Antibacterial aryl-crowned polyketide from Bacillus subtilis associated with seaweed Anthophycus longifolius

Abstract

Aims: Microbiological, biotechnological and chemical characterization of a previously undescribed aryl-crowned polyketide from Bacillus subtilis MTCC 10403 isolated from brown seaweed Anthophycus longifolius with activity against opportunistic Gram-negative food-borne pathogenic bacterial strains. Methods and Results: A culture-dependent method was used to isolate heterotrophic B. subtilis associated with A. longifolius and assessed for its antimicrobial properties. Minimum inhibitory concentration (MIC) of the title compound against the test pathogens was analysed by microtube dilution coupled with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromidebased colorimetric endpoint detection. Bacillus subtilis MTCC 10403 was found to be antagonistic against Gram-negative food-borne pathogenic Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, Salmonella enterica serotype Typhi, Aeromonas hydrophila and Vibrio sp. (diameter of zone of growth inhibition 13-22 mm). Bacillus subtilis was assessed for the presence of secondary metabolite coding polyketide synthase (pks) gene (KC589397, 700-bp gene product) and carboxylate siderophore framework in the aryl-crowned polyketide designated as 7-O-6 0 -(2″-acetylphenyl)-5 0 -hydroxyhexanoate-macrolactin by exhaustive spectroscopic techniques. The MIC assay showed that the reference antibiotics tetracycline and ampicillin were active at 25 lg ml À1 against the test pathogens, whereas the newly isolated polyketide displayed anti-infective properties against E. coli, A. hydrophilla, P. aeruginosa and Vibrio sp. at a lower concentration (MIC <13 lg ml À1 ). The MIC of the aryl macrolactin against K.pneumoniae was comparable with that of the referral antibiotics (~25 lg ml À1 ).The mode of antimicrobial action of acryl-crowned macrolactin was found to be iron chelating similar to siderophores. Putative biosynthetic pathway of the pks gene product further validated its molecular attributions.Conclusions: This study recognized new variant of antimicrobial aryl-crowned polyketide bearing methyl 6 0 -(2″-acetylphenyl)-5 0 -hydroxyhexanoate moiety at the C-7 position of the macrolactin system from A. longifolius-associated bacterium B. subtilis. Significance and Impact of the Study: This study revealed seaweed-associated micro-organisms as promising biological strata to produce new-generation anti-infective agents.

Complete Genome Sequence of Industrial Biocontrol Strain Paenibacillus polymyxa HY96-2 and Further Analysis of Its Biocontrol Mechanism

“…In contrast, only four were detected in strain E681, as the genes or gene clusters for tridecaptin and kalimantacin synthesis were absent. Among the six antibiotics, polymyxin, tridecaptin, and polyketide are able to suppress G - bacteria ( Cochrane et al, 2015 ; Chakraborty et al, 2018 ; Gounani et al, 2018 ), whereas mersacidin, kalimantacin, and bacitracin show activity against G + bacteria ( Konzl et al, 1997 ; Sahl and Bierbaum, 1998 ; Thistlethwaite et al, 2017 ). The identities of the genes or gene clusters related to the six antibiotics were clearly higher between strains HY96-2 and SC2 than between strains HY96-2 and E681.…”

Marine macroalgae-associated heterotrophic Firmicutes and Gamma-proteobacteria: prospective anti-infective agents against multidrug resistant pathogens

“…Various researches were focused on the antifouling and antibiotic activities of macroalgae-associated bacterial species (Zheng et al 2005;Kanagasabhapathy et al 2008;Penesyan et al 2009;Wiese et al 2009;Chakraborty et al 2018). In 1997, Imamura et al reported the production of a phenazine compound with antimicrobial activity, by a strain of Pelagiobacter variabilis isolated from the brown marine macroalgae Pocockiella variegata.…”

Macrolactins: biological activity and biosynthesis

“…Compared with 1, 7, 37 and 7-O-malonyl macrolactin A (MMA, 16), 38 exhibited greater anti-inflammatory activity owing to the existence of the epoxy ring. Further analysis revealed that 38 could (Chakraborty et al 2014(Chakraborty et al , 2017Gustafson et al 1989;Jaruchoktaweechai et al 2000;Ji et al 2010;Lu et al 2008;Mohamad et al 2012;Mondol et al 2011b;Muhammad and Hee 2014;Nagao et al 2001;Schneider et al 2007;Tareq et al 2013;Xue et al 2008;Yan et al 2016;Yoo et al 2006;Zheng et al 2007) significantly inhibit the mRNA expression of inducible nitric oxide synthase (iNOS), interleukin-1β (IL-1β) and interleukin-6 (IL-6), which are important targets in the treatment of inflammatory diseases.…”

“…The antimicrobial mode of 39 was found to be iron chelating similar to siderophores. It was proposed that the side chain 6-(2-acetylphenyl)-5-hydroxyhexanoate moiety and pentane-2,4-diol moiety of the lactone ring might potentially bind freely available Fe 3+ , resulting in inadequacy of the essential elements required for multiplication of pathogens (Chakraborty et al 2017).…”

“…7-O-glucosyl-13-O-[glucosyl-(1 → 3)-glucosyl] macrolactin A (46) To further explore the application potential of BmmGT1, Liu et al (2018) probed its regioselectivity on MLN A by optimization of the reaction time and working concentration of the enzyme. When the reaction time was extended to 1 h, BmmGT1 could transfer two glucosyl groups onto the 7-OH of MLN A, generating the di-O-glucosyl analog 7-O-[glucosyl-(1 → 3)-glucosyl] (Chakraborty et al 2014;Chakraborty et al 2017;Mondol et al 2011a;Muhammad and Hee 2014;Yan et al 2016) Fig. 3 The proposed biosynthetic pathway of MLNs.…”