A brand new antibiotic has been discovered in the soil of a tropical rainforest, and its unique properties could make it particularly attractive for use in agriculture.

Known as phazolicin, this previously unknown compound was recently isolated deep in the tropical forests of Los Tuxtlas, Mexico; it appears the new antibiotic can strike against several types of bacteria.

"Antibiotic resistance is a huge problem in both medicine and agriculture, and continuing searches for new antibiotics are very important as they may provide leads for future anti-bacterial agents," says Konstantin Severinov, a molecular biologist and biochemist at Rutgers University-New Brunswick.

Found in the root nodules of wild beans (Phaseolus vulgaris), this unusual antibiotic is produced by a symbiotic soil bacterium that fixes nitrogen for the plant and keeps harmful microbes away.

The symbiotic microbe in question belongs to the Rhizobium genus of bacteria, which form nodules on bean plant roots. Unlike other rhizobia, however, this particular bacterium also produces phazolicin.

(Dmitrii Travin)

The antibiotic phazolicin is a class of peptide produced in the ribosome, and is part of a diverse class of natural products with a variety of biological uses that we are only beginning to uncover.

"Even with dozens of full-genome sequences, the number of rhizobial natural products that were characterised to date remains extremely small in comparison to such fruitful groups as the Actinobacteria or the Enterobacteriales," the authors say.

Using computer and bioinformatic analysis, the team decided to mine for any natural product gene clusters within the genome of the wild bean bacterium, which is how their search turned up phazolicin.

Not only could this antibiotic attack a diverse group of bacterial cells, the authors found it could also enter the bacteria and bind to its ribosomes, messing with its ability to synthesise proteins - only the second peptide known to do this.

"This diversity of modes of action, unprecedented for peptides sharing common chemical features, makes [these ribosomal peptides] a group of special interest for the search of new antibacterials," the authors conclude.

On top of its potential antibiotic properties, researchers think the compound could also be leveraged to directly assist plants.

"We hope to show the bacterium can be used as a 'plant probiotic'," explains Severinov, "because phazolicin will prevent other, potentially harmful bacteria from growing in the root system of agriculturally important plants."

Like a human probiotic, a soil probiotic requires mixing 'good' microbes into fertiliser, so they can protect legumes such as beans, peas, chickpeas, lentils, peanuts, and soybeans from harmful bacteria, allowing them to flourish.

Used in this way, the new peptide could one day help us to grow food more sustainably, increasing the yield of legumes and their ability to resist pests.

This research was published in Nature Communications.