Search for novel Arsenic-Containing Antibiotics

Objective

Arsenic (As), the “king of poisons”, surprisingly shows promise in medicine. With the increasing threat of antibiotic-resistant bacteria, there is an urgent need for new antibiotics. Notably, some bacteria utilize environmental As to produce unique antibiotics, as represented by arsinothricin (AST). AST effectively controls various pathogens while spare human cells, demonstrating the potential of As-containing antibiotics. Our objective is to build upon this unique connection and discover further As-containing antibiotics.

Experimental Methods

We mined bacterial genome databases using the arsinothricin (AST) biosynthetic gene cluster (BGC), leading to the discovery of novel BGCs in two Actynomyces strains, Microbispora rosea and Amycolatopsis tolypomycina. Gene analyses suggest that these BGCs encode arsenic-containing ribosomally synthesized and post-translationally modified peptides (RiPPs), which we named AsRiPP. From the M. rosea AsRiPP BGC, we selected four genes, which we hypothesize are the minimum required gene set to produce an As-containing precursor of the encoded AsRiPP. These genes were heterologously expressed in Escherichia coli in the presence of As and the AsRiPP production was analyzed. As an alternate approach, A. tolypomycina was directly cultured with inorganic arsenic and arsenic species in the culture medium was analyzed using liquid chromatography coupled with inductively coupled plasma mass spectrometry (LC-ICP-MS). The major arsenic species was further purified using anion exchange column chromatography and the antibiotic activity of the purified fraction was analyzed.

Results

While heterologous expression in E. coli was unsuccessful, the crudely purified As species exhibited moderate antibiotic activity, supporting our hypothesis that the strain produces an As-containing antibiotic, presumably the AsRiPP.

Conclusions

Our results suggest that more As-containing antibiotics exist in nature, demonstrating their potential as a resource for antibiotic development. Further investigation will focus on verifying the association of the AsRiPP BGCs and the obtained As species.