Genetic diversity in Mediterranean diploid and tetraploid Bromus L. (section Bromus Sm.) populations.

The levels of genetic diversity assessed from allozyme data were investigated in 25 populations of Mediterranean Bromus intermedius, B. squarrosus, B. lanceolatus, and B. hordeaceus from Algeria. The geographically restricted diploids B. intermedius and B. squarrosus displayed less genetic diversity (the mean population gene diversity of Nei (Hu) ranged from 0.03 to 0.12) than the widespread tetraploid colonizers B. lanceolatus and B. hordeaceus (Hu = 0.07-0.27). Deviations from Hardy-Weinberg expectations in diploid populations of B. intermedius and B. squarrosus were observed owing to heterozygote excess at several loci and suggested that these self-fertilizing species may have substantial amounts of allogamy. Tetraploid populations of B. lanceolatus and B. hordeaceus were largely homozygous at homologous loci and frequently exhibited intergenomic fixed heterozygosity in accordance with their alloploid origin. Genetic variation at the infraspecific level was mostly distributed within populations in the four species, B. hordeaceus showing the lowest level of interpopulation differentiation (Gst = 0.06) and the highest level of gene flow (Nm = 3.75). Consistent gene flows are in agreement with the strongest intercontinental invasive behaviour of B. hordeaceus. Less differentiation was reported in the literature among later introduced B. hordeaceus populations from England and Australia, indicating reduced differentiation under the process of colonization. Moderate divergence occured among the four taxa, with interspecific genetic identities ranging from 0.87 to 0.93. In spite of substantial genetic similarity, species were clearly differentiated, with each tetraploid being more closely related to a diploid: B. hordeaceus to B. squarrosus and B. lanceolatus to B. intermedius.     

Régulation de la biosynthèse de l'aspartate-ammonium lyase (aspartase) de Pseudomonas fluorescens

Variations in aspartasic activity in various media are due to aspartate-ammonium lyase induction and to regulation of the biosynthesis of this enzyme. Evidence for neosynthesis of the enzyme is provided by labelling and separation of the protein. The inducer appears to be aspartic acid. The biosynthesis is subject to pronounced catabolic repression. The physiological function of aspartate-ammonium lyase is discussed.     

Whole Genome Sequencing of Field Isolates Reveals a Common Duplication of the Duffy Binding Protein Gene in Malagasy Plasmodium vivax Strains

Background

Plasmodium vivax is the most prevalent human malaria parasite, causing serious public health problems in malaria-endemic countries. Until recently the Duffy-negative blood group phenotype was considered to confer resistance to vivax malaria for most African ethnicities. We and others have reported that P. vivax strains in African countries from Madagascar to Mauritania display capacity to cause clinical vivax malaria in Duffy-negative people. New insights must now explain Duffy-independent P. vivax invasion of human erythrocytes.

Methods/Principal Findings

Through recent whole genome sequencing we obtained ≥70× coverage of the P. vivax genome from five field-isolates, resulting in ≥93% of the Sal I reference sequenced at coverage greater than 20×. Combined with sequences from one additional Malagasy field isolate and from five monkey-adapted strains, we describe here identification of DNA sequence rearrangements in the P. vivax genome, including discovery of a duplication of the P. vivax Duffy binding protein (PvDBP) gene. A survey of Malagasy patients infected with P. vivax showed that the PvDBP duplication was present in numerous locations in Madagascar and found in over 50% of infected patients evaluated. Extended geographic surveys showed that the PvDBP duplication was detected frequently in vivax patients living in East Africa and in some residents of non-African P. vivax-endemic countries. Additionally, the PvDBP duplication was observed in travelers seeking treatment of vivax malaria upon returning home. PvDBP duplication prevalence was highest in west-central Madagascar sites where the highest frequencies of P. vivax-infected, Duffy-negative people were reported.

Conclusions/Significance

The highly conserved nature of the sequence involved in the PvDBP duplication suggests that it has occurred in a recent evolutionary time frame. These data suggest that PvDBP, a merozoite surface protein involved in red cell adhesion is rapidly evolving, possibly in response to constraints imposed by erythrocyte Duffy negativity in some human populations.     

Assessing the impacts of imperfect detection on estimates of diversity and community structure through multispecies occupancy modeling

Detecting all species in a given survey is challenging, regardless of sampling effort. This issue, more commonly known as imperfect detection, can have negative impacts on data quality and interpretation, most notably leading to false absences for rare or difficult‐to‐detect species. It is important that this issue be addressed, as estimates of species richness are critical to many areas of ecological research and management. In this study, we set out to determine the impacts of imperfect detection, and decisions about thresholds for inclusion in occupancy, on estimates of species richness and community structure. We collected data from a stream fish assemblage in Algonquin Provincial Park to be used as a representation of ecological communities. We then used multispecies occupancy modeling to estimate species‐specific occurrence probabilities while accounting for imperfect detection, thus creating a more informed dataset. This dataset was then compared to the original to see where differences occurred. In our analyses, we demonstrated that imperfect detection can lead to large changes in estimates of species richness at the site level and summarized differences in the community structure and sampling locations, represented through correspondence analyses.     

Ocean acidification affects marine chemical communication by changing structure and function of peptide signalling molecules

Ocean acidification is a global challenge that faces marine organisms in the near future with a predicted rapid drop in pH of up to 0.4 units by the end of this century. Effects of the change in ocean carbon chemistry and pH on the development, growth and fitness of marine animals are well documented. Recent evidence also suggests that a range of chemically mediated behaviours and interactions in marine fish and invertebrates will be affected. Marine animals use chemical cues, for example, to detect predators, for settlement, homing and reproduction. But, while effects of high CO₂ conditions on these behaviours are described across many species, little is known about the underlying mechanisms, particularly in invertebrates. Here, we investigate the direct influence of future oceanic pH conditions on the structure and function of three peptide signalling molecules with an interdisciplinary combination of methods. NMR spectroscopy and quantum chemical calculations were used to assess the direct molecular influence of pH on the peptide cues, and we tested the functionality of the cues in different pH conditions using behavioural bioassays with shore crabs (Carcinus maenas) as a model system. We found that peptide signalling cues are susceptible to protonation in future pH conditions, which will alter their overall charge. We also show that structure and electrostatic properties important for receptor binding differ significantly between the peptide forms present today and the protonated signalling peptides likely to be dominating in future oceans. The bioassays suggest an impaired functionality of the signalling peptides at low pH. Physiological changes due to high CO₂ conditions were found to play a less significant role in influencing the investigated behaviour. From our results, we conclude that the change of charge, structure and consequently function of signalling molecules presents one possible mechanism to explain altered behaviour under future oceanic pH conditions.     

Indirect evidence that agricultural pesticides select for insecticide resistance in the malaria vector Anopheles gambiae

We investigated the possible relationship between the agricultural use of insecticides and the emergence of insecticide resistance. Bioassays were conducted using simulated mosquito larval habitats and well known Anopheles gambiae strains. Soil samples were collected from vegetable production areas in Benin, including one site with insecticide use, one site where insecticides had not been used for two months, and a third where insecticides had not been used. Pupation and emergence rates were very low in pyrethroid‐susceptible strains when exposed to soil that had been recently exposed to insecticides. Pupation and emergence rates in strains with the kdr mutation alone or both the kdr and Ace‐1 mutations were much higher. Overall, strains with the kdr mutation survived at higher rates compared to that without kdr mutation. Although this study is observational, we provide indirect evidence indicating that soils from agricultural areas contain insecticide residues that can play a role in the emergence of insecticide resistance in Anopheles. This aspect should be taken into account to better utilize the insecticide in the context of integrated pest management programs.     

Preparation and biological properties of native and recombinant ciliary neurotrophic factor.

CNTF (ciliary neurotrophic factor), purified from rabbit sciatic nerves by a relatively simple procedure, is bioactive in tissue culture at low picomolar concentration and appears as a doublet on polyacrylamide gel electrophoresis (PAGE). In these nerves, CNTF accounts for more than one-half of the survival-promoting activity on ciliary neurons. The concentration of CNTF in rabbit sciatic nerves is estimated to be 5 nmol/kg, more than 1000 times higher than would seem to be required to support neurons if the neurotrophic factor were homogeneously distributed. With recombinant DNA technology, rat CNTF has been synthesized in Escherichia coli, purified without denaturating agents, and found to be bioactive at a slightly lower concentration than CNTF extracted from rabbit sciatic nerves. After radioiodination, CNTF retains biological activity but is not specifically internalized and retrogradely transported in motor and sensory axons. In peripheral nerves, ciliary neurotrophic factor differs biologically from nerve growth factor (NGF) by its much higher tissue concentration and apparent lack of internalization by peripheral nerve axons.     

Dermal gland secretion improves the heat tolerance of the brown dog tick, Rhipicephalus sanguineus, allowing for their prolonged exposure to host body temperature

Dermal glands (sensilla sagittiformia) secrete when brown dog ticks, Rhipicephalus sanguineus, are mechanically disturbed, presumably as a defensive mechanism. Recently, we observed that these glands secrete due to the pressure stimulation of engorgement. In this study, we examine how dermal gland secretion alters the physiology of R. sanguineus, particularly if this secretion is an important mechanism during blood feeding. The ability of ticks to retain water was not modified by dermal gland secretion, but heat tolerance was enhanced. Short-term heat shock was improved slightly (1 h at 50 °C to 1 h at 56 °C) and featured reduced injury responses and greater recovery after heat shock. When exposed to their host body temperature (37 °C) for prolonged periods, individuals that had secreted survived over 1 week longer than individuals that did not secrete. Dorsal application of squalene, the main component of dermal gland secretion, did not increase temperature tolerance, suggesting that the act of secreting rather than the physical properties of the secretion itself is responsible for the increase in heat tolerance. Based on our results, dermal gland secretion may be an essential mechanism in certain tick species (Amblyomma, Dermacentor, Hyalomma, Rhipicephalus, but not Ixodes) for tolerating body temperature and not succumbing to heat stress during the extended time periods of feeding on a mammalian host, serving as a mechanism to prevent heat damage from the host during feeding.     

Design of a specific colonic mucus marker using a human commensal bacterium cell surface domain

Imaging living cells and organs requires innovative, specific, efficient, and well tolerated fluorescent markers targeting cellular components. Such tools will allow proceeding to the dynamic analysis of cells and the adaptation of tissues to environmental cues. In this study, we have identified and synthesized a novel non-toxic fluorescent marker allowing a specific fluorescent staining of the human colonic mucus. Our strategy to identify a molecule able to specifically bind to the human colonic mucus was on the basis of the mucus adhesion properties of commensal bacteria. We identified and characterized the mucus-binding property of a 70-amino acid domain (MUB(70)) expressed on the surface of Lactobacillus strains. The chemical synthesis of MUB(70) was achieved using the human commensal bacterium Lactobacillus reuteri AF120104 protein as a template. The synthesized Cy5-conjugated MUB(70) marker specifically stained the colonic mucus on fixed human, rabbit, and guinea pig tissues. Interestingly, murine tissue was not stained, suggesting significant differences in the composition of the murine colonic mucus. In addition, this marker stained the mucus of living cultured human colonic cells (HT29-MTX) and human colonic tissue explants. Using a biotinylated derivative of MUB(70), we demonstrated that this peptide binds specifically to Muc2, the most abundant secreted mucin, through its glycosylated moieties. Hence, Cy5-MUB(70) is a novel and specific fluorescent marker for mammalian colonic mucus. It may be used for live imaging analysis but also, as demonstrated in this study, as a marker for the diagnosis and the prognosis of colonic mucinous carcinomas.