The Effect of the purA gene on E. Coli Growth & Bacteriophage Replication

Abstract

We investigated how the purA gene influences bacterial growth and phage replication in E.coli. purA is a gene involved in purine biosynthesis responsible for the synthesis of adenine, a crucial nucleotide required for many biological functions, including DNA replication, transcription, translation, and ATP synthesis. Deletion of purA has been shown to increase bacteria's susceptibility to bacteriophages, viruses specific to bacteria, and to enhance phage therapy, an alternative to antibiotics. Through our research, we aim to assess the growth and phage susceptibility of purA-deficient E. coli to better understand the role of purA in E. coli metabolic processes and to gauge the effectiveness of purA deletion in improving phage therapy. A series of experiments was conducted using microbiological techniques, including growth curves, plaque assays, and lysis curves, in both LB and M9 media, to compare bacterial growth patterns and phage susceptibility between the wild-type and knockout strains under different nutrient conditions. Growth curve data on LB media showed that the wild-type strain grew faster than the knockout strain. However, the growth curve on M9 media suggested that the purA knockout strain grew superiorly to the wildtype strain, indicating that the lack of purines in M9 media may prove beneficial for growth and replication. Plaque assay data revealed that the wild-type strain E. coli is more susceptible to phage attack compared to its knockout counterpart, as greater PFU were observed in all three dilution plates of the wild type compared to the knockout strain. Lysis data suggest both strains follow similar lysis patterns, as the stationary phase and death phase durations are similar. The log-phase concentrations pre-lysis differ between strains, with the wild-type strain concentration at the end of the log phase being double that of the knockout strain. At the two measured time points, we observed that the E. coli purA knockout strain had lower OD values than the parent strain, indicating lower bacterial growth. This trend remains consistent between both time points, demonstrating that, as hypothesized, although purA is a non-essential gene, bacterial growth decreases under these conditions. These results are significant because they show that the effect of purA knockout can be environment-dependent, affecting growth, metabolism, and susceptibility to phage. This data reveals that although purA is non-essential, it can still play a significant role in how E. coli responds to various environmental factors. Our findings show that deleting the purA gene alters E. coli growth and phage interactions, with effects that depend heavily on nutrient availability. Overall, this indicates that although purA is non-essential, our data suggest it still influences how well the bacteria grow and how they handle phage exposure across different environments. Future studies should examine how the knockout strain behaves across a broader range of nutrient conditions and stressors, which would help determine under what circumstances purA truly becomes essential for growth and phage resistance.