CHAPTER 1: Biomass and its Biorefinery: Novel Approaches from Nature-Inspired Strategies and Technology

Biofuels have been around since modern cars were invented. Early engines were designed to be able to run on ethanol or vegetable oil. However, the discovery of huge deposits of petroleum led to the development of refinery-based fossil fuels, and have provided a cheap supply of gasoline and diesel for decades. Although the concept of biofuels has never been forgotten, industrial-scale biofuel production has yet to be developed. Recently, increased gasoline prices, environmental concerns, and the security of energy supplies have drawn much public attention. Many countries have therefore promoted the research and development (R&D) of alternative fuels in response to these concerns. One of the promising routes towards alternative energy is biofuels produced from lignocellulosic biomass through biological conversion processes, in which non-food resources, such as agricultural and forestry waste, and energy crops, are utilized as feedstock. Processes that include thermochemical pretreatment, enzymatic saccharification, and microbial fermentation are used to convert polysaccharides in biomass into alcohol fuels, such as ethanol for transportation.¹  Although carbohydrates are an energy source for many organisms in nature, the natural decay process by microorganisms is slow, albeit efficient.²  In order to establish biorefinery and achieve economically competitive biofuel production from biomass, technical challenges and barriers must be overcome to accelerate the development of the growing biofuel industry. The key components involved are sustainable feedstock supply, optimized bioconversion technologies, and integrated biorefinery on an industrial scale.

The R&D of feedstock supply and logistics has been focused on developing techniques to provide sustainable biomass supply (quantity) and quality in production, harvest, storage, handling, and transportation. Preprocessing treatments, such as reduction of particle size, drying, blending, and densification, have also been tested to standardize the feedstock supply chain, reduce transportation costs, and to upgrade biomass reactivity in down-stream operations.

Current biomass conversion technology normally consists of three steps: thermochemical pretreatment, enzymatic saccharification, and microbial fermentation. Pretreatment is a process that conditions biomass feedstock to be amenable to cellulolytic enzymes to break down structural polysaccharides to fermentable sugars. Physical pretreatment may include mechanical milling to reduce biomass particle size, steam explosion, and hydrothermolysis. Thermochemical pretreatment normally involves a dilute acid (e.g., H₂SO₄) or base (e.g., NaOH) to promote hydrolysis by removing hemicellulose and/or lignin. Many other solvents have also been explored and shown to disrupt biomass and promote hydrolysis, such as alkaline H₂O₂, ozone, organosolv, glycerol, dioxane, phenol, ethylene glycol, concentrated mineral acid, ammonia, metal complexes, and others. For any given feedstock, some methods may be more effective than others. Many pretreatment technologies have been developed aiming to achieve a high yield of sugars and limit the degradation products that may inhibit microbial fermentation. Some of these methods, while effective, are not economically feasible.³  Due to the limited understanding of the complex structure of biomass, pretreatment is still considered to be the most costly step when the overall cost of the process is taken into account.⁴  A recent study seemed to shed light on the rational design of the pretreatment process, suggesting a focus on eliminating the lignin while leaving the structural polysaccharides (i.e., hemicellulose as well as cellulose) intact within the plant cell walls. Such pretreatment would leave an open structure that allows easy access by the enzymes and rapid digestion of polysaccharides.⁵ 

Enzymatic saccharification is a process which uses an enzyme cocktail that contains a mixture of cellulases, hemicellulases, and accessory enzymes to depolymerize polysaccharides into simple sugars. Currently, commercial enzyme mixtures are developed based exclusively on the fungal cellulases, i.e., Trichoderma reesei enzymes. After decades of strain development and study of T. reesei genetics, the enzyme performance and production has been significantly improved, and the cost is acceptable.

Biomass hydrolysates from pretreatment and enzymatic hydrolysis are usually a mixture of different sugar monomers, oligomers, and degraded intermediates. Conventional fermentation microorganisms can utilize hexose sugars (glucose, mannose, and galactose) but not pentose sugars (xylose and arabinose), and their growth is normally inhibited by the degraded compounds. Research has been focused on the development of a strain that can co-ferment both C6 and C5 sugars, and on improvement of tolerance to the inhibitor. Today, biomass saccharification and fermentation are usually performed as an integrated process, such as simultaneous saccharification and fermentation (SSF) which consolidates enzyme hydrolysis and microbial fermentation of cellulose products into one process step using cellulases produced elsewhere. Simultaneous saccharification and co-fermentation (SSCF) that integrate hemicellulose hydrolysis products into SSF is a second such integrated process. Another concept that has been proposed is known as “consolidated bioprocessing” (CBP), and combines enzyme production, biomass saccharification, and fermentation as a single step. This may theoretically further reduce the process cost, however, challenges remain in the development of strain(s) that produce highly active enzymes (cellulases, hemicellulases and accessory enzymes), and are capable of fermenting these mixed hydrolysis products into biofuels with high yield.^6,7 

It is worth noting that the proposed biorefinery of biomass to biofuels is a man-made process and does not occur in nature. In other words, natural organisms may effectively mediate one of the steps in the course of converting biomass to fuels, but there is no single microorganism that can utilize biomass as carbon and as an energy source to produce a form of biofuels, such ethanol, as the main end-product. Significant application of mechanical, chemical, and biological engineering is, therefore, required for biorefinery, the environmental impact of which has yet to be assessed. Leaning from natural systems is the key to advancing the aforementioned biological processes and ensure the economic success of biorefinery.

Degradation of lignocellulosic biomass in nature is generally considered to be a microbial deconstruction process carried out by a variety of microorganisms or microbial communities, including bacteria and fungi. The three major components of lignocellulose, cellulose, hemicellulose, and lignin, all require separate classes of enzymes to cleave their polymeric forms into shorter chains or monomers for further conversion processes. Explorations of several biomass utilization systems (from a single microorganism to comprehensive digestion systems) are presented in Chapters 7–14. Individual microorganisms capable of degrading plant-cell-wall polymers (usually cellulose and hemicellulose) followed by conversion of those polymers into a single product are desirable for industrial processes. However, single microorganisms with the ability to degrade multiple polymers usually produce multiple products via fermentation of the resultant sugars. In addition to the fermentable carbohydrates, lignin can constitute a significant percentage of plant biomass on a weight basis and is a complex polymer of phenylpropane units cross-linked to each other with different chemical bonds. Some individual organisms, predominantly the white-rot fungi, produce enzymes to deconstruct the lignin fraction, mediated by extra-cellular lignin and manganese peroxidases.⁸  Actinomycetes can also deconstruct lignin, but they are much less efficient and usually degrade less than 20% of the total lignin present.^9–11  Representative lignocellulose-degrading organisms and their average percentage of plant-cell-wall deconstruction is depicted for cellulose, hemicellulose and lignin in Figure 1.1.

Organisms surviving on lignocellulosic biomass possess many adaptations, including specialized gut systems, which can be considered to be natural bioreactors. Examination of natural biomass-utilization systems, in order to identify mechanisms, enzymes, and/or organisms for further improving managed industrial processes for biomass conversion is the main focus of the book.

Lignocellulose-degrading bacteria have been isolated from natural environments and if they also ferment the hydrolytic products of their enzyme activities, they may be referred to as “consolidated bioprocessing bacteria” (CBP bacteria). Clostridium thermocellum^12,13  and Clostridium phytofermentans¹⁴  are the most thoroughly studied of the CBP bacteria and Chapter 7 summarizes the technologies used to study plant biomass fermentation using the single model bacterium C. phytofermentans. This mesophilic organism isolated from forest soil and grows on both the soluble and insoluble parts of plant biomass by first enzymatically digesting the plant polysaccharides and then fermenting the resulting sugars to mainly ethanol and acetate.^14,15  Industrial processes would be relatively simple if a robust CBP organism could be isolated or genetically engineered for the conversion of biomass to biofuel. However, a CBP organism with very fast conversion rates and highly efficient fermentation to produce a single product does not exist, yet. This chapter provides a detailed analysis of molecular techniques used to study the genome, transcriptome, and proteome of a single microorganism and provides insight into improving fermentation yields for C. phytofermentans and other CBP bacteria.

In addition to characterizing individual microorganisms capable of degrading plant cell walls and isolating individual enzymes from lignocellulose-degrading bacteria or insects, there is a great deal of interest in studying whole systems where a consortium of microorganisms with multiple capabilities interact, oftentimes with the host, to degrade lignocellulose. There are multiple examples of lignocellulose-conversion processes in nature including herbivorous mammals and lignocellulose-degrading insects, and these are used as examples in Chapters 8–14.

Chapter 8 details lignocellulose degradation in termite symbiotic systems and notes that termites, notorious for the tremendous damage they cause, are now considered an informative bioreactor because they can dissimilate 74–99% of the cellulose and 65–87% of the hemicellulose that they ingest (Figure 1.1).¹⁶  To achieve these high conversion percentages in a short timeframe, termites have evolved alimentary tracts and symbiotic microbial systems to constitute a small-scale, yet highly efficient bioreactor, consisting of a grinding machine (mandible and proventriculus), a reaction chamber (digestive tract), and the microbial community and their own enzymes. The authors then describe how, within this micro-scale bioreactor, mechanical and enzymatic action, via the microbial community or protist symbionts, work together with the insect to achieve extensive lignocellulose degradation.

A survey of functional genes from cellulose-feeding insects is presented in Chapter 9, highlighting the many plant-cell-wall-deconstructing enzymes with high specific activities that have been isolated from herbivorous and xylophagous insect species. One recurring theme in these chapters and in the literature in general is that the wealth of sequence information that is now available has now caused a bottleneck in our ability to clone, identify, characterize, evaluate, and over-produce each enzyme. A major limitation is the capacity to evaluate the biochemical activities of gene products,¹⁷  and substantial yield increases and cost reductions will be required to make large-scale fermentation of lignocellulosic biomass possible.¹⁸  The authors of Chapter 9 also caution against using only homologues defined by amino acid sequence homology so that we do not miss the opportunity to define novel enzymes with potential industrial relevancy.

Chapter 10 describes the biological pretreatment of biomass by wood-feeding termites and examines the contributions of the insect itself to biomass deconstruction. The authors suggest that the wood-degrading process that has evolved in termite gut systems supports a new concept that complete degradation or removal of lignin may not be required for enhanced cellulose hydrolysis. Instead, the authors discuss the potential of selective modification of lignin functional groups and ether linkages, which play critical roles in lignin recalcitrance to enzymatic cellulose hydrolysis, to result in efficient pretreatment. This nature-inspired pretreatment scheme can be implemented under ambient conditions with no heat, no pressure, needing few chemicals, and results in mainly lignin modification. If such a method could be developed for industrial processes, this would represent a breakthrough in pretreatment technology.

Chapter 11 introduces the depth and breadth of wood-feeding insects with potential for biofuel production by providing an inventory of wood-feeding insects and evidence for their ability to digest cellulose. Cellulose digestion has been demonstrated in insect species from many diverse taxonomic groups including: various wood-feeding insects (woodroaches – Dictyoptera, lower and higher termites – Isoptera, various beetles – Coleoptera, and wood wasps – Hymenoptera), detritus/litter-feeding insects (e.g., immature stages of leaf-shedding aquatic insects – Trichoptera, Diptera, and Plecoptera, silverfish – Thysanura, crickets – Orthoptera), and forage-feeding insects (beetles – Coleoptera). More than 20 families representing 10 distinct insect orders, e.g., Thysanura, Plecoptera, Dictyoptera, Orthoptera, Isoptera, Coleoptera, Trichoptera, Hymenoptera, Phasmida, and Diptera have representative members capable of digesting cellulose.¹⁹ 

Chapter 12 presents the characteristics of the wood-feeding cockroach that make it an efficient mini bioreactor that involves a suite of specialized enzymes which synergistically break down the matrix of cellulose, hemicelluloses, and lignin in plant cell walls. Both termites and wood cockroaches convert over 90% of lignocellulose into fermentable sugars in their hindguts, making them an ideal habitat from which to identify novel enzymes specifically adapted to hydrolyze biomass.

A survey of selected natural lignocellulose-degrading systems is presented in Chapter 13, with the focus on -omics technologies and systems biology approaches for the reverse design of biocatalysts for biofuel production. The authors indicate that only a few fungi have high lignin-degradation selectivity that could greatly increase cellulose hydrolysis and saccharification efficiency, and that these processes are aerobic. Processes such as anaerobic degradation use mainly mesophilic, rumen-derived bacteria.^20,21  Compared to anaerobic systems, aerobic bacterial pretreatment has a higher efficiency in degrading high lignin biomass.^22,23  Despite long processing times and low saccharification efficiency via fungal pretreatment methods, recent biological pretreatment by termite systems indicate that it only takes 4–5 hours to move from modification of lignin components in the foregut/midgut to the hindgut for biomass hydrolysis and processing.²⁴  Exploring the best performance parameters for multiple systems may enable scientists to reverse design a more efficient industrial process using a combination of different natural biocatalytic systems.

Chapter 14 provides an in-depth study of the ruminant animal as a natural biomass conversion platform, noting that over 60 years ago, Hungate developed the analogy of the ruminant as a self-feeding, self-replicating, mobile, cellulose-degrading bioreactor.²⁵  Also discussed are the many different microorganisms with potential applications in bioconversion processes that have been isolated and characterized from ruminants. The author also points out that the ease with which ruminal fermentations are run in bioreactors provides support for integrating these innovations into an industrial volatile fatty acids platform for fuel and chemical production.

It has been generally accepted that alternative and renewable fuels and chemicals derived from lignocellulosic biomass will offer the potential to reduce our dependence on petroleum and other traditional non-renewable energy sources. However, breakthrough technologies in biomass conversion are still very limited, from both theoretical and application aspects, in realizing large-scale success due to the intractable barriers in efficiency and processing economy. We could potentially benefit from a review of our ongoing strategies and technology development and exploring other lignocellulolytic systems in nature, such as wood-feeding termites, cows, or other sound biological systems that could reveal new insights.¹⁹  Such animal lignocellulolytic systems can process cellulosic biomass efficiently with their highly specialized digestive systems, which can truly be considered as highly efficient natural bioreactors.²⁶  The biggest challenge in biological conversion of biomass is to acquire a deeper understanding of biomass recalcitrance as well as the conversion processing mechanisms from the advanced lignocellulolytic systems evolved by some animals.^27,28  With some of the most intractable issues facing the world regarding efficient and economic conversion of cellulosic biomass, this book intends to demonstrate the opportunities, breakthroughs, remaining challenges and perspectives in employing nature-inspired lignocellulolytic systems for the development of robust, effective, and environmentally friendly biorefineries.

The collective resistance that lignocellulosic materials pose to deconstruction by microbes and enzymes is generally referred to as “biomass recalcitrance”.²⁷  This term is used in several contexts that may, or may not reflect the same underlying structural elements. For example, it can be used to highlight the substantial differences in severity required for the dilute acid hydrolysis of lignocellulose and starch and to explain why pretreated lignocellulose requires 100 times more enzyme for complete saccharification than pretreated starch does. In addition, “recalcitrance” is also used when describing the kinetic phenomena in which the rate of cellulose digestion slows during extended reaction times. It has been reported that a variety of natural factors, including both chemical and structural elements, is believed to contribute to the recalcitrance of lignocellulosic feedstock conversion to chemicals or enzymes. In the context of biorefinery, these chemical and structural features of biomass would affect liquid penetration and/or enzyme accessibility and activity and, thus, conversion costs.¹ 

Plant biomass types, particularly terrestrial higher plants, have evolved superb mechanisms for resisting assault on their structural sugars from microorganisms and most animals. It has been speculated that the recalcitrance trait developed in terrestrial higher plants during evolution, in part, as a consequence of their moving from the protection of the aquatic environment.²⁷  As a comparison, lower plants, such as green algae growing in aquatic environments as well as other non-flowering plants, virtually lack the well-developed plant cell walls providing protection against attack by microbes and enzymes. In addition, their cell wall structures typically lack lignin elements to protect structural sugars [Figure 1.2(a)]. Although little is known from current references about the evolutionary steps or the intermediate forms presented during evolution, higher plants have indeed developed many systems to cope with the challenges of physical, chemical, and biological factors in nature to extract the structural sugars buried in the plant-cell-wall matrix. These defense systems against biological attacks include, but are not limited to, the epidermis, or outer layer of plant anatomy, as well as the structure and organization of vascular tissues and even of the cell walls. Further information regarding this subject is available from the recent reviews by Himmel et al.^1,27  and Foston and Ragauskas,²⁹  and need not be repeated in detail here.

Research efforts to redirect the evolutionarily imposed protection of plants’ cell-wall polysaccharides are now underway, mainly using genetic approaches to modify cell-wall characteristics and to also express the foreign cellulolytic enzymes in plant cells, thus permitting more efficient and economic biological/chemical hydrolysis processes, as well as improved agronomic productivity.²⁸  With these research innovations, we may potentially optimize both plant-cell-wall production and its down-stream deconstruction in ways not normally achievable in nature.

To acquire a deeper understanding of biomass recalcitrance and access to an efficient and economic conversion, five chapters (Chapters 2–6) of this book describe the state-of-the-art, as well as promising novel approaches to overcoming fundamental science and engineering barriers to reducing the recalcitrance of biomass as well as the enzymatic cost involved in the processing. Chapter 2 presents a short overview of the lignocellulose structure and chemistry so as to offer a better understanding of the deconstruction mechanism of the biomass to biofuels and other bioproduct processes. Chapter 3 reviews various microscopy and spectroscopy tools used to characterize plant-cell-wall structure, including optical microscopy, atomic force microscopy, and electron microscopy, which will provide insight into the fundamental mechanisms that contribute the native recalcitrance of lignocelluloses. Chapter 4 primarily deals with the challenges of better understanding how the structure of lignin changes during pretreatment processing and also demonstrates recent advances in the fundamental characteristics of ethanol organosolv lignin via NMR spectroscopy techniques and molecular weight analysis. Chapter 5 assesses advances in the genetic manipulation of cellulosic bioenergy crops for ethanol production that utilize dedicated energy plants as the biofactories to produce foreign lignocellulosic enzymes, which can reduce exogenous enzyme loading for industry, thereby reducing the cost of biorefinery processing. Chapter 6 is concerned primarily with the diverse distribution of lignocellulosic resources, their composition, current application as feedstock and the state-of-the-art in modification of plant-cell-wall structure to increase biomass digestibility and its conversion efficiency through genetic engineering of energy crops. These five chapters provide current advances in the understanding of plant-cell-wall structure and future strategies for modifying cell walls to improve the current conversion efficiency and economy.

Different glycolytic activities exist in various biological systems, such as from bacteria, fungi, marine isopods, cellulose-feeding arthropods, and cellulose-feeding mammals, and these may have co-evolved with the recalcitrance development of plant cell walls as a chemical or structural defense. In general, as we have proposed in Figures 1.2(a) and (b), each party in a co-evolutionary relationship exerts selective pressure on the other, thereby affecting each other's evolution. Clearly, different biological systems may present a different strategy to cope with the recalcitrance of plant cell walls under the chronically selective pressure in a particular environment, which eventually leads to a unique cellulolytic system that may function with different efficiencies in time and different competences in the degradation of cellulose and hemicellulose, as well as lignin (Figure 1.1).

For example, wood-feeding termites efficiently deconstruct various major polymer components of biomass within 24 hours with their well-developed lignocellulolytic systems. The evolutionary direction for various biological systems in the utilization of lignocellulosic feedstocks appears to be directly opposed to the evolution path taken by the plant kingdom (Figure 1.2). Although lignocellulolytic activities were originally thought to be restricted to plants, bacteria, and fungi, there is rapidly accumulating evidence for the existence of animal lignocellulases (cellulases, hemicellulases, and lignases), especially in wood-feeding termites.^19,26  In particular, these cellulose-feeding animals have had to develop a strategy and superb enzyme system to overcome the recalcitrance of lignocellulosic biomass and get the carbohydrate energy embedded in lignocellulose in a quick and efficient manner. These diverse and highly adapted digestive systems can efficiently deconstruct various lignocellulosic feedstocks, will inform us of unique lignocellulolytic systems, and will help us develop a novel and nature-inspired system for modern biorefinery.

Recent exploration of these unique lignocellulolytic systems using advanced molecular biotechnologies, including meta-genomics, proteomics, transcriptomics, and synthetic biology, have brought new insight into the mechanisms of biomass deconstruction within these efficient, but complicated digestive gut systems. However, the integration of nature-inspired technologies into the modern biorefinery system is another important challenge and task in our research agenda. To meet this demand, this book has made an effort to address this obligation in Chapters 15–19.

Chapter 15 describes a unique insect gut system, Tipula abdominalis (in the larval stages), as a natural bioreactor, where these larvae host a diverse hindgut microbiota presenting some new microorganisms with novel enzymatic activities. The inventory of gut microorganisms, followed by characterization of selected isolates, then identification of novel enzymes from one of the isolates is presented. Using this novel enzyme in fermentations of pectin-rich biomass for ethanol production is described as an example of applying insect-associated microbial enzymes to improve an existing bioconversion process. Exploring various insect lignocellulolytic systems could lead to the discovery of a variety of novel biocatalysts and the genes that encode them, as well as associated unique mechanisms for efficient biomass conversion.

With thousands of new genes identified from a variety of lignocellulolytic systems in nature, including those from cellulose-feeding animal origins and their gut microbiota (most of them are culture-independent), gene expression from these origins has become a critical bottleneck for identification, characterization, evaluation, and over-expression of each single enzyme. Chapter 16 reviews the most up to date technologies, as well as promising novel approaches, such as the Hsh expression system invented by the authors for E. coli, to overcome fundamental science and engineering barriers to enabling heat–shock induction repression in industrial fermenters, soluble expression of aggregation-prone protein, and in situ error-prone PCR. This chapter also introduces the tools and technologies developed in recent years for improvements in recombinant enzyme production and the properties desired for cost-efficient industrial processes.

Lignin-unlocking processes by wood-feeding termites, an important biological pretreatment step, operate in a specific gut physiochemical environment with a variety of lignolytic oxidases and some non-biological co-factors in their gut system, such as redox potential, pH, metal elements and H₂O₂ which need to be eventually integrated and converted into a novel nature-inspired technology system. Chapter 17 provides a summary and research update for cellulose-dissolving systems that would inevitably affect the subsequent enzymatic hydrolysis of the regenerated cellulose. In contrast to traditional pretreatment methods, cellulose solvents that mimic the activity of lignin-degrading enzymes from a biological system have some unique advantages, including milder operation conditions, which can function well with some important co-factors, fewer degradation by-products, and higher cellulose accessibility to cellulase.

It is instructive to investigate the solutions and strategies resulting from nature-inspired evolution for overcoming biomass recalcitrance, and then applying promising strategies to help solve those intractable issues in developing an efficient and economic biomass conversion process for fuels and chemicals. Chapter 18 aims to discuss what we can learn from natural biomass-utilization systems for developing novel bioreactors; the authors review the current state-of-the-art biomimetics and its potential for nature-inspired technology and innovation.

Overall process economics and sustainability perspectives are critical for the development of a robust, effective, and environmentally friendly biorefinery system and for potentially realizing industrial-level applications. Chapter 19 conducts a techno-economic analysis and life-cycle assessment (LCA) of lignocellulosic biomass to sugars using various pretreatment technologies; the authors report the process economic analysis and LCA of the six leading pretreatment processes using hybrid poplar as the biomass feedstock. They also further introduce an integrated and commercial-scale lignocellulosic sugar process module that has been proposed as the foundation of the cost analysis for a specific biomass pretreatment process.

These five chapters of this book mainly focus on integrating the advanced nature-inspired strategies and technologies into a modern biorefinery system for the viable biological conversion of biomass.

The biological conversion of lignocellulosic biomass has long been recognized as a promising approach to access the fermentable sugars for biofuels and other bioproducts. However, in practice, the current state of technology with respect to biomass conversion is still far away from being suitable for large-scale application due to its efficiency and processing economics.²⁶  It is the property of biomass recalcitrance that is largely responsible for the high cost and low efficiency of lignocellulose conversion.¹  Thus, our inevitable challenge is to acquire a deeper understanding of biomass recalcitrance and the optimized conversion mechanisms presented by some unique lignocellulolytic systems in nature, which may provide real solutions to these problems. We have much to learn from the sound cellulolytic systems in nature that have successfully cracked the code for lignocellulose deconstruction using amazing strategies and mechanism development throughout evolutionary history.

With the science and engineering issues facing the world regarding the efficient and economic conversion of lignocellulosic biomass, and the cutting edge technologies that have emerged in the past decade, this book comes at a critical and timely moment. The ultimate goal of this book is to acquire a deeper understanding of biomass recalcitrance to deconstruction and to develop a novel approach for modern biorefinery processing with nature-inspired strategies and technologies. Using biomimetic strategies from a systems biology approach combined with other advanced technologies may pave the way for future breakthroughs and innovations in associated areas of industrial biotechnology. It is further hoped that this book can promote productive dialog and collaboration between scientists working in the various disciplines needed to address this global challenge.