Comparative evolutionary analyses of eight whitefly Bemisia tabaci sensu lato genomes: cryptic species, agricultural pests and plant-virus vectors.

BACKGROUND: The group of > 40 cryptic whitefly species called Bemisia tabaci sensu lato are amongst the world's worst agricultural pests and plant-virus vectors. Outbreaks of B. tabaci s.l. and the associated plant-virus diseases continue to contribute to global food insecurity and social instability, particularly in sub-Saharan Africa and Asia. Published B. tabaci s.l. genomes have limited use for studying African cassava B. tabaci SSA1 species, due to the high genetic divergences between them. Genomic annotations presented here were performed using the 'Ensembl gene annotation system', to ensure that comparative analyses and conclusions reflect biological differences, as opposed to arising from different methodologies underpinning transcript model identification. RESULTS: We present here six new B. tabaci s.l. genomes from Africa and Asia, and two re-annotated previously published genomes, to provide evolutionary insights into these globally distributed pests. Genome sizes ranged between 616-658 Mb and exhibited some of the highest coverage of transposable elements reported within Arthropoda. Many fewer total protein coding genes (PCG) were recovered compared to the previously published B. tabaci s.l. genomes and structural annotations generated via the uniform methodology strongly supported a repertoire of between 12.8-13.2 × 103 PCG. An integrative systematics approach incorporating phylogenomic analysis of nuclear and mitochondrial markers supported a monophyletic Aleyrodidae and the basal positioning of B. tabaci Uganda-1 to the sub-Saharan group of species. Reciprocal cross-mating data and the co-cladogenesis pattern of the primary obligate endosymbiont 'Candidatus Portiera aleyrodidarum' from 11 Bemisia genomes further supported the phylogenetic reconstruction to show that African cassava B. tabaci populations consist of just three biological species. We include comparative analyses of gene families related to detoxification, sugar metabolism, vector competency and evaluate the presence and function of horizontally transferred genes, essential for understanding the evolution and unique biology of constituent B. tabaci. s.l species. CONCLUSIONS: These genomic resources have provided new and critical insights into the genetics underlying B. tabaci s.l. biology. They also provide a rich foundation for post-genomic research, including the selection of candidate gene-targets for innovative whitefly and virus-control strategies.

Simultaneous Single-Cell Genome and Transcriptome Sequencing of Termite Hindgut Protists Reveals Metabolic and Evolutionary Traits of Their Endosymbionts.

Some of the protist species which colonize the hindguts of wood-feeding Reticulitermes termites are associated with endosymbiotic bacteria belonging to the genus Endomicrobium. In this study, we focused on the endosymbionts of three protist species from Reticulitermes flavipes, as follows: Pyrsonympha vertens, Trichonympha agilis, and Dinenympha species II. Since these protist hosts represented members of different taxa which colonize separate niches within the hindguts of their termite hosts, we investigated if these differences translated to differential gene content and expression in their endosymbionts. Following assembly and comparative genome and transcriptome analyses, we discovered that these endosymbionts differed with respect to some possible niche-specific traits, such as carbon metabolism. Our analyses suggest that species-specific genes related to carbon metabolism were acquired by horizontal gene transfer (HGT) and may have come from taxa which are common in the termite hind gut. In addition, our analyses suggested that these endosymbionts contain and express genes related to natural transformation (competence) and recombination. Taken together, the presence of genes acquired by HGT and a putative competence pathway suggest that these endosymbionts are not cut off from gene flow and that competence may be a mechanism by which members of Endomicrobium can acquire new traits. IMPORTANCE The composition and structure of wood, which contains cellulose, hemicellulose, and lignin, prevent most organisms from using this common food source. Termites are a rare exception among animals, and they rely on a complex microbiota housed in their hindguts to use wood as a source of food. The lower termite, Reticulitermes flavipes, houses a variety of protists and prokaryotes that are the key players in the disassembly of lignocellulose. Here, we describe the genomes and the gene expression profiles of five Endomicrobium endosymbionts living inside three different protist species from R. flavipes. Data from these genomes suggest that these Endomicrobium species have different mechanisms for using carbon. In addition, they harbor genes that may be used to import DNA from their environment. This process of DNA uptake may contribute to the high levels of horizontal gene transfer noted previously in Endomicrobium species.

Single-cell amplicon sequencing reveals community structures and transmission trends of protist-associated bacteria in a termite host.

The hindgut protists of wood-feeding termites are usually colonized by prokaryotic symbionts. Many of the hurdles that have prevented a better understanding of these symbionts arise from variation among protist and termite host species and the inability to maintain prominent community members in culture. These issues have made it difficult to study the fidelity, acquisition, and differences in colonization of protists by bacterial symbionts. In this study, we use high throughput amplicon sequencing of the V4 region of 16S rRNA genes to determine the composition of bacterial communities associated with single protist cells of six protist species, from the genera Pyrsonympha, Dinenympha, and Trichonympha that are present in the hindgut of the termite Reticulitermes flavipes. By analyzing amplicon sequence variants (ASVs), the diversity and distribution of protist-associated bacteria was compared within and across these six different protist species. ASV analysis showed that, in general, each protist genus associated with a distinct community of bacterial symbionts which were conserved across different termite colonies. However, some ASVs corresponding to ectosymbionts (Spirochaetes) were shared between different Dinenympha species and to a lesser extent with Pyrsonympha and Trichonympha hosts. This suggested that certain bacterial symbionts may be cosmopolitan to some degree and perhaps acquired by horizontal transmission. Using a fluorescence-based cell assay, we could observe the horizontal acquisition of surface-bound bacteria. This acquisition was shown to be time-dependent, involve active processes, and was non-random with respect to binding locations on some protists.