Lunaemycins are produced by Streptomyces lunaelactis, a species of bacterium that inhabits the moonmilk deposits of La Grotte Des Collemboles in Belgium and are active against antibiotic resistant Gram-positive bacteria.
The potent antibacterial activity of lunaemycins against antibiotic resistant Gram-positive bacteria may in part explain how Streptomyces lunaelactis strains have found their own place in extremely oligotrophic and competitive environments such as moonmilk deposits. Image credit: Martinet et al., doi: 10.3390/ijms24021114.
“Streptomyces and other actinomycetes are Gram-positive filamentous bacteria that offered most of the molecules of microbial origin that are now used in human and animal therapy,” said senior author Dr. Sébastien Rigali, a molecular microbiologist with the InBioS-Centre for Protein Engineering at the University of Liège’s Institut de Chimie and Hedera-22, and colleagues.
“The urge for new structural leads for both the agro-food and pharmaceutical fields has revitalized the interest for bioprospection of microorganisms dwelling in the most diverse and extreme environmental niches.”
“This quest for metabolite-producing bacteria in environments far from the ecological niches where they were mainly/originally isolated — such as rich organic soils for actinomycetes — is motivated by the idea that they would possess genetic features adapted to these specific and unusual environments, allowing them to produce uncommon ‘specialized’ metabolites.”
“Caves, being inorganic and extreme oligotrophic environments, were initially considered as inhospitable places for streptomycetes and other microorganisms programmed for primarily consuming nutrients derived from the plant decomposing organic matter,” they added.
“Instead, this phylum is surprisingly omnipresent, displaying relative abundance and diversity depending on the type of cave and speleothem.”
“One such geological formation that was previously unexpected to house a huge diversity of actinomycetes is the so-called moonmilk, a soft white carbonate deposit in limestone caves mainly consisting of microfibers of calcite.”
“Even within the same cave, the diversity of actinomycetes can widely differ from one moonmilk deposit to another.”
“More astonishingly, these bacteria do not only inhabit moonmilk to benefit from the nutrients carried by the water percolating from the surface, but they also actively participate in the creation of the mineral structure itself.”
In their new research, the authors focused on several strains of Streptomyces lunaelactis, a species of bacterium isolated from the moonmilk deposits of La Grotte Des Collemboles in Comblain-au-Pont, Belgium.
“The decision of our laboratory to search for antibiotic-producing bacteria in moonmilk deposits originated from evidence of hundreds of years of mining activities for the use of this speleothem as powder with antimicrobial properties,” they explained.
They were able to identify a previously unknown cyclic hexapeptide antibiotic, lunaemycin A, as the main compound synthesized by Streptomyces lunaelactis.
“It is an antibiotic named lunaemycin and produced by the new bacterium Streptomyces lunaelactis,” Dr. Rigali said.
“Lunaemycin and lunaelactis refer to the ecological niche from which this molecule and this bacterium originate, the moonmilk.”
“The lunaemycin has interesting properties, particularly active against Gram-positive bacteria that are multi-resistant to antibiotics.”
The researchers also identified 18 additional lunaemycins and demonstrated their significant bactericidal activity against Gram-positive bacteria, including multi-drug resistant clinical isolates.
“This means that these strains constitute a real reservoir for the discovery of new bioactive molecules,” Dr. Rigali said.
The study was published in the International Journal of Molecular Sciences.
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Loïc Martinet et al. 2023. Lunaemycins, New Cyclic Hexapeptide Antibiotics from the Cave Moonmilk-Dweller Streptomyces lunaelactis MM109T. Int. J. Mol. Sci 24 (2): 1114; doi: 10.3390/ijms24021114
