In an attempt to study the antibacterial, antivirulence and antibiofilm potentials of bacteria residing the tissue and surface mucus layers of the pristine corals, we screened a total of 43 distinct bacterial morphotypes from the coral Favites sp. Among the isolates, Pseudomonas aeruginosa strain CBMGL12 with showed antibacterial, antivirulence and antibiofilm activity against multidrug resistant pathogenic strains of Staphylococcus aureus (reference strain: MTCC96; community-acquired methicillin resistant strain: CA-MRSA). Extracellular products (ECP) from the coral-associated bacterium P. aeruginosa were solvent extracted, fractionated by chromatographic techniques such as silica column and HPLC-UV with concomitant bioassays guiding the fractionation of metabolites. Identification of bioactive chemical moieties was performed by FT-IR analysis, GC-MS/MS equipped with NIST library, 1H and 13C NMR spectral studies. We report the differential production of extracellular and cell-associated virulence and biofilm phenotypes in multi-drug resistant strains of S. aureus, post-treatment with the ECP containing aromatic fatty acid methyl esters (FAME) such as methyl benzoate and methyl phenyl acetate produced by a coral-associated bacterium. In conclusion, this study has identified antibacterial, antibiofilm and antivirulent FAME from the coral-associated P. aeruginosa for its ability to attenuate virulence and biofilms phenotypes in multi-drug resistant pathogenic strains of S. aureus.
Aim
Tomato‐associated plant‐growth‐promoting rhizosphere bacteria were screened for effective antagonistic activity against the fungal vascular wilt pathogens; tolerance to heavy metals; and enhancing the bioavailability of iron for tomato plants through in vitro and in vivo approaches.
Methods and Results
Among the 121 rhizobacteria screened for siderophores, 25 isolates were observed to be siderophore producers and out of these, seven isolates chelate copper and iron thus exhibiting in vitro antagonism against the virulent strains of Fusarium oxysporum f. sp. lycopersici MTCC10270 (Fol), Fusarium equiseti MFol and Sarocladium sp. SWL isolated from infected tomatoes. Pseudomonas stutzeri KRP8 was identified to be the most potent strain among the siderophore producers and its siderophores were chemically characterized by mass spectra as metal bound and metal‐free forms. Upon bio‐inoculation of fortified bacterial consortium (siderozote) into the rhizosphere of vermiculite pot cultured tomatoes supplied with varying concentrations of iron and copper ions, we observed in planta growth improvements, antagonism, enhancement of bioavailability of iron and heavy metal tolerance using Inductively Coupled Plasma‐Optical Emission Spectrometry.
Conclusion and Significance of the Study
Our rhizobacterial consortium provides an opportunity for soil reclamation through an ecofriendly method for a heavy metal‐free agricultural landscape.
In an in vitro study of antagonistic mangrove actinobacteria for its antifungal compounds to eliminate Fusarium oxysporum f. sp. lycopersici, the extracellular metabolites from the actinobacterium Kutzneria sp. strain TSII was documented. A total of 24 useful ligands were identified when profiled with Gas Chromatography-Mass Spectrometry after purification through silica gel column chromatography. Molecular modeling of Short-chain Dehydrogenases / Reductases (SDRs) was performed in the prime module of Schrodinger 2018-4 software using SDR of Bacillus anthracis as a template (PDB: 3I3OA). In silico studies utilizing the molecular docking of the 24 ligands with SDR responsible for pathogenicity, distributed on the membrane of the Fusarium oxysporum were carried out in Schrodinger 2018-4. Results were indicated as 1,4-Benzenedicarboxylic acid, Bis(2-ethylhexyl) ester, Spiro[Cyclopentane-1,2'(1'H)-quinoxaline], Decanedioic acid, Didecyl ester with docking scores (Kcal/mol) of-8.151,-7.231,-6.031 and low binding free energy (ΔG b) values (Kcal/mol) of-68.11,-42.23,-79.41 respectively, relating to their potential use as antifungal agents in Fusarium wilt infections. As SDRs are involved in melanin biosynthesis, binding of these ligands may interfere with melanin biosynthetic pathways conferring pathogenicity to Fusarium oxysporum f. sp. lycopersici. Hence, the present research study uncovers in vitro antagonistic potential of marine actinobacterial metabolites towards the most devastating vascular wilt pathogen Fusarium oxysporum in tomatoes and identifies the probable involvement of SDR as the potential target in an in silico molecular docking approach.
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