O-heterocyclic derivatives with antibacterial properties from marine bacterium Bacillus subtilis associated with seaweed, Sargassum myriocystum

Abstract

The brown seaweed, Sargassum myriocystum associated with heterotrophic bacterium, Bacillus subtilis MTCC 10407 (JF834075) exhibited broad-spectra of potent antibacterial activities against pathogenic bacteria Aeromonas hydrophila, Vibrio vulnificus, and Vibrio parahaemolyticus. B. subtilis MTCC 10407 was found to be positive for polyketide synthetase (pks) gene, and therefore, was considered to characterize secondary metabolites bearing polyketide backbone. Using bioassay-guided fractionation, two new antibacterial O-heterocyclic compounds belonging to pyranyl benzoate analogs of polyketide origin, with activity against pathogenic bacteria, have been isolated from the ethyl acetate extract of B. subtilis MTCC 10407. In the present study, the secondary metabolites of B. subtilis MTCC 10407 with potent antibacterial action against bacterial pathogens was recognized to represent the platform of pks-1 gene-encoded products. Two homologous compounds 3 (3-(methoxycarbonyl)-4-(5-(2-ethylbutyl)-5,6-dihydro-3-methyl-2H-pyran-2-yl)-butyl benzoate) and 4 [2-(8-butyl-3-ethyl-3,4,4a,5,6,8a-hexahydro-2H-chromen-6-yl)-ethyl benzoate] also have been isolated from the ethyl acetate extract of host seaweed S. myriocystum. The two compounds isolated from ethyl acetate extract of S. myriocystum with lesser antibacterial properties shared similar structures with the compounds purified from B. subtilis that suggested the ecological and metabolic relationship between these compounds in seaweed-bacterial relationship. Tetrahydropyran-2-one moiety of the tetrahydropyrano-[3,2b]-pyran-2(3H)-one system of 1 might be cleaved by the metabolic pool of seaweeds to afford methyl 3-(dihydro-3-methyl-2H-pyranyl)-propanoate moiety of 3, which was found to have no significant antibacterial activity. It is therefore imperative that the presence of dihydro-methyl-2H-pyran-2-yl propanoate system is essentially required to impart the greater activity. The direct involvement of polarisability (Pl) with the target bioactivity in 2 implied that inductive (field/polar) rather than the steric effect (parachor) appears to be the key factor influencing the induction of antibacterial activity. The present work may have a footprint on the use of novel O-heterocyclic polyketide products from seaweed-associated bacterium for biotechnological, food, and pharmaceutical applications mainly as novel antimicrobial secondary metabolites.

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

“…Previous studies demonstrated that the seaweed‐associated heterotrophic microbiota are prolific sources of antibacterial metabolites, particularly belonging to polyketide class of chemistries, and were found to prove significant antibacterial activities against human pathogens (Chakraborty et al . , , ). Although bacterial polyketides are of potential pharmacological significance, there have been fewer reports on aryl polyketides, particularly from seaweed‐associated symbiotic bacteria (Schneider et al .…”

“…Seaweeds and their associated bacterial communities are potential sources in the field of functional food and biotechnology due to their abilities to produce diverse groups of compounds with a broad range of bioactivities (Zubia et al 2009;Chakraborty et al 2016;Le Lann et al 2016;Thilakan et al 2016). Among different species of marine bacteria, Bacillus sp.…”

Macrocyclic polyketides with siderophore mode of action from marine heterotrophic Shewanella algae : Prospective anti‐infective leads attenuate drug‐resistant pathogens

“…The furan‐enclosed antimicrobial polyketide from macroalgae‐associated bacterium recorded proton peaks at δ 7·09–7·48 with three‐proton integral, which perceived the presence of mono‐substituted furanyl ring (Chakraborty et al . 2017). Notwithstanding, the studied compound recorded protons at δ 7·33 and 6·88 with proton integral of two, thereby inferred the possibilities of di‐substituted furanyl ring.…”

“…Moreover, the slightly lesser chemical shift values of the titled compound ( δ 6·88, decreases of ~1 ppm), when compared with the previously reported polyketides from Bacillus amyloliquefaciens associated with seaweed Laurenciae papillosa (Chakraborty et al . 2017) suggested that the furanyl ring might be attached to any electron‐rich centres, like hydroxyl. The previously reported furan carboxylic acid compounds recorded protons at δ H 7·10/6·21 ( δ C 142·8, 121·3, 108·8, 163·1) (Chen et al .…”

Current Status and Future Prospects of Marine Natural Products (MNPs) as Antimicrobials

“…It was evident from the study that the presence of dihydro-methyl-2 H -pyran-2-yl propanoate system was essential to impart the antibacterial activity. Tetrahydropyran-2-one moiety of the tetrahydropyrano-[3,2 b ]-pyran-2(3 H )-one system of compound 128 might be cleaved by the metabolic pool of seaweeds to afford biologically active methyl 3-(dihydro-3-methyl-2 H -pyranyl)-propanoate moiety of compound 130 (which was shown to have no significant antibacterial activity in intact form) [ 78 ].…”