Findings indicate that Symbiopectobacterium represents an intermediate stage in the transition from environmentally associated bacteria to obligate intracellular mutualists in Triatominae.
Abstract
Blood-feeding insects typically depend on obligate intracellular bacterial symbionts that provide essential B vitamins absent from vertebrate blood. In contrast, kissing bugs (Triatominae) have long been considered atypical because they rely primarily on extracellular gut-associated bacteria. Recent reports of the genus Symbiopectobacterium in Rhodnius species raise questions about the diversity and evolution of symbiosis in these insects. Here, we investigate the distribution, genome evolution, and tissue localization of Symbiopectobacterium in the genus Rhodnius. Using comparative metagenomics, phylogenomics, fluorescence in situ hybridization, transmission electron microscopy, and hemolymph screening, we characterize a Symbiopectobacterium genome from Rhodnius prolixus and assess its occurrence across publicly available datasets representing multiple Rhodnius species. The R. prolixus strain possesses a large, highly dynamic genome enriched in mobile genetic elements, pseudogenes, and remnants of secretion systems, while retaining biosynthetic pathways for several B vitamins. Comparative analysis revealed variation in genome reduction among Rhodnius-associated strains, suggesting ongoing and potentially independent transitions toward host-restricted symbiosis. Localization analyses detected Symbiopectobacterium intracellularly within posterior midgut epithelial cells and occasionally in the hemolymph, consistent with a facultative intracellular lifestyle. However, no bacteriomes or stable intracellular structures were observed. Together, these findings indicate that Symbiopectobacterium represents an intermediate stage in the transition from environmentally associated bacteria to obligate intracellular mutualists in Triatominae.
Bacterial symbionts of insects undergo dramatic genome reduction during their evolutionary transition from free-living to host-dependent lifestyles, but the dynamics of genome degradation remain poorly understood due to the difficulty of observing these processes in real-time. Sodalis glossinidius, a facultative bacterial endosymbiont of tsetse flies, provides an exceptional opportunity to study this transition experimentally: Unlike highly specialised obligate symbionts, S. glossinidius can be cultured in vitro and retains a large genome (4 Mbp) with extensive pseudogene content (49%, vs. ~ 1% in free-living bacteria), suggesting a recent evolutionary transition. Here, we present a comparative genomic analysis of S. glossinidius strains isolated from laboratory colony-derived Glossina morsitans morsitans, comparing one strain after ten years of serial passaging in laboratory culture (SgGmmC1*) to a counterpart isolated at the same time from the same colony (SgGmmB4). Hybrid genome assembly using Oxford Nanopore and Illumina technologies produced a high-quality 4.29 Mbp genome comprising one circular chromosome and four plasmids. Comparative analysis revealed a significant deletion (16,493 bp) containing 31 genes, including thiM (involved in thiamine biosynthesis) and genes encoding sulfur transporters. Additionally, we identified multiple small-scale chromosomal mutations (8 deletions, 39 insertions, 11 SNPs) resulting in frameshifts in genes including a hemolysin precursor (shlA). Our findings demonstrate that, under stable laboratory conditions without the selective pressures of the host environment, S. glossinidius continues to undergo genome degradation. The loss of thiM supports previous hypotheses of complementary metabolic pathways between S. glossinidius and the primary symbiont Wigglesworthia glossinidia for thiamine biosynthesis. This study provides insights into the evolutionary trajectory of facultative symbionts and has implications for studying the patterns of genome evolution in bacterial symbionts adapting to novel ecological niches, as well as paratransgenic approaches using S. glossinidius for trypanosome control.
Poppy Pescod, Lee R. Haines, Alistair C. Darby et al.· PLoS Neglected Tropical Dise...· 0 citations
This study provides genome- and spatially resolved views of dominant SCB in holothurians and offers evolutionary insights into host-interface diversification in the deep-sea holothurian body wall.
The evolution of multicellularity has long been linked to reproductive strategies. A long-standing debate concerns whether multicellular organisms are primarily stabilized by small single-cell propagules that minimize genetic heterogeneity or by larger multicellular and multinucleate propagules that may improve developmental success and survival of individuals. the Xanthophyceae provides an excellent model for investigating these questions, exhibiting transitions between unicellular to multicellular filamentous and coenocytic forms together with diverse reproductive modes, including single-cell zoospores and autospores, and multinucleate monospores and akinetes. However, a robust phylogenetic framework and systematic analyses of character evolution have remained lacking in this lineage. Here, we present a phylogenomic framework based on a nuclear dataset of 680 genes from 18 species, including 17 newly generated transcriptomes. Nuclear phylogenies robustly resolve all sampled inter-ordinal and inter-familial relationships with full concordance between concatenation and coalescent analyses, while plastid (141 genes) and mitochondrial (31 genes) datasets from 33 species recover identical topologies. Based on these results, we establish one new order (Pseudopleurochloridales), emend one order (Heterococcales), and propose five new families. Ancestral character reconstruction indicates at least four independent transitions from unicellular ancestors to simple multicellularity. Bayesian analyses of multicellularity and reproductive characters show that these transitions were consistently accompanied by shifts from multiple autospore-type propagules toward single monospore- and akinete-type propagules, whereas reversions to unicellularity were associated with the reappearance of autospore-based reproduction. These results provide a phylogenomic framework for understanding multicellular evolution in Xanthophyceae and shed light on the relationship between reproductive modes and the emergence of simple multicellularity.
Seok-Wan Choi, P. Broady, P. Novis et al.· bioRxiv· 0 citations
Detailed genomic, biochemical and physiological analyses revealed a vertical inheritance and long ancestral history of aerobic anoxygenic photosynthesis in Rhizobiaceae rather than multiple recent horizontal transfers, indicating a vertical inheritance and long ancestral history of aerobic anoxygenic photosynthesis in Rhizobiaceae.
Steven B. Kuzyk, Philipp Halama, M. Saini et al.· bioRxiv· 0 citations
It is found that Spirogyra deploys a molecular program characteristic of Phragmoplastophyta yet lacks the deeply conserved plastid division machinery found in other archaeplastid plastids.
Elisa S. Goldbecker, Deepti Varshney, A. Holzhausen et al.· The Plant Cell· 1 citation
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