Project description:We conducted whole genome sequencing on eight evolved E. coli strains (S1–S8) and the parental wild-type (WT) strain to identify mutations arising from ofloxacin treatments. These strains (S1-S8), generated through fluoroquinolone-mediated adaptive laboratory evolution (ALE), exhibited varying levels of tolerance and resistance. The ALE experiment involved intermittent antibiotic treatments of eight independent cultures over 22 days. The untreated WT strain served as a baseline to pinpoint mutations in the evolved strains.
Project description:The NS1 protein of influenza A virus (IAV) is a multifunctional virulence factor. Mouse adaptive mutations in the NS1 protein of the human isolate A/Hong Kong/1/1968(H3N2) (HK) have been previously reported to increase virulence, viral fitness, and interferon antagonism, but differ in binding to post-transcriptional processing factor CPSF30. Because nuclear trafficking is a major genetic determinant of influenza virus host adaptation, we assessed subcellular localization and host gene expression of NS1 adaptive mutations. Recombinant HK viruses with adaptive mutations in the NS1 gene were assessed for NS1 protein subcellular localization in mouse and human cells using confocal microscopy and cellular fractionation. HK-wt virus NS1 partitioned equivalently between the cytoplasm and nucleus in human cells but was defective in cytoplasmic localization in mouse cells. The adaptive mutations either increased the proportion or abundance of NS1 in the cytoplasm, and/or the nucleus. NS1 mutations that increased cytoplasmic distribution identified a putative second nuclear export signal (NES) spanning aa positions 98-106 LSEDWFMLM, (mutation sites in bold); with the strongest effect seen for mutation M106I. The putative NES in the NS3 protein was associated with cytoplasmic localization. The host gene expression profile of the adaptive mutants was determined by microarray analysis of infected mouse cells to show either high or low gene regulation (HGR or LGR) phenotypes that mapped to the amino-terminal and the carboxy-terminal regions respectively. The HGR and LGR mutations were predominantly down regulating versus up regulating respectively. The greatest effect on host gene expression in the HGR group correlated with the ability of the NS1 protein to bind CPSF30. To our knowledge this is the first report of roles of adaptive NS1 mutations that affect intracellular localization and regulation of host gene expression. biological triplicates of mock infected mouse M1 cells; cells infected with A/HK/1/1968(H3N2) wt and NS1 mtuatn with mutaions, D2N, V23A, L98S, L98S + M106I, F103L, M106V, M106V + M124I, D125G, V180A, V226I, M106I, and R227K. Cells were infected at a multiplicty of infection of 2 and cels were incubated for 8 hr at 37 C for 8 hrs before RNA extraction and analysis relative to mock PBS infected cells.
Project description:High-throughput sequencing has enabled genetic screens that can rapidly identify mutations that occur during experimental evolution. The presence of a mutation in an evolved lineage does not, however, constitute proof that the mutation is adaptive, given the well-known and widespread phenomenon of genetic hitchhiking, in which a non-adaptive or even detrimental mutation can co-occur in a genome with a beneficial mutation and the combined genotype is carried to high frequency by selection. We approximated the spectrum of possible beneficial mutations in Saccharomyces cerevisiae using sets of single-gene deletions and amplifications of almost all the genes in the S. cerevisiae genome. We determined the fitness effects of each mutation in three different nutrient-limited conditions using pooled competitions followed by barcode sequencing. Although most of the mutations were neutral or deleterious, ~500 of them increased fitness. We then compared those results to the mutations that actually occurred during experimental evolution in the same three nutrient-limited conditions. On average, ~35% of the mutations that occurred during experimental evolution were predicted by the systematic screen to be beneficial. We found that the distribution of fitness effects depended on the selective conditions. In the phosphate-limited and glucose-limited conditions, a large number of beneficial mutations of nearly equivalent, small effects drove the fitness increases. In the sulfate-limited condition, one type of mutation, the amplification of the high-affinity sulfate transporter, dominated. In the absence of that mutation, evolution in the sulfate-limited condition involved mutations in other genes that were not observed previously—but were predicted by the systematic screen. Thus, gross functional screens have the potential to predict and identify adaptive mutations that occur during experimental evolution. Previously version available on bioRXiv.
Project description:The NS1 protein of influenza A virus (IAV) is a multifunctional virulence factor. Mouse adaptive mutations in the NS1 protein of the human isolate A/Hong Kong/1/1968(H3N2) (HK) have been previously reported to increase virulence, viral fitness, and interferon antagonism, but differ in binding to post-transcriptional processing factor CPSF30. Because nuclear trafficking is a major genetic determinant of influenza virus host adaptation, we assessed subcellular localization and host gene expression of NS1 adaptive mutations. Recombinant HK viruses with adaptive mutations in the NS1 gene were assessed for NS1 protein subcellular localization in mouse and human cells using confocal microscopy and cellular fractionation. HK-wt virus NS1 partitioned equivalently between the cytoplasm and nucleus in human cells but was defective in cytoplasmic localization in mouse cells. The adaptive mutations either increased the proportion or abundance of NS1 in the cytoplasm, and/or the nucleus. NS1 mutations that increased cytoplasmic distribution identified a putative second nuclear export signal (NES) spanning aa positions 98-106 LSEDWFMLM, (mutation sites in bold); with the strongest effect seen for mutation M106I. The putative NES in the NS3 protein was associated with cytoplasmic localization. The host gene expression profile of the adaptive mutants was determined by microarray analysis of infected mouse cells to show either high or low gene regulation (HGR or LGR) phenotypes that mapped to the amino-terminal and the carboxy-terminal regions respectively. The HGR and LGR mutations were predominantly down regulating versus up regulating respectively. The greatest effect on host gene expression in the HGR group correlated with the ability of the NS1 protein to bind CPSF30. To our knowledge this is the first report of roles of adaptive NS1 mutations that affect intracellular localization and regulation of host gene expression.