Biofilms in Plant and Soil Health

Iqbal Ahmad, Fohad Mabood Husain, Iqbal Ahmad, Fohad Mabood Husain

• Publisher: Wiley-Blackwell
• Year: 2017
• ISBN:
  9781119246374
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Microbiology
• Index: Biological Sciences

Biofilms are predominant mode of life for microbes under natural conditions. The three-dimensional structure of the biofilm provides enhanced protection from physical, chemical and biological stress conditions to associated microbial communities. These complex and highly structured microbial communities play a vital role in maintaining the health of plants, soils and waters. Biofilm associated with plants may be pathogenic or beneficial based on the nature of their interactions. Pathogenic or undesirable biofilm requires control in many situations, including soil, plants, food and water.

Written by leading experts from around the world, Biofilms in Plant and Soil Health provides an up-to-date review on various aspects of microbial biofilms, and suggests future and emerging trends in biofilms in plant and soil health.

Issues are addressed in four sub areas:

I) The fundamentals and significance of biofilm in plant and soil health, and the concept of mono and mixed biofilms by PGPR and fungal biofilms.

II) Biochemical and molecular mechanisms in biofilm studies in plant associated bacteria, and techniques in studying biofilms and their characterization, gene expression and enhanced antimicrobial resistance in biofilms, as well as biotic and biotic factors affecting biofilm in vitro.

III) The ecological significance of soil associated biofilms and stress management and bioremediation of contaminated soils and degraded ecosystems.

IV) Pathogenic biofilm associated with plant and food and its control measures.

This book is recommended for students and researchers working in agricultural and environmental microbiology, biotechnology, soil sciences, soil and plant health and plant protection. Researchers working in the area of quorum sensing, biofilm applications, and understanding microbiome of soil and plants will also find it useful.

Chapter 1
Biofilms: An Overview of Their Significance in Plant and Soil Health

Iqbal Ahmad¹, Mohammad Shavez Khan¹, Mohd Musheer Altaf¹, Faizan Abul Qais¹, Firoz Ahmad Ansari¹ and Kendra P. Rumbaugh²

¹Department of Agricultural Microbiology, Aligarh Muslim University, Aligarh, India

²Department of Surgery, Texas Tech University Health Sciences Center, Lubbock, Texas, USA

1.1 Introduction

The green revolution has enhanced agricultural productivity to a great extent with the increased use of high-yielding crop varieties, heavy farm equipment, synthetic fertilizers, pesticide applications, improved irrigation, better soil management, and massive conversion of forest to agricultural lands [1, 2]. But there is a growing concern that intensive agricultural practices promote large-scale ecosystem degradation and loss of productivity. Adverse environmental effects include deforestation, soil degradation, large-scale greenhouse gas emissions, accumulation of pesticides and chemical fertilizers, 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 feeding 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 employment 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 competitive exclusion of deleterious rhizosphere organisms is directly linked to the ability to successfully colonize a root surface. However, disease suppressive mechanisms were shown by plant growth–promoting rhizobacteria (PGPR) to be of no use until these microbes successfully colonized and established themselves on root surfaces [9, 10].

Bacterial root colonization is primarily influenced by the presence of the specific character of bacteria necessary for adherence and subsequent colonization. Moreover, several biotic and abiotic factors also play significant roles in bacterial-plant root interactions and colonization. When an organism colonizes a root, factors like water content, temperature, pH, soil characteristics, composition of root exudates, mineral contents, and other microorganisms may influence the process of root colonization. However, plants are the major determinant of microbial diversity [11]. Recent studies on the root-microbe interaction have indicated that rhizobacteria can colonize the root zone and form biofilm and biofilm-like structures. This phenomenon is considered to be a survival strategy by the rhizobacteria, which provides protection to the plant under stress conditions [12].

Traditionally, microbes have been characterized as freely suspended (planktonic) cells; although, many pioneering microbiologists recognized the surface-associated growth of microorganisms on tooth surfaces, aquatic environments, and other biotic and abiotic surfaces. However, a detailed examination of biofilms only became possible after observation under the electron microscope [13, 14]. Based on the observation of dental plaque and other sessile communities, in 1987 Costerton et al. put forth a theory on biofilms that explained the mechanisms of microbial adherence to living and nonliving material, and the benefits associated with this lifestyle. Since then, studies on biofilms in environmental, industrial, and ecological settings relevant to public health have increased significantly [15]. Much of the work on biofilms in the last few decades has demonstrated tremendous growth and understanding through the utilization of scanning electron microscopy, scanning confocal laser microscopy, and both standard microbiology cultural techniques and molecular-based investigation. The ultrastructures of biofilm, roles of various adhesins, genes, and regulatory pathways have all been explored in model organisms [16]. Our understanding of biofilms in natural settings has also substantially improved as new methods allow us to better distinguish different microbial species within complex communities [17–19].

According to Costerton, “the father of biofilm,” a biofilm is defined as “a structural community of bacterial cells enclosed in a self-produced polymeric matrix and adherent to an inert or living surface” [20]. However, this definition was later modified to include other characteristics of biofilm such as irreversible cell attachment, altered phenotype with respect to growth rate, and characteristic changes in gene transcription [21]. The composition of the self-produced polymeric material is mainly exopolysaccharide, protein, lipid, and DNA [19]. (Chapter 9 provides details of EPS composition.)

Biofilm formation is a complex process involving various steps such as initial adsorption or reversible attachment, irreversible attachment and the formation of a microbial monolayer on the substrate, early development of microcolonies, maturation of the biofilm structure, including the formation of characteristic architectural features, and lastly, the dispersion (or shedding) of planktonic cells from the biofilm [22]. Each of these stages is very distinct in their morphology and regulation [23]. The sessile growth of microorganisms has distinct phenotypes compared to planktonic cells and exhibits enhanced resistance to antimicrobial compounds and alterations in nutrient uptake [24].

Biofilms provide an important and fundamental strategy for adaptation and survival in the environment, as well as in the pathogenesis of various bacterial pathogens associated with humans, animals and plants [25]. Other applications of biofilms, which have been subsequently studied and are under active investigation, relate to the environmental sciences and food industry. However, in this chapter we will only address the roles of biofilm in plant and soil health, as well as briefly touch on their public health perspective.

1.2 Biofilm Associated with Plants

Biofilms are assemblages of microorganisms adhered to each other and/or to a surface and embedded in a matrix of exopolymers [26]. Biofilms are microniches, which are entirely different from their surrounding environment, and which allow microbes to work as a functional unit, accomplishing tasks not possible in their planktonic state or outside biofilms. The list of the possible effects of biofilms on bacterial ecology and biology, such as protection from desiccation, salinity, UV exposures, acid exposures, metal toxicity, predation and bactericides, and enhancement of genetic exchange and of synergistic interactions is impressive [22, 26]. Biofilms might also foster the expression of density-dependent phenotypes. Induction of the e...

Table of contents

• Cover
• Title Page
• Copyright
• Table of Contents
• Preface
• List of Contributors
• Chapter 1: Biofilms: An Overview of Their Significance in Plant and Soil Health
• Chapter 2: Role of PGPR in Biofilm Formations and Its Importance in Plant Health
• Chapter 3: Concept of Mono and Mixed Biofilms and Their Role in Soil and in Plant Association
• Chapter 4: Bacillus Biofilms and Their Role in Plant Health
• Chapter 5: Biofilm Formation by Pseudomonas spp. and Their Significance as a Biocontrol Agent
• Chapter 6: Quorum Sensing Mechanisms in Rhizosphere Biofilms
• Chapter 7: Biofilm Formation and Quorum Sensing in Rhizosphere
• Chapter 8: The Significance of Fungal Biofilms in Association with Plants and Soils
• Chapter 9: Chemical Nature of Biofilm Matrix and Its Significance
• Chapter 10: Root Exudates: Composition and Impact on Plant–Microbe Interaction
• Chapter 11: Biochemical and Molecular Mechanisms in Biofilm Formation of Plant-Associated Bacteria
• Chapter 12: Techniques in Studying Biofilms and Their Characterization: Microscopy to Advanced Imaging System in vitro and in situ
• Chapter 13: Gene Expression and Enhanced Antimicrobial Resistance in Biofilms
• Chapter 14: In Vitro Assessment of Biofilm Formation by Soil- and Plant-Associated Microorganisms
• Chapter 15: Factors Affecting Biofilm Formation in in vitro and in the Rhizosphere
• Chapter 16: Ecological Significance of Soil-Associated Plant Growth–Promoting Biofilm-Forming Microbes for Stress Management
• Chapter 17: Developed Biofilm-Based Microbial Ameliorators for Remediating Degraded Agroecosystems and the Environment
• Chapter 18: Plant Root–Associated Biofilms in Bioremediation
• Chapter 19: Biofilms for Remediation of Xenobiotic Hydrocarbons—A Technical Review
• Chapter 20: Plant Pathogenic Bacteria: Role of Quorum Sensing and Biofilm in Disease Development
• Chapter 21: Biofilm Instigation of Plant Pathogenic Bacteria and Its Control Measures
• Chapter 22: Applications of Biofilm and Quorum Sensing Inhibitors in Food Protection and Safety
• Chapter 23: Biofilm Inhibition by Natural Products of Marine Origin and Their Environmental Applications
• Chapter 24: Plant-Associated Biofilms Formed by Enteric Bacterial Pathogens and Their Significance
• Chapter 25: Anti-QS/Anti-Biofilm Agents in Controlling Bacterial Disease: An in silico Approach
• Index
• End User License Agreement