Publications

4537

Background The chicken is the most abundant food animal in the world. However, despite its importance, the chicken gut microbiome remains largely undefined. Here, we exploit culture-independent and culture-dependent approaches to reveal extensive taxonomic diversity within this complex microbial community. Results We performed metagenomic sequencing of fifty chicken faecal samples from two breeds and analysed these, alongside all (n = 582) relevant publicly available chicken metagenomes, to cluster over 20 million non-redundant genes and to construct over 5,500 metagenome-assembled bacterial genomes. In addition, we recovered nearly 600 bacteriophage genomes. This represents the most comprehensive view of taxonomic diversity within the chicken gut microbiome to date, encompassing hundreds of novel candidate bacterial genera and species. To provide a stable, clear and memorable nomenclature for novel species, we devised a scalable combinatorial system for the creation of hundreds of well-formed Latin binomials. We cultured and genome-sequenced bacterial isolates from chicken faeces, documenting over forty novel species, together with three species from the genus Escherichia, including the newly named species Escherichia whittamii. Conclusions Our metagenomic and culture-based analyses provide new insights into the bacterial, archaeal and bacteriophage components of the chicken gut microbiome. The resulting datasets expand the known diversity of the chicken gut microbiome and provide a key resource for future high-resolution taxonomic and functional studies on the chicken gut microbiome.

AbstractAnaplasmosis, caused by infection with bacteria of the genusAnaplasmais an important veterinary and zoonotic disease. The characterization of transmission has concentrated on ticks and little is known about non-tick vectors of livestock anaplasmosis. This study investigated the presence ofAnaplasmaspp. in camels in northern Kenya and whether the hematophagous camel ked,Hippobosca camelina, acts as a vector. Camels (n =976) and > 10,000 keds were sampled over a three-year study period and the presence ofAnaplasmaspecies was determined by PCR-based assays targeting theAnaplasmataceae16S rRNA gene. Camels were infected by‘CandidatusAnaplasma camelii’occurring from 63 - 78% during the dry (September 2017), wet (June-July 2018), and late wet seasons (July-August 2019). 10 - 29% of camel keds harbored ‘Ca. Anaplasma camelii’ acquired from infected camels during blood feeding. We determined whetherAnaplasmapositive camel keds could transmit ‘Ca. Anaplasma camelii’ to small laboratory animals via blood-feeding. We show competence in pathogen transmission and subsequent infection in mice and rabbits by both direct detection in blood smears and subsequent molecular identification by PCR. Transmission of ‘Ca. Anaplasma camelii’ to mice (8 - 47%) and rabbits (25%) occurred readily after ked bites. Hence, we demonstrate, for the first time, the potential ofH. camelinaas a vector of anaplasmosis. This key finding provides the basis for establishing ked control programmes for improvement of livestock and human health.Author summaryHematophagous flies such as Tabanids andStomoxys, among other biting flies, are mechanical transmitters of various pathogens such as African trypanosomes andAnaplasmaspecies. However, little is known about the role of common camel-specific biting keds (also known as camel flies or louse flies, genusHippobosca) in pathogen transmission. Keds inflict painful bites to access host blood, and in the process may transmit bacterial hemopathogens frequently detected in both camels and their keds. We confirmed by experimental blood-feeding, gene amplification, and amplicon sequencing that camel keds can transmit “CandidatusAnaplasma camelii” from naturally-infected camels to healthy mice and rabbits. The high prevalence of camel anaplasmosis throughout the year in northern Kenya could be explained by the infestation camel-specificH. camelina, whose capacity as efficient fliers, unlike ticks, promotes disease transmission and maintenance within and among camel herds. Although this study focused on the transmission ofAnaplasmasp. by camel keds, it is possible that other hemopathogens could also be transmitted by these flies through a similar mechanism. Notably, in the absence of their preferred hosts, keds occasionally bite humans and other vertebrates they come across in order to acquire bloodmeals, and in the process could transmit zoonotic pathogens.

AbstractNonulosonic acids (NulOs) are a family of acidic carbohydrates with a nine-carbon backbone, which include different related structures, such as sialic acids. They have mainly been studied for their relevance in animal cells and pathogenic bacteria. Recently, sialic acids have been discovered as an important compound in the extracellular matrix of virtually all microbial life and in “CandidatusAccumulibacter phosphatis”, a well-studied polyphosphate-accumulating organism, in particular. Here, bioaggregates highly enriched with these bacteria (approx. 95% based on proteomic data) were used to study the production of NulOs in an enrichment of this microorganism. Fluorescence lectin-binding analysis, enzymatic quantification, and mass spectrometry were used to analyze the different NulOs present, showing a wide distribution and variety of these carbohydrates, such as sialic acids and bacterial NulOs, in the bioaggregates. Phylogenetic analysis confirmed the potential of “Ca. Accumulibacter” to produce different types of NulOs. Proteomic analysis showed the ability of “Ca. Accumulibacter” to reutilize and reincorporate these carbohydrates. This investigation points out the importance of diverse NulOs in non-pathogenic bacteria, which are normally overlooked. Sialic acids and other NulOs should be further investigated for their role in the ecology of “Ca. Accumulibacter” in particular, and biofilms in general.Key Points•“Ca. Accumulibacter” has the potential to produce a range of nonulosonic acids.•Mass spectrometry and lectin binding can reveal the presence and location of nonulosonic acids.•The role of nonulosonic acid in non-pathogenic bacteria needs to be studied in detail.

‘Candidatus Liberibacter asiaticus’ is an insect-transmitted, phloem-restricted α-proteobacterium associated with huanglongbing. Here, we provide the whole genome sequence of ‘Ca. L. asiaticus’ strain ReuSP1 from its insect vector Diaphorina citri (Hemiptera: Liviidae) collected in La Réunion. The genome is composed of 1,230,064 bp and has a 36.5% G+C content. This study reports the first ‘Ca. L. asiaticus’ genome sequence from La Réunion, which will add to ‘Ca. L. asiaticus’ genome resources and help elucidate our understanding of the introduction pathway into La Réunion.

Melatonin is synthesized from the amino acid L-tryptophan via the shikimic acid pathway and ubiquitously distributed in both prokaryotes and eukaryotes. Although most of melatonin biosynthesis genes were characterized in several plants and animal species including the insect model, Drosophila melanogaster, none of these enzymes have been identified from the Asian citrus psyllid, Diaphorina citri. We used comprehensive in silico analysis and gene expression techniques to identify the melatonin biosynthesis-related genes of D. citri and to evaluate the expression patterns of these genes within the adults of D. citri with gradient infection rates (0, 28, 34, 50, 58, and 70%) of the phytopathogenic bacterium Candidatus Liberibacter asiaticus and after the treatment with exogenous melatonin. We showed that the D. citri genome possesses six putative melatonin biosynthesis-related genes including two putative tryptophan 5-hydroxylase (DcT5H-1 and DcT5H-2), a putative aromatic amino acid decarboxylase (DcAADC), two putative arylalkylamine N-acetyltransferase (DcAANAT-1 and DcAANAT-2), and putative N-acetylserotonin O-methyltransferase (DcASMT). The infection with Ca. L. asiaticus decreased the transcript levels of all predicted genes in the adults of D. citri. Moreover, melatonin supplementation induced their expression levels in both healthy and Ca. L. asiaticus-infected psyllids. These findings confirm the association of these genes with the melatonin biosynthesis pathway.