Lactobacilli-Host mutualism: "learning on the fly"

Metazoans establish with microorganisms complex interactions for their mutual benefits. Drosophila, which has already proven useful host model to study several aspects of innate immunity and host-bacteria pathogenic associations has become a powerful model to dissect the mechanisms behind mutualistic host-microbe interactions. Drosophila microbiota is composed of simple and aerotolerant bacterial communities mostly composed of Lactobacillaceae and Acetobactereaceae. Drosophila mono- or poly-associated with lactobacilli strains constitutes a powerful model to dissect the complex interplay between lactobacilli and host biologic traits. Thanks to the genetic tractability of both Drosophila and lactobacilli this association model offers a great opportunity to reveal the underlying molecular mechanisms. Here, we review our current knowledge about how the Drosophila model is helping our understanding of how lactobacilli shapes host biology.     

The distribution and location of the symbiont Lagenophrys aselli on the freshwater isopod Asellus aquaticus

1. The distribution and location of the ciliated protozoan Lagenophrys aselli on the freshwater isopod Asellus aquaticus were studied in relation to water flow over the third pleopod surface. 2. At low densities L. aselli had a significant preference for the anterior centre of the pleopod; however, at the highest densities this preference was no longer significant. The distribution ranged from closer than random at low densities to further than random at the highest densities, and may have been a product of feeding and reproduction of L. aselli as well as the short intermoult period of the host. 3. An individual L. aselli has an effective area of both the lorica and the ciliated feeding disc. The ciliated feeding disc, when extended, may contribute to the presence of a small anterior–posterior gap being left between individuals.     

Distribution of the ticks <Emphasis Type="Italic">Ixodes persulcatus</Emphasis> and <Emphasis Type="Italic">Ixodes pavlovskyi</Emphasis> on the boundary of the forest and forest-steppe zones in the Ob region

Surveys of ixodoid ticks were performed in Novosibirsk Province (Novosibirsk and Toguchin Districts) and in the vicinity of Akademgorodok (Novosibirsk) in 2009–2010. The abundance and distribution of ticks were assessed in 8 types of habitats. Ixodes persulcatus (Schulze, 1930) was collected by flagging in Novosibirsk and Toguchin Districts, with the highest densities of 19 ind./km being observed in habitats with small-leaved trees. Three species of ticks: Ixodes persulcatus, I. pavlovskyi (subspecies I. pavlovskyi occidentalis Filip. et Pan., 1998), and Dermacentor reticulatus (Fabricius, 1794) were recorded in a recreational forest of Akademgorodok. A high abundance (22 ind./km) of I. pavlovskyi was observed in pine forests subjected to considerable recreational load. The abundance of I. persulcatus was the highest in aspen-birch and birch-aspen forests. D. reticulatus was captured in pine forests and fallow lands, its abundance varying from 0.2 to 2 ind./km.     

On the First-Order Rao—Scott Correction of the Umesh—Loughin—Scherer Statistic

Decady and Thomas (2000, Biometrics 56, 893-896) propose a first-order corrected Umesh-Loughin-Scherer statistic to test for association in an r x c contingency table with multiple column responses. Agresti and Liu (1999, Biometrics 55, 936-943) point out that such statistics are not invariant to the arbitrary designation of a zero or one to a positive response. This paper shows that, in addition, the proposed testing procedure does not hold the correct size when there are strong pairwise associations between responses.     

Evolution of the C<Subscript>4</Subscript> phosphoenolpyruvate carboxylase promoter of the C<Subscript>4</Subscript> species <Emphasis Type="Italic">Flaveria trinervia</Emphasis>: the role of the proximal promoter region

Background  

The key enzymes of photosynthetic carbon assimilation in C₄ plants have evolved independently several times from C₃ isoforms that were present in the C₃ ancestral species. The C₄ isoform of phosphoenolpyruvate carboxylase (PEPC), the primary CO₂-fixing enzyme of the C₄ cycle, is specifically expressed at high levels in mesophyll cells of the leaves of C₄ species. We are interested in understanding the molecular changes that are responsible for the evolution of this C₄-characteristic PEPC expression pattern, and we are using the genus Flaveria (Asteraceae) as a model system. It is known that cis-regulatory sequences for mesophyll-specific expression of the ppcA1 gene of F. trinervia (C₄) are located within a distal promoter region (DR).     

Probing the role of copper in the biosynthesis of the molybdenum cofactor in <Emphasis Type="Italic">Escherichia coli</Emphasis> and <Emphasis Type="Italic">Rhodobacter sphaeroides</Emphasis>

The crystal structure of Cnx1G, an enzyme involved in the biosynthesis of the molybdenum cofactor (Moco) in Arabidopsis thaliana, revealed the remarkable feature of a copper ion bound to the dithiolene unit of a molybdopterin intermediate (Kuper et al. Nature 430:803-806, 2004). To characterize further the role of copper in Moco biosynthesis, we examined the in vivo and/or in vitro activity of two Moco-dependent enzymes, dimethyl sulfoxide reductase (DMSOR) and nitrate reductase (NR), from cells grown under a variety of copper conditions. We found the activities of DMSOR and NR were not affected when copper was depleted from the media of either Escherichia coli or Rhodobacter sphaeroides. These data suggest that while copper may be utilized during Moco biosynthesis when it is available, copper does not appear to be strictly required for Moco biosynthesis in these two organisms.     

Study of the enhancer-blocking activities of new boundaries in the <Emphasis Type="Italic">bithorax</Emphasis> complex of <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

It was shown earlier that the Mcp, Fab-7, and Fab-8 boundaries of the bithorax complex contain insulators that effectively block the enhancers of the yellow and white genes. Other boundaries have not been studied so far. The recent mapping of binding sites for the insulator protein dCTCF in the regulatory regions of the bithorax complex genes permitted the Fab-3, Fab-4, and Fab-6 boundaries to be localized. Here, we showed that, despite the presence of dCTCF-binding sites, fragments of the Fab-3, Fab-4, and Fab-6 boundaries do not exhibit the properties of insulators in the model system with the yellow and white genes. Moreover, in some regions of the genome the Fab-4 and Fab-6 boundaries display the properties of silencers.