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Mandel CG, Sanchez SE, Monahan CC, Phuklia W, Omsland A. Metabolism and physiology of pathogenic bacterial obligate intracellular parasites. Front Cell Infect Microbiol 2024; 14:1284701. [PMID: 38585652 PMCID: PMC10995303 DOI: 10.3389/fcimb.2024.1284701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2023] [Accepted: 02/01/2024] [Indexed: 04/09/2024] Open
Abstract
Bacterial obligate intracellular parasites (BOIPs) represent an exclusive group of bacterial pathogens that all depend on invasion of a eukaryotic host cell to reproduce. BOIPs are characterized by extensive adaptation to their respective replication niches, regardless of whether they replicate within the host cell cytoplasm or within specialized replication vacuoles. Genome reduction is also a hallmark of BOIPs that likely reflects streamlining of metabolic processes to reduce the need for de novo biosynthesis of energetically costly metabolic intermediates. Despite shared characteristics in lifestyle, BOIPs show considerable diversity in nutrient requirements, metabolic capabilities, and general physiology. In this review, we compare metabolic and physiological processes of prominent pathogenic BOIPs with special emphasis on carbon, energy, and amino acid metabolism. Recent advances are discussed in the context of historical views and opportunities for discovery.
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Affiliation(s)
- Cameron G. Mandel
- Paul G. Allen School for Global Health, College of Veterinary Medicine, Washington State University, Pullman, WA, United States
| | - Savannah E. Sanchez
- Paul G. Allen School for Global Health, College of Veterinary Medicine, Washington State University, Pullman, WA, United States
- Department of Microbiology and Immunology, Virginia Commonwealth University School of Medicine, Richmond, VA, United States
| | - Colleen C. Monahan
- Paul G. Allen School for Global Health, College of Veterinary Medicine, Washington State University, Pullman, WA, United States
| | - Weerawat Phuklia
- Paul G. Allen School for Global Health, College of Veterinary Medicine, Washington State University, Pullman, WA, United States
- Lao-Oxford-Mahosot Hospital-Wellcome Trust Research Unit, Microbiology Laboratory, Mahosot Hospital, Vientiane, Lao People’s Democratic Republic
| | - Anders Omsland
- Paul G. Allen School for Global Health, College of Veterinary Medicine, Washington State University, Pullman, WA, United States
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Cortez D, Neira G, González C, Vergara E, Holmes DS. A Large-Scale Genome-Based Survey of Acidophilic Bacteria Suggests That Genome Streamlining Is an Adaption for Life at Low pH. Front Microbiol 2022; 13:803241. [PMID: 35387071 PMCID: PMC8978632 DOI: 10.3389/fmicb.2022.803241] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2021] [Accepted: 02/07/2022] [Indexed: 01/04/2023] Open
Abstract
The genome streamlining theory suggests that reduction of microbial genome size optimizes energy utilization in stressful environments. Although this hypothesis has been explored in several cases of low-nutrient (oligotrophic) and high-temperature environments, little work has been carried out on microorganisms from low-pH environments, and what has been reported is inconclusive. In this study, we performed a large-scale comparative genomics investigation of more than 260 bacterial high-quality genome sequences of acidophiles, together with genomes of their closest phylogenetic relatives that live at circum-neutral pH. A statistically supported correlation is reported between reduction of genome size and decreasing pH that we demonstrate is due to gene loss and reduced gene sizes. This trend is independent from other genome size constraints such as temperature and G + C content. Genome streamlining in the evolution of acidophilic bacteria is thus supported by our results. The analyses of predicted Clusters of Orthologous Genes (COG) categories and subcellular location predictions indicate that acidophiles have a lower representation of genes encoding extracellular proteins, signal transduction mechanisms, and proteins with unknown function but are enriched in inner membrane proteins, chaperones, basic metabolism, and core cellular functions. Contrary to other reports for genome streamlining, there was no significant change in paralog frequencies across pH. However, a detailed analysis of COG categories revealed a higher proportion of genes in acidophiles in the following categories: "replication and repair," "amino acid transport," and "intracellular trafficking". This study brings increasing clarity regarding the genomic adaptations of acidophiles to life at low pH while putting elements, such as the reduction of average gene size, under the spotlight of streamlining theory.
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Affiliation(s)
- Diego Cortez
- Center for Bioinformatics and Genome Biology, Centro Ciencia & Vida, Fundación Ciencia & Vida, Santiago, Chile
| | - Gonzalo Neira
- Center for Bioinformatics and Genome Biology, Centro Ciencia & Vida, Fundación Ciencia & Vida, Santiago, Chile
| | - Carolina González
- Center for Bioinformatics and Genome Biology, Centro Ciencia & Vida, Fundación Ciencia & Vida, Santiago, Chile
| | - Eva Vergara
- Center for Bioinformatics and Genome Biology, Centro Ciencia & Vida, Fundación Ciencia & Vida, Santiago, Chile
| | - David S. Holmes
- Center for Bioinformatics and Genome Biology, Centro Ciencia & Vida, Fundación Ciencia & Vida, Santiago, Chile
- Facultad de Medicina y Ciencia, Universidad San Sebastian, Santiago, Chile
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3
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Malerba ME, Ghedini G, Marshall DJ. Genome Size Affects Fitness in the Eukaryotic Alga Dunaliella tertiolecta. Curr Biol 2020; 30:3450-3456.e3. [PMID: 32679103 DOI: 10.1016/j.cub.2020.06.033] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2020] [Revised: 04/28/2020] [Accepted: 06/09/2020] [Indexed: 11/18/2022]
Abstract
Genome size is tightly coupled to morphology, ecology, and evolution among species [1-5], with one of the best-known patterns being the relationship between cell size and genome size [6, 7]. Classic theories, such as the "selfish DNA hypothesis," posit that accumulating redundant DNA has fitness costs but that larger cells can tolerate larger genomes, leading to a positive relationship between cell size and genome size [8, 9]. Yet the evidence for fitness costs associated with relatively larger genomes remains circumstantial. Here, we estimated the relationships between genome size, cell size, energy fluxes, and fitness across 72 independent lineages in a eukaryotic phytoplankton. Lineages with relatively smaller genomes had higher fitness, in terms of both maximum growth rate and total biovolume reached at carrying capacity, but paradoxically, they also had lower energy fluxes than lineages with relative larger genomes. We then explored the evolutionary trajectories of absolute genome size over 100 generations and across a 10-fold change in cell size. Despite consistent directional selection across all lineages, genome size decreased by 11% in lineages with absolutely larger genomes but showed little evolution in lineages with absolutely smaller genomes, implying a lower absolute limit in genome size. Our results suggest that the positive relationship between cell size and genome size in nature may be the product of conflicting evolutionary pressures, on the one hand, to minimize redundant DNA and maximize performance-as theory predicts-but also to maintain a minimum level of essential function. VIDEO ABSTRACT.
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Affiliation(s)
- Martino E Malerba
- Centre of Geometric Biology, School of Biological Sciences, Monash University, Melbourne, VIC 3800, Australia.
| | - Giulia Ghedini
- Centre of Geometric Biology, School of Biological Sciences, Monash University, Melbourne, VIC 3800, Australia.
| | - Dustin J Marshall
- Centre of Geometric Biology, School of Biological Sciences, Monash University, Melbourne, VIC 3800, Australia.
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4
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Martinez-Gutierrez CA, Aylward FO. Strong Purifying Selection Is Associated with Genome Streamlining in Epipelagic Marinimicrobia. Genome Biol Evol 2020; 11:2887-2894. [PMID: 31539038 PMCID: PMC6798728 DOI: 10.1093/gbe/evz201] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/08/2019] [Indexed: 12/21/2022] Open
Abstract
Marine microorganisms inhabiting nutrient-depleted waters play critical roles in global biogeochemical cycles due to their abundance and broad distribution. Many of these microbes share similar genomic features including small genome size, low % G + C content, short intergenic regions, and low nitrogen content in encoded amino acid residue side chains (N-ARSC), but the evolutionary drivers of these characteristics are unclear. Here, we compared the strength of purifying selection across the Marinimicrobia, a candidate phylum which encompasses a broad range of phylogenetic groups with disparate genomic features, by estimating the ratio of nonsynonymous and synonymous substitutions (dN/dS) in conserved marker genes. Our analysis reveals that epipelagic Marinimicrobia that exhibit features consistent with genome streamlining have significantly lower dN/dS values when compared with their mesopelagic counterparts. We also found a significant positive correlation between median dN/dS values and % G + C content, N-ARSC, and intergenic region length. We did not identify a significant correlation between dN/dS ratios and estimated genome size, suggesting the strength of selection is not a primary factor shaping genome size in this group. Our findings are generally consistent with genome streamlining theory, which postulates that many genomic features of abundant epipelagic bacteria are the result of adaptation to oligotrophic nutrient conditions. Our results are also in agreement with previous findings that genome streamlining is common in epipelagic waters, suggesting that microbes inhabiting this region of the ocean have been shaped by strong selection together with prevalent nutritional constraints characteristic of this environment.
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Affiliation(s)
| | - Frank O Aylward
- Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia
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5
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Bartelme RP, Custer JM, Dupont CL, Espinoza JL, Torralba M, Khalili B, Carini P. Influence of Substrate Concentration on the Culturability of Heterotrophic Soil Microbes Isolated by High-Throughput Dilution-to-Extinction Cultivation. mSphere 2020; 5:e00024-20. [PMID: 31996418 PMCID: PMC6992367 DOI: 10.1128/msphere.00024-20] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2020] [Accepted: 01/14/2020] [Indexed: 12/17/2022] Open
Abstract
The vast majority of microbes inhabiting oligotrophic shallow subsurface soil environments have not been isolated or studied under controlled laboratory conditions. In part, the challenges associated with isolating shallow subsurface microbes may persist because microbes in deeper soils are adapted to low nutrient availability or quality. Here, we use high-throughput dilution-to-extinction culturing to isolate shallow subsurface microbes from a conifer forest in Arizona, USA. We hypothesized that the concentration of heterotrophic substrates in microbiological growth medium would affect which microbial taxa were culturable from these soils. To test this, we diluted cells extracted from soil into one of two custom-designed defined growth media that differed by 100-fold in the concentration of amino acids and organic carbon. Across the two media, we isolated a total of 133 pure cultures, all of which were classified as Actinobacteria or Alphaproteobacteria The substrate availability dictated which actinobacterial phylotypes were culturable but had no significant effect on the culturability of Alphaproteobacteria We isolated cultures that were representative of the most abundant phylotype in the soil microbial community (Bradyrhizobium spp.) and representatives of five of the top 10 most abundant Actinobacteria phylotypes, including Nocardioides spp., Mycobacterium spp., and several other phylogenetically divergent lineages. Flow cytometry of nucleic acid-stained cells showed that cultures isolated on low-substrate medium had significantly lower nucleic acid fluorescence than those isolated on high-substrate medium. These results show that dilution-to-extinction is an effective method to isolate abundant soil microbes and that the concentration of substrates in culture medium influences the culturability of specific microbial lineages.IMPORTANCE Isolating environmental microbes and studying their physiology under controlled conditions are essential aspects of understanding their ecology. Subsurface ecosystems are typically nutrient-poor environments that harbor diverse microbial communities-the majority of which are thus far uncultured. In this study, we use modified high-throughput cultivation methods to isolate subsurface soil microbes. We show that a component of whether a microbe is culturable from subsurface soils is the concentration of growth substrates in the culture medium. Our results offer new insight into technical approaches and growth medium design that can be used to access the uncultured diversity of soil microbes.
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Affiliation(s)
- Ryan P Bartelme
- Department of Environmental Science, University of Arizona, Tucson, Arizona, USA
| | - Joy M Custer
- Department of Environmental Science, University of Arizona, Tucson, Arizona, USA
| | - Christopher L Dupont
- Department of Environment and Sustainability, J. Craig Venter Institute, La Jolla, California, USA
| | - Josh L Espinoza
- Department of Environment and Sustainability, J. Craig Venter Institute, La Jolla, California, USA
| | - Manolito Torralba
- Department of Environment and Sustainability, J. Craig Venter Institute, La Jolla, California, USA
| | - Banafshe Khalili
- Department of Ecology and Evolutionary Biology, University of California, Irvine, California, USA
| | - Paul Carini
- Department of Environmental Science, University of Arizona, Tucson, Arizona, USA
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6
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Liu J, Zhao R, Zhang J, Zhang G, Yu K, Li X, Li B. Occurrence and Fate of Ultramicrobacteria in a Full-Scale Drinking Water Treatment Plant. Front Microbiol 2018; 9:2922. [PMID: 30568635 PMCID: PMC6290093 DOI: 10.3389/fmicb.2018.02922] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2018] [Accepted: 11/14/2018] [Indexed: 12/23/2022] Open
Abstract
Ultramicrobacteria (UMB) are omnipresent and numerically dominate in freshwater, as microbes can present in drinking water systems, however, the UMB communities that occur and their removal behaviors remain poorly characterized in drinking water treatment plants (DWTPs). To gain insights into these issues, we profiled bacterial cell density, community structure and functions of UMB and their counterpart large bacteria (LB) using flow cytometry and filtration paired with 16S rRNA gene high-throughput sequencing in a full-scale DWTP. Contrary to the reduction of bacterial density and diversity, the proportion of UMB in the total bacteria community increased as the drinking water treatment process progressed, and biological activated carbon facilitated bacterial growth. Moreover, UMB were less diverse than LB, and their community structure and predicted functions were significantly different. In the DWTP, UMB indicator taxa were mainly affiliated with α/β/γ-Proteobacteria, Deinococcus-Thermus, Firmicutes, Acidobacteria, and Dependentiae. In particular, the exclusive clustering of UMB at the phylum level, e.g., Parcubacteria, Elusimicrobia, and Saccharibacteria, confirmed the fact that the ultra-small size of UMB is a naturally and evolutionarily conserved trait. Additionally, the streamlined genome could be connected to UMB, such as candidate phyla radiation (CPR) bacteria, following a symbiotic or parasitic lifestyle, which then leads to the observed high connectedness, i.e., non-random intra-taxa co-occurrence patterns within UMB. Functional prediction analysis revealed that environmental information processing and DNA replication and repair likely contribute to the higher resistance of UMB to drinking water treatment processes in comparison to LB. Overall, the study provides valuable insights into the occurrence and fate of UMB regarding community structure, phylogenetic characteristics and potential functions in a full-scale DWTP, and it is a useful reference for beneficial manipulation of the drinking water microbiome.
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Affiliation(s)
- Jie Liu
- Guangdong Provincial Engineering Research Center for Urban Water Recycling and Environmental Safety, Graduate School at Shenzhen, Tsinghua University, Shenzhen, China
| | - Renxin Zhao
- Guangdong Provincial Engineering Research Center for Urban Water Recycling and Environmental Safety, Graduate School at Shenzhen, Tsinghua University, Shenzhen, China
| | - Jiayu Zhang
- Guangdong Provincial Engineering Research Center for Urban Water Recycling and Environmental Safety, Graduate School at Shenzhen, Tsinghua University, Shenzhen, China
| | - Guijuan Zhang
- Guangdong Provincial Engineering Research Center for Urban Water Recycling and Environmental Safety, Graduate School at Shenzhen, Tsinghua University, Shenzhen, China
| | - Ke Yu
- School of Environment and Energy, Shenzhen Graduate School, Peking University, Shenzhen, China
| | - Xiaoyan Li
- Guangdong Provincial Engineering Research Center for Urban Water Recycling and Environmental Safety, Graduate School at Shenzhen, Tsinghua University, Shenzhen, China
| | - Bing Li
- Guangdong Provincial Engineering Research Center for Urban Water Recycling and Environmental Safety, Graduate School at Shenzhen, Tsinghua University, Shenzhen, China
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Getz EW, Tithi SS, Zhang L, Aylward FO. Parallel Evolution of Genome Streamlining and Cellular Bioenergetics across the Marine Radiation of a Bacterial Phylum. mBio 2018; 9:e01089-18. [PMID: 30228235 DOI: 10.1128/mBio.01089-18] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Understanding long-term patterns of microbial evolution is critical to advancing our knowledge of past and present role microbial life in driving global biogeochemical cycles. Historically, it has been challenging to study the evolution of environmental microbes due to difficulties in obtaining genome sequences from lineages that could not be cultivated, but recent advances in metagenomics and single-cell genomics have begun to obviate many of these hurdles. Here we present an evolutionary genomic analysis of the Marinimicrobia, a diverse bacterial group that is abundant in the global ocean. We demonstrate that distantly related Marinimicrobia species that reside in similar habitats have converged to assume similar genome architectures and cellular bioenergetics, suggesting that common factors shape the evolution of a broad array of marine lineages. These findings broaden our understanding of the evolutionary forces that have given rise to microbial life in the contemporary ocean. Diverse bacterial and archaeal lineages drive biogeochemical cycles in the global ocean, but the evolutionary processes that have shaped their genomic properties and physiological capabilities remain obscure. Here we track the genome evolution of the globally abundant marine bacterial phylum Marinimicrobia across its diversification into modern marine environments and demonstrate that extant lineages are partitioned between epipelagic and mesopelagic habitats. Moreover, we show that these habitat preferences are associated with fundamental differences in genomic organization, cellular bioenergetics, and metabolic modalities. Multiple lineages present in epipelagic niches independently acquired genes necessary for phototrophy and environmental stress mitigation, and their genomes convergently evolved key features associated with genome streamlining. In contrast, lineages residing in mesopelagic waters independently acquired nitrate respiratory machinery and a variety of cytochromes, consistent with the use of alternative terminal electron acceptors in oxygen minimum zones (OMZs). Further, while epipelagic clades have retained an ancestral Na+-pumping respiratory complex, mesopelagic lineages have largely replaced this complex with canonical H+-pumping respiratory complex I, potentially due to the increased efficiency of the latter together with the presence of the more energy-limiting environments deep in the ocean’s interior. These parallel evolutionary trends indicate that key features of genomic streamlining and cellular bioenergetics have occurred repeatedly and congruently in disparate clades and underscore the importance of environmental conditions and nutrient dynamics in driving the evolution of diverse bacterioplankton lineages in similar ways throughout the global ocean.
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8
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Cabello-Yeves PJ, Ghai R, Mehrshad M, Picazo A, Camacho A, Rodriguez-Valera F. Reconstruction of Diverse Verrucomicrobial Genomes from Metagenome Datasets of Freshwater Reservoirs. Front Microbiol 2017; 8:2131. [PMID: 29163419 PMCID: PMC5673642 DOI: 10.3389/fmicb.2017.02131] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2017] [Accepted: 10/18/2017] [Indexed: 12/19/2022] Open
Abstract
The phylum Verrucomicrobia contains freshwater representatives which remain poorly studied at the genomic, taxonomic, and ecological levels. In this work we present eighteen new reconstructed verrucomicrobial genomes from two freshwater reservoirs located close to each other (Tous and Amadorio, Spain). These metagenome-assembled genomes (MAGs) display a remarkable taxonomic diversity inside the phylum and comprise wide ranges of estimated genome sizes (from 1.8 to 6 Mb). Among all Verrucomicrobia studied we found some of the smallest genomes of the Spartobacteria and Opitutae classes described so far. Some of the Opitutae family MAGs were small, cosmopolitan, with a general heterotrophic metabolism with preference for carbohydrates, and capable of xylan, chitin, or cellulose degradation. Besides, we assembled large copiotroph genomes, which contain a higher number of transporters, polysaccharide degrading pathways and in general more strategies for the uptake of nutrients and carbohydrate-based metabolic pathways in comparison with the representatives with the smaller genomes. The diverse genomes revealed interesting features like green-light absorbing rhodopsins and a complete set of genes involved in nitrogen fixation. The large diversity in genome sizes and physiological properties emphasize the diversity of this clade in freshwaters enlarging even further the already broad eco-physiological range of these microbes.
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Affiliation(s)
- Pedro J Cabello-Yeves
- Evolutionary Genomics Group, Departamento de Producción Vegetal y Microbiología, Universidad Miguel Hernández, San Juan de Alicante, Spain
| | - Rohit Ghai
- Department of Aquatic Microbial Ecology, Institute of Hydrobiology, Biology Centre of the Academy of Sciences of the Czech Republic, České Budějovice, Czechia
| | - Maliheh Mehrshad
- Department of Aquatic Microbial Ecology, Institute of Hydrobiology, Biology Centre of the Academy of Sciences of the Czech Republic, České Budějovice, Czechia
| | - Antonio Picazo
- Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia, Valencia, Spain
| | - Antonio Camacho
- Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia, Valencia, Spain
| | - Francisco Rodriguez-Valera
- Evolutionary Genomics Group, Departamento de Producción Vegetal y Microbiología, Universidad Miguel Hernández, San Juan de Alicante, Spain
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R Marcelino V, Cremen MCM, Jackson CJ, Larkum AAW, Verbruggen H. Evolutionary Dynamics of Chloroplast Genomes in Low Light: A Case Study of the Endolithic Green Alga Ostreobium quekettii. Genome Biol Evol 2016; 8:2939-2951. [PMID: 27566760 PMCID: PMC5633697 DOI: 10.1093/gbe/evw206] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Some photosynthetic organisms live in extremely low light environments. Light limitation is associated with selective forces as well as reduced exposure to mutagens, and over evolutionary timescales it can leave a footprint on species’ genomes. Here, we present the chloroplast genomes of four green algae (Bryopsidales, Ulvophyceae), including the endolithic (limestone-boring) alga Ostreobium quekettii, which is a low light specialist. We use phylogenetic models and comparative genomic tools to investigate whether the chloroplast genome of Ostreobium corresponds to our expectations of how low light would affect genome evolution. Ostreobium has the smallest and most gene-dense chloroplast genome among Ulvophyceae reported to date, matching our expectation that light limitation would impose resource constraints reflected in the chloroplast genome architecture. Rates of molecular evolution are significantly slower along the phylogenetic branch leading to Ostreobium, in agreement with the expected effects of low light and energy levels on molecular evolution. We expected the ability of Ostreobium to perform photosynthesis in very low light to be associated with positive selection in genes related to the photosynthetic machinery, but instead, we observed that these genes may be under stronger purifying selection. Besides shedding light on the genome dynamics associated with a low light lifestyle, this study helps to resolve the role of environmental factors in shaping the diversity of genome architectures observed in nature.
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Affiliation(s)
| | | | | | - Anthony A W Larkum
- Plant Functional Biology and Climate Change Cluster, University of Technology Sydney, NSW 2007, Australia
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10
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Abstract
Bacteria and archaea typically possess small genomes that are tightly packed with protein-coding genes. The compactness of prokaryotic genomes is commonly perceived as evidence of adaptive genome streamlining caused by strong purifying selection in large microbial populations. In such populations, even the small cost incurred by nonfunctional DNA because of extra energy and time expenditure is thought to be sufficient for this extra genetic material to be eliminated by selection. However, contrary to the predictions of this model, there exists a consistent, positive correlation between the strength of selection at the protein sequence level, measured as the ratio of nonsynonymous to synonymous substitution rates, and microbial genome size. Here, by fitting the genome size distributions in multiple groups of prokaryotes to predictions of mathematical models of population evolution, we show that only models in which acquisition of additional genes is, on average, slightly beneficial yield a good fit to genomic data. These results suggest that the number of genes in prokaryotic genomes reflects the equilibrium between the benefit of additional genes that diminishes as the genome grows and deletion bias (i.e., the rate of deletion of genetic material being slightly greater than the rate of acquisition). Thus, new genes acquired by microbial genomes, on average, appear to be adaptive. The tight spacing of protein-coding genes likely results from a combination of the deletion bias and purifying selection that efficiently eliminates nonfunctional, noncoding sequences.
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11
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Beites T, Mendes MV. Chassis optimization as a cornerstone for the application of synthetic biology based strategies in microbial secondary metabolism. Front Microbiol 2015; 6:906. [PMID: 26441855 PMCID: PMC4563238 DOI: 10.3389/fmicb.2015.00906] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Accepted: 08/19/2015] [Indexed: 02/06/2023] Open
Abstract
The increased number of bacterial genome sequencing projects has generated over the last years a large reservoir of genomic information. In silico analysis of this genomic data has renewed the interest in bacterial bioprospecting for bioactive compounds by unveiling novel biosynthetic gene clusters of unknown or uncharacterized metabolites. However, only a small fraction of those metabolites is produced under laboratory-controlled conditions; the remaining clusters represent a pool of novel metabolites that are waiting to be “awaken”. Activation of the biosynthetic gene clusters that present reduced or no expression (known as cryptic or silent clusters) by heterologous expression has emerged as a strategy for the identification and production of novel bioactive molecules. Synthetic biology, with engineering principles at its core, provides an excellent framework for the development of efficient heterologous systems for the expression of biosynthetic gene clusters. However, a common problem in its application is the host-interference problem, i.e., the unpredictable interactions between the device and the host that can hamper the desired output. Although an effort has been made to develop orthogonal devices, the most proficient way to overcome the host-interference problem is through genome simplification. In this review we present an overview on the strategies and tools used in the development of hosts/chassis for the heterologous expression of specialized metabolites biosynthetic gene clusters. Finally, we introduce the concept of specialized host as the next step of development of expression hosts.
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Affiliation(s)
- Tiago Beites
- I3S Instituto de Investigação e Inovação em Saúde, Universidade do Porto Porto, Portugal ; Instituto de Biologia Molecular e Celular, Universidade do Porto Porto, Portugal
| | - Marta V Mendes
- I3S Instituto de Investigação e Inovação em Saúde, Universidade do Porto Porto, Portugal ; Instituto de Biologia Molecular e Celular, Universidade do Porto Porto, Portugal
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12
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Abstract
A microbe's growth rate helps to set its ecological success and its contribution to food web dynamics and biogeochemical processes. Growth rates at the community level are constrained by biomass and trophic interactions among bacteria, phytoplankton, and their grazers. Phytoplankton growth rates are approximately 1 d(-1), whereas most heterotrophic bacteria grow slowly, close to 0.1 d(-1); only a few taxa can grow ten times as fast. Data from 16S rRNA and other approaches are used to speculate about the growth rate and the life history strategy of SAR11, the most abundant clade of heterotrophic bacteria in the oceans. These strategies are also explored using genomic data. Although the methods and data are imperfect, the available data can be used to set limits on growth rates and thus on the timescale for changes in the composition and structure of microbial communities.
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Affiliation(s)
- David L Kirchman
- School of Marine Science and Policy, University of Delaware, Lewes, Delaware 19958;
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13
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Luo H, Moran MA. How do divergent ecological strategies emerge among marine bacterioplankton lineages? Trends Microbiol 2015; 23:577-84. [PMID: 26051014 DOI: 10.1016/j.tim.2015.05.004] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2014] [Revised: 05/04/2015] [Accepted: 05/11/2015] [Indexed: 12/16/2022]
Abstract
Heterotrophic bacteria in pelagic marine environments are frequently categorized into two canonical ecological groups: patch-associated and free-living. This framework provides a conceptual basis for understanding bacterial utilization of oceanic organic matter. Some patch-associated bacteria are ecologically linked with eukaryotic phytoplankton, and this observation fits with predicted coincidence of their genome expansion with marine phytoplankton diversification. By contrast, free-living bacteria in today's oceans typically live singly with streamlined metabolic and regulatory functions that allow them to grow in nutrient-poor seawater. Recent analyses of marine Alphaproteobacteria suggest that some free-living bacterioplankton lineages evolved from patch-associated ancestors up to several hundred million years ago. While evolutionary analyses agree with the hypothesis that natural selection has maintained these distinct ecological strategies and genomic traits in present-day populations, they do not rule out a major role for genetic drift in driving ancient ecological switches. These two evolutionary forces may have acted on ocean bacteria at different geological time scales and under different geochemical constraints, with possible implications for future adaptations to a changing ocean. New evolutionary models and genomic data are leading to a more comprehensive understanding of marine bacterioplankton evolutionary history.
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Affiliation(s)
- Haiwei Luo
- Simon F. S. Li Marine Science Laboratory, School of Life Sciences, The Chinese University of Hong Kong, Shatin, Hong Kong, China
| | - Mary Ann Moran
- Department of Marine Sciences, University of Georgia, Athens, GA 30602, USA.
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Santoro AE, Dupont CL, Richter RA, Craig MT, Carini P, McIlvin MR, Yang Y, Orsi WD, Moran DM, Saito MA. Genomic and proteomic characterization of "Candidatus Nitrosopelagicus brevis": an ammonia-oxidizing archaeon from the open ocean. Proc Natl Acad Sci U S A 2015; 112:1173-8. [PMID: 25587132 DOI: 10.1073/pnas.1416223112] [Citation(s) in RCA: 151] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Thaumarchaeota are among the most abundant microbial cells in the ocean, but difficulty in cultivating marine Thaumarchaeota has hindered investigation into the physiological and evolutionary basis of their success. We report here a closed genome assembled from a highly enriched culture of the ammonia-oxidizing pelagic thaumarchaeon CN25, originating from the open ocean. The CN25 genome exhibits strong evidence of genome streamlining, including a 1.23-Mbp genome, a high coding density, and a low number of paralogous genes. Proteomic analysis recovered nearly 70% of the predicted proteins encoded by the genome, demonstrating that a high fraction of the genome is translated. In contrast to other minimal marine microbes that acquire, rather than synthesize, cofactors, CN25 encodes and expresses near-complete biosynthetic pathways for multiple vitamins. Metagenomic fragment recruitment indicated the presence of DNA sequences >90% identical to the CN25 genome throughout the oligotrophic ocean. We propose the provisional name "Candidatus Nitrosopelagicus brevis" str. CN25 for this minimalist marine thaumarchaeon and suggest it as a potential model system for understanding archaeal adaptation to the open ocean.
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Borrel G, Parisot N, Harris HMB, Peyretaillade E, Gaci N, Tottey W, Bardot O, Raymann K, Gribaldo S, Peyret P, O’Toole PW, Brugère JF. Comparative genomics highlights the unique biology of Methanomassiliicoccales, a Thermoplasmatales-related seventh order of methanogenic archaea that encodes pyrrolysine. BMC Genomics 2014; 15:679. [PMID: 25124552 PMCID: PMC4153887 DOI: 10.1186/1471-2164-15-679] [Citation(s) in RCA: 183] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2014] [Accepted: 07/18/2014] [Indexed: 02/08/2023] Open
Abstract
BACKGROUND A seventh order of methanogens, the Methanomassiliicoccales, has been identified in diverse anaerobic environments including the gastrointestinal tracts (GIT) of humans and other animals and may contribute significantly to methane emission and global warming. Methanomassiliicoccales are phylogenetically distant from all other orders of methanogens and belong to a large evolutionary branch composed by lineages of non-methanogenic archaea such as Thermoplasmatales, the Deep Hydrothermal Vent Euryarchaeota-2 (DHVE-2, Aciduliprofundum boonei) and the Marine Group-II (MG-II). To better understand this new order and its relationship to other archaea, we manually curated and extensively compared the genome sequences of three Methanomassiliicoccales representatives derived from human GIT microbiota, "Candidatus Methanomethylophilus alvus", "Candidatus Methanomassiliicoccus intestinalis" and Methanomassiliicoccus luminyensis. RESULTS Comparative analyses revealed atypical features, such as the scattering of the ribosomal RNA genes in the genome and the absence of eukaryotic-like histone gene otherwise present in most of Euryarchaeota genomes. Previously identified in Thermoplasmatales genomes, these features are presently extended to several completely sequenced genomes of this large evolutionary branch, including MG-II and DHVE2. The three Methanomassiliicoccales genomes share a unique composition of genes involved in energy conservation suggesting an original combination of two main energy conservation processes previously described in other methanogens. They also display substantial differences with each other, such as their codon usage, the nature and origin of their CRISPRs systems and the genes possibly involved in particular environmental adaptations. The genome of M. luminyensis encodes several features to thrive in soil and sediment conditions suggesting its larger environmental distribution than GIT. Conversely, "Ca. M. alvus" and "Ca. M. intestinalis" do not present these features and could be more restricted and specialized on GIT. Prediction of the amber codon usage, either as a termination signal of translation or coding for pyrrolysine revealed contrasted patterns among the three genomes and suggests a different handling of the Pyl-encoding capacity. CONCLUSIONS This study represents the first insights into the genomic organization and metabolic traits of the seventh order of methanogens. It suggests contrasted evolutionary history among the three analyzed Methanomassiliicoccales representatives and provides information on conserved characteristics among the overall methanogens and among Thermoplasmata.
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Affiliation(s)
- Guillaume Borrel
- />EA-4678 CIDAM, Clermont Université, Université d’Auvergne, 28 Place Henri Dunant, BP 10448, 63000 Clermont-Ferrand, France
- />School of Microbiology and Alimentary Pharmabiotic Centre, University College Cork, Cork, Ireland
| | - Nicolas Parisot
- />EA-4678 CIDAM, Clermont Université, Université d’Auvergne, 28 Place Henri Dunant, BP 10448, 63000 Clermont-Ferrand, France
- />CNRS, UMR 6023, Université Blaise Pascal, 63000 Clermont-Ferrand, France
| | - Hugh MB Harris
- />School of Microbiology and Alimentary Pharmabiotic Centre, University College Cork, Cork, Ireland
| | - Eric Peyretaillade
- />EA-4678 CIDAM, Clermont Université, Université d’Auvergne, 28 Place Henri Dunant, BP 10448, 63000 Clermont-Ferrand, France
| | - Nadia Gaci
- />EA-4678 CIDAM, Clermont Université, Université d’Auvergne, 28 Place Henri Dunant, BP 10448, 63000 Clermont-Ferrand, France
| | - William Tottey
- />EA-4678 CIDAM, Clermont Université, Université d’Auvergne, 28 Place Henri Dunant, BP 10448, 63000 Clermont-Ferrand, France
| | - Olivier Bardot
- />GReD, CNRS, UMR 6293, Inserm, UMR 1103, Clermont Université, Université d’Auvergne 28 Place Henri Dunant, BP 10448, 63000 Clermont-Ferrand, France
| | - Kasie Raymann
- />Département de Microbiologie, Unité de Biologie Moléculaire du Gène chez les Extrêmophiles, Paris Cedex 15, 75724 France
- />Cellule Pasteur UPMC, Université Pierre et Marie Curie, Paris Cedex 15, 75724 France
| | - Simonetta Gribaldo
- />Département de Microbiologie, Unité de Biologie Moléculaire du Gène chez les Extrêmophiles, Paris Cedex 15, 75724 France
- />Cellule Pasteur UPMC, Université Pierre et Marie Curie, Paris Cedex 15, 75724 France
| | - Pierre Peyret
- />EA-4678 CIDAM, Clermont Université, Université d’Auvergne, 28 Place Henri Dunant, BP 10448, 63000 Clermont-Ferrand, France
| | - Paul W O’Toole
- />School of Microbiology and Alimentary Pharmabiotic Centre, University College Cork, Cork, Ireland
| | - Jean-François Brugère
- />EA-4678 CIDAM, Clermont Université, Université d’Auvergne, 28 Place Henri Dunant, BP 10448, 63000 Clermont-Ferrand, France
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Boscaro V, Felletti M, Vannini C, Ackerman MS, Chain PSG, Malfatti S, Vergez LM, Shin M, Doak TG, Lynch M, Petroni G. Polynucleobacter necessarius, a model for genome reduction in both free-living and symbiotic bacteria. Proc Natl Acad Sci U S A 2013; 110:18590-5. [PMID: 24167248 PMCID: PMC3831957 DOI: 10.1073/pnas.1316687110] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We present the complete genomic sequence of the essential symbiont Polynucleobacter necessarius (Betaproteobacteria), which is a valuable case study for several reasons. First, it is hosted by a ciliated protist, Euplotes; bacterial symbionts of ciliates are still poorly known because of a lack of extensive molecular data. Second, the single species P. necessarius contains both symbiotic and free-living strains, allowing for a comparison between closely related organisms with different ecologies. Third, free-living P. necessarius strains are exceptional by themselves because of their small genome size, reduced metabolic flexibility, and high worldwide abundance in freshwater systems. We provide a comparative analysis of P. necessarius metabolism and explore the peculiar features of a genome reduction that occurred on an already streamlined genome. We compare this unusual system with current hypotheses for genome erosion in symbionts and free-living bacteria, propose modifications to the presently accepted model, and discuss the potential consequences of translesion DNA polymerase loss.
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Affiliation(s)
| | | | | | | | | | | | - Lisa M. Vergez
- Lawrence Livermore National Laboratory, Livermore, CA 94550; and
| | | | - Thomas G. Doak
- Department of Biology, Indiana University, Bloomington, IN 47401
| | - Michael Lynch
- Department of Biology, Indiana University, Bloomington, IN 47401
| | - Giulio Petroni
- Department of Biology, Pisa University, 56126 Pisa, Italy
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