Background: This study investigates the effect of chloroform, an organic compound with anti-bacterial properties, produced both naturally and due to anthropogenic activities on the viability of temperate bacteriophage lambda (phage lambda) and its host, Escherichia coli (E. coli). The study was initiated while repurposing phage lambda for testing efficacy and efficiency of disinfectants.

Results: Plaque assays and Polymerase Chain Reaction (PCR) using primers specific to the Lambda Tail Protein (LTP) demonstrated a decrease in plaque-forming units and the log copy number of phage lambda following chloroform treatment of phage lysates. Interestingly, PCR with 16 S rRNA primers detected the presence of bacteria in both chloroform-treated and untreated lysates, suggesting that E. coli lysogens, small enough to pass through 0.2 μm filters, which is commonly used for sterilization, were present in the phage lysates. The presence of lysogens in the phage lysates was further supported by the absence of a 16 S rRNA amplicon in lysates prepared without phage lambda infection and the presence of an amplicon in DNase-treated lysates. Additionally, PCR and microscopy revealed that chloroform treatment of phage lysates increased the lysogen copy number, decreased lysogen size, and altered lysogens phage-producing ability.

Conclusion: In summary, while chloroform had a slight effect on the viability of phage lambda, most of the phage remained resistant to chloroform because they lack a lipid coat. Phage lambda transitioned to a lysogenic life cycle under sub-optimal growth conditions, leading to the formation of E. coli lysogens. These lysogens were more resistant to stresses like chloroform, ensuring the survival of both the phage and the host during adverse conditions