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Effective rhizosphere colonization by plant growth promoting rhizobacteria (PGPR) is a prerequisite for its persistence performance under plant-root soil system. Therefore, to obtain effective strains, we have evaluated twelve strains of fluorescent Pseudomonas sp. from wheat rhizosphere exhibiting multifarious plant growth promoting (PGP) activities. These strains formed varying level of biofilm in vitro on abiotic surface. Two strains MW3 and MW4 with promising PGP activity but differing in biofilm forming ability. The biofilms were characterized by crystal violet assay, scanning electron and confocal laser scanning microscopy. The MW4 strain, a strong biofilm former is identified by16S rRNA gene sequence analysis. Strain MW4 showed strong biofilms compared to MW3. Similarly, wheat seeds treated with MW3 and MW4 revealed enhanced rhizospheric colonization by MW4 strain significantly (P ≤ 0.05) in higher number (logCFU g-1) up to 45 days after sowing compared to MW3. These findings suggested that strong biofilm forming ability of MW4 might have resulted in enhanced rhizosphere colonization. Therefore, biofilm forming ability of PGPR should be considered as an additional criterion in screening of fluorescent Pseudomonas sp.

Accomplishing the food requirements of ever-growing inhabitants of the earth at the same time restricting environmental degradation necessitates the increased use of beneficial agricultural practices. Specifically, for enhancing food production and security will need judicious use of natural resources and various chemical compounds. At this point, we focus on the agricultural applicability of volatile organic compounds (VOCs) produced by rhizobacteria that appeared competent, economical, and environment-friendly possible substitute. Volatile organic compounds are lipophilic molecules product of microorganism’s metabolic network having low molecular weight (

The concept of functional diversity assists in comprehension of natural intricacy during the widespread cooperation that microorganisms depict with other populations and ecological systems as how they communicate. Principally, microorganisms consist of several traits that describe their function inside ecological systems. Plant root associated bacteria that inhabit the plant root as ectophytes or endophytes and be capable of precisely boosting plant development through enhanced nourishment, production of plant hormones, mitigation of deleterious effect of different plant associated pathogens, and fighting for colonization sites on plants are referred as plant growth-promoting rhizobacteria (PGPR). Therefore, the application of specific nitrogen-fixing plant growth-promoting rhizobacteria in the form of microbial inoculants (single or mixed) can minimize the addiction of chemically synthesized fertilizers without compromising the crop yield. Despite their potential to enhance crop productivity and improved crop protection, nitrogen-fixing PGPR still have to cover a long distance to compete as effective bioinoculants. Therefore, there is urgent need to learn the functional diversity of nitrogen-fixing PGPR for sustainable crop production. Keeping in view the author make effort to evaluate the current development related with functional diversity about nitrogen-fixing PGPR along with their mode of action.

Water scarcity and its pollution has become a concern in recent times. The disposal of nutrient-rich (nitrogen and phosphorous) wastewater is also one of the main cause of water pollution through eutrophication, reduced dissolved oxygen that poses threat to aquatic ecosystems. As a result, nutrient removal has become a mandate apart from the removal of organics. However, the removal of nutrients from sewage is a challenging task. Conversely, conventional biological treatment processes provide little relief in nutrient removal. The treated effluents from conventional biological processes do not achieve the stringent nutrient removal disposal standard limits and become primary cause of pollution in the receiving water bodies. This has stressed upon the need for eco-friendly, low-energy and cost-efficient nutrient removal treatment technologies. Various biological treatment combinations or variants are in use for the efficient removal of nutrients. The biological processes in itself or in combination with chemical processes are preferred over technologies based solely on physico-chemical processes for its treatment performance at lower cost. This review summarizes the existing treatment processes and their possible up-gradation with the aim to accomplish the marked effluent standards for the nutrients. The concept of conventional systems and advanced systems for nutrients (nitrogen and phosphorous) removal which are already developed or under development are deeply discussed. Further, the challenges of each treatment systems are abridged. Finally, the possible suggestions for the modification/retrofitting of existing treatment systems for achieving stringent disposal standards are pointed out.

The mortality and morbidity due to infectious fungal diseases have been alarming in the last decade. Existing chemotherapeutic agents are incapable of dealing the situation as their improper and illogical use has caused in advent of resistant microbial strains. It has been observed that the majority of fungal infections are associated with biofilm formation by yeasts and filamentous fungi. Biofilms are three-dimensional structures of cells encased in matrix exhibiting 1,000-fold increased drug resistance. To combat such problem, there is utmost need for the discovery and development of newer and alternative agents to combat mycoses. Essential oils have ethnomedicinal values in treating a variety of infectious diseases. Essential oils are products of secondary metabolism of medicinal plants and are complex volatile compounds with the occurrence of diverse types of aldehydes, phenolics, terpenes, and other antimicrobial compounds. This feature underlines the possibility of finding novel broad-spectrum key molecules from phyto-compounds against a broad range of drug-resistant pathogenic microbes. This chapter briefly describes the human fungal infections caused by Candida spp., Aspergillus spp., and Trichophyton spp. and emphasizes on essential oils and its bioactive molecules that could be used as antibiofilm agents, their mechanisms of action, and use in combination with conventional antifungal drugs.

Twelve Azotobacter isolates exhibited varying levels of biofilm formation in a microtiter plate assay. The most efficient biofilm-forming isolate, as identified by partial 16S rRNA gene sequencing analysis, was Azotobacter vinelandii (AZCH6). Two isolates (AZCH5 and AZCH6), showing similar plant growth-promoting traits but differing in in vitro biofilm forming capacity, were further investigated for biofilm characterization on glass coverslips and on roots of wheat seedlings using confocal laser scanning microscopy and scanning electron microscopy. Rhizosphere colonization by AZCH6 in terms of CFU g−1 of soil, was significantly higher (P≤0.05) as compared to AZCH5. The data revealed that AZCH6 and AZCH5 exhibits similar pattern between biofilm formation and rhizosphere colonization. Therefore, strong biofilm-forming ability of Azotobacter on plant roots should be considered an important criterion for selection of effective isolates for enhanced root colonization.

Microbes play an important role in the discovery and development of newer drugs by secreting secondary metabolites, which are organic compounds of low molecular weight that are not essential for the growth, development, or reproduction of the microbial cell itself. However, humans have exploited these secondary metabolites to combat many diseases. The extraordinary diversity in the structures and bioactivities of these natural products have facilitated them to become key components in drug discovery. The secondary metabolites of medicinal importance are gathered and transformed in the host organism by biosynthetic pathways. However, natural bioactive products can be engineered to obtain newer, bioactive and more effective hybrid bioactive products. This approach is termed as combinatorial biosynthesis and also includes the use of genetics for medicinal chemistry. It can lead to the production of huge libraries of multifaceted compounds to nurse a modern high-throughput screening process. Combinatorial biosynthesis exploits the natural product biosynthetic pathways of enzymes like antibiotics to generate unique chemical structures. In order to manipulate and grind these multifunctional enzymes many newer tools have been used, such as the involvement of multiple hosts and expression systems, in vitro study of enzymes, and engineering techniques used for pre-polyketide synthases (PKS) and post-PKS pathways. One of the most focused efforts in this regard is the manipulation of modular PKSs leading to the creation of a number of erythromycin analogs. We have briefly summarized here the combinatorial approaches focusing on the multimodular enzymes producing polyketides, nonribosomal peptides, and hybrid polyketide peptides. We have also addressed the exploitation of high-throughput techniques in testing the activity of many nonnatural combinations of these enzymes modules.

Traditionally, medicinal plants are an important source of compounds with therapeutic potential, and still represent a significant pool for the discovery of new drugs. The medicinal properties of plants are mainly due to the presence of active primary metabolites. Although medicinal plants continue to be an important source of new therapeutic leads, its scientific validation remains inadequate due to the lack of adequate plant material, choice and execution of suitable high-throughput screening bioassays, availability of bioactive compounds in large quantities, and finally their regulatory approval and clinical trials. Although the inherent complication of natural product-based pharmaceutical invention demands integrative research and protocol; the systemic study, latest scientific approaches, and regulatory approvals, but scientific developments unmistakably showed that plant-based products will be the significant upcoming resources of novel therapeutic compounds. This chapter presents collective information about the characterization and isolation of various bioactive phyto-compounds along with their therapeutic potential.

Maintaining soil health and increased crop productivity are the two major challenges for sustainable agriculture and food security. Effective microorganisms are considered as the key elements to overcome this problem. Soil fungi are known to play a significant role in soil fertility and plant nutrient turnover. In this chapter, we focus on the characteristics, diversity, and role of a common soil fungus, Penicillium in plant-growth promotion. Penicillium is widely known for its secondary metabolite production. In this chapter the various plant-growth promoting activities of Penicillium such as phosphate solubilization, production of siderophore, and plant-growth regulators are highlighted. The effect of Penicillium as a bioinoculant in enhancing crop productivity and its potential role in sustainable agriculture is also reviewed.

The aim of present study was to initiate preliminary work on heavy metal contamination in farm soil (contaminated with processed tannery effluent) and its potential influence on the development of metal resistance among N2fixing bacterium, Sinorhizobium sp. Contaminated plant samples were analyzed for various metals and minimum inhibitory concentration (MIC) of metals was determined. Fenugreek (Trigonella sp.) plants revealed accumulation of these metals in root and leaves. Sinorhizobium sp. were isolated (25) from the root nodules of fenugreek-treated with processed tannery wastewater and characterized morpho-biochemically. All isolates were evaluated for their resistance against Cr3+, Cr6+, Cd2+, Cu2+, Zn2+ and Ni2+. The maximum MIC of 1600 μg mL−1 was noticed against Cr3+ in 64% isolates. Among all the isolates, the lowest MIC of 25 μg mL−1 was detected against Ni2+. Some metal resistant isolates were evaluated for their resistance against frequently used antibiotics viz., tetracycline, ampicillin, gentamycin, kanamycin, chloramphenicol and nalidixic acid. About 46% Sinorhizobium isolates were resistant to nalidixic acid whereas 26.6% showed resistance to ampicillin and kanamycin. The isolates demonstrated confluent growth upto a salt concentration of 3%; whereas isolates (SM17, SM24) tolerated 10% NaCl. Acidic pH eliminated almost all the test population and neutral pH had no suppressive effect on growth while majority were tolerant to pH 9.

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.

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.

Endophytic bacteria are widely distributed among plants and colonize both intracellular and intercellular spaces and do not harm the host plant. However, the distributions of endophytic diazotrophs are limited. Endophytic diazotrophs like Gluconacetobacter diazotrophicus are mainly associated with sugarcane and some other plants and responsible for significant contribution of biological nitrogen fixation with sugarcane. In this article, we described the diversity and role of quorum sensing. We also discussed the contributions of different bacterial traits that are necessary for successful colonization of the plant interior part. Further mechanisms of plant growth promotion are elaborated. Molecular characterization and identification of endophytic diazotrophs will further help in better understanding of plant colonization and plant growth promotion.