Thermal robustness of signaling in bacterial chemotaxis

Temperature is a global factor that affects the performance of all intracellular networks. Robustness against temperature variations is thus expected to be an essential network property, particularly in organisms without inherent temperature control. Here, we combine experimental analyses with computational modeling to investigate thermal robustness of signaling in chemotaxis of Escherichia coli, a relatively simple and well-established model for systems biology. We show that steady-state and kinetic pathway parameters that are essential for chemotactic performance are indeed temperature-compensated in the entire physiological range. Thermal robustness of steady-state pathway output is ensured at several levels by mutual compensation of temperature effects on activities of individual pathway components. Moreover, the effect of temperature on adaptation kinetics is counterbalanced by preprogrammed temperature dependence of enzyme synthesis and stability to achieve nearly optimal performance at the growth temperature. Similar compensatory mechanisms are expected to ensure thermal robustness in other systems.     

Campylobacter troglodytis sp. nov., isolated from feces of human-habituated wild chimpanzees (Pan troglodytes schweinfurthii) in Tanzania

The transmission of simian immunodeficiency and Ebola viruses to humans in recent years has heightened awareness of the public health significance of zoonotic diseases of primate origin, particularly from chimpanzees. In this study, we analyzed 71 fecal samples collected from 2 different wild chimpanzee (Pan troglodytes) populations with different histories in relation to their proximity to humans. Campylobacter spp. were detected by culture in 19/56 (34%) group 1 (human habituated for research and tourism purposes at Mahale Mountains National Park) and 0/15 (0%) group 2 (not human habituated but propagated from an introduced population released from captivity over 30 years ago at Rubondo Island National Park) chimpanzees, respectively. Using 16S rRNA gene sequencing, all isolates were virtually identical (at most a single base difference), and the chimpanzee isolates were most closely related to Campylobacter helveticus and Campylobacter upsaliensis (94.7% and 95.9% similarity, respectively). Whole-cell protein profiling, amplified fragment length polymorphism analysis of genomic DNA, hsp60 sequence analysis, and determination of the mol% G+C content revealed two subgroups among the chimpanzee isolates. DNA-DNA hybridization experiments confirmed that both subgroups represented distinct genomic species. In the absence of differential biochemical characteristics and morphology and identical 16S rRNA gene sequences, we propose to classify all isolates into a single novel nomenspecies, Campylobacter troglodytis, with strain MIT 05-9149 as the type strain; strain MIT 05-9157 is suggested as the reference strain for the second C. troglodytis genomovar. Further studies are required to determine whether the organism is pathogenic to chimpanzees and whether this novel Campylobacter colonizes humans and causes enteric disease.     

Host habitat assessment by a parasitoid using fungal volatiles

Background

The genus Mantella, endemic poison frogs of Madagascar with 16 described species, are known in the field of international pet trade and entered under the CITES control for the last four years. The phylogeny and phylogeography of this genus have been recently subject of study for conservation purposes. Here we report on the studies of the phylogeography of the Mantella cowani group using a fragment of 453 bp of the mitochondrial cytochrome b gene from 195 individuals from 21 localities. This group is represented by five forms: M. cowani, a critically endangered species, a vulnerable species, M. haraldmeieri, and the non-threatened M. baroni, M. aff. baroni, and M. nigricans.

Results

The Bayesian phylogenetic and haplotype network analyses revealed the presence of three separated haplotype clades: (1) M. baroni, M. aff. baroni, M. nigricans, and putative hybrids of M. cowani and M. baroni, (2) M. cowani and putative hybrids of M. cowani and M. baroni, and (3) M. haraldmeieri. The putative hybrids were collected from sites where M. cowani and M. baroni live in sympatry.

Conclusion

These results suggest (a) a probable hybridization between M. cowani and M. baroni, (b) a lack of genetic differentiation between M. baroni/M. aff. baroni and M. nigricans, (c) evidence of recent gene-flow between the northern (M. nigricans), eastern (M. baroni), and south-eastern (M. aff. baroni) forms of distinct coloration, and (d) the existence of at least three units for conservation in the Mantella cowani group.     

Subgingival Microbial Communities in Leukocyte Adhesion Deficiency and Their Relationship with Local Immunopathology

Leukocyte Adhesion Deficiency I (LAD-I) is a primary immunodeficiency caused by single gene mutations in the CD18 subunit of β2 integrins which result in defective transmigration of neutrophils into the tissues. Affected patients suffer from recurrent life threatening infections and severe oral disease (periodontitis). Microbial communities in the local environment (subgingival plaque) are thought to be the triggers for inflammatory periodontitis, yet little is known regarding the microbial communities associated with LAD-I periodontitis. Here we present the first comprehensive characterization of the subgingival communities in LAD-I, using a 16S rRNA gene-based microarray, and investigate the relationship of this tooth adherent microbiome to the local immunopathology of periodontitis. We show that the LAD subgingival microbiome is distinct from that of health and Localized Aggressive Periodontitits. Select periodontitis-associated species in the LAD microbiome included Parvimonas micra, Porphyromonas endodontalis, Eubacterium brachy and Treponema species. Pseudomonas aeruginosa, a bacterium not typically found in subgingival plaque is detected in LAD-I. We suggest that microbial products from LAD-associated communities may have a role in stimulating the local inflammatory response. We demonstrate that bacterial LPS translocates into the lesions of LAD-periodontitis potentially triggering immunopathology. We also show in in vitro assays with human macrophages and in vivo in animal models that microbial products from LAD-associated subgingival plaque trigger IL-23-related immune responses, which have been shown to dominate in patient lesions. In conclusion, our current study characterizes the subgingival microbial communities in LAD-periodontitis and supports their role as triggers of disease pathogenesis.     

Treponema saccharophilum sp. nov., a large pectinolytic spirochete from the bovine rumen.

A large, obligately anaerobic spirochete (strain PB) was isolated from bovine rumen fluid by a procedure involving rifampin as a selective agent. The helical cells measured 0.6 to 0.7 micron by 12 to 20 micron and possessed approximately 16 periplasmic flagella inserted near each end of the protoplasmic cylinder. The periplasmic flagella were arranged in a bundle wound around the cell body. Strain PB utilized as fermentable substrates various plant polysaccharides (e.g., pectin, arabinogalactan, starch, and inulin) as well as pentoses, hexoses, disaccharides, and uronic acids. Glucose was fermented to acetate, formate, and ethanol, whereas the fermentation of pectin or glucuronic acid yielded only acetate and formate as major end products. Determinations of radioactivity in end products and assays of enzymatic activities indicated that strain PB catabolized glucose via the Embden-Meyerhof pathway. Extracts of cells grown in pectin-containing media possessed relatively high levels of phospho-2-keto-3-deoxygluconate aldolase activity, an enzymatic activity typical of the Entner-Doudoroff pathway. The guanine-plus-cytosine content of the DNA of strain PB (54 mol%) was considerably higher than that of known host-associated anaerobic spirochetes. This study indicates that strain PB represents a new species of Treponema, for which we propose the name Treponema saccharophilum.     

Helicobacter muridarum sp. nov., a microaerophilic helical bacterium with a novel ultrastructure isolated from the intestinal mucosa of rodents.

Helical organisms with novel ultrastructural characteristics were isolated from the intestinal mucosa of rats and mice. These bacteria were characterized by the presence of 9 to 11 periplasmic fibers which appeared as concentric helical ridges on the surface of each cell. The cells were motile with a rapid corkscrewlike motion and had bipolar tufts of 10 to 14 sheathed flagella. The bacteria were microaerophilic, nutritionally fastidious, and physiologically similar to Helicobacter species and Wolinella succinogenes but could be differentiated from these organisms by their unique cellular ultrastructure. Using 16S rRNA sequencing, we found that strain ST1T (T = type strain) was related to previously described Helicobacter species, "Flexispira rappini," and W. succinogenes. The closest relatives of strain ST1T were Helicobacter mustelae and "F. rappini" (average similarity value, 96%). On the basis of phylogenetic data, strain ST1T (= ATCC 49282T) represents a new species of the genus Helicobacter, for which we propose the name Helicobacter muridarum.     

Phylogenetic analysis of the spirochetes.

The 16S rRNA sequences were determined for species of Spirochaeta, Treponema, Borrelia, Leptospira, Leptonema, and Serpula, using a modified Sanger method of direct RNA sequencing. Analysis of aligned 16S rRNA sequences indicated that the spirochetes form a coherent taxon composed of six major clusters or groups. The first group, termed the treponemes, was divided into two subgroups. The first treponeme subgroup consisted of Treponema pallidum, Treponema phagedenis, Treponema denticola, a thermophilic spirochete strain, and two species of Spirochaeta, Spirochaeta zuelzerae and Spirochaeta stenostrepta, with an average interspecies similarity of 89.9%. The second treponeme subgroup contained Treponema bryantii, Treponema pectinovorum, Treponema saccharophilum, Treponema succinifaciens, and rumen strain CA, with an average interspecies similarity of 86.2%. The average interspecies similarity between the two treponeme subgroups was 84.2%. The division of the treponemes into two subgroups was verified by single-base signature analysis. The second spirochete group contained Spirochaeta aurantia, Spirochaeta halophila, Spirochaeta bajacaliforniensis, Spirochaeta litoralis, and Spirochaeta isovalerica, with an average similarity of 87.4%. The Spirochaeta group was related to the treponeme group, with an average similarity of 81.9%. The third spirochete group contained borrelias, including Borrelia burgdorferi, Borrelia anserina, Borrelia hermsii, and a rabbit tick strain. The borrelias formed a tight phylogenetic cluster, with average similarity of 97%. THe borrelia group shared a common branch with the Spirochaeta group and was closer to this group than to the treponemes. A single spirochete strain isolated fromt the shew constituted the fourth group. The fifth group was composed of strains of Serpula (Treponema) hyodysenteriae and Serpula (Treponema) innocens. The two species of this group were closely related, with a similarity of greater than 99%. Leptonema illini, Leptospira biflexa, and Leptospira interrogans formed the sixth and most deeply branching group. The average similarity within this group was 83.2%. This study represents the first demonstration that pathogenic and saprophytic Leptospira species are phylogenetically related. The division of the spirochetes into six major phylogenetic clusters was defined also by sequence signature elements. These signature analyses supported the conclusion that the spirochetes represent a monophylectic bacterial phylum.