatic analysis recently identified an overlapping ORF (ORFX) in Seg-9. We show that ORFX encodes a new non-structural protein, identified here as NS4. Western blotting and confocal fluorescence microscopy, using antibodies raised against recombinant NS4 from Bluetongue virus (BTV, which is insect-borne), or Great Island virus (GIV, which is tick-borne), demonstrate that these proteins are synthesised in BTV or GIV infected mammalian cells, respectively. BTV NS4 is also expressed in Culicoides insect cells. NS4 forms aggregates throughout the cytoplasm as well as in the nucleus, consistent with identification of nuclear localisation signals within the NS4 sequence. Bioinformatic analyses indicate that NS4 contains coiled-coils, is related to proteins that bind nucleic acids, or are associated with membranes and shows similarities to nucleolar protein UTP20 (a processome subunit). Recombinant NS4 of GIV protects dsRNA from degradation by endoribonucleases of the RNAse III family, indicating that it interacts with dsRNA. However, BTV NS4, which is only half the putative size of the GIV NS4, did not protect dsRNA from RNAse III cleavage. NS4 of both GIV and BTV protect DNA from degradation by DNAse. NS4 was found to associate with lipid droplets in cells infected with BTV or GIV or transfected with a plasmid expressing NS4.