Biology subjects

Barbe, V.

Publications and source records attributed to Barbe, V..

3 recordsLinked to original sources

bioRxiv2018

A Freeloader?: The Highly Eroded Yet Big-Genomed Serratia symbiotica symbiont of Cinara strobi

Genome reduction is pervasive among maternally-inherited bacterial endosymbionts. This genome reduction can eventually lead to serious deterioration of essential metabolic pathways, thus rendering an obligate endosymbiont unable to provide essential nutrients to its host. This loss of essential pathways can lead to either symbiont complementation (sharing of the nutrient production with a novel co-obligate symbiont) or symbiont replacement (complete takeover of nutrient production by the novel symbiont). However, the process by which these two evolutionary events happen remains somewhat enigmatic by the lack of examples of intermediate stages of this process. Cinara aphids (Hemiptera: Aphididae) typically harbour two obligate bacterial symbionts: Buchnera and Serratia symbiotica. However, the latter has been replaced by different bacterial taxa in specific lineages, and thus species within this aphid lineage could provide important clues into the process of symbiont replacement. In the present study, using 16S rRNA high-throughput amplicon sequencing, we determined that the aphid Cinara strobi harbours not two, but three fixed bacterial symbionts: Buchnera aphidicola, a Sodalis sp., and S. symbiotica. Through genome assembly and genome-based metabolic inference, we have found that only the first two symbionts (Buchnera and Sodalis) actually contribute to the hosts supply of essential nutrients while S. symbiotica has become unable to contribute towards this task. We found that S. symbiotica has a rather large and highly eroded genome which codes only for a few proteins and displays extensive pseudogenisation. Thus, we propose an ongoing symbiont replacement within C. strobi, in which a once competent\" S. symbiotica does no longer contribute towards the beneficial association. These results suggest that in dual symbiotic systems, when a substitute co-symbiont is available, genome deterioration can precede genome reduction and a symbiont can be maintained despite the apparent lack of benefit to its host.

genomics↗

bioRxiv2017

High-throughput optical mapping of replicating DNA

DNA replication is a crucial process for the universal ability of living organisms to reproduce. Existing methods to map replication genome-wide use large cell populations and therefore smooth out variability between chromosomal copies. Single-molecule methods may in principle reveal this variability. However, current methods remain refractory to automated molecule detection and measurements. Their low throughput has therefore precluded genome-wide analyses. Here, we have repurposed a commercial optical DNA mapping device, the Bionano Genomics Irys system, to map the replication signal of single DNA molecules onto genomic position at high throughput. Our methodology (HOMARD) combines fluorescent labelling of replication tracks and nicking endonuclease (NE) sites with DNA linearization in nanochannel arrays and dedicated image processing. We demonstrate the robustness of our approach by providing an ultra-high coverage (23,311 x) replication map of bacteriophage {lambda} DNA in Xenopus egg extracts. HOMARD opens the way to genome-wide analysis of DNA replication at the single-molecule level.

genomics↗

bioRxiv2016

Modeling trophic dependencies and exchanges among insects’ bacterial symbionts in a host-simulated environment

Individual organisms are linked to their communities and ecosystems via metabolic activities. Metabolic exchanges and co-dependencies have long been suggested to have a pivotal role in determining community structure. Metabolic interactions with bacteria have been key drivers in the evolution of sap-feeding insects, enabling complementation of their deprived nutrition. The sap-feeding whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) harbors an obligatory symbiotic bacterium, as well as varying combinations of facultative symbionts. We took advantage of the well-defined bacterial community in B. tabaci as a case study for a comprehensive and systematic survey of metabolic interactions within the bacterial community and their associations with documented frequency of bacterial combinations. We first reconstructed the metabolic networks of five common B. tabaci symbionts (Portiera, Rickettsia, Hamiltonella, Cardinium and Wolbachia), and then used network analysis approaches to predict: (1) species-specific metabolic capacities in a simulated bacteriocyte-like environment; (2) metabolic capacities of the corresponding species combinations, and (3) dependencies of each species on different media components.\n\nThe automatic-based predictions for metabolic capacities of the symbionts in the host environment were in general agreement with previously reported genome analyses, each focused on the single-species level. The analysis suggested several previously un-reported routes for complementary interactions. Highly abundant symbiont combinations were found to have the potential to produce a diverse set of complementary metabolites, in comparison to un-detected combinations. No clear association was detected between metabolic codependencies and co-occurrence patterns. The findings indicate a potential key role for metabolic exchanges as key determinants shaping community structure in this system.

systems biology↗