Chakraborty Kajal, Thilakan Bini, Chakraborty Rekha Devi, Raola Vamshi Krishna, Joy Minju
Marine Biotechnology Division, Central Marine Fisheries Research Institute, Ernakulam North, P.B. No. 1603, Cochin, India.
Crustacean Fisheries Division, Central Marine Fisheries Research Institute, Ernakulam North, P.B. No. 1603, Cochin, India.
Appl Microbiol Biotechnol. 2017 Jan;101(2):569-583. doi: 10.1007/s00253-016-7810-3. Epub 2016 Sep 13.
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.
与异养细菌枯草芽孢杆菌MTCC 10407（JF834075）相关的褐藻多胞马尾藻，对致病性嗜水气单胞菌、创伤弧菌和副溶血性弧菌表现出广谱强效抗菌活性。发现枯草芽孢杆菌MTCC 10407的聚酮合酶（pks）基因呈阳性，因此，被认为具有带有聚酮骨架的次生代谢产物的特征。通过生物测定指导的分级分离，从枯草芽孢杆菌MTCC 10407的乙酸乙酯提取物中分离出两种新的具有抗菌活性的O-杂环化合物，它们属于聚酮来源的吡喃基苯甲酸酯类似物，对病原菌有活性。在本研究中，枯草芽孢杆菌MTCC 10407对细菌病原体具有强效抗菌作用的次生代谢产物被认为代表了pks-1基因编码产物的平台。还从宿主海藻多胞马尾藻的乙酸乙酯提取物中分离出了两种同源化合物3（3-（甲氧基羰基）-4-（5-（2-乙基丁基）-5,6-二氢-3-甲基-2H-吡喃-2-基）-丁基苯甲酸酯）和4 [2-（8-丁基-3-乙基-3,4,4a,5,6,8a-六氢-2H-色烯-6-基）-乙基苯甲酸酯]。从多胞马尾藻乙酸乙酯提取物中分离出的这两种抗菌性能较弱的化合物与从枯草芽孢杆菌中纯化出的化合物结构相似，这表明了这些化合物在海藻-细菌关系中的生态和代谢关系。1的四氢吡喃并-[3,2b]-吡喃-2（3H）-酮系统的四氢吡喃-2-酮部分可能被海藻的代谢库裂解，得到3的3-（二氢-3-甲基-2H-吡喃基）-丙酸甲酯部分，发现其没有明显的抗菌活性。因此，二氢-甲基-2H-吡喃-2-基丙酸酯系统的存在对于赋予更大的活性至关重要。2中极化率（Pl）与目标生物活性的直接关联表明，诱导（场/极性）而非空间效应（等张比容）似乎是影响抗菌活性诱导的关键因素。目前的工作可能会为将海藻相关细菌产生的新型O-杂环聚酮产物用于生物技术、食品和制药应用（主要作为新型抗菌次生代谢产物）留下印记。
