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1.
    
Theory predicts that fitness decline via mutation accumulation will depend on population size, but there are only a few direct tests of this key idea. To gain a qualitative understanding of the fitness effect of new mutations, we performed a mutation accumulation experiment with the facultative sexual rotifer Brachionus calyciflorus at six different population sizes under UV‐C radiation. Lifetime reproduction assays conducted after ten and sixteen UV‐C radiations showed that while small populations lost fitness, fitness losses diminished rapidly with increasing population size. Populations kept as low as 10 individuals were able to maintain fitness close to the nonmutagenized populations throughout the experiment indicating that selection was able to remove the majority of large effect mutations in small populations. Although our results also seem to imply that small populations are effectively immune to mutational decay, we caution against this interpretation. Given sufficient time, populations of moderate to large size can experience declines in fitness from accumulating weakly deleterious mutations as demonstrated by fitness estimates from simulations and, tentatively, from a long‐term experiment with populations of moderate size. There is mounting evidence to suggest that mutational distributions contain a heavier tail of large effects. Our results suggest that this is also true when the mutational spectrum is altered by UV radiation.  相似文献   

2.
    
Glycolate is produced in autotrophic cells under high temperatures and Ci‐limitation via oxygenation of ribulose‐1,5‐bisphosphate. In unicellular algae, glycolate is lost via excretion or metabolized via the C2 cycle by consuming reductants, ATP and CO2 emission (photorespiration). Therefore, photorespiration is an inhibitory process for biomass production. However, cells can be manipulated in a way that they become glycolate‐producing ‘cell factories’, when the ratio carboxylation/oxygenation is 2. If under these conditions the C2 cycle is blocked, glycolate excretion becomes the only pathway of photosynthetic carbon flow. The study aims to proof the biotechnological applicability of algal‐based glycolate excretion as a new biotechnological platform. It is shown that cells of Chlamydomonas can be cultivated under specific conditions to establish a constant and long‐term stable glycolate excretion during the light phase. The cultures achieved a high efficiency of 82% of assimilated carbon transferred into glycolate biosynthesis without losses of function in cell vitality. Moreover, the glycolate accumulation in the medium is high enough to be directly used for microbial fermentation but does not show toxic effects to the glycolate‐producing cells.  相似文献   

3.
    
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4.
    
Genome editing by CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9 (CRISPR‐associated gene 9) system has been transformative in biology. Originally discovered as an adaptive prokaryotic immune system, CRISPR/Cas9 has been repurposed for genome editing in a broad range of model organisms, from yeast to mammalian cells. Protist parasites are unicellular organisms producing important human diseases that affect millions of people around the world. For many of these diseases, such as malaria, Chagas disease, leishmaniasis and cryptosporidiosis, there are no effective treatments or vaccines available. The recent adaptation of the CRISPR/Cas9 technology to several protist models will be playing a key role in the functional study of their proteins, in the characterization of their metabolic pathways, and in the understanding of their biology, and will facilitate the search for new chemotherapeutic targets. In this work we review recent studies where the CRISPR/Cas9 system was adapted to protist parasites, particularly to Apicomplexans and trypanosomatids, emphasizing the different molecular strategies used for genome editing of each organism, as well as their advantages. We also discuss the potential usefulness of this technology in the green alga Chlamydomonas reinhardtii.  相似文献   

5.
    
One of the major factors limiting biomass productivity in algae is the low thermodynamic efficiency of photosynthesis. The greatest thermodynamic inefficiencies in photosynthesis occur during the conversion of light into chemical energy. At full sunlight the light‐harvesting antenna captures photons at a rate nearly 10 times faster than the rate‐limiting step in photosynthetic electron transport. Excess captured energy is dissipated by non‐productive pathways including the production of reactive oxygen species. Substantial improvements in photosynthetic efficiency have been achieved by reducing the optical cross‐section of the light‐harvesting antenna by selectively reducing chlorophyll b levels and peripheral light‐harvesting complex subunits. Smaller light‐harvesting antenna, however, may not exhibit optimal photosynthetic performance in low or fluctuating light environments. We describe a translational control system to dynamically adjust light‐harvesting antenna sizes for enhanced photosynthetic performance. By expressing a chlorophyllide a oxygenase (CAO) gene having a 5′ mRNA extension encoding a Nab1 translational repressor binding site in a CAO knockout line it was possible to continuously alter chlorophyll b levels and correspondingly light‐harvesting antenna sizes by light‐activated Nab1 repression of CAO expression as a function of growth light intensity. Significantly, algae having light‐regulated antenna sizes had substantially higher photosynthetic rates and two‐fold greater biomass productivity than the parental wild‐type strains as well as near wild‐type ability to carry out state transitions and non‐photochemical quenching. These results have broad implications for enhanced algae and plant biomass productivity.  相似文献   

6.
    
Understanding the impact of spontaneous mutations on fitness has many theoretical and practical applications in biology. Although mutational effects on individual morphological or life‐history characters have been measured in several classic genetic model systems, there are few estimates of the rate of decline due to mutation for complex fitness traits. Here, we estimate the effects of mutation on competitive ability, an important complex fitness trait, in a model system for ecological and evolutionary genomics, Daphnia. Competition assays were performed to compare fitness between mutation‐accumulation (MA) lines and control lines from eight different genotypes from two populations of Daphnia pulicaria after 30 and 65 generations of mutation accumulation. Our results show a fitness decline among MA lines relative to controls as expected, but highlight the influence of genomic background on this effect. In addition, in some assays, MA lines outperform controls providing insight into the frequency of beneficial mutations.  相似文献   

7.
    
Some studies have found that dispersal rates and distances increase with density, indicating that density‐dependent dispersal likely affects spatial genetic structure. In an 11‐year mark–recapture study on a passerine, the dark‐eyed junco, we tested whether density affected dispersal distance and/or fine‐scale spatial genetic structure. Contrary to expectations, we found no effect of predispersal density on dispersal distance or the proportion of locally produced juveniles returning to the population from which they hatched. However, even though density did not affect dispersal distance or natal return rates, we found that density still did affect spatial genetic structure. We found significant positive spatial genetic structure at low densities of (postdispersal) adults but not at high densities. In years with high postdispersal (adult) densities that also had high predispersal (juvenile) densities in the previous year, we found negative spatial genetic structure, indicating high levels of dispersal. We found that density also affected fitness of recruits, and fitness of immigrants, potentially linking these population parameters with the spatial genetic structure detected. Immigrants and recruits rarely nested in low postdispersal density years. In contrast, in years with high postdispersal density, recruits were common and immigrants had equal success to local birds, so novel genotypes diluted the gene pool and effectively eliminated positive spatial genetic structure. In relation to fine‐scale spatial genetic structure, fitness of immigrants and new recruits is poorly understood compared to dispersal movements, but we conclude that it can have implications for the spatial distribution of genotypes in populations.  相似文献   

8.
    
as1, for antenna size mutant 1, was obtained by insertion mutagenesis of the unicellular green alga Chlamydomonas reinhardtii. This strain has a low chlorophyll content, 8% with respect to the wild type, and displays a general reduction in thylakoid polypeptides. The mutant was found to carry an insertion into a homologous gene, prokaryotic arsenite transporter (ARSA), whose yeast and mammal counterparts were found to be involved in the targeting of tail‐anchored (TA) proteins to cytosol‐exposed membranes, essential for several cellular functions. Here we present the characterization in a photosynthetic organism of an insertion mutant in an ARSA‐homolog gene. The ARSA1 protein was found to be localized in the cytosol, and yet its absence in as1 leads to a small chloroplast and a strongly decreased chlorophyll content per cell. ARSA1 appears to be required for optimal biogenesis of photosynthetic complexes because of its involvement in the accumulation of TOC34, an essential component of the outer chloroplast membrane translocon (TOC) complex, which, in turn, catalyzes the import of nucleus‐encoded precursor polypeptides into the chloroplast. Remarkably, the effect of the mutation appears to be restricted to biogenesis of chlorophyll‐binding polypeptides and is not compensated by the other ARSA homolog encoded by the C. reinhardtii genome, implying a non‐redundant function.  相似文献   

9.
    
Organismal performance in a changing environment is dependent on temporal patterns and duration of exposure to thermal variability. We experimentally assessed the time‐dependent effects of thermal variability (i.e., patterns of thermal exposure) on the hatching performance of Drosophila melanogaster. Flies were collected in central Chile and maintained for four generations in laboratory conditions. Fourth generation eggs were acclimated to different thermal fluctuation cycles until hatching occurred. Our results show that the frequency of extreme thermal events has a significant effect on hatching success. Eggs exposed to 24 hr cycles of thermal fluctuation had a higher proportion of eggs that hatched than those acclimated to shorter (6 and 12 hr) and longer cycles (48 hr). Furthermore, eggs subjected to frequent thermal fluctuations hatched earlier than those acclimated to less frequent thermal fluctuations. Overall, we show that, egg‐to‐adult viability is dependent on the pattern of thermal fluctuations experienced during ontogeny; thus, the pattern of thermal fluctuation experienced by flies has a significant and until now unappreciated impact on fitness.  相似文献   

10.
    
Freshwater green microalgae are diverse and widely distributed across the globe, yet the population structuring of these organisms is poorly understood. We assessed the degree of genetic diversity and differentiation of the desmid species, Micrasterias rotata. First, we compared the sequences of four nuclear regions (actin, gapC1, gapC2, and oee1) in 25 strains and selected the gapC1 and actin regions as the most appropriate markers for population structure assessment in this species. Population genetic structure was subsequently analyzed, based on seven populations from the Czech Republic and Ireland. Hudson's Snn statistics indicated that nearest‐neighbor sequences occurred significantly more frequently within geographical populations than within the wider panmictic population. Moreover, Irish populations consistently showed higher genetic diversity than the Czech samples. These results are in accordance with the unbalanced distribution of alleles in many land plant species; however, the large genetic diversity in M. rotata differs from levels of genetic diversity found in most land plants.  相似文献   

11.
    
The green microalga Apatococcus lobatus is widely distributed in terrestrial habitats throughout many climatic zones. It dominates green biofilms on natural and artificial substrata in temperate latitudes and is regarded as a key genus of obligate terrestrial consortia. Until now, its isolation, cultivation and application as a terrestrial model organism has been hampered by slow growth rates and low growth capacities. A mixotrophic culturing approach clearly enhanced the accumulation of biomass, thereby permitting the future application of A. lobatus in different types of bio‐assays necessary for material and biofilm research. The ability of A. lobatus to grow mixotrophically is assumed as a competitive advantage in terrestrial habitats.  相似文献   

12.
    
Ice‐associated algae produce ice‐binding proteins (IBPs) to prevent freezing damage. The IBPs of the three chlorophytes that have been examined so far share little similarity across species, making it likely that they were acquired by horizontal gene transfer (HGT). To clarify the importance and source of IBPs in chlorophytes, we sequenced the IBP genes of another Antarctic chlorophyte, Chlamydomonas sp. ICE‐MDV (Chlamy‐ICE). Genomic DNA and total RNA were sequenced and screened for known ice‐associated genes. Chlamy‐ICE has as many as 50 IBP isoforms, indicating that they have an important role in survival. The IBPs are of the DUF3494 type and have similar exon structures. The DUF3494 sequences are much more closely related to prokaryotic sequences than they are to sequences in other chlorophytes, and the chlorophyte IBP and ribosomal 18S phylogenies are dissimilar. The multiple IBP isoforms found in Chlamy‐ICE and other algae may allow the algae to adapt to a greater variety of ice conditions than prokaryotes, which typically have a single IBP gene. The predicted structure of the DUF3494 domain has an ice‐binding face with an orderly array of hydrophilic side chains. The results indicate that Chlamy‐ICE acquired its IBP genes by HGT in a single event. The acquisitions of IBP genes by this and other species of Antarctic algae by HGT appear to be key evolutionary events that allowed algae to extend their ranges into polar environments.  相似文献   

13.
    
Phosphatidylcholine (PC) is an almost ubiquitous phospholipid in eukaryotic algae and plants but is not found in a few species, for example Chlamydomonas reinhardtii. We recently found that some species of the genus Chlamydomonas possess PC. In the universal pathway, PC is synthesized de novo by methylation of phosphatidylethanolamine (PE) or transfer of phosphocholine from cytidine diphosphate (CDP)‐choline to diacylglycerol. Phosphocholine, the direct precursor to CDP‐choline, is synthesized either by methylation of phosphoethanolamine or phosphorylation of choline. Here we analyzed the mechanism of PC biosynthesis in two species of Chlamydomonas (asymmetrica and sphaeroides) as well as in a red alga, Cyanidioschyzon merolae. Comparative genomic analysis of enzymes involved in PC biosynthesis indicated that C. merolae possesses only the PE methylation pathway. Radioactive tracer experiments using [32P]phosphate showed delayed labeling of PC with respect to PE, which was consistent with the PE methylation pathway. In Chlamydomonas asymmetrica, labeling of PC was detected from the early time of incubation with [32P]phosphate, suggesting the operation of phosphoethanolamine methylation pathway. Genomic analysis indeed detected the genes for the phosphoethanolamine methylation pathway. In contrast, the labeling of PC in C. sphaeroides was slow, suggesting that the PE methylation pathway was at work. These results as well as biochemical and computational results uncover an unexpected diversity of the mechanisms for PC biosynthesis in algae. Based on these results, we will discuss plausible mechanisms for the scattered distribution of the ability to biosynthesize PC in the genus Chlamydomonas.  相似文献   

14.
    
Longevity is modulated by a range of conserved genes in eukaryotes, but it is unclear how variation in these genes contributes to the evolution of longevity in nature. Mutations that increase life span in model organisms typically induce trade‐offs which lead to a net reduction in fitness, suggesting that such mutations are unlikely to become established in natural populations. However, the fitness consequences of manipulating longevity have rarely been assessed in heterogeneous environments, in which stressful conditions are encountered. Using laboratory selection experiments, we demonstrate that long‐lived, stress‐resistant Caenorhabditis elegans age‐1(hx546) mutants have higher fitness than the wild‐type genotype if mixed genotype populations are periodically exposed to high temperatures when food is not limited. We further establish, using stochastic population projection models, that the age‐1(hx546) mutant allele can confer a selective advantage if temperature stress is encountered when food availability also varies over time. Our results indicate that heterogeneity in environmental stress may lead to altered allele frequencies over ecological timescales and indirectly drive the evolution of longevity. This has important implications for understanding the evolution of life‐history strategies.  相似文献   

15.
    
The taxonomy of the Cladophoraceae, a large family of filamentous green algae, has been problematic for a long time due to morphological simplicity, parallel evolution, phenotypic plasticity, and unknown distribution ranges. Partial large subunit (LSU) rDNA sequences were generated for 362 isolates, and the analyses of a concatenated dataset consisting of unique LSU and small subunit (SSU) rDNA sequences of 95 specimens greatly clarified the phylogeny of the Cladophoraceae. The phylogenetic reconstructions showed that the three currently accepted genera Chaetomorpha, Cladophora, and Rhizoclonium are polyphyletic. The backbone of the phylogeny is robust and the relationships of the main lineages were inferred with high support, only the phylogenetic position of both Chaetomorpha melagonium and Cladophora rupestris could not be inferred unambiguously. There have been at least three independent switches between branched and unbranched morphologies within the Cladophoraceae. Freshwater environments have been colonized twice independently, namely by the freshwater Cladophora species as well as by several lineages of the Rhizoclonium riparium clade. In an effort to establish monophyletic genera, the genera Acrocladus and Willeella are resurrected and two new genera are described: Pseudorhizoclonium and Lurbica.  相似文献   

16.
    
Polytomella is a genus of colorless green algae in the Reinhardtinia clade of the Chlamydomonadales, which has proven useful for a broad range of studies particularly those exploring the evolutionary loss of photosynthesis and mitochondrial genomics/biochemistry. Although 13 Polytomella strain accessions are currently available from public culture collections, the taxonomic status and redundancy of many of these strains is not clear because of possible mix‐ups, deficient historical records, and incomplete molecular data. This study therefore considers previously available and/or new cox1 and mitochondrial DNA telomere sequences from all 13 Polytomella strain accessions. Among four of these, namely P. parva SAG 63‐3, P. piriformis SAG 63‐10, P. capuana SAG 63‐5, and P. magna SAG 63‐9, cox1 and mitochondrial telomere regions are both highly divergent between strains. All of the remaining nine Polytomella strain accessions have cox1 sequences that are identical to that of P. parva SAG 63‐3 and although five of these have a mitochondrial telomere haplotype that is identical to that of P. parva SAG 63‐3, the remaining four have one of three different haplotypes. Among the 10 strains with identical cox1 sequences, we suggest that three of the telomere haplotypes are associated with distinct geographical isolates of Polytomella and the fourth evolved from one of these isolates during 50 years of active culture.  相似文献   

17.
    
Photosynthetic microbes exhibit light‐dependent electron export across the cell membrane, which can generate electricity in biological photovoltaic (BPV) devices. How electrons are exported remains to be determined; the identification of mechanisms would help selection or generation of photosynthetic microbes capable of enhanced electrical output. We show that plasma membrane NADPH oxidase activity is a significant component of light‐dependent generation of electricity by the unicellular green alga Chlamydomonas reinhardtii. NADPH oxidases export electrons across the plasma membrane to form superoxide anion from oxygen. The C. reinhardtii mutant lacking the NADPH oxidase encoded by RBO1 is impaired in both extracellular superoxide anion production and current generation in a BPV device. Complementation with the wild‐type gene restores both capacities, demonstrating the role of the enzyme in electron export. Monitoring light‐dependent extracellular superoxide production with a colorimetric assay is shown to be an effective way of screening for electrogenic potential of candidate algal strains. The results show that algal NADPH oxidases are important for superoxide anion production and open avenues for optimizing the biological component of these devices.  相似文献   

18.
    
Septins are a group of GTP‐binding proteins that are multi‐functional, with a well‐known role in cytokinesis in animals and fungi. Although the functions of septins have been thoroughly studied in opisthokonts (fungi and animals), the function and evolution of plant/algal septins are not as well characterized. Here we describe septin localization and expression in the green algae Nannochloris bacillaris and Marvania geminata. The present data suggest that septins localize at the division site when cytokinesis occurs. In addition, we show that septin homologs may be found only in green algae, but not in other major plant lineages, such as land plants, red algae and glaucophytes. We also found other septin homolog‐possessing organisms among the diatoms, Rhizaria and cryptomonad/haptophyte lineages. Our study reveals the potential role of algal septins in cytokinesis and/or cell elongation, and confirms that septin genes appear to have been lost in the Plantae lineage, except in some green algae.  相似文献   

19.
    
Temperature determines the rates of all biochemical and biophysical processes, and is also believed to be a key driver of macroevolutionary patterns. It is suggested that physiological constraints at low temperatures may diminish the fitness advantages of otherwise beneficial mutations; by contrast, relatively high, benign, temperatures allow beneficial mutations to efficiently show their phenotypic effects. To experimentally test this “mutational effects” mechanism, we examined the fitness effects of mutations across a temperature gradient using bacterial genotypes from the early stage of a mutation accumulation experiment with Escherichia coli. While the incidence of beneficial mutations did not significantly change across environmental temperatures, the number of mutations that conferred strong beneficial fitness effects was greater at higher temperatures. The results therefore support the hypothesis that warmer temperatures increase the chance and magnitude of positive selection, with implications for explaining the geographic patterns in evolutionary rates and understanding contemporary evolution under global warming.  相似文献   

20.
    
Nitrogen (N) deficiency promotes lipid accumulation in many oleaginous algae, but we have a poor understanding of the associations between the initiation of lipid accumulation and algal N retention and partitioning. Here, we report on total cell N, five bulk pools of N in the cell (protein, free amino acids, DNA, RNA, chl), and lipids from N saturation to growth cessation in three species. While the maximum level of N uptake differed among species, the ratio of minimum retained N to N retained at the initiation of lipid accumulation was consistent among species at 0.5 ± 0.04. This suggests that the cellular initiation of lipid accumulation was associated with a common magnitude of N deficiency among species. Concerning the partitioning of N, the concentration of RNA and the protein to RNA ratio were most similar among species at the initiation of lipid accumulation with averages of 3.2 ± 0.26 g · L?1 (8.2% variation) and 16 ± 1.5 (9.2% variation), respectively. All other pools and physiologically relevant ratios were considerably more variable. The species commonalities in RNA and protein show a similar reduction in general cellular function due to N deficiency before cellular initiation of lipid accumulation. These results provide insight into the physiological drivers for lipid accumulation in N‐deficient algae and data for modeling these associations.  相似文献   

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