Concentration Dependent Effect of Azadirachta indica (Neem) Seed Oil and Neem Bark extract on Planktonic and Established Biofilm Growth of Pseudomonas aeruginosa and Staphylococcus aureus

Azadirachta indica Juss (Neem) is well documented for its antimicrobial activity. The effect of varying concentrations (0.1 to 50% v/v) of Azadirachta indica derived neem seed oil (NSO), neem seed oil with tween 20 and neem bark extract was evaluated on planktonic, biofilm formation and mature biofilms of multiple drug resistant Pseudomonas aeruginosa ATCC 15442 and Staphylococcus aureus ATCC 25923 using the crystal violet assay and scanning electron microscopy. NSO showed antimicrobial activity at 25% v/v for P. aeruginosa but not S. aureus in zone of inhibition assay. Neem bark extract on the contrary showed antimicrobial activity against both the isolates at 50% v/v concentrations. Interestingly, in biofilm formation assay, low concentrations of NSO (3.5 to 0.2% v/v) induced biofilm formation while inhibition of both planktonic and biofilm was seen in concentration dependent manner from 12.5% v/v onwards. Complex of NSO and tween in comparison of NSO alone caused low induction in S.aureus biofilm formation, while inhibiting biofilm formation of P. aeruginosa at all the concentrations. In biofilm eradication assay, NSO induced biofilm of both P. aeruginosa (50 to 0.1%v/v) and S. aureus (50 to 3.13%v/v). Eradication effect of neem bark extract was found on P. aeruginosa biofilm in a dose dependent fashion from 50 to 20% v/v followed by 0.2 to 0.1%v/v concentration respectively. S. aureus biofilm were eradicated at 50 to 25%v/v concentrations. At low concentrations, both the neem derivatives induced biofilm mediated growth of the pathogenic organisms. The data also indicate that neem seed oil was more effective against Gram negative P. aeruginosa while neem bark extract was effective against Gram positive S. aureus. This study highlights the crucial but variable effects of concentration dependent effect of phytochemicals and their composition on biofilm induction as well as eradication, the primary growth form in clinical settings. This challenges the notion that all herbal products are safe as antimicrobial activities differ as per microbial growth modes. Hence, concentration dependent effect of medicinal plant derived products requires thorough investigation prior to their use as antimicrobial agents

Multifaceted Interactions Between Endophytes and Plant: Developments and Prospects

Microbial endophytes are present in all known plant species. The ability to enter and thrive in the plant tissues makes endophytes unique, showing multidimensional interactions within the host plant. Several vital activities of the host plant are known to be influenced by the presence of endophytes. They can promote plant growth, elicit defense response against pathogen attack, and can act as remediators of abiotic stresses. To date, most of the research has been done assuming that the interaction of endophytes with the host plant is similar to the plant growth-promoting (PGP) microbes present in the rhizosphere. However, a new appreciation of the difference of the rhizosphere environment from that of internal plant tissues is gaining attention. It would be interesting to explore the impact of endosymbionts on the host’s gene expression, metabolism, and other physiological aspects essential in conferring resistance against biotic and abiotic stresses. A more intriguing and inexplicable issue with many endophytes that has to be critically evaluated is their ability to produce host metabolites, which can be harnessed on a large scale for potential use in diverse areas. In this review, we discuss the concept of endophytism, looking into the latest insights related to the multifarious interactions beneficial for the host plant and exploring the importance of these associations in agriculture and the environment and in other vital aspects such as human health

Effect of enrichment material on the shelf life and field efficiency of bioformulation of Rhizobium sp. and P-solubilizing Pseudomonas fluorescens

ABSTRACT In the present investigation seven carriers -talc, saw dust, fuller's earth, rice husk, sugarcane bagasse, charcoal and wheat bran were evaluated for the production of bioformulation. The bacteria used for bioformulation development were root nodulating Rhizobium sp. RASH6 Chl+Kan+ and phosphate solubilizing Pseudomonas fluorescens PB6 Amp+Str+ . Both bacterial strains were inoculated in all the carriers separately and in combination with each other (coinoculants). The bacterial population was determined in each carrier up to six month storage. Sawdust proved to be the best carrier in both water holding capacity (350 %) and also in maintaining the bacterial population for both individual and co-inoculation. Saw dust based formulation was separately amended with CMC, sucrose, molasses and gum. Enrichment of saw dust with molasses brought maximum increment in population both in mono and coinoculants. Finally the impact of six month-stored enrichment inoculants on plant productivity was determined taking chickpea as a test crop. The co-inoculants proved much better in enhancing the seedling biomass and the nodule number. Molasses enriched saw dust based formulation showed 48.43 %, 52.02 % and 57.41 % enhancement in dry weight with RASH6, PB6 and their co-inoculant respectively after 60 days of sowing. Results showed that enrichment of carrier is expected to permit the retention of cell viability thus increasing the effectiveness of the active material

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Revisiting the plant growth-promoting rhizobacteria: lessons from the past and objectives for the futurePlant beneficial rhizobacteria (PBR) is a group of naturally occurring rhizospheric microbes that enhance nutrient availability and induce biotic and abiotic stress tolerance through a wide array of mechanisms to enhance agricultural sustainability. Application of PBR has the potential to reduce worldwide requirement of agricultural chemicals and improve agro-ecological sustainability. The PBR exert their beneficial effects in three major ways; (1) fix atmospheric nitrogen and synthesize specific compounds to promote plant growth, (2) solubilize essential mineral nutrients in soils for plant uptake, and (3) produce antimicrobial substances and induce systemic resistance in host plants to protect them from biotic and abiotic stresses. Application of PBR as suitable inoculants appears to be a viable alternative technology to synthetic fertilizers and pesticides. Furthermore, PBR enhance nutrient and water use efficiency, influence dynamics of mineral recycling, and tolerance of plants to other environmental stresses by improving health of soils. This report provides comprehensive reviews and discusses beneficial effects of PBR on plant and soil health. Considering their multitude of functions to improve plant and soil health, we propose to call the plant growth-promoting bacteria (PGPR) as PBR.Not Availabl