Mitochondrial Capture Misleads about Ecological Speciation in the Daphnia pulex Complex

The North American ecological species Daphnia pulicaria and Daphnia pulex are thought to have diverged from a common ancestor by adaptation to sympatric but ecologically distinct lake and pond habitats respectively. Based on mtDNA relationships, European D . pulicaria is considered a different species only distantly related to its North American counterpart, but both species share a lactate dehydrogenase (Ldh) allele F supposedly involved in lake adaptation in North America, and the same allele is also carried by the related Holarctic Daphnia tenebrosa . The correct inference of the species’ ancestral relationships is therefore critical for understanding the origin of their adaptive divergence. Our species tree inferred from unlinked nuclear loci for D . pulicaria and D . pulex resolved the European and North American D . pulicaria as sister clades, and we argue that the discordant mtDNA gene tree is best explained by capture of D . pulex mtDNA by D . pulicaria in North America. The Ldh gene tree shows that F-class alleles in D . pulicaria and D . tenebrosa are due to common descent (as opposed to introgression), with D . tenebrosa alleles paraphyletic with respect to D . pulicaria alleles. That D . tenebrosa still segregates the ancestral and derived amino acids at the two sites distinguishing the pond and lake alleles suggests that D . pulicaria inherited the derived states from the D . tenebrosa ancestry. Our results suggest that some adaptations restricting the gene flow between D . pulicaria and D . pulex might have evolved in response to selection in ancestral environments rather than in the species’ current sympatric habitats. The Arctic ( D . tenebrosa ) populations are likely to provide important clues about these issues.     

Impact of subacute ruminal acidosis (SARA) adaptation and recovery on the density and diversity of bacteria in the rumen of dairy cows

Subacute ruminal acidosis (SARA) is characterized by ruminal pH depression and microbial perturbation. The impact of SARA adaptation and recovery on rumen bacterial density and diversity was investigated following high-grain feeding. Four ruminally cannulated dairy cows were fed a hay diet, transitioned to a 65% grain diet for 3 weeks, and returned to the hay diet for 3 weeks. Rumen fluid, rumen solids, and feces were sampled during weeks 0 (hay), 1 and 3 (high grain), and 4 and 6 (hay). SARA was diagnosed during week 1, with a pH below 5.6 for 4.6±1.4 h. Bacterial density was significantly lower in the rumen solids with high grain (P=0.047). Rumen fluid clone libraries from weeks 0, 3, and 6 were assessed at the 98% level and 154 operational taxonomic units were resolved. Week 3 diversity significantly differed from week 0, and community structure differed from weeks 0 and 6 (P<0.0001). Clones belonging to the phylum Firmicutes predominated. Compared with the hay diet, the high-grain diet contained clones from Selenomonas ruminantium and Succiniclasticum ruminis, but lacked Eubacterium spp. SARA adaptation was found to significantly alter bacterial density, diversity, and community structure, warranting further investigation into the role bacteria play in SARA adaptation.     

Elucidation of molecular mechanisms underlying the protective effects of thymoquinone against rheumatoid arthritis

Thymoquinone (TQ) is the major active compound derived from the medicinal Nigella sativa. A few studies have shown that TQ exhibits anti‐inflammatory activities in experimental models of rheumatoid arthritis (RA) through mechanisms that are not fully understood. The aim of this work was to evaluate the in vitro and in vivo effects of TQ and to investigate its influence on the major signalling pathways involved in pathophysiological RA changes. We used isolated human RA fibroblast‐like synoviocytes (FLS) and a rat adjuvant‐induced arthritis model of RA. In isolated RA FLS, TQ (0–10 µM) was not cytotoxic and inhibited slightly lipopolysaccharide (LPS)‐induced FLS proliferation and strongly H₂O₂‐induced 4‐hydroxynonenal (HNE) generation. By studying different inflammatory and catabolic factors, we determined that TQ significantly abolished LPS‐induced interleukin‐1beta (IL‐1β), tumour necrosis factor‐alpha (TNFα), metalloproteinase‐13, cyclooxygenase‐2, and prostaglandin E₂. Furthermore, LPS‐induced the phosphorylation of p38 mitogen‐activated protein kinase, extracellular‐regulated kinases ½, and nuclear factor‐kappaB‐p65 were also blocked by TQ in time‐dependent manner. In our experimental RA model, the oral administration of TQ 5 mg/kg/day significantly reduced the serum levels of HNE, IL‐1β and TNFα as well as bone turnover markers, such as alkaline phosphatase and tartrate‐resistant acid phosphatase. The protective effects of TQ against RA were also evident from the decrease in arthritis scoring and bone resorption. In conclusion, the fact that TQ abolishes a number of factors known to be involved in RA pathogenesis renders it a clinically valuable agent in the prevention of articular diseases, including RA. J. Cell. Biochem. 112: 107–117, 2011. © 2010 Wiley‐Liss, Inc.     

4-Thiophenoxy-2-trichloromethyquinazolines display in vitro selective antiplasmodial activity against the human malaria parasite Plasmodium falciparum

A series of original quinazolines bearing a 4-thiophenoxy and a 2-trichloromethyl group was synthesized in a convenient and efficient way and was evaluated toward its in vitro antiplasmodial potential. The series revealed global good activity against the K1-multi-resistant Plasmodium falciparum strain, especially with hit compound 5 (IC(50)=0.9 μM), in comparison with chloroquine and doxycycline chosen as reference-drugs. Both the in vitro cytotoxicity study which was conducted on the human HepG2 cell line and the in vitro antitoxoplasmic screening against Toxoplasma gondii indicate that this series presents an interesting selective antiplasmodial profile. Structure-activity- and toxicity relationships highlight that the trichloromethyl group plays a key role in the antiplasmodial activity and also show that the modulation of the thiophenol moiety influences the toxicity/activity ratio.     

Heterorhabditis atacamensis n. sp. (Nematoda: Heterorhabditidae), a new entomopathogenic nematode from the Atacama Desert, Chile

A new Heterorhabditis species of entomopathogenic nematode was isolated from soil of the Atacama Desert in Chile. The new species is characterized by morphometrics of the infective juvenile (IJ) with length (L)?=?611 (578-666)?μm, head to excretory pore length (EP)?=?115 (101-126)?μm, tail?=?69 (62-79)?μm long, (EP/tail)?×?100 (E%)?=?165 (149-182) and L/maximum body diameter (ratio a)?=?28 (25-31). The male has spicules 45 (40-49)?μm long, gubernaculum 20 (17-22)?μm long and (spicule length/anal body diameter)?×?100 (SW%)?=?205 (179-249). The hermaphroditic adult has shallow cuticular folds immediately anterior and posterior to the vulva, a slight post-anal swelling and a finely rounded tail terminus. Morphologically, H. atacamensis n. sp. resembles H. safricana, H. marelatus, H. downesi and H. amazonensis, but can be distinguished by characters of adult and IJ stages. In particular, for adult males, H. atacamensis n. sp. differs from H. amazonensis by the number and orientation of the genital papillae and from H. downesi by the position of the excretory pore; by the shape of the female tail terminus from H. downesi and by the position of the IJ hemizonid from H. marelatus. Heterorhabditis atacamensis n. sp. is further characterized by internal transcribed spacer (ITS) and D2D3 rDNA sequences, the closest species, H. safricana, being separated by 13?bp across 730?bp of the ITS (incorporating ITS1 (partial sequence), 5.8S (complete sequence), ITS2 (complete sequence)) and 5?bp across 592?bp of the partial 28S (incorporating D2D3) sequence. The morphological and molecular data confirm that H. atacamensis n. sp. is a valid species.     

Reticulate evolution of the Daphnia pulex complex as revealed by nuclear markers

The study of species complexes is of particular interest to understand how evolutionary young species maintain genomic integrity. The Daphnia pulex complex has been intensively studied as it includes species that dominate freshwater environments in the Northern hemisphere and as it is the sole North American complex that shows transitions to obligate parthenogenesis. Past studies using mitochondrial markers have revealed the presence of 10 distinct lineages in the complex. This study is the first to examine genetic relationships among seven species of the complex at nuclear markers (nine microsatellite loci and one protein-coding gene). Clones belonging to the seven species of the Daphnia pulex complex were characterized at the mitochondrial NADH dehydrogenase (ND5) gene and at the Lactate dehydrogenase (LDH) locus. K-means, principal coordinate analyses and phylogenetic network analyses on the microsatellite data all separated European D. pulicaria, D. tenebrosa, North American D. pulex, D. pulicaria and their hybrids into distinct clusters. The hybrid cluster was composed of diploid and polyploid hybrids with D. pulex mitochondria and some clones with D. pulicaria mitochondria. By contrast, the phylogeny of the D. pulex complex using Rab4 was not well resolved but still showed clusters consisting mostly of D. pulex alleles and others of D. pulicaria alleles. Incomplete lineage sorting and hybridization may obscure genetic relationships at this locus. This study shows that hybridization and introgression have played an important role in the evolution of this complex.     

O-linked glycosylation ensures the normal conformation of the autotransporter adhesin involved in diffuse adherence

The Escherichia coli adhesin involved in diffuse adherence (AIDA-I) is one of the few glycosylated proteins found in Escherichia coli. Glycosylation is mediated by a specific heptosyltransferase encoded by the aah gene, but little is known about the role of this modification and the mechanism involved. In this study, we identified several peptides of AIDA-I modified by the addition of heptoses by use of mass spectrometry and N-terminal sequencing of proteolytic fragments of AIDA-I. One threonine and 15 serine residues were identified as bearing heptoses, thus demonstrating for the first time that AIDA-I is O-glycosylated. We observed that unglycosylated AIDA-I is expressed in smaller amounts than its glycosylated counterpart and shows extensive signs of degradation upon heat extraction. We also observed that unglycosylated AIDA-I is more sensitive to proteases and induces important extracytoplasmic stress. Lastly, as was previously shown, we noted that glycosylation is required for AIDA-I to mediate adhesion to cultured epithelial cells, but purified mature AIDA-I fused to GST was found to bind in vitro to cells whether or not it was glycosylated. Taken together, our results suggest that glycosylation is required to ensure a normal conformation of AIDA-I and may be only indirectly necessary for its cell-binding function.     

Use of selective capture of transcribed sequences to identify genes preferentially expressed by Streptococcus suis upon interaction with porcine brain microvascular endothelial cells

By using the selective capture of transcribed sequences (SCOTS) approach, we identified 28 genes preferentially expressed by the major swine pathogen and zoonotic agent Streptococcus suis upon interaction with porcine brain microvascular endothelial cells. Several of these genes may be considered new S. suis candidate virulence factors. Results from this study demonstrate the suitability of SCOTS for the elucidation of gene expression in streptococcal species and may contribute to a better understanding of the pathogenesis of S. suis infections.