Showing papers by "Iqbal Ahmad published in 2017"

Leaf Extracts of Mangifera indica L. Inhibit Quorum Sensing – Regulated Production of Virulence Factors and Biofilm in Test Bacteria

Abstract: Quorum sensing (QS) is a global gene regulatory mechanism in bacteria for various traits including virulence factors. Disabling QS system with anti-infective agent is considered as a potential strategy to prevent bacterial infection. Mangifera indica L. (mango) has been shown to possess various biological activities including anti-QS. This study investigates the efficacy of leaf extracts on QS-regulated virulence factors and biofilm formation in Gram negative pathogens. Mango leaf (ML) extract was tested for QS inhibition and QS-regulated virulence factors using various indicator strains. It was further correlated with the biofilm inhibition and confirmed by electron microscopy. Phytochemical analysis was carried out using ultra performance liquid chromatography (UPLC) and gas chromatography-mass spectrometry (GC-MS) analysis. In vitro evaluation of anti-QS activity of ML extracts against Chromobacterium violaceum revealed promising dose-dependent interference in violacein production, by methanol extract. QS inhibitory activity is also demonstrated by reduction in elastase (76%), total protease (56%), pyocyanin (89%), chitinase (55%), exopolysaccharide production (58%) and swarming motility (74%) in Pseudomonas aeruginosa PAO1 at 800 μg/ml concentration. Biofilm formation by P. aeruginosa PAO1 and Aeromonas hydrophila WAF38 was reduced considerably (36-82%) over control. The inhibition of biofilm was also observed by scanning electron microscopy. Moreover, ML extracts significantly reduced mortality of Caenorhabditis elegans pre-infected with PAO1 at the tested concentration. Phytochemical analysis of active extracts revealed very high content of phenolics in methanol extract and a total of 14 compounds were detected by GC-MS and UPLC. These findings suggest that phytochemicals from the ML could provide bioactive anti-infective and needs further investigation to isolate and uncover their therapeutic efficacy.

Antioxidant and antimutagenic potential of Psidium guajava leaf extracts.

Abstract: Fruits, vegetables and medicinal herbs rich in phenolics antioxidants contribute toward reduced risk of age-related diseases and cancer. In this study, Psidium guajava leaf extract was fractionated in various organic solvents viz. petroleum ether, benzene, ethyl acetate, ethanl and methanol and tested for their antioxidant and antimutagenic properties. Methanolic fraction showed maximum antioxidant activity comparable to ascorbic acid and butylated hydroxyl toluene (BHT) as tested by DPPH free radical scavenging, phosphomolybdenum, FRAP (Fe3 + reducing power) and CUPRAC (cupric ions (Cu2+) reducing ability) assays. The fraction was analyzed for antimutagenic activities against sodium azide (NaN3), methylmethane sulfonate (MMS), 2-aminofluorene (2AF) and benzo(a)pyrene (BP) in Ames Salmonella tester strains. The methanol extracted fraction at 80 μg/ml concentration inhibited above 70% mutagenicity. Further, phytochemical analysis of methanol fraction that was found to be most active revealed the pr...

Eugenol inhibits quorum sensing and biofilm of toxigenic MRSA strains isolated from food handlers employed in Saudi Arabia

Abstract: Food handlers are important component in assessment and maintenance of food quality as they are carriers of food pathogens causing spoilage. Food spoilage is attributed to quorum sensing (QS) contr...

Impact of Metal Oxide Nanoparticles on Beneficial Soil Microorganisms and their Secondary Metabolites

Abstract: In this study, the effect of ZnO and TiO2-NPs on beneficial soil microorganisms and their secondary metabolite production was investigated. The antibacterial potential of NPs was determined by the growth kinetics of Pseudomonas aeruginosa, P. fluorescens and Bacillus amyloliquefaciens. Significantly decreased in the cell viability based on optical density measurements were observed upon treatment with increasing concentrations of NPs. While comparing the effect of the different concentrations of the NPs (200 μg/ml) on IAA production by different bacterial strains, ZnO nanoparticles showed greater inhibitory effect than TiO2-NPs on IAA production by bacterial strains. The effect of Nanoparticles on phosphate solubilization was found inhibitory at 200 μg/ml. Treatment with ZnO shown concentration dependent enhancement in siderophore production by bacteriaby exposure to ZnO-NPs whereas TiO2-NPs showed concentration dependent progressive decline for iron binding siderophore molecules. Reduction in antibiotic production by P. aeruginosa and P. fluorescens was noticed in the presence of ZnO and TiO2 as compared to the control. The fluorescence of NADH released by P. aeruginosa was observed to be quenched in the presence of ZnO and TiO2-NPs as compared to control. The present study highlights that the impact of nanoparticles on bacterial strains and the release of plant growth promoting substances by PGPR strains was dose dependent, which gives an idea about the level of toxicity of these nanoparticles in the environment. Therefore, the discharge of nanoparticles in the environment should be carefully monitored so that the loss of both structure and functions of agronomically important microbes could be protected from the toxicity of MO-NPs. Key-wordsMO-NPs, IAA, Phosphate Solubilization, Siderophore, PCA, NADH, ZnO-NPs, TiO2-NPs

Horizontal Gene Transfer in Soil and the Rhizosphere: Impact on Ecological Fitness of Bacteria

Abstract: The ecological fitness of soil- and root-associated bacterial communities is a key element for soil fertility and plant health as well as plant stress tolerance. Genetic variability in bacterial populations is maintained through mutation and gene acquisition. Horizontal gene transfer (HGT) is accomplished by conjugation, transformation, and transduction both in vitro and under natural conditions. Mobile genetic elements (MGEs) play a significant role in gene dissemination in bacterial communities and increase their adaptability, survival, and ability to colonize different environmental niches. In this context, bacterial conjugative plasmids encoding resistance genes, degradative genes, and tolerance to stress conditions are of much significance. The biofilm mode of bacterial growth further enhances gene exchange and increase the fitness and competitiveness of bacteria. Microcosm studies reveal a number of factors influencing the HGT process in soil. Considering the importance of HGT, a better understanding of genetic processes in the rhizosphere will further help in effective exploitation of naturally engineered bacteria for sustainable agriculture.

Quorum Sensing in Plant Growth-Promoting Rhizobacteria and Its Impact on Plant-Microbe Interaction

Abstract: Quorum sensing is a widespread mechanism in enormous number of bacteria for regulating various gene expression in a cell density-dependent manner through production and recognition of small molecules known as autoinducer Diverse kinds of quorum-sensing networks are found in different bacterial species Among various signal molecules, acyl homoserine lactone (AHL) signal molecules are the most and widely studied in bacteria A number of simple to advanced techniques are being used to identify and characterize signal molecules Production of signal molecules in a number of rhizospheric bacteria is documented Rhizosphere is an active atmosphere where microbe-microbe and microbe-plant interaction is highest due to rich availability of nutrients provided in the form of root exudates Several ecological and interdependent key characters of bacteria, like antibiotic, siderophore, or enzyme secretion, virulence factors of phytopathogens, as well as plant-microbe communications, are coordinated through quorum sensing (QS) In this chapter, we have provided brief fundamental aspects of quorum sensing and then addressed the recent trends on the significance of quorum sensing and signal molecules in microbe-microbe and microbe-plant interactions in the rhizosphere with special reference to plant growth-promoting rhizobacteria and plant health

Biofilms: An Overview of Their Significance in Plant and Soil Health

Abstract: The green revolution has enhanced agricultural productivity to a great extent with the increased use of high‐yielding crop varieties, heavy farm equipment, synthetic fertiliz­ ers, pesticide applications, improved irrigation, better soil management, and massive conversion of forest to agricultural lands [1, 2]. But there is a growing concern that inten­ sive agricultural practices promote large‐scale ecosystem degradation and loss of pro­ ductivity. Adverse environmental effects include deforestation, soil degradation, large‐scale greenhouse gas emissions, accumulation of pesticides and chemical fertiliz­ ers, pollution of groundwater, and decreased water table due to excessive irrigation [1, 3]. The world population is currently around 7 billion and is projected to approximately 8 billion by the year 2025 and 9 billion by 2050. Considering this population growth and the environmental damage due to ever‐increasing industrialization, it is clear that feed­ ing the world’s population will be a daunting task over the next 50 years. Therefore, there is a need for new strategies and approaches to improve agricultural productivity in a sustainable and environmentally friendly manner [4]. The effective use of beneficial microorganisms in agriculture in an integrated manner is an attractive technology to address these problems. The role of soil microorganisms in agriculture to improve the availability of plant nutrients and plant health is well known [5]. However, the ability of root‐associated microbes to improve nutrient supply and plant protection has yet to be fully exploited [6]. The colonization of the adjacent volume of soil under the plant root is known as rhizosphere colonization. Rhizosphere colonization not only works as a fundamental step in the pathogenesis of soil microbes but also plays an important role in the employ­ ment of microorganisms for beneficial purposes [7]. Beneficial rhizobacteria normally promote plant growth by establishing themselves on plant roots and suppressing the colonization or eliminating the presence of pathogenic microorganisms [8]. The com­ petitive exclusion of deleterious rhizosphere organisms is directly linked to the ability to successfully colonize a root surface. However, disease suppressive mechanisms were Biofilms: An Overview of Their Significance in Plant and Soil Health Iqbal Ahmad, Mohammad Shavez Khan, Mohd Musheer Altaf, Faizan Abul Qais, Firoz Ahmad Ansari and Kendra P. Rumbaugh

Bacterial Volatiles: Potential Applications in Plant Growth and Health

Abstract: Microorganisms including bacteria produce several kinds of volatile organic compounds (VOCs). In the last decade, an increasing research confirmed the role of VOCs as environmental friendly and potential growth inducers. These volatile compounds can help in mitigating dependence on synthetic chemicals and recombinant DNA technology. Recent experiments carried out under field conditions successfully established the role of bacterial volatiles in increasing food production. However, the information on the contribution of bacterial volatiles in plant growth and development is scattered. In this chapter, we have discussed the role of volatile organic compounds in microbe-microbe and microbe-plant interactions. Effect of VOCs as inducers for enhancing crop productivity is reviewed. Problems associated with field applications are also highlighted.

Rhizobacterial Biofilms: Diversity and Role in Plant Health

Abstract: The diverse nature of rhizobacteria and their interaction with plant roots involves complex processes and provides a unique microbial niche in the rhizosphere both beneficial and harmful to plant health depending on nature of bacteria. Biofilms are defined as the bacterial populations which stick to living and nonliving surfaces and encased in a self-produced extracellular polymeric substances (EPS). Both disease-causing and beneficial plant growth-encouraging bacteria may form biofilm on abiotic and biotic surfaces including plant surface and in soil. It is now well known that a microbe under natural condition forms mixed/polymicrobial biofilm. The process of biofilm development and their regulation are well studied among human pathogenic bacteria such as Pseudomonas aeruginosa. However, recent investigations indicated an increased interest in the research on biofilm on plant-associated rhizobacteria such as Azotobacter, Acinetobacter, Bacillus, Burkholderia, Klebsiella, Pantoea, Pseudomonas and Rhizobium. In this chapter we have made an attempt to review recent studies on rhizobacterial biofilms and their possible impact on plant health under natural and stress conditions.