Structural diversity and possible functional roles of free fatty acids of the novel soil isolate Streptomyces sp. NP10

Herein, a novel soil bacterium Streptomyces sp. NP10 able to grow outside usual streptomycetes optimum conditions (e.g., at 4 °C, pH 9 and high NaCl concentration), exhibiting atypical hemolytic, DNAse, and cellulolytic activities, is described. This strain produces and excretes into the growth medium large amounts of free long-chain fatty acids (FAs). A concurrent lipidomics study revealed a large structural diversity of FAs with over 50 different n - and branched-chain, (un)saturated, and cyclopropane FAs (C 7 –C 30 ) produced by this strain. Two of these, i -17:0cy9-10 and a -18:0cy9-10, represent new natural products and the first ever identified branched cyclopropane FAs. Both free and bound lipid profiles of Streptomyces sp. NP10 were dominated by saturated branched chain FAs ( i -14:0, a -15:0, and i -16:0). Although these free FAs showed only a moderate antimicrobial activity, our results suggest that they could have an ecophysiological role in interspecies signaling with another soil microorganism Pseudomonas aeruginosa . This work represents the first comprehensive report on the structural diversity and complexity of the free FA pool in Streptomyces . A naturally occurring streptomycete, such as Streptomyces sp. NP10, which secretes significant amounts of free long-chain FAs (non-cytotoxic) into the medium, could be useful in microbial biodiesel production.