Distribution and ecology of campylobacters in coastal plain streams (Georgia, United States of America)

Campylobacter is the leading cause of bacterium-associated diarrhea in the United States and most developed countries. While this disease is considered a food-borne disease, many clinical cases cannot be linked to a food source. In rural and agrarian areas environmental transmission may be an important factor contributing to case loads. Here we investigated the waterborne prevalence of campylobacters in a mixed-use rural watershed in the coastal plain of southern Georgia (United States). Six sites representing various degrees of agricultural and human influence were surveyed biweekly to monthly for 1 year for the presence of culturable thermophilic campylobacters and other measures of water quality. Campylobacters were frequently present in agriculture- and sewage-impacted stretches of streams. The mean campylobacter counts and overall prevalence were highest downstream from a wastewater treatment plant that handled both human and poultry slaughterhouse waste (相似文献   

Isolation of polymer-degrading bacteria and characterization of the hindgut bacterial community from the detritus-feeding larvae of Tipula abdominalis (Diptera: Tipulidae)

The Tipula abdominalis larval hindgut microbial community presumably facilitates digestion of the lignocellulosic diet. The microbial community was investigated through characterization of bacterial isolates and analysis of 16S rRNA gene clone libraries. This initial study revealed novel bacteria and provides a framework for future studies of this symbiosis.     

Aging alters the skeletal response to disuse in the rat

Disuse has been shown to cause a rapid and dramatic loss of skeletal mass and strength in the load-bearing bones of young and mature animals and humans. However, little is known about the skeletal effects of disuse in aged mammals. The present study was designed to determine whether the skeletal effects of disuse are maintained with extreme age. Fischer 344/Brown Norway male rats (6 and 32 mo old) were hindlimb suspended (HS) or housed individually for 2 wk. Trabecular volume and microarchitecture in the proximal tibia were significantly decreased by HS only in young rats. HS significantly reduced cortical bone mineral density and increased cortical porosity only in old rats by inducing new pore formation. Cortical pore diameter was also increased in old rats, regardless of loading condition. Ex vivo osteogenic and adipogenic cultures established from each group demonstrated that age and HS decreased osteoblastogenesis. Age, but not HS, decreased sensitivity to endogenous bone morphogenetic protein stimulation, as measured by treatment with exogenous Noggin. Adipocyte development increased with age, whereas HS suppressed sensitivity to peroxisome proliferator-activated receptor-gamma-induced differentiation. Serum insulin-like growth factor I levels were reduced with HS in young rats and with age in control and HS rats. These results suggest that the site of bone loss due to disuse is altered with age and that the loss of osteogenic potential with disuse in the old rats may be due to the combined effects of decreased insulin-like growth factor I levels and sensitivity, as well as diminished bone morphogenetic protein production.     

Role of endosomal Na+-K+-ATPase and cardiac steroids in the regulation of endocytosis

Plasma membrane Na⁺-K⁺-ATPase, which drives potassium into and sodium out of the cell, has important roles in numerous physiological processes. Cardiac steroids (CS), such as ouabain and bufalin, specifically interact with the pump and affect ionic homeostasis, signal transduction, and endocytosed membrane traffic. CS-like compounds are present in mammalian tissues, synthesized in the adrenal gland, and considered to be new family of steroid hormones. In this study, the mechanism of Na⁺-K⁺-ATPase involvement in the regulation of endocytosis is explored. We show that the effects of various CS on changes in endosomal pH are mediated by the pump and correspond to their effects on endosomal membrane traffic. In addition, it was found that CS-induced changes in endocytosed membrane traffic were dependent on alterations in [Na⁺] and [H⁺] in the endosome. Furthermore, we show that various CS differentially regulate endosomal pH and membrane traffic. The results suggest that these differences are due to specific binding characteristics. Based on our observations, we propose that Na⁺-K⁺-ATPase is a key player in the regulation of endosomal pH and endocytosed membrane traffic. Furthermore, our results raise the possibility that CS-like hormones regulate differentially intracellular membrane traffic. bufalin; ouabain; endosomal pH     

Urokinase-type plasminogen activator and macrophages are required for skeletal muscle hypertrophy in mice

Adult skeletal muscle possesses remarkable potential for growth in response to mechanical loading; however, many of the cellular and molecular mechanisms involved remain undefined. The hypothesis of this study was that the extracellular serine protease, urokinase-type plasminogen activator (uPA), is required for muscle hypertrophy, in part by promoting macrophage accumulation in muscle subjected to increased mechanical loading. Compensatory muscle hypertrophy was induced in mouse plantaris (PLT) muscles by surgical ablation of synergist muscles. Following synergist ablation, PLT muscles in wild-type mice demonstrated edema and infiltration of neutrophils and macrophages but an absence of overt muscle fiber damage. Sham procedures resulted in no edema or accumulation of inflammatory cells. In addition, synergist ablation was associated with a large increase in activity of uPA in the PLT muscle. uPA-null mice demonstrated complete abrogation of compensatory hypertrophy associated with reduced macrophage accumulation, indicating that uPA is required for hypertrophy. Macrophages isolated from wild-type PLT muscle during compensatory hypertrophy expressed uPA and IGF-I, both of which may contribute to hypertrophy. To determine whether macrophages are required for muscle hypertrophy, clodronate liposomes were administered to deplete macrophages in wild-type mice; this resulted in reduced muscle hypertrophy. Decreased macrophage accumulation was associated with reduced cell proliferation but did not alter signaling through the mammalian target of rapamycin pathway. These data indicate that uPA and macrophages are required for muscle hypertrophy following synergist ablation.     

Recovery of maize (Zea mays L.) inbreds and hybrids from chilling stress of various duration: photosynthesis and antioxidant enzymes

The differences between two maize (Zea mays L.) inbred lines and their F1 hybrids in their response to chilling periods of various duration (1, 2, 3 or 4 weeks) and subsequent return to optimum temperatures were analysed by the measurement of the photosystem (PS) 1 and 2 activity, the photosynthetic pigments' content and the activity of antioxidant enzymes. The PS2 activity and the chlorophyll content decreased in plants subjected to 3 or 4 weeks of chilling, but not in those subjected to 1 or 2 weeks of chilling. This decrease was more pronounced in inbreds compared to their hybrids. The activity of superoxide dismutase did not much change with the increasing length of chilling period in the inbreds but decreased in the hybrids, the glutathione reductase activity increased in both types of genotypes but more in the inbred lines, while for ascorbate peroxidase and catalase the changes in parents-hybrids relationship did not show any specific trend. The PS1 activity and the carotenoids' content was not much affected.     

Novel mechanism of inhibition of rat kidney-type glutaminase by bis-2-(5-phenylacetamido-1,2,4-thiadiazol-2-yl)ethyl sulfide (BPTES)

The release of GA (mitochondrial glutaminase) from neurons following acute ischaemia or during chronic neurodegenerative diseases may contribute to the propagation of glutamate excitotoxicity. Thus an inhibitor that selectively inactivates the released GA may limit the accumulation of excess glutamate and minimize the loss of neurological function that accompanies brain injury. The present study examines the mechanism of inactivation of rat KGA (kidney GA isoform) by the small-molecule inhibitor BPTES [bis-2-(5-phenylacetamido-1,2,4-thiadiazol-2-yl)ethyl sulfide]. BPTES is a potent inhibitor of KGA, but not of the liver GA isoform, glutamate dehydrogenase or gamma-glutamyl transpeptidase. Kinetic studies indicate that, with respect to glutamine, BPTES has a K(i) of approx. 3 microM. Moreover, these studies suggest that BPTES inhibits the allosteric activation caused by phosphate binding and promotes the formation of an inactive complex. Gel-filtration chromatography and sedimentation-velocity analysis were used to examine the effect of BPTES on the phosphate-dependent oligomerization of KGA. This established that BPTES prevents the formation of large phosphate-induced oligomers and instead promotes the formation of a single oligomeric species with distinct physical properties. Sedimentation-equilibrium studies determined that the oligomer produced by BPTES is a stable tetramer. Taken together, the present work indicates that BPTES is a unique and potent inhibitor of rat KGA and elucidates a novel mechanism of inactivation.     

Mammalian NLR proteins; discriminating foe from friend

Eukaryotic organisms of the plant and animal kingdoms have developed evolutionarily conserved systems of defence against microbial pathogens. These systems depend on the specific recognition of microbial products or structures by molecules of the host innate immune system. The first mammalian molecules shown to be involved in innate immune recognition of, and defence against, microbial pathogens were the Toll-like receptors (TLRs). These proteins are predominantly but not exclusively located in the transmembrane region of host cells. Interestingly, mammalian hosts were subsequently found to also harbour cytosolic proteins with analogous structures and functions to plant defence molecules. The members of this protein family exhibit a tripartite domain structure and are characterized by a central nucleotide-binding oligomerization domain (NOD). Moreover, in common with TLRs, most NOD proteins possess a C-terminal leucine-rich repeat (LRR) domain, which is required for the sensing of microbial products and structures. Recently, the name 'nucleotide-binding domain and LRR' (NLR) was coined to describe this family of proteins. It is now clear that NLR proteins play key roles in the cytoplasmic recognition of whole bacteria or their products. Moreover, it has been demonstrated in animal studies that NLRs are important for host defence against bacterial infection. This review will particularly focus on two subfamilies of NLR proteins, the NODs and 'NALPs', which specifically recognize bacterial products, including cell wall peptidoglycan and flagellin. We will discuss the downstream signalling events and host cell responses to NLR recognition of such products, as well as the strategies that bacterial pathogens employ to trigger NLR signalling in host cells. Cytosolic recognition of microbial factors by NLR proteins appears to be one mechanism whereby the innate immune system is able to discriminate between pathogenic bacteria ('foe') and commensal ('friendly') members of the host microflora.     

Dynorphin knockout reduces fat mass and increases weight loss during fasting in mice

Endogenous opioids, particularly dynorphins, have been implicated in regulation of energy balance, but it is not known how they mediate this in vivo. We investigated energy homeostasis in dynorphin knockout mice (Dyn(-/-) mice) and probed the interactions between dynorphins and the neuropeptide Y (NPY) system. Dyn(-/-) mice were no different from wild types with regards to body weight and basal and fasting-induced food intake, but fecal output was increased, suggesting decreased nutrient absorption, and they had significantly less white fat and lost more weight during a 24-h fast. The neuroendocrine and thermal responses to fasting were at least as pronounced in Dyn(-/-) as in wild types, and there was no stimulatory effect of dynorphin knockout on 24-h energy expenditure (kilocalories of heat produced) or physical activity. However, Dyn(-/-) mice showed increased circulating concentrations of 3,4-dihydroxyphenlacetic acid and 3,4-dihydroxyphenylglycol, suggesting increased activity of the sympathetic nervous system. The respiratory exchange ratio of male but not female Dyn(-/-) mice was reduced, demonstrating increased fat oxidation. Interestingly, expression of the orexigenic acting NPY in the hypothalamic arcuate nucleus was reduced in Dyn(-/-) mice. However, fasting-induced increases in pre-prodynorphin expression in the arcuate nucleus, the paraventricular nucleus, and the ventromedial hypothalamus but not the lateral hypothalamus were abolished by deletion of Y(1) but not Y(2) receptors. Therefore, ablation of dynorphins results in increases in fatty acid oxidation in male mice, reductions in adiposity, and increased weight loss during fasting, possibly via increases in sympathetic activity, decreases in intestinal nutrient absorption, and interactions with the NPYergic system.     

Identification and structural characterization of heme binding in a novel dye-decolorizing peroxidase, TyrA

TyrA is a member of the dye-decolorizing peroxidase (DyP) family, a new family of heme-dependent peroxidase recently identified in fungi and bacteria. Here, we report the crystal structure of TyrA in complex with iron protoporphyrin (IX) at 2.3 A. TyrA is a dimer, with each monomer exhibiting a two-domain, alpha/beta ferredoxin-like fold. Both domains contribute to the heme-binding site. Co-crystallization in the presence of an excess of iron protoporphyrin (IX) chloride allowed for the unambiguous location of the active site and the specific residues involved in heme binding. The structure reveals a Fe-His-Asp triad essential for heme positioning, as well as a novel conformation of one of the heme propionate moieties compared to plant peroxidases. Structural comparison to the canonical DyP family member, DyP from Thanatephorus cucumeris (Dec 1), demonstrates conservation of this novel heme conformation, as well as residues important for heme binding. Structural comparisons with representative members from all classes of the plant, bacterial, and fungal peroxidase superfamily demonstrate that TyrA, and by extension the DyP family, adopts a fold different from all other structurally characterized heme peroxidases. We propose that a new superfamily be added to the peroxidase classification scheme to encompass the DyP family of heme peroxidases.