1. New Paenibacillus strain produces a family of linear and cyclic antimicrobial lipopeptides: cyclization is not essential for their antimicrobial activity
En Huang, Xu Yang, Liwen Zhang, Sun Hee Moon, Ahmed E Yousef FEMS Microbiol Lett. 2017 Apr 1;364(8). doi: 10.1093/femsle/fnx049.
A new bacterial isolate, Paenibacillus sp. OSY-N, showed potent antimicrobial activity against Gram-negative and Gram-positive bacteria. Antimicrobials produced by this strain were purified by reverse-phase high-performance liquid chromatography. Structural analysis, using mass spectrometry, of a single active HPLC fraction revealed two known cyclic lipopeptides (BMY-28160 and permetin A), a new cyclic lipopeptide, and the linear counterparts of these cyclic compounds. The latter were designated as paenipeptins A, B and C, respectively. The paenipeptins have not been reported before as naturally occurring products. Paenipeptins B and C differ at the acyl side chain; paenipeptin C contains a C8-, instead of C7-fatty acyl side chain. To demonstrate unequivocally the antimicrobial activity of the linear forms of this family of cyclic lipopeptides, analogs of the paenipeptins were synthesized chemically and their antimicrobial activity was tested individually. The synthetic linear lipopeptide with an octanoic acid side chain (designated as paenipeptin C') showed potent antimicrobial activity with minimum inhibitory concentrations of 0.5-4.0 μg/mL for Gram-negative and 0.5-32 μg/mL for Gram-positive bacteria. Findings demonstrated that peptide cyclization in this lipopeptide family is not essential for their antimicrobial activity. Most importantly, linear lipopeptides are more accessible than their cyclic counterparts through chemical synthesis.
2. Biochemical, structural, and genetic characterization of tridecaptin A₁, an antagonist of Campylobacter jejuni
Christopher T Lohans, Marco J van Belkum, Stephen A Cochrane, Zedu Huang, Clarissa S Sit, Lynn M McMullen, John C Vederas Chembiochem. 2014 Jan 24;15(2):243-9. doi: 10.1002/cbic.201300595. Epub 2013 Dec 30.
Bacillus circulans NRRL B-30644 (now Paenibacillus terrae) was previously reported to produce SRCAM 1580, a bacteriocin active against the food pathogen Campylobacter jejuni. We have been unable to isolate SRCAM 1580, and did not find any genetic determinants in the genome of this strain. We now report the reassignment of this activity to the lipopeptide tridecaptin A₁. Structural characterization of tridecaptin A1 was achieved through NMR, MS/MS and GC-MS studies. The structure was confirmed through the first chemical synthesis of tridecaptin A₁, which also revealed the stereochemistry of the lipid chain. The impact of this stereochemistry on antimicrobial activity was examined. The biosynthetic machinery responsible for tridecaptin production was identified through bioinformatic analyses. P. terrae NRRL B-30644 also produces paenicidin B, a novel lantibiotic active against Gram-positive bacteria. MS/MS analyses indicate that this lantibiotic is structurally similar to paenicidin A.
3. Purification and biological activity of natural variants synthesized by tridecaptin M gene cluster and in vitro drug-kinetics of this antibiotic class
Manoj Jangra, Manpreet Kaur, Mansi Podia, Rushikesh Tambat, Vidhu Singh, Nishtha Chandal, Nisha Mahey, Navdezda Maurya, Hemraj Nandanwar Sci Rep. 2019 Dec 11;9(1):18870. doi: 10.1038/s41598-019-54716-8.
The flexibility of the adenylation domains of non-ribosomal peptide synthetases (NRPSs) to different substrates creates a diversity of structurally similar peptides. In the present study, we investigated the antimicrobial activity of different natural variants synthesized by tridecaptin M gene cluster and performed the in vitro drug kinetics on this class. The natural variants were isolated and characterized using MALDI-MS and tandem mass spectrometry. All the peptides were studied for their antimicrobial activity in different pathogens, including colistin-resistant bacteria, and for haemolytic activity. Furthermore, in vitro drug kinetics was performed with tridecaptin M (or M1, the major product of the gene cluster). The natural variants displayed a varying degree of bioactivity with M11 showing the most potent antibacterial activity (MIC, 1-8 µg/ml), even against A. baumannii and P. aeruginosa strains. The in vitro kinetic studies revealed that tridecaptin M at a concentration of 16 µg/ml eradicated the bacteria completely in high-density culture. The compound demonstrated desirable post-antibiotic effect after two-hour exposure at MIC concentration. We also observed the reversal of resistance to this class of antibiotics in the presence of carbonyl cyanide m-chlorophenyl hydrazine (CCCP). Altogether, the study demonstrated that tridecaptins are an excellent drug candidate against drug-resistant Gram-negative bacteria. Future studies are required to design a superior tridecaptin by investigating the interactions of different natural variants with the target.
