Publications

4364

Abstract Dissimilatory perchlorate reduction is an anaerobic respiratory pathway that in communities might be influenced by metabolic interactions. Because the genes for perchlorate reduction are horizontally transferred, previous studies have been unable to identify uncultivated perchlorate-reducing populations. Here we recovered metagenome-assembled genomes from perchlorate-reducing sediment enrichments and employed a manual scaffolding approach to reconstruct gene clusters for perchlorate reduction found within mobile genetic elements. De novo assembly and binning of four enriched communities yielded 48 total draft genomes. In addition to canonical perchlorate reduction gene clusters and taxa, a new type of gene cluster with an alternative perchlorate reductase was identified. Phylogenetic analysis indicated past exchange between these gene clusters, and the presence of plasmids with either gene cluster shows that the potential for gene transfer via plasmid persisted throughout enrichment. However, a majority of genomes in each community lacked perchlorate reduction genes. Putative chlorate-reducing or sulfur-reducing populations were dominant in most communities, supporting the hypothesis that metabolic interactions might result from perchlorate reduction intermediates and byproducts. Other populations included a novel phylum-level lineage (Ca. Muirbacteria) and epibiotic prokaryotes with no known role in perchlorate reduction. These results reveal unexpected genetic diversity, suggest that perchlorate-reducing communities involve substantial metabolic interactions, and encourage expanded strategies to further understand the evolution and ecology of this metabolism.

AbstractBackgroundThe olive fly,Bactrocera oleae, is the most important insect pest in olive production, causing economic damage to olive crops worldwide. In addition to extensive research onB. oleaecontrol methods, scientists have devoted much effort in the last century to understanding olive fly endosymbiosis with a bacterium eventually identified asCandidatusErwinia dacicola. This bacterium plays a relevant role in olive fly fitness. It is vertically transmitted, and it benefits both larvae and adults in wild populations; however, the endosymbiont is not present in lab colonies, probably due to the antibiotics and preservatives required for the preparation of artificial diets. Endosymbiont transfer from wildB. oleaepopulations to laboratory-reared ones allows olive fly mass-rearing, thus producing more competitive flies for future Sterile Insect Technique (SIT) applications.ResultsWe tested the hypothesis thatCa.E. dacicola might be transmitted from wild, naturally symbiotic adults to laboratory-reared flies. Several trials have been performed with different contamination sources ofCa.E. dacicola, such as ripe olives and gelled water contaminated by wild flies, wax domes containing eggs laid by wild females, cages dirtied by faeces dropped by wild flies and matings between lab and wild adults. PCR-DGGE, performed with the primer set 63F-GC/518R, demonstrated that the transfer of the endosymbiont from wild flies to lab-reared ones occurred only in the case of cohabitation.ConclusionsCohabitation of symbiotic wild flies and non-symbiotic lab flies allows the transfer ofCa.E. dacicola through adults. Moreover, PCR-DGGE performed with the primer set 63F-GC/518R was shown to be a consistent method for screeningCa.E. dacicola, also showing the potential to distinguish between the two haplotypes (htA and htB). This study represents the first successful attempt at horizontal transfer ofCa.E. dacicola and the first step in acquiring a better understanding of the endosymbiont physiology and its relationship with the olive fly. Our research also represents a starting point for the development of a laboratory symbiotic olive fly colony, improving perspectives for future applications of the Sterile Insect Technique.

ABSTRACTCandidatus Ornithobacterium hominissp. nov. represents a new member of the Flavobacteriaceae detected in 16S rRNA gene surveys from Southeast Asia, Africa and Australia. It frequently colonises the infant nasopharynx at high proportional abundance, and we demonstrate its presence in 42% of nasopharyngeal swabs from 12 month old children in the Maela refugee camp in Thailand. The species, a Gram negative bacillus, has not yet been cultured but the cells can be identified in mixed samples by fluorescent hybridisation. Here we report seven genomes assembled from metagenomic data, two to improved draft standard. The genomes are approximately 1.9Mb, sharing 62% average amino acid identity with the only other member of the genus, the bird pathogenOrnithobacterium rhinotracheale.The draft genomes encode multiple antibiotic resistance genes, competition factors,Flavobacterium johnsoniae-like gliding motility genes and a homolog of thePasteurella multocidamitogenic toxin. Intra- and inter-host genome comparison suggests that colonisation with this bacterium is both persistent and strain exclusive.

AbstractThe newly discoveredCandidatus‘Methanoperedens nitroreducens’ (M.nitroreducens), mediating nitrate-dependent anaerobic oxidation of methane, is an important microorganism in linking carbon and nitrogen cycles. In order to explore the diversity ofM.nitroreducens-like archaea in various environmental niches with advanced high-throughput sequencing, new primers based on alpha subunit of methyl-coenzyme M reductase gene were designed. The PCR results demonstrated that the new primers could effectively detectM.nitroreducens-like archaea from an enrichment culture dominated byM.nitroreducensas well as samples collected from a natural freshwater lake and a full-scale wastewater treatment plant (WWTP). By high-throughput sequencing, more than 30,000M.nitroreducens-like sequences were obtained. Phylogenetic analysis of these sequences along with published sequences showed thatM.nitroreducens-like archaea could be divided into three sub-branches (named as Group A, Group B and Group C in this study). Clear geographical difference was observed, with Group A and Group B dominating samples in Queensland (Australia) and in European ecosystems, respectively. Further quantitative PCR revealed that theM.nitroreducens-like archaea were more abundant in WWTP than the freshwater lake. The study provided a large number of sequences forM.nitroreducens-like archaeal communities, thus expanded our understanding on the ecological diversity ofM.nitroreducens-like archaea.