Work

Involvement of Escherichia coli- encoded Lon protease and its substrates in phenotypic antibiotic resistance elicited by 4-amino-2-nitrophenol

Year: 2025

Type: article

Abstract: ABSTRACT In prokaryotes, the energy-dependent protein degradation is controlled, primarily, by two ATP-dependent proteases, Lon and Clp. This study investigates the roles of Escherichia coli ( E. coli )-encoded Lon protease in the metabolism of 2,4-dinitrophenol (2,4-DNP), a toxic industrial compound. Enhanced conversion of yellow-colored 2,4-DNP to a reddish-brown product was observed in a strain lacking Lon protease (Δ lon ). This observation led us to characterize and understand the mechanisms of 2,4-DNP metabolism. UV-visible and LC-MS analyses revealed differences in the conversion products between the wild-type and Δ lon . One of the substrates of Lon protease is MarA, a transcription factor, and studies with different mutants followed by trans complementation demonstrated MarA-dependent conversion. The bathochromic shift of spectral peaks suggested reduction processes and possible involvement of nitroreductase enzymes. Indeed, the expression of two genes encoding nitroreductases, nfsA and nfsB , increased with 2,4-DNP and was dependent on MarA. Importantly, the production of the reddish-brown product was lower in strains lacking nfsA or nfsB . Finally, LC-MS analysis identified one of the conversion products of 2,4-DNP to be 4-amino-2-nitrophenol (4,2-ANP). Dose studies with purified 4,2-ANP demonstrated that it did not lower the growth of E. coli (unlike 2,4-DNP) and induced phenotypic antibiotic resistance in an acrB- dependent (like 2,4-DNP) but in a marA- independent (unlike 2,4-DNP) manner. This study revealed how E. coli in the environment converts a toxic compound (2,4-DNP) into a lesser toxic compound (4,2-ANP) and helps survive in the presence of antibiotics. Overall, this study contributes to our understanding of biological responses to nitroaromatics. IMPORTANCE E. coli is one of the common microorganisms in feces-contaminated sewage and often interacts with several pollutants. This study identifies the roles of Lon protease and its substrate MarA in inducing nitroreductases, NfsA and NfsB, in reducing toxic 2,4-DNP to less toxic 4,2-ANP, a novel inducer of phenotypic antibiotic resistance in E. coli . This study sheds light on the roles of E. coli -encoded Lon protease upon exposure to harmful nitroaromatics. Common environmental pollutants can act as a selective pressure, favoring the survival as well as proliferation of bacteria containing antibiotic-resistant genes, which can easily be transferred to other bacteria through horizontal gene transfer. This study offers insights into mitigation methods in E. coli , a well-characterized model. It is possible that such environmental pollution strategies may be translated to other models, such as Pseudomonas , which are commonly used in bioremediation studies.

Source: Applied and Environmental Microbiology

DOI: 10.1128/aem.01603-25

Authors: Santhi Sanil Nandini, Sirisha Jagdish, Subinoy Rana, Dipankar Nandi

Institution: Indian Institute of Science Bangalore

Language: English

Topic: Bacterial Genetics and Biotechnology

Subfield: Genetics

Field: Biochemistry, Genetics and Molecular Biology

Domain: Life Sciences

Open Access status: diamond

Funder: University Grants Commission of Bangladesh

Award: G3538799017