1
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Jebali A, Sanchez MR, Hanschen ER, Starkenburg SR, Corcoran AA. Trait drift in microalgae and applications for strain improvement. Biotechnol Adv 2022; 60:108034. [PMID: 36089253 DOI: 10.1016/j.biotechadv.2022.108034] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2022] [Revised: 08/06/2022] [Accepted: 09/05/2022] [Indexed: 11/29/2022]
Abstract
Microalgae are increasingly used to generate a wide range of commercial products, and there is growing evidence that microalgae-based products can be produced sustainably. However, industrial production of microalgal biomass is not as developed as other biomanufacturing platform technologies. In addition, results of bench-scale research often fail to translate to large-scale or mass production systems. This disconnect may result from trait drift and evolution occurring, through time, in response to unique drivers in each environment, such as cultivation regimes, weather, and pests. Moreover, outdoor and indoor cultivation of microalgae has the potential to impose negative selection pressures, which makes the maintenance of desired traits a challenge. In this context, this review sheds the light on our current understanding of trait drift and evolution in microalgae. We delineate the basics of phenotype plasticity and evolution, with a focus on how microalgae respond under various conditions. In addition, we review techniques that exploit phenotypic plasticity and evolution for strain improvement in view of industrial commercial applications, highlighting associated advantages and shortcomings. Finally, we suggest future research directions and recommendations to overcome unwanted trait drift and evolution in microalgae cultivation.
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Affiliation(s)
- Ahlem Jebali
- New Mexico Consortium, 4200 W. Jemez Road, Los Alamos, NM 87544, USA.
| | - Monica R Sanchez
- Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, USA
| | - Erik R Hanschen
- Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, USA
| | | | - Alina A Corcoran
- New Mexico Consortium, 4200 W. Jemez Road, Los Alamos, NM 87544, USA
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2
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Hasan AR, Lachapelle J, El-Shawa SA, Potjewyd R, Ford SA, Ness RW. Salt stress alters the spectrum of de novo mutation available to selection during experimental adaptation of Chlamydomonas reinhardtii. Evolution 2022; 76:2450-2463. [PMID: 36036481 DOI: 10.1111/evo.14604] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2022] [Accepted: 08/12/2022] [Indexed: 01/22/2023]
Abstract
The genetic basis of adaptation is driven by both selection and the spectrum of available mutations. Given that the rate of mutation is not uniformly distributed across the genome and varies depending on the environment, understanding the signatures of selection across the genome is aided by first establishing what the expectations of genetic change are from mutation. To determine the interaction between salt stress, selection, and mutation across the genome, we compared mutations observed in a selection experiment for salt tolerance in Chlamydomonas reinhardtii to those observed in mutation accumulation (MA) experiments with and without salt exposure. MA lines evolved under salt stress had a single-nucleotide mutation rate of 1.1 × 10 - 9 $1.1 \times 10^{-9}$ , similar to that of MA lines under standard conditions ( 9.6 × 10 - 10 $9.6 \times 10^{-10}$ ). However, we found that salt stress led to an increased rate of indel mutations, but that many of these mutations were removed under selection. Finally, lines adapted to salt also showed excess clustering of mutations in the genome and the co-expression network, suggesting a role for positive selection in retaining mutations in particular compartments of the genome during the evolution of salt tolerance. Our study shows that characterizing mutation rates and spectra expected under stress helps disentangle the effects of environment and selection during adaptation.
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Affiliation(s)
- Ahmed R Hasan
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, M5S 3G5, Canada.,Department of Biology, University of Toronto Mississauga, Mississauga, ON, L5L 1C6, Canada
| | - Josianne Lachapelle
- Department of Biology, University of Toronto Mississauga, Mississauga, ON, L5L 1C6, Canada
| | - Sara A El-Shawa
- Department of Biology, University of Toronto Mississauga, Mississauga, ON, L5L 1C6, Canada.,Department of Mathematical and Computational Sciences, University of Toronto Mississauga, Mississauga, ON, L5L 1C6, Canada
| | - Roman Potjewyd
- Department of Biology, University of Toronto Mississauga, Mississauga, ON, L5L 1C6, Canada
| | - Scott A Ford
- Department of Biology, University of Toronto Mississauga, Mississauga, ON, L5L 1C6, Canada
| | - Rob W Ness
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, M5S 3G5, Canada.,Department of Biology, University of Toronto Mississauga, Mississauga, ON, L5L 1C6, Canada.,Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada
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3
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Trovão M, Schüler LM, Machado A, Bombo G, Navalho S, Barros A, Pereira H, Silva J, Freitas F, Varela J. Random Mutagenesis as a Promising Tool for Microalgal Strain Improvement towards Industrial Production. Mar Drugs 2022; 20:440. [PMID: 35877733 PMCID: PMC9318807 DOI: 10.3390/md20070440] [Citation(s) in RCA: 28] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2022] [Revised: 06/27/2022] [Accepted: 06/27/2022] [Indexed: 02/06/2023] Open
Abstract
Microalgae have become a promising novel and sustainable feedstock for meeting the rising demand for food and feed. However, microalgae-based products are currently hindered by high production costs. One major reason for this is that commonly cultivated wildtype strains do not possess the robustness and productivity required for successful industrial production. Several strain improvement technologies have been developed towards creating more stress tolerant and productive strains. While classical methods of forward genetics have been extensively used to determine gene function of randomly generated mutants, reverse genetics has been explored to generate specific mutations and target phenotypes. Site-directed mutagenesis can be accomplished by employing different gene editing tools, which enable the generation of tailor-made genotypes. Nevertheless, strategies promoting the selection of randomly generated mutants avoid the introduction of foreign genetic material. In this paper, we review different microalgal strain improvement approaches and their applications, with a primary focus on random mutagenesis. Current challenges hampering strain improvement, selection, and commercialization will be discussed. The combination of these approaches with high-throughput technologies, such as fluorescence-activated cell sorting, as tools to select the most promising mutants, will also be discussed.
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Affiliation(s)
- Mafalda Trovão
- Allmicroalgae Natural Products S.A., R&D Department, Rua 25 de Abril s/n, 2445-413 Pataias, Portugal; (M.T.); (A.M.); (A.B.); (J.S.)
- GreenCoLab—Associação Oceano Verde, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal; (L.M.S.); (G.B.); (S.N.); (H.P.)
- Associate Laboratory i4HB—Institute for Health and Bioeconomy, School of Science and Technology, NOVA University Lisbon, 2829-516 Caparica, Portugal;
- UCIBIO—Applied Molecular Biosciences Unit, Department of Chemistry, School of Science and Technology, NOVA University Lisbon, 2829-516 Caparica, Portugal
| | - Lisa M. Schüler
- GreenCoLab—Associação Oceano Verde, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal; (L.M.S.); (G.B.); (S.N.); (H.P.)
| | - Adriana Machado
- Allmicroalgae Natural Products S.A., R&D Department, Rua 25 de Abril s/n, 2445-413 Pataias, Portugal; (M.T.); (A.M.); (A.B.); (J.S.)
| | - Gabriel Bombo
- GreenCoLab—Associação Oceano Verde, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal; (L.M.S.); (G.B.); (S.N.); (H.P.)
| | - Sofia Navalho
- GreenCoLab—Associação Oceano Verde, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal; (L.M.S.); (G.B.); (S.N.); (H.P.)
| | - Ana Barros
- Allmicroalgae Natural Products S.A., R&D Department, Rua 25 de Abril s/n, 2445-413 Pataias, Portugal; (M.T.); (A.M.); (A.B.); (J.S.)
| | - Hugo Pereira
- GreenCoLab—Associação Oceano Verde, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal; (L.M.S.); (G.B.); (S.N.); (H.P.)
| | - Joana Silva
- Allmicroalgae Natural Products S.A., R&D Department, Rua 25 de Abril s/n, 2445-413 Pataias, Portugal; (M.T.); (A.M.); (A.B.); (J.S.)
| | - Filomena Freitas
- Associate Laboratory i4HB—Institute for Health and Bioeconomy, School of Science and Technology, NOVA University Lisbon, 2829-516 Caparica, Portugal;
- UCIBIO—Applied Molecular Biosciences Unit, Department of Chemistry, School of Science and Technology, NOVA University Lisbon, 2829-516 Caparica, Portugal
| | - João Varela
- GreenCoLab—Associação Oceano Verde, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal; (L.M.S.); (G.B.); (S.N.); (H.P.)
- CCMAR—Centre of Marine Sciences, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
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4
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Bleisch R, Freitag L, Ihadjadene Y, Sprenger U, Steingröwer J, Walther T, Krujatz F. Strain Development in Microalgal Biotechnology-Random Mutagenesis Techniques. LIFE (BASEL, SWITZERLAND) 2022; 12:life12070961. [PMID: 35888051 PMCID: PMC9315690 DOI: 10.3390/life12070961] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/25/2022] [Revised: 06/15/2022] [Accepted: 06/22/2022] [Indexed: 11/17/2022]
Abstract
Microalgal biomass and metabolites can be used as a renewable source of nutrition, pharmaceuticals and energy to maintain or improve the quality of human life. Microalgae’s high volumetric productivity and low impact on the environment make them a promising raw material in terms of both ecology and economics. To optimize biotechnological processes with microalgae, improving the productivity and robustness of the cell factories is a major step towards economically viable bioprocesses. This review provides an overview of random mutagenesis techniques that are applied to microalgal cell factories, with a particular focus on physical and chemical mutagens, mutagenesis conditions and mutant characteristics.
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Affiliation(s)
- Richard Bleisch
- Institute of Natural Materials Technology, Technische Universität Dresden, 01069 Dresden, Germany; (R.B.); (L.F.); (Y.I.); (U.S.); (J.S.); (T.W.)
| | - Leander Freitag
- Institute of Natural Materials Technology, Technische Universität Dresden, 01069 Dresden, Germany; (R.B.); (L.F.); (Y.I.); (U.S.); (J.S.); (T.W.)
| | - Yob Ihadjadene
- Institute of Natural Materials Technology, Technische Universität Dresden, 01069 Dresden, Germany; (R.B.); (L.F.); (Y.I.); (U.S.); (J.S.); (T.W.)
| | - Una Sprenger
- Institute of Natural Materials Technology, Technische Universität Dresden, 01069 Dresden, Germany; (R.B.); (L.F.); (Y.I.); (U.S.); (J.S.); (T.W.)
| | - Juliane Steingröwer
- Institute of Natural Materials Technology, Technische Universität Dresden, 01069 Dresden, Germany; (R.B.); (L.F.); (Y.I.); (U.S.); (J.S.); (T.W.)
| | - Thomas Walther
- Institute of Natural Materials Technology, Technische Universität Dresden, 01069 Dresden, Germany; (R.B.); (L.F.); (Y.I.); (U.S.); (J.S.); (T.W.)
| | - Felix Krujatz
- Institute of Natural Materials Technology, Technische Universität Dresden, 01069 Dresden, Germany; (R.B.); (L.F.); (Y.I.); (U.S.); (J.S.); (T.W.)
- Biotopa gGmbH—Center for Applied Aquaculture & Bioeconomy, 01454 Radeberg, Germany
- Faculty of Natural and Environmental Sciences, University of Applied Sciences Zittau/Görlitz, 02763 Zittau, Germany
- Correspondence:
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Abstract
Non-random usage of synonymous codons, known as “codon bias”, has been described in many organisms, from bacteria to Drosophila, but little is known about it in phytoplankton. This phenomenon is thought to be driven by selection for translational efficiency. As the efficacy of selection is proportional to the effective population size, species with large population sizes, such as phytoplankton, are expected to have strong codon bias. To test this, we measured codon bias in 215 strains from Haptophyta, Chlorophyta, Ochrophyta (except diatoms that were studied previously), Dinophyta, Cryptophyta, Ciliophora, unicellular Rhodophyta and Chlorarachniophyta. Codon bias is modest in most groups, despite the astronomically large population sizes of marine phytoplankton. The strength of the codon bias, measured with the effective number of codons, is the strongest in Haptophyta and the weakest in Chlorarachniophyta. The optimal codons are GC-ending in most cases, but several shifts to AT-ending codons were observed (mainly in Ochrophyta and Ciliophora). As it takes a long time to reach a new equilibrium after such shifts, species having AT-ending codons show a lower frequency of optimal codons compared to other species. Genetic diversity, calculated for species with more than three strains sequenced, is modest, indicating that the effective population sizes are many orders of magnitude lower than the astronomically large census population sizes, which helps to explain the modest codon bias in marine phytoplankton. This study represents the first comparative analysis of codon bias across multiple major phytoplankton groups.
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6
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Barten R, Peeters T, Navalho S, Fontowicz L, Wijffels RH, Barbosa M. Expanding the upper‐temperature boundary for the microalga
Picochlorum sp. (BPE23)
by adaptive laboratory evolution. Biotechnol J 2022; 17:e2100659. [DOI: 10.1002/biot.202100659] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Revised: 01/12/2022] [Accepted: 01/13/2022] [Indexed: 11/08/2022]
Affiliation(s)
- Robin Barten
- Bioprocess Engineering & AlgaePARC Wageningen University and Research Wageningen PO Box 16, 6700 AA The Netherlands
| | - Teun Peeters
- Bioprocess Engineering & AlgaePARC Wageningen University and Research Wageningen PO Box 16, 6700 AA The Netherlands
| | - Sofia Navalho
- Bioprocess Engineering & AlgaePARC Wageningen University and Research Wageningen PO Box 16, 6700 AA The Netherlands
| | - Louis Fontowicz
- Bioprocess Engineering & AlgaePARC Wageningen University and Research Wageningen PO Box 16, 6700 AA The Netherlands
| | - Rene H. Wijffels
- Bioprocess Engineering & AlgaePARC Wageningen University and Research Wageningen PO Box 16, 6700 AA The Netherlands
- Biosciences and Aquaculture Nord University Bodø N‐8049 Norway
| | - Maria Barbosa
- Bioprocess Engineering & AlgaePARC Wageningen University and Research Wageningen PO Box 16, 6700 AA The Netherlands
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7
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López-Cortegano E, Craig RJ, Chebib J, Samuels T, Morgan AD, Kraemer SA, Böndel KB, Ness RW, Colegrave N, Keightley PD. De Novo Mutation Rate Variation and Its Determinants in Chlamydomonas. Mol Biol Evol 2021; 38:3709-3723. [PMID: 33950243 PMCID: PMC8383909 DOI: 10.1093/molbev/msab140] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
De novo mutations are central for evolution, since they provide the raw material for natural selection by regenerating genetic variation. However, studying de novo mutations is challenging and is generally restricted to model species, so we have a limited understanding of the evolution of the mutation rate and spectrum between closely related species. Here, we present a mutation accumulation (MA) experiment to study de novo mutation in the unicellular green alga Chlamydomonas incerta and perform comparative analyses with its closest known relative, Chlamydomonas reinhardtii. Using whole-genome sequencing data, we estimate that the median single nucleotide mutation (SNM) rate in C. incerta is μ = 7.6 × 10-10, and is highly variable between MA lines, ranging from μ = 0.35 × 10-10 to μ = 131.7 × 10-10. The SNM rate is strongly positively correlated with the mutation rate for insertions and deletions between lines (r > 0.97). We infer that the genomic factors associated with variation in the mutation rate are similar to those in C. reinhardtii, allowing for cross-prediction between species. Among these genomic factors, sequence context and complexity are more important than GC content. With the exception of a remarkably high C→T bias, the SNM spectrum differs markedly between the two Chlamydomonas species. Our results suggest that similar genomic and biological characteristics may result in a similar mutation rate in the two species, whereas the SNM spectrum has more freedom to diverge.
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Affiliation(s)
- Eugenio López-Cortegano
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Rory J Craig
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Jobran Chebib
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Toby Samuels
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Andrew D Morgan
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | | | - Katharina B Böndel
- Institute of Plant Breeding, Seed Science and Population Genetics, University of Hohenheim, Stuttgart, Germany
| | - Rob W Ness
- Department of Biology, University of Toronto Mississauga, Mississauga, ON, Canada
| | - Nick Colegrave
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Peter D Keightley
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
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8
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Krasovec M, Rickaby REM, Filatov DA. Evolution of Mutation Rate in Astronomically Large Phytoplankton Populations. Genome Biol Evol 2021; 12:1051-1059. [PMID: 32645145 PMCID: PMC7486954 DOI: 10.1093/gbe/evaa131] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/02/2020] [Indexed: 02/06/2023] Open
Abstract
Genetic diversity is expected to be proportional to population size, yet, there is a well-known, but unexplained lack of genetic diversity in large populations-the "Lewontin's paradox." Larger populations are expected to evolve lower mutation rates, which may help to explain this paradox. Here, we test this conjecture by measuring the spontaneous mutation rate in a ubiquitous unicellular marine phytoplankton species Emiliania huxleyi (Haptophyta) that has modest genetic diversity despite an astronomically large population size. Genome sequencing of E. huxleyi mutation accumulation lines revealed 455 mutations, with an unusual GC-biased mutation spectrum. This yielded an estimate of the per site mutation rate µ = 5.55×10-10 (CI 95%: 5.05×10-10 - 6.09×10-10), which corresponds to an effective population size Ne ∼ 2.7×106. Such a modest Ne is surprising for a ubiquitous and abundant species that accounts for up to 10% of global primary productivity in the oceans. Our results indicate that even exceptionally large populations do not evolve mutation rates lower than ∼10-10 per nucleotide per cell division. Consequently, the extreme disparity between modest genetic diversity and astronomically large population size in the plankton species cannot be explained by an unusually low mutation rate.
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Affiliation(s)
- Marc Krasovec
- Department of Plant Sciences, University of Oxford, United Kingdom
| | | | - Dmitry A Filatov
- Department of Plant Sciences, University of Oxford, United Kingdom
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9
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Gao F, Woolschot S, Cabanelas ITD, Wijffels RH, Barbosa MJ. Light spectra as triggers for sorting improved strains of Tisochrysis lutea. BIORESOURCE TECHNOLOGY 2021; 321:124434. [PMID: 33257166 DOI: 10.1016/j.biortech.2020.124434] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Revised: 11/15/2020] [Accepted: 11/16/2020] [Indexed: 06/12/2023]
Abstract
It is known that microalgae respond to different light colors, but not at single-cell level. This work aimed to assess if different light colors could be used as triggers to sort over-producing cells. Six light spectra were used: red + green + blue (RGBL), blue (BL), red (RL), green (GL), blue + red (BRL) and blue + green (BGL). Fluorescence-activated cell sorting method was used to analyse single-cell fluorescence and sort cells. BGL and RGBL lead to the highest fucoxanthin production, while RL showed the lowest. Therefore, it was hypothesized that hyper-producing cells can be isolated efficiently under the adverse condition (RL). After exposure to all light colors for 14 days, the top 1% fucoxanthin producing cells were sorted. A sorted strain from RL showed higher (16-19%) growth rate and fucoxanthin productivity. This study showed how light spectra affected single-cell fucoxanthin and lipid contents and productivities. Also, it supplied an approach to sort for high-fucoxanthin or high-lipid cells.
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Affiliation(s)
- Fengzheng Gao
- Wageningen University, Bioprocess Engineering, AlgaePARC, P.O. Box 16, 6700 AA Wageningen, Netherlands.
| | - Sep Woolschot
- Wageningen University, Bioprocess Engineering, AlgaePARC, P.O. Box 16, 6700 AA Wageningen, Netherlands
| | | | - René H Wijffels
- Wageningen University, Bioprocess Engineering, AlgaePARC, P.O. Box 16, 6700 AA Wageningen, Netherlands; Faculty Biosciences and Aquaculture, Nord University, N-8049 Bodø, Norway
| | - Maria J Barbosa
- Wageningen University, Bioprocess Engineering, AlgaePARC, P.O. Box 16, 6700 AA Wageningen, Netherlands
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10
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Krasovec M, Sanchez-Brosseau S, Piganeau G. First Estimation of the Spontaneous Mutation Rate in Diatoms. Genome Biol Evol 2020; 11:1829-1837. [PMID: 31218358 PMCID: PMC6604790 DOI: 10.1093/gbe/evz130] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/17/2019] [Indexed: 12/25/2022] Open
Abstract
Mutations are the origin of genetic diversity, and the mutation rate is a fundamental parameter to understand all aspects of molecular evolution. The combination of mutation-accumulation experiments and high-throughput sequencing enabled the estimation of mutation rates in most model organisms, but several major eukaryotic lineages remain unexplored. Here, we report the first estimation of the spontaneous mutation rate in a model unicellular eukaryote from the Stramenopile kingdom, the diatom Phaeodactylum tricornutum (strain RCC2967). We sequenced 36 mutation accumulation lines for an average of 181 generations per line and identified 156 de novo mutations. The base substitution mutation rate per site per generation is μbs = 4.77 × 10-10 and the insertion-deletion mutation rate is μid = 1.58 × 10-11. The mutation rate varies as a function of the nucleotide context and is biased toward an excess of mutations from GC to AT, consistent with previous observations in other species. Interestingly, the mutation rates between the genomes of organelles and the nucleus differ, with a significantly higher mutation rate in the mitochondria. This confirms previous claims based on indirect estimations of the mutation rate in mitochondria of photosynthetic eukaryotes that acquired their plastid through a secondary endosymbiosis. This novel estimate enables us to infer the effective population size of P. tricornutum to be Ne∼8.72 × 106.
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Affiliation(s)
- Marc Krasovec
- Sorbonne Universités, UPMC Univ Paris 06, CNRS, Biologie Intégrative des Organismes Marins (BIOM), Observatoire Océanologique, Banyuls/Mer, France
| | - Sophie Sanchez-Brosseau
- Sorbonne Universités, UPMC Univ Paris 06, CNRS, Biologie Intégrative des Organismes Marins (BIOM), Observatoire Océanologique, Banyuls/Mer, France
| | - Gwenael Piganeau
- Sorbonne Universités, UPMC Univ Paris 06, CNRS, Biologie Intégrative des Organismes Marins (BIOM), Observatoire Océanologique, Banyuls/Mer, France.,Department of Plant Sciences, University of Oxford, Oxford, United Kingdom
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11
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Krasovec M, Filatov DA. Evolution of Codon Usage Bias in Diatoms. Genes (Basel) 2019; 10:genes10110894. [PMID: 31698749 PMCID: PMC6896221 DOI: 10.3390/genes10110894] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2019] [Revised: 10/29/2019] [Accepted: 11/02/2019] [Indexed: 12/22/2022] Open
Abstract
Codon usage bias (CUB)-preferential use of one of the synonymous codons, has been described in a wide range of organisms from bacteria to mammals, but it has not yet been studied in marine phytoplankton. CUB is thought to be caused by weak selection for translational accuracy and efficiency. Weak selection can overpower genetic drift only in species with large effective population sizes, such as Drosophila that has relatively strong CUB, while organisms with smaller population sizes (e.g., mammals) have weak CUB. Marine plankton species tend to have extremely large populations, suggesting that CUB should be very strong. Here we test this prediction and describe the patterns of codon usage in a wide range of diatom species belonging to 35 genera from 4 classes. We report that most of the diatom species studied have surprisingly modest CUB (mean Effective Number of Codons, ENC = 56), with some exceptions showing stronger codon bias (ENC = 44). Modest codon bias in most studied diatom species may reflect extreme disparity between astronomically large census and modest effective population size (Ne), with fluctuations in population size and linked selection limiting long-term Ne and rendering selection for optimal codons less efficient. For example, genetic diversity (pi ~0.02 at silent sites) in Skeletonema marinoi corresponds to Ne of about 10 million individuals, which is likely many orders of magnitude lower than its census size. Still, Ne ~107 should be large enough to make selection for optimal codons efficient. Thus, we propose that an alternative process-frequent changes of preferred codons, may be a more plausible reason for low CUB despite highly efficient selection for preferred codons in diatom populations. The shifts in the set of optimal codons should result in the changes of the direction of selection for codon usage, so the actual codon usage never catches up with the moving target of the optimal set of codons and the species never develop strong CUB. Indeed, we detected strong shifts in preferential codon usage within some diatom genera, with switches between preferentially GC-rich and AT-rich 3rd codon positions (GC3). For example, GC3 ranges from 0.6 to 1 in most Chaetoceros species, while for Chaetoceros dichaeta GC3 = 0.1. Both variation in selection intensity and mutation spectrum may drive such shifts in codon usage and limit the observed CUB. Our study represents the first genome-wide analysis of CUB in diatoms and the first such analysis for a major phytoplankton group.
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