Publications

4367

AbstractSeveral species of luminous bacteria in the genusPhotobacteriumare the light organ symbionts of teleost fishes.Photobacterium leiognathiand its subspecies,P. mandapamensis, in particular, commonly form bioluminescent symbioses with fish hosts in the Leiognathidae and Acropomatidae families as well as with cardinalfish in the genusSiphamia(Apogonidae). These two closely related lineages ofPhotobacteriumare right at the cutoff average nucleotide identity used to delimit bacterial species (95-96%) and show overlapping ecological niches, including their host fish range. However, there are only a few whole genome assemblies available for these bacterial species, particularly for symbiotic strains isolated from fish light organs, that can be used to explore genome evolution of these two lineages. Here we used Oxford Nanopore Technologies sequencing to produce long reads for assembling highly contiguous genomes ofPhotobacteriumstrains isolated from fish light organs, including severalP. kishitaniistrains isolated from deep water fishes. We were able to assemble 31 high-quality genomes with near complete BUSCO scores, many at the chromosome-level, and compare their gene contents, including plasmid genes. In doing so, we discovered a new candidate species ofPhotobacterium, CandidatusPhotobacterium acropomis, which originated from the light organ of the acropomid fish,Acropoma japonicum. We also describe a lack of congruency between the presence of theluxFgene, which is involved in light production, and the phylogenetic relationships between closely relatedP. leiognathiandP. mandapamensisstrains. In contrast, there was strong congruency betweenluxFand the host fish family of origin, suggesting this gene might be essential to initiate bioluminescent symbioses with certain hosts, includingSiphamiaandAcropomaspecies. Our study shows the benefit of using long reads in the assembly of bacterial genomes and outlines an assembly pipeline that results in highly contiguous genomes, even from low-coverage ONT reads.

AbstractMicrobes perform critical functions in corals yet most knowledge is derived from the photic zone. Here, we discovered two mollicutes that dominate the microbiome of the deep-sea octocoral,Callogorgia delta,and reside in the mesoglea. These symbionts were abundant across the host’s range, absent in the water, and rare in sediments. The symbionts lack all known fermentative capabilities including glycolysis and can only generate energy from arginine provided by the coral host. Their genomes feature extensive mechanisms to interact with foreign DNA which may be indicative of their role in symbiosis. We erect the novel family Oceanoplasmataceae which includes these symbionts and others associated with four marine invertebrate phyla. Its exceptionally broad host range suggests that the diversity of this enigmatic family remains largely undiscovered. Oceanoplasmataceae genomes are the most highly reduced among mollicutes providing new insight into their reductive evolution and the roles of coral symbionts.

In Saudi Arabia (SA), the citrus greening disease is caused by ‘Candidatus Liberibacter asiaticus’ (CLas) transmitted by the Asian citrus psyllid (ACP) Diaphorina citri. The origin and route(s) of the ACP-CLas pathosystem invasion in SA have not been studied. Adult ACP were collected from citrus trees in SA and differentiated by analysis of the mitochondrial cytochrome oxidase I (mtCOI) and nuclear copper transporting protein (atox1) genes. A phylogenetic analysis of the Wolbachia spp. surface protein (wsp) gene was used to identify the ACP-associated Wolbachia spp. A phylogenetic analysis of the atox1 and mtCOI gene sequences revealed one predominant ACP haplotype most closely related to the Indian subcontinent founder populations. The detection and identification of CLas in citrus trees were carried out by polymerase chain reaction (PCR) amplification and sequencing of the 16S rDNA gene. The CLas-integrated prophage genomes were sequenced, annotated, and used to differentiate CLas populations. The ML and ASTRAL trees reconstructed with prophages type 1 and 2 genome sequences, separately and concatenated, resolved two major lineages, CLas-1 and -2. The CLas-1 clade, reported here for the first time, consisted of isolates from SA isolates and Pakistan. The CLas-2 sequences formed two groups, CLas-2-1 and -2-2, previously the ‘Asiatic’ and ‘Floridian’ strains, respectively. Members of CLas-2-1 originated from Southeast Asia, the USA, and other worldwide locations, while CLas-2-2 was identified only in Florida. This study provides the first snapshot into the status of the ACP-CLas pathosystem in SA. In addition, the results provide new insights into the pathosystem coevolution and global invasion histories of two ACP-CLas lineages with a predicted center of origin in South and Southeast Asia, respectively.

AbstractThe methyl-coenzyme M reductase (Mcr) enables archaea to produce and oxidize methane, critically impacting the global greenhouse gas budget. Recently cultured archaea activate short- and long-chainn-alkanes with divergent Mcr variants, termed alkyl-coenzyme M reductases (Acrs). Here, we probed the anaerobic oxidation of mid-chain petroleum alkanes at 70°C using oil-rich sediments from the Guaymas Basin. Incubations with alkanes from pentane to tetradecane produced active cultures. In these cultures, archaea of the genusCandidatusAlkanophaga activate the alkanes with Acrs and completely oxidize the alkyl groups to CO2.Ca.Alkanophaga form a deep-branching sister clade to the methanotrophs ANME-1 and are closely related to the short-chain alkane oxidizersCa.Syntrophoarchaeum. This suggests that multi-carbon alkane metabolism preceded methane metabolism in the class Syntrophoarchaeia.Ca.Alkanophaga shuttle the electrons from alkane oxidation to sulfate-reducingThermodesulfobacteria. The two partners form consortia that are potential key players in petroleum degradation in heated oil reservoirs.