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McCutcheon JP, Garber AI, Spencer N, Warren JM. How do bacterial endosymbionts work with so few genes? PLoS Biol 2024; 22:e3002577. [PMID: 38626194 PMCID: PMC11020763 DOI: 10.1371/journal.pbio.3002577] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/18/2024] Open
Abstract
The move from a free-living environment to a long-term residence inside a host eukaryotic cell has profound effects on bacterial function. While endosymbioses are found in many eukaryotes, from protists to plants to animals, the bacteria that form these host-beneficial relationships are even more diverse. Endosymbiont genomes can become radically smaller than their free-living relatives, and their few remaining genes show extreme compositional biases. The details of how these reduced and divergent gene sets work, and how they interact with their host cell, remain mysterious. This Unsolved Mystery reviews how genome reduction alters endosymbiont biology and highlights a "tipping point" where the loss of the ability to build a cell envelope coincides with a marked erosion of translation-related genes.
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Affiliation(s)
- John P. McCutcheon
- Biodesign Institute and School of Life Sciences, Arizona State University, Tempe, Arizona, United States of America
- Howard Hughes Medical Institute, Chevy Chase, Maryland, United States of America
| | - Arkadiy I. Garber
- Biodesign Institute and School of Life Sciences, Arizona State University, Tempe, Arizona, United States of America
| | - Noah Spencer
- Biodesign Institute and School of Life Sciences, Arizona State University, Tempe, Arizona, United States of America
| | - Jessica M. Warren
- Biodesign Institute and School of Life Sciences, Arizona State University, Tempe, Arizona, United States of America
- Howard Hughes Medical Institute, Chevy Chase, Maryland, United States of America
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2
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Spencer N, Łukasik P, Meyer M, Veloso C, McCutcheon JP. No Transcriptional Compensation for Extreme Gene Dosage Imbalance in Fragmented Bacterial Endosymbionts of Cicadas. Genome Biol Evol 2023; 15:evad100. [PMID: 37267326 PMCID: PMC10287537 DOI: 10.1093/gbe/evad100] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2023] [Revised: 05/25/2023] [Accepted: 05/26/2023] [Indexed: 06/04/2023] Open
Abstract
Bacteria that form long-term intracellular associations with host cells lose many genes, a process that often results in tiny, gene-dense, and stable genomes. Paradoxically, the some of the same evolutionary processes that drive genome reduction and simplification may also cause genome expansion and complexification. A bacterial endosymbiont of cicadas, Hodgkinia cicadicola, exemplifies this paradox. In many cicada species, a single Hodgkinia lineage with a tiny, gene-dense genome has split into several interdependent cell and genome lineages. Each new Hodgkinia lineage encodes a unique subset of the ancestral unsplit genome in a complementary way, such that the collective gene contents of all lineages match the total found in the ancestral single genome. This splitting creates genetically distinct Hodgkinia cells that must function together to carry out basic cellular processes. It also creates a gene dosage problem where some genes are encoded by only a small fraction of cells while others are much more abundant. Here, by sequencing DNA and RNA of Hodgkinia from different cicada species with different amounts of splitting-along with its structurally stable, unsplit partner endosymbiont Sulcia muelleri-we show that Hodgkinia does not transcriptionally compensate to rescue the wildly unbalanced gene and genome ratios that result from lineage splitting. We also find that Hodgkinia has a reduced capacity for basic transcriptional control independent of the splitting process. Our findings reveal another layer of degeneration further pushing the limits of canonical molecular and cell biology in Hodgkinia and may partially explain its propensity to go extinct through symbiont replacement.
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Affiliation(s)
- Noah Spencer
- Biodesign Center for Mechanisms of Evolution and School of Life Sciences, Arizona State University, Tempe, Arizona, USA
| | - Piotr Łukasik
- Division of Biological Sciences, University of Montana, Missoula, Montana, USA
- Institute of Environmental Sciences, Jagiellonian University, Kraków, Poland
| | - Mariah Meyer
- Division of Biological Sciences, University of Montana, Missoula, Montana, USA
- Department of Biomedical Informatics, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Claudio Veloso
- Department of Ecological Sciences, Science Faculty, University of Chile, Santiago, Chile
| | - John P McCutcheon
- Biodesign Center for Mechanisms of Evolution and School of Life Sciences, Arizona State University, Tempe, Arizona, USA
- Division of Biological Sciences, University of Montana, Missoula, Montana, USA
- Howard Hughes Medical Institute, Chevy Chase, Maryland, USA
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3
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Li Z, Li Y, Xue AZ, Dang V, Renee Holmes V, Spencer Johnston J, Barrick JE, Moran NA. The genomic basis of evolutionary novelties in a leafhopper. Mol Biol Evol 2022; 39:6677381. [PMID: 36026509 PMCID: PMC9450646 DOI: 10.1093/molbev/msac184] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Evolutionary innovations generate phenotypic and species diversity. Elucidating the genomic processes underlying such innovations is central to understanding biodiversity. In this study, we addressed the genomic basis of evolutionary novelties in the glassy-winged sharpshooter (Homalodisca vitripennis, GWSS), an agricultural pest. Prominent evolutionary innovations in leafhoppers include brochosomes, proteinaceous structures that are excreted and used to coat the body, and obligate symbiotic associations with two bacterial types that reside within cytoplasm of distinctive cell types. Using PacBio long-read sequencing and Dovetail Omni-C technology, we generated a chromosome-level genome assembly for the GWSS and then validated the assembly using flow cytometry and karyotyping. Additional transcriptomic and proteomic data were used to identify novel genes that underlie brochosome production. We found that brochosome-associated genes include novel gene families that have diversified through tandem duplications. We also identified the locations of genes involved in interactions with bacterial symbionts. Ancestors of the GWSS acquired bacterial genes through horizontal gene transfer (HGT), and these genes appear to contribute to symbiont support. Using a phylogenomics approach, we inferred HGT sources and timing. We found that some HGT events date to the common ancestor of the hemipteran suborder Auchenorrhyncha, representing some of the oldest known examples of HGT in animals. Overall, we show that evolutionary novelties in leafhoppers are generated by the combination of acquiring novel genes, produced both de novo and through tandem duplication, acquiring new symbiotic associations that enable use of novel diets and niches, and recruiting foreign genes to support symbionts and enhance herbivory.
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Affiliation(s)
- Zheng Li
- Department of Integrative Biology, The University of Texas at Austin, Austin, TX, USA
| | - Yiyuan Li
- Department of Integrative Biology, The University of Texas at Austin, Austin, TX, USA.,State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-products, Key Laboratory of Biotechnology in Plant Protection of Ministry of Agriculture and Zhejiang Province, Institute of Plant Virology, Ningbo University, Ningbo, Zhejiang, China
| | - Allen Z Xue
- Department of Integrative Biology, The University of Texas at Austin, Austin, TX, USA
| | - Vy Dang
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, TX, USA
| | - V Renee Holmes
- Department of Entomology, Texas A&M University, College Station, TX,USA
| | | | - Jeffrey E Barrick
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, TX, USA
| | - Nancy A Moran
- Department of Integrative Biology, The University of Texas at Austin, Austin, TX, USA
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Vasquez YM, Bennett GM. A complex interplay of evolutionary forces continues to shape ancient co-occurring symbiont genomes. iScience 2022; 25:104786. [PMID: 35982793 PMCID: PMC9379567 DOI: 10.1016/j.isci.2022.104786] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2022] [Revised: 06/03/2022] [Accepted: 07/13/2022] [Indexed: 01/03/2023] Open
Abstract
Many insects depend on ancient associations with intracellular bacteria for essential nutrition. The genomes of these bacteria are often highly reduced. Although drift is a major driver of symbiont evolution, other evolutionary forces continue to influence them. To understand how ongoing molecular evolution and gene loss shape symbiont genomes, we sequenced two of the most ancient symbionts known, Sulcia and Nasuia, from 20 Hawaiian Nesophrosyne leafhoppers. We leveraged the parallel divergence of Nesophrosyne lineages throughout Hawaii as a natural experimental framework. Sulcia and Nasuia experience ongoing-but divergent-gene loss, often in a convergent fashion. Although some genes are under relaxed selection, purifying and positive selection are also important drivers of genome evolution, particularly in maintaining certain nutritional and cellular functions. Our results further demonstrate that symbionts experience dramatically different evolutionary environments, as evidenced by the finding that Sulcia and Nasuia have one of the slowest and fastest rates of molecular evolution known.
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Affiliation(s)
- Yumary M. Vasquez
- Department of Life and Environmental Sciences, University of California, Merced, CA, USA,Corresponding author
| | - Gordon M. Bennett
- Department of Life and Environmental Sciences, University of California, Merced, CA, USA,Corresponding author
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Perreau J, Moran NA. Genetic innovations in animal-microbe symbioses. Nat Rev Genet 2021; 23:23-39. [PMID: 34389828 DOI: 10.1038/s41576-021-00395-z] [Citation(s) in RCA: 51] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/28/2021] [Indexed: 02/07/2023]
Abstract
Animal hosts have initiated myriad symbiotic associations with microorganisms and often have maintained these symbioses for millions of years, spanning drastic changes in ecological conditions and lifestyles. The establishment and persistence of these relationships require genetic innovations on the parts of both symbionts and hosts. The nature of symbiont innovations depends on their genetic population structure, categorized here as open, closed or mixed. These categories reflect modes of inter-host transmission that result in distinct genomic features, or genomic syndromes, in symbionts. Although less studied, hosts also innovate in order to preserve and control symbiotic partnerships. New capabilities to sequence host-associated microbial communities and to experimentally manipulate both hosts and symbionts are providing unprecedented insights into how genetic innovations arise under different symbiont population structures and how these innovations function to support symbiotic relationships.
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Affiliation(s)
- Julie Perreau
- Department of Integrative Biology, University of Texas at Austin, Austin, Texas, USA
| | - Nancy A Moran
- Department of Integrative Biology, University of Texas at Austin, Austin, Texas, USA.
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Williams TJ, Allen MA, Ivanova N, Huntemann M, Haque S, Hancock AM, Brazendale S, Cavicchioli R. Genome Analysis of a Verrucomicrobial Endosymbiont With a Tiny Genome Discovered in an Antarctic Lake. Front Microbiol 2021; 12:674758. [PMID: 34140946 PMCID: PMC8204192 DOI: 10.3389/fmicb.2021.674758] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2021] [Accepted: 04/23/2021] [Indexed: 01/25/2023] Open
Abstract
Organic Lake in Antarctica is a marine-derived, cold (−13∘C), stratified (oxic-anoxic), hypersaline (>200 gl–1) system with unusual chemistry (very high levels of dimethylsulfide) that supports the growth of phylogenetically and metabolically diverse microorganisms. Symbionts are not well characterized in Antarctica. However, unicellular eukaryotes are often present in Antarctic lakes and theoretically could harbor endosymbionts. Here, we describe Candidatus Organicella extenuata, a member of the Verrucomicrobia with a highly reduced genome, recovered as a metagenome-assembled genome with genetic code 4 (UGA-to-Trp recoding) from Organic Lake. It is closely related to Candidatus Pinguicocccus supinus (163,218 bp, 205 genes), a newly described cytoplasmic endosymbiont of the freshwater ciliate Euplotes vanleeuwenhoeki (Serra et al., 2020). At 158,228 bp (encoding 194 genes), the genome of Ca. Organicella extenuata is among the smallest known bacterial genomes and similar to the genome of Ca. Pinguicoccus supinus (163,218 bp, 205 genes). Ca. Organicella extenuata retains a capacity for replication, transcription, translation, and protein-folding while lacking any capacity for the biosynthesis of amino acids or vitamins. Notably, the endosymbiont retains a capacity for fatty acid synthesis (type II) and iron–sulfur (Fe-S) cluster assembly. Metagenomic analysis of 150 new metagenomes from Organic Lake and more than 70 other Antarctic aquatic locations revealed a strong correlation in abundance between Ca. Organicella extenuata and a novel ciliate of the genus Euplotes. Like Ca. Pinguicoccus supinus, we infer that Ca. Organicella extenuata is an endosymbiont of Euplotes and hypothesize that both Ca. Organicella extenuata and Ca. Pinguicocccus supinus provide fatty acids and Fe-S clusters to their Euplotes host as the foundation of a mutualistic symbiosis. The discovery of Ca. Organicella extenuata as possessing genetic code 4 illustrates that in addition to identifying endosymbionts by sequencing known symbiotic communities and searching metagenome data using reference endosymbiont genomes, the potential exists to identify novel endosymbionts by searching for unusual coding parameters.
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Affiliation(s)
- Timothy J Williams
- School of Biotechnology and Biomolecular Sciences, UNSW Sydney, Sydney, NSW, Australia
| | - Michelle A Allen
- School of Biotechnology and Biomolecular Sciences, UNSW Sydney, Sydney, NSW, Australia
| | - Natalia Ivanova
- U.S. Department of Energy Joint Genome Institute, Berkeley, CA, United States
| | - Marcel Huntemann
- U.S. Department of Energy Joint Genome Institute, Berkeley, CA, United States
| | - Sabrina Haque
- School of Biotechnology and Biomolecular Sciences, UNSW Sydney, Sydney, NSW, Australia
| | - Alyce M Hancock
- School of Biotechnology and Biomolecular Sciences, UNSW Sydney, Sydney, NSW, Australia
| | - Sarah Brazendale
- School of Biotechnology and Biomolecular Sciences, UNSW Sydney, Sydney, NSW, Australia
| | - Ricardo Cavicchioli
- School of Biotechnology and Biomolecular Sciences, UNSW Sydney, Sydney, NSW, Australia
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Waneka G, Vasquez YM, Bennett GM, Sloan DB. Mutational Pressure Drives Differential Genome Conservation in Two Bacterial Endosymbionts of Sap-Feeding Insects. Genome Biol Evol 2020; 13:6020258. [PMID: 33275136 PMCID: PMC7952229 DOI: 10.1093/gbe/evaa254] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/28/2020] [Indexed: 11/16/2022] Open
Abstract
Compared with free-living bacteria, endosymbionts of sap-feeding insects have tiny and rapidly evolving genomes. Increased genetic drift, high mutation rates, and relaxed selection associated with host control of key cellular functions all likely contribute to genome decay. Phylogenetic comparisons have revealed massive variation in endosymbiont evolutionary rate, but such methods make it difficult to partition the effects of mutation versus selection. For example, the ancestor of Auchenorrhynchan insects contained two obligate endosymbionts, Sulcia and a betaproteobacterium (BetaSymb; called Nasuia in leafhoppers) that exhibit divergent rates of sequence evolution and different propensities for loss and replacement in the ensuing ∼300 Ma. Here, we use the auchenorrhynchan leafhopper Macrosteles sp. nr. severini, which retains both of the ancestral endosymbionts, to test the hypothesis that differences in evolutionary rate are driven by differential mutagenesis. We used a high-fidelity technique known as duplex sequencing to measure and compare low-frequency variants in each endosymbiont. Our direct detection of de novode novo mutations reveals that the rapidly evolving endosymbiont (Nasuia) has a much higher frequency of single-nucleotide variants than the more stable endosymbiont (Sulcia) and a mutation spectrum that is potentially even more AT-biased than implied by the 83.1% AT content of its genome. We show that indels are common in both endosymbionts but differ substantially in length and distribution around repetitive regions. Our results suggest that differences in long-term rates of sequence evolution in Sulcia versus BetaSymb, and perhaps the contrasting degrees of stability of their relationships with the host, are driven by differences in mutagenesis.
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Affiliation(s)
- Gus Waneka
- Department of Biology, Colorado State University, Fort Collins, CO, USA
| | - Yumary M Vasquez
- Department of Life and Environmental Sciences, University of California, Merced, CA, USA
| | - Gordon M Bennett
- Department of Life and Environmental Sciences, University of California, Merced, CA, USA
| | - Daniel B Sloan
- Department of Biology, Colorado State University, Fort Collins, CO, USA
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Abstract
The genomes of bacteria contain fewer genes and substantially less noncoding DNA than those of eukaryotes, and as a result, they have much less raw material to invent new traits. Yet, bacteria are vastly more taxonomically diverse, numerically abundant, and globally successful in colonizing new habitats compared to eukaryotes. Although bacterial genomes are generally considered to be optimized for efficient growth and rapid adaptation, nonadaptive processes have played a major role in shaping the size, contents, and compact organization of bacterial genomes and have allowed the establishment of deleterious traits that serve as the raw materials for genetic innovation.
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Affiliation(s)
- Paul C Kirchberger
- Department of Integrative Biology, University of Texas at Austin, Texas 78712, USA; ; ;
| | - Marian L Schmidt
- Department of Integrative Biology, University of Texas at Austin, Texas 78712, USA; ; ;
| | - Howard Ochman
- Department of Integrative Biology, University of Texas at Austin, Texas 78712, USA; ; ;
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Symbiont replacements reset the co-evolutionary relationship between insects and their heritable bacteria. ISME JOURNAL 2020; 14:1384-1395. [PMID: 32076126 DOI: 10.1038/s41396-020-0616-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Revised: 01/31/2020] [Accepted: 02/07/2020] [Indexed: 01/03/2023]
Abstract
Auchenorrhynchan insects (Hemiptera) generally depend on two bacterial symbionts for nutrition. These bacteria experience extreme genome reduction and loss of essential cell functions that require direct host support, or the replacement of failing symbionts with more capable ones. However, it remains unclear how hosts adapt to integrate symbionts into their systems, particularly when they are replaced. Here, we comparatively investigated the evolution of host-support mechanisms in the glassy-winged sharpshooter, Homalodisca vitripennis (GWSS), and the aster leafhopper, Macrosteles quadrilineatus (ALF). ALF harbors the ancestral co-symbionts of the Auchenorrhyncha that have tiny genomes, Sulcia (190 kb) and Nasuia (112 kb). In GWSS, Sulcia retains an expanded genome (245 kb), but Nasuia was replaced by the more capable Baumannia (686 kb). To support their symbionts, GWSS and ALF have evolved novel mechanisms via horizontal gene transfer, gene duplication, and co-option of mitochondrial support genes. However, GWSS has fewer support systems targeting essential bacterial processes. In particular, although both hosts use ancestral mechanisms to support Sulcia, GWSS does not encode all of the same support genes required to sustain Sulcia-ALF or Nasuia. Moreover, GWSS support of Baumannia is far more limited and tailored to its expanded capabilities. Our results demonstrate how symbiont replacements shape host genomes and the co-evolutionary process.
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