scholarly journals Positive Selection Inhibits Plasmid Coexistence in Bacterial Genomes

mBio ◽  
2021 ◽  
Vol 12 (3) ◽  
Author(s):  
Laura Carrilero ◽  
Anastasia Kottara ◽  
David Guymer ◽  
Ellie Harrison ◽  
James P. J. Hall ◽  
...  
Keyword(s):  
Positive Selection ◽  
Fitness Costs ◽  
Accessory Gene ◽  
Bacterial Genomes ◽  
Compensatory Evolution ◽  
A Genome ◽  
Gene Functions ◽  
Fitness Benefits ◽  
Selection For ◽  
Plasmid Replicons

ABSTRACT Plasmids play an important role in bacterial evolution by transferring niche-adaptive functional genes between lineages, thus driving genomic diversification. Bacterial genomes commonly contain multiple, coexisting plasmid replicons, which could fuel adaptation by increasing the range of gene functions available to selection and allowing their recombination. However, plasmid coexistence is difficult to explain because the acquisition of plasmids typically incurs high fitness costs for the host cell. Here, we show that plasmid coexistence was stably maintained without positive selection for plasmid-borne gene functions and was associated with compensatory evolution to reduce fitness costs. In contrast, with positive selection, plasmid coexistence was unstable despite compensatory evolution. Positive selection discriminated between differential fitness benefits of functionally redundant plasmid replicons, retaining only the more beneficial plasmid. These data suggest that while the efficiency of negative selection against plasmid fitness costs declines over time due to compensatory evolution, positive selection to maximize plasmid-derived fitness benefits remains efficient. Our findings help to explain the forces structuring bacterial genomes: coexistence of multiple plasmids in a genome is likely to require either rare positive selection in nature or nonredundancy of accessory gene functions among the coexisting plasmids. IMPORTANCE Bacterial genomes often contain multiple coexisting plasmids that provide important functions like antibiotic resistance. Using lab experiments, we show that such plasmid coexistence within a genome is stable only in environments where the function they encode is useless but is unstable if the function is useful and beneficial for bacterial fitness. Where competing plasmids perform the same useful function, only the most beneficial plasmid is kept by the cell, a process that is similar to competitive exclusion in ecological communities. This process helps explain how bacterial genomes are structured: bacterial genomes expand in size by acquiring multiple plasmids when selection is relaxed but subsequently contract during periods of strong selection for the useful plasmid-encoded function.

scholarly journals Positive selection inhibits plasmid coexistence in bacterial genomes

2020 ◽  
Author(s):  
Laura Carrilero ◽  
Anastasia Kottara ◽  
David Guymer ◽  
Ellie Harrison ◽  
James P. J. Hall ◽  
...  
Keyword(s):  
Positive Selection ◽  
Fitness Costs ◽  
Accessory Gene ◽  
Bacterial Genomes ◽  
Compensatory Evolution ◽  
A Genome ◽  
Gene Functions ◽  
Fitness Benefits ◽  
Selection For ◽  
Plasmid Replicons

AbstractPlasmids play an important role in bacterial evolution by transferring niche adaptive functional genes between lineages, thus driving genomic diversification. Bacterial genomes commonly contain multiple, coexisting plasmid replicons (i.e., plasmid coinfection), which could fuel adaptation by increasing the range of gene functions available to selection and allowing their recombination. However, plasmid coinfection is difficult to explain because the acquisition of plasmids typically incurs high fitness costs for the host cell. Here, we show that plasmid coinfection was stably maintained without positive selection for plasmid-encoded gene functions and was associated with compensatory evolution to reduce fitness costs. By contrast, with positive selection, plasmid coinfection was unstable despite compensatory evolution. Positive selection discriminated between differential fitness benefits of functionally redundant plasmid replicons, retaining only the more beneficial plasmid. These data suggest that while the efficiency of negative selection against plasmid fitness costs declines over time due to compensatory evolution, positive selection to maximise plasmid-derived fitness benefits remains efficient. Our findings help to explain the forces structuring bacterial genomes: Coexistence of multiple plasmids in a genome is likely to require either rare positive selection in nature or non-redundancy of accessory gene functions among coinfecting plasmids.

scholarly journals Migration promotes plasmid stability under spatially heterogeneous positive selection

2018 ◽  
Vol 285 (1879) ◽  
pp. 20180324 ◽  
Author(s):  
Ellie Harrison ◽  
James P. J. Hall ◽  
Michael A. Brockhurst
Keyword(s):  
Positive Selection ◽  
Plasmid Stability ◽  
Mercury Resistance ◽  
Natural Environments ◽  
Compensatory Evolution ◽  
Long Term Stability ◽  
Compensatory Mutations ◽  
Selection For ◽  
The Stability

Bacteria–plasmid associations can be mutualistic or antagonistic depending on the strength of positive selection for plasmid-encoded genes, with contrasting outcomes for plasmid stability. In mutualistic environments, plasmids are swept to high frequency by positive selection, increasing the likelihood of compensatory evolution to ameliorate the plasmid cost, which promotes long-term stability. In antagonistic environments, plasmids are purged by negative selection, reducing the probability of compensatory evolution and driving their extinction. Here we show, using experimental evolution of Pseudomonas fluorescens and the mercury-resistance plasmid, pQBR103, that migration promotes plasmid stability in spatially heterogeneous selection environments. Specifically, migration from mutualistic environments, by increasing both the frequency of the plasmid and the supply of compensatory mutations, stabilized plasmids in antagonistic environments where, without migration, they approached extinction. These data suggest that spatially heterogeneous positive selection, which is common in natural environments, coupled with migration helps to explain the stability of plasmids and the ecologically important genes that they encode.

scholarly journals Serodiagnosis and Bacterial Genome of Helicobacter pylori Infection

Toxins ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 467
Author(s):  
Aina Ichihara ◽  
Hinako Ojima ◽  
Kazuyoshi Gotoh ◽  
Osamu Matsushita ◽  
Susumu Take ◽  
...  
Keyword(s):  
Helicobacter Pylori ◽  
Antibody Titer ◽  
Bacterial Genome ◽  
Serum Antibody ◽  
Gene Mutations ◽  
Bacterial Genomes ◽  
Western Blots ◽  
A Genome ◽  
Vaca Gene ◽  
H Pylori

The infection caused by Helicobacter pylori is associated with several diseases, including gastric cancer. Several methods for the diagnosis of H. pylori infection exist, including endoscopy, the urea breath test, and the fecal antigen test, which is the serum antibody titer test that is often used since it is a simple and highly sensitive test. In this context, this study aims to find the association between different antibody reactivities and the organization of bacterial genomes. Next-generation sequences were performed to determine the genome sequences of four strains of antigens with different reactivity. The search was performed on the common genes, with the homology analysis conducted using a genome ring and dot plot analysis. The two antigens of the highly reactive strains showed a high gene homology, and Western blots for CagA and VacA also showed high expression levels of proteins. In the poorly responsive antigen strains, it was found that the inversion occurred around the vacA gene in the genome. The structure of bacterial genomes might contribute to the poor reactivity exhibited by the antibodies of patients. In the future, an accurate serodiagnosis could be performed by using a strain with few gene mutations of the antigen used for the antibody titer test of H. pylori.

scholarly journals A Genome-Wide Scan for Evidence of Selection in a Maize Population Under Long-Term Artificial Selection for Ear Number

Genetics ◽  
2013 ◽  
Vol 196 (3) ◽  
pp. 829-840 ◽  
Author(s):  
Timothy M. Beissinger ◽  
Candice N. Hirsch ◽  
Brieanne Vaillancourt ◽  
Shweta Deshpande ◽  
Kerrie Barry ◽  
...  
Keyword(s):  
Artificial Selection ◽  
Maize Population ◽  
Genome Wide ◽  
A Genome ◽  
Selection For ◽  
Ear Number ◽  
Genome Wide Scan

scholarly journals Positive Selection Affects the Expression of Systemic Lupus Erythematosus Associated Loci in Human Populations

2021 ◽  
Author(s):  
Victoria Oberreiter ◽  
Tobias Goellner ◽  
David L. Morris ◽  
Helmut Schaschl
Keyword(s):  
Gene Expression ◽  
Systemic Lupus Erythematosus ◽  
Positive Selection ◽  
Lupus Erythematosus ◽  
Lifestyle Changes ◽  
Genetic Ancestry ◽  
Selection Function ◽  
Human Populations ◽  
Systemic Lupus ◽  
A Genome

Abstract Background: Systemic lupus erythematosus (SLE) shows marked population-specific disparities in disease prevalence, including substantial variation in manifestations and complications according to genetic ancestry. Several recent studies suggest that a substantial proportion of variation of gene expression shows genetic ancestry-associated differences in gene regulation on immune responses. Positive selection may act in a population-specific manner on expression quantitative trait loci (eQTLs) and thereby contributes to the difference in the differences of SLE prevalence and manifestation in human populations. We tested the hypothesises that some of the identified SLE risk polymorphisms display pleiotropic effects or polygenicity driven by positive selection. We performed a genome-wide scan for recent positive selection by using integrated Haplotype Score (iHS) statistics in different human populations. In addition, we estimated the timing of beneficial mutations to understand what possible selective pressures drive positive selection at SLE-associated loci. Results: We identified several SLE risk loci that are population-specifically under positive selection. Almost all SNPs that are under positive selection function as cis-eQTLs in different tissue types. We determined that adaptive eQTLs affect the expression of fewer genes than non-adaptive eQTLs, suggesting a limited range of effect of an eQTL at SLE risk sites that show signatures of positive selection. Furthermore, some positively selected SNPs are located in transcription factor binding sequences. The timing of positive selection for the studied loci suggests that both environmental and recent lifestyle changes during as well as after the Neolithic Transition may have become selectively effective. We propose a novel link between positively selected eQTLs at a certain SLE risk locus in Europeans and a physiological pathway not previously considered in SLE.Conclusions: We conclude that population-specific adaptive eQTLs contribute to the observed variation in specific manifestations and complications of SLE in different ethnicities. Our results suggest also that human populations adapt more rapidly to environmental and lifestyle stimuli via modification of gene expression without having to alter the genetic code.

scholarly journals SkewIT: The Skew Index Test for large-scale GC Skew analysis of bacterial genomes

2020 ◽  
Vol 16 (12) ◽  
pp. e1008439
Author(s):  
Jennifer Lu ◽  
Steven L. Salzberg
Keyword(s):  
Large Scale ◽  
Analysis Tool ◽  
Index Test ◽  
Bacterial Genomes ◽  
Phylogenetic Groups ◽  
Bacterial Phyla ◽  
Link Type ◽  
Gc Skew ◽  
A Genome ◽  
Web App

GC skew is a phenomenon observed in many bacterial genomes, wherein the two replication strands of the same chromosome contain different proportions of guanine and cytosine nucleotides. Here we demonstrate that this phenomenon, which was first discovered in the mid-1990s, can be used today as an analysis tool for the 15,000+ complete bacterial genomes in NCBI’s Refseq library. In order to analyze all 15,000+ genomes, we introduce a new method, SkewIT (Skew Index Test), that calculates a single metric representing the degree of GC skew for a genome. Using this metric, we demonstrate how GC skew patterns are conserved within certain bacterial phyla, e.g. Firmicutes, but show different patterns in other phylogenetic groups such as Actinobacteria. We also discovered that outlier values of SkewIT highlight potential bacterial mis-assemblies. Using our newly defined metric, we identify multiple mis-assembled chromosomal sequences in previously published complete bacterial genomes. We provide a SkewIT web app https://jenniferlu717.shinyapps.io/SkewIT/ that calculates SkewI for any user-provided bacterial sequence. The web app also provides an interactive interface for the data generated in this paper, allowing users to further investigate the SkewI values and thresholds of the Refseq-97 complete bacterial genomes. Individual scripts for analysis of bacterial genomes are provided in the following repository: https://github.com/jenniferlu717/SkewIT.

scholarly journals A novel positive selection for identifying cold-sensitive myosin II mutants in Dictyostelium.

Genetics ◽  
1995 ◽  
Vol 140 (2) ◽  
pp. 505-515 ◽  
Author(s):  
B Patterson ◽  
J A Spudich
Keyword(s):  
Positive Selection ◽  
Myosin Heavy Chain ◽  
Heavy Chain ◽  
Time Scale ◽  
Myosin Ii ◽  
Rapid Onset ◽  
Chemical Mutagenesis ◽  
Wild Type ◽  
Cold Sensitive ◽  
Selection For

Abstract We developed a positive selection for myosin heavy chain mutants in Dictyostelium. This selection is based on the fact that brief exposure to azide causes wild-type cells to release from the substrate, whereas myosin null cells remain adherent. This procedure assays myosin function on a time scale of minutes and has therefore allowed us to select rapid-onset cold-sensitive mutants after random chemical mutagenesis of Dictyostelium cells. We developed a rapid technique for determining which mutations lie in sequences of the myosin gene that encode the head (motor) domain and localized 27 of 34 mutants to this domain. We recovered the appropriate sequences from five of the mutants and demonstrated that they retain their cold-sensitive properties when expressed from extrachromosomal plasmids.

scholarly journals Local genic base composition impacts protein production and cellular fitness

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e4286 ◽  
Author(s):  
Erik M. Quandt ◽  
Charles C. Traverse ◽  
Howard Ochman
Keyword(s):  
Escherichia Coli ◽  
Base Composition ◽  
Protein Production ◽  
Purifying Selection ◽  
Specific Protein ◽  
Compositional Variation ◽  
Terminal Portion ◽  
A Genome ◽  
Selection For ◽  
Protein Feature

The maintenance of a G + C content that is higher than the mutational input to a genome provides support for the view that selection serves to increase G + C contents in bacteria. Recent experimental evidence fromEscherichia colidemonstrated that selection for increasing G + C content operates at the level of translation, but the precise mechanism by which this occurs is unknown. To determine the substrate of selection, we asked whether selection on G + C content acts across all sites within a gene or is confined to particular genic regions or nucleotide positions. We systematically altered the G + C contents of the GFP gene and assayed its effects on the fitness of strains harboring each variant. Fitness differences were attributable to the base compositional variation in the terminal portion of the gene, suggesting a connection to the folding of a specific protein feature. Variants containing sequence features that are thought to result in rapid translation, such as low G + C content and high levels of codon adaptation, displayed highly reduced growth rates. Taken together, our results show that purifying selection acting against A and T mutations most likely results from their tendency to increase the rate of translation, which can perturb the dynamics of protein folding.

scholarly journals Is formal employment sector hereditary? Determinants of formal/informal sector choice for Mexican male workers

2019 ◽  
pp. 91-121
Author(s):  
Adelaido García-Andrés ◽  
Ernesto Aguayo-Téllez ◽  
Jose N. Martínez
Keyword(s):  
Positive Selection ◽  
Social Mobility ◽  
Informal Sector ◽  
Formal Sector ◽  
Strong Connection ◽  
Employment Sector ◽  
Formal Employment ◽  
Selection For ◽  
The Relationship ◽  
Employment Choices

Understanding the relationship between parents’ and sons’ formal employment is essential for promoting social mobility in Mexico. Using the 2011 Survey of Social Mobility in Mexico (EMOVI), this paper contributes to the literature by addressing the intergenerational mobility of employment. Findings show a strong connection between intergenerational employment choices and suggest a positive selection for workers. Individuals with parents who worked in the formal sector are more likely to be enrolled in formal work and vice versa. Also, after controlling for parent’s employment sector, schooling remains as a significant vehicle to transit to the formal sector.

scholarly journals Positive Selection on Two Mitochondrial Coding Genes and Adaptation Signals in Hares (Genus Lepus) from China

2020 ◽  
Author(s):  
Asma Awadi ◽  
Hichem Ben Slimen ◽  
Helmut Schaschl ◽  
Felix Knauer ◽  
Franz Suchentrunk
Keyword(s):  
Amino Acid ◽  
Positive Selection ◽  
Protein Function ◽  
Transmembrane Domain ◽  
Proton Translocation ◽  
Introgressive Hybridization ◽  
Vibrational Entropy ◽  
Mutant Type ◽  
Selection For ◽  
Protein Variants

Abstract Background: Animal mitochondria play a central role in energy production in the cells through the oxidative phosphorylation (OXPHOS) pathway. Recent studies of selection on different mitochondrial OXPHOS genes have revealed the adaptive implications of amino acid changes in these subunits. In hares, climatic variation and/or introgression were suggested to be at the origin of such adaptation. Here we looked for evidence of positive selection in three mitochondrial OXPHOS genes, using tests of selection, protein structure modelling and effects of amino acid substitutions on the protein function and stability. We also used statistical models to test for climate and introgression effects on sites under positive selection. Results: Our results revealed seven sites under positive selection in ND4 and three sites in Cytb. However, no sites under positive selection were observed in the COX1 gene. All three subunits presented a high number of codons under negative selection. Sites under positive selection were mapped on the tridimensional structure of the predicted models for the respective mitochondrial subunit. Of the ten amino acid replacements inferred to have evolved under positive selection for both subunits, six were located in the transmembrane domain. On the other hand, three codons were identified as sites lining proton translocation channels. Furthermore, four codons were identified as destabilizing with a significant variation of Δ vibrational entropy energy between wild and mutant type. Moreover, the PROVEAN analysis suggested that among all positively selected sites two fixed amino acid replacements altered the protein functioning. The statistical model runs indicated significant effects of climate on the presence of ND4 and Cytb protein variants, but no effect by trans-specific mitochondrial DNA introgresson.Conclusions: Positive selection was observed in several codons in two OXPHOS genes. We found that substitutions in the positively selected codons have structural and functional impacts on the encoded proteins. Our results are concordantly suggesting that adaptations have strongly affected the evolution of mtDNA of hare species with potential effects on the protein function. Environmental/climatic changes appear to be a major trigger of this adaptation, whereas trans-specific introgressive hybridization seems to play no major role for the occurrence of protein variants.

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