Precise measurement of the fitness effects of spontaneous mutations by droplet digital PCR in Burkholderia cenocepacia. Issue 2 (21st July 2021)

• Record Type: Journal Article
• Authors: Rana, Anita; Patton, David; Turner, Nathan T; Dillon, Marcus M; Cooper, Vaughn S; Sung, Way
• Editors: Wittkopp, P J
• Is Part Of: Genetics. Volume 219:Issue 2(2021)
• Publication Date: 2021-07-21
• Subjects: Burkholderia cenocepacia -- droplet digital polymerase chain reaction -- fitness effects of mutations -- mutation accumulation; Genetics -- Periodicals; 576.5
• DOI: 10.1093/genetics/iyab117
• Languages: English
• ISSNs: 0016-6731

Abstract

Abstract: Understanding how mutations affect survivability is a key component to knowing how organisms and complex traits evolve. However, most mutations have a minor effect on fitness and these effects are difficult to resolve using traditional molecular techniques. Therefore, there is a dire need for more accurate and precise fitness measurements methods. Here, we measured the fitness effects in Burkholderia cenocepacia HI2424 mutation accumulation (MA) lines using droplet-digital polymerase chain reaction (ddPCR). Overall, the fitness measurements from ddPCR-MA are correlated positively with fitness measurements derived from traditional phenotypic marker assays ( r = 0.297, P = 0.05), but showed some differences. First, ddPCR had significantly lower measurement variance in fitness ( F = 3.78, P < 2.6 × 10 −13 ) in control experiments. Second, the mean fitness from ddPCR-MA measurements were significantly lower than phenotypic marker assays (−0.0041 vs −0.0071, P = 0.006). Consistent with phenotypic marker assays, ddPCR-MA measurements observed multiple (27/43) lineages that significantly deviated from mean fitness, suggesting that a majority of the mutations are neutral or slightly deleterious and intermixed with a few mutations that have extremely large effects. Of these mutations, we found a significant excess of mutations within DNA excinuclease and Lys R transcriptional regulators that have extreme deleterious and beneficial effects, indicating that modifications to transcription and replication may have a strong effect on organismal fitness. This study demonstrates the power of ddPCR as a ubiquitous method for high-throughput fitness measurements in both DNA- and RNA-based organisms regardless of cell type or physiology.