Reframing gene essentiality in terms of adaptive flexibility

Essentiality assays are important tools commonly utilized for the discovery of gene functions. Growth/no growth screens of single gene knockout strain collections are also often utilized to test the predictive power of genome-scale models. False positive predictions occur when computational analysis...

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Published in:	BMC systems biology Vol. 12; no. 1; p. 143
Main Authors:	Guzmán, Gabriela I, Olson, Connor A, Hefner, Ying, Phaneuf, Patrick V, Catoiu, Edward, Crepaldi, Lais B, Micas, Lucas Goldschmidt, Palsson, Bernhard O, Feist, Adam M
Format:	Journal Article
Language:	English
Published:	England BioMed Central Ltd 17-12-2018 BioMed Central
Subjects:	Accuracy Adaptation, Physiological - genetics Analysis Cognitive psychology Computer applications E coli Escherichia coli - enzymology Escherichia coli - genetics Escherichia coli - physiology Evolution & development Evolution, Molecular Experiments Gene deletion Gene Expression Profiling Gene mutation Gene sequencing Genes Genes, Essential - genetics Genomes Genomics Isoenzymes Isoenzymes - metabolism Lag phase Mathematical models Metabolism Mutation Organisms Phenotypes Predictions Scale models Screens Single-nucleotide polymorphism Studies Systems biology Whole Genome Sequencing Adaptive evolution Genome-scale model Essentiality
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Summary:	Essentiality assays are important tools commonly utilized for the discovery of gene functions. Growth/no growth screens of single gene knockout strain collections are also often utilized to test the predictive power of genome-scale models. False positive predictions occur when computational analysis predicts a gene to be non-essential, however experimental screens deem the gene to be essential. One explanation for this inconsistency is that the model contains the wrong information, possibly an incorrectly annotated alternative pathway or isozyme reaction. Inconsistencies could also be attributed to experimental limitations, such as growth tests with arbitrary time cut-offs. The focus of this study was to resolve such inconsistencies to better understand isozyme activities and gene essentiality. In this study, we explored the definition of conditional essentiality from a phenotypic and genomic perspective. Gene-deletion strains associated with false positive predictions of gene essentiality on defined minimal medium for Escherichia coli were targeted for extended growth tests followed by population sequencing and transcriptome analysis. Of the twenty false positive strains available and confirmed from the Keio single gene knock-out collection, 11 strains were shown to grow with longer incubation periods making these actual true positives. These strains grew reproducibly with a diverse range of growth phenotypes. The lag phase observed for these strains ranged from less than one day to more than 7 days. It was found that 9 out of 11 of the false positive strains that grew acquired mutations in at least one replicate experiment and the types of mutations ranged from SNPs and small indels associated with regulatory or metabolic elements to large regions of genome duplication. Comparison of the detected adaptive mutations, modeling predictions of alternate pathways and isozymes, and transcriptome analysis of KO strains suggested agreement for the observed growth phenotype for 6 out of the 9 cases where mutations were observed. Longer-term growth experiments followed by whole genome sequencing and transcriptome analysis can provide a better understanding of conditional gene essentiality and mechanisms of adaptation to such perturbations. Compensatory mutations are largely reproducible mechanisms and are in agreement with genome-scale modeling predictions to loss of function gene deletion events.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	1752-0509 1752-0509
DOI:	10.1186/s12918-018-0653-z