Microbial and Natural Macromolecules

Synthesis and Applications

Surajit Das, Hirak Ranjan Dash, Surajit Das, Hirak Ranjan Dash

• Publisher: Academic Press
• Year: 2020
• ISBN:
  9780128200858
• Topic: Ciencias biológicas
• Subtopic: Microbiología

Microbial and Natural Macromolecules: Synthesis and Applications brings together active scientists and academicians in the field who share updated information and research outcomes from global experts. Microbial macromolecular diversity, molecular composure, genetics, usability of advanced molecular tools and techniques for their study as well as their applicability are discussed with detailed research perspectives.

• Illustrates fundamental discoveries and methodological advancements
• Discusses novel functional attributes of macromolecules
• Updates progress on microbial macromolecular research

Section D

Functional attributes of biological macromolecules

Chapter 19: Role of biological macromolecules of microbes in metal bioremediation

Celin Acharyaa^,b; Devanshi Kharea^,b; Divya TVa^,b; Pallavi Chandwadkara; Nilesh Kolhea^,c ^a Molecular Biology Division, Bhabha Atomic Research Centre, Trombay, Mumbai, India
^b Homi Bhabha National Institute, Mumbai, India
^c Institute of Bioinformatics and Biotechnology, Savitribai Phule Pune University, Pune, India

Abstract

Microbes share a long history with heavy metals. The microbial ancestors deduced the use of metals for catalyzing energy generation and the formation of cellular components. As a result, metals were incorporated into various cellular macromolecules and became integral to the functioning of such macromolecules. Microbes utilized some metals relevant to their physiology while developed mechanisms to defend against toxic metals. Anthropogenic activities in the last few decades have released heavy metals into the environment in bioavailable forms. Microbes are known to respond immediately to the environmental changes thereby employing a host of processes like efflux, immobilization, translocation, transformation, biosorption, and bioaccumulation to alleviate metal toxicity. Biological macromolecules in microbes like carbohydrates, proteins, and nucleic acids contribute immensely toward metal bioremediation. This chapter discusses the imperative roles exhibited by microbial macromolecules in the transformation/reduction of metal toxicity in the environment. Extracellular polymeric substances comprising of polysaccharides that represent carbohydrates, various proteins like metallothioneins, metal-binding peptides, metal effluxing P_IB ATPases, several enzymes important for alleviating metal-induced oxidative stress or precipitating metals have been highlighted here in the context of metal detoxification or remediation. Metal detection is the first step toward any remediation process. In recent times, there has been a great emphasis on developing functional nucleic acids-based sensors for the detection of heavy metal ions. In this regard, aptamers, DNAzymes, metal ion-specific DNAs, G-quadruplexes, and riboswitches have been detailed in this chapter. Overall, the information augments our understanding of the essential interactions of microbial macromolecules with the metals which are useful for metal remediation applications.

Keywords

Microbial macromolecules; Metals; EPS; Remediation

1: Introduction

The natural interaction of the molecules existing in the primitive earth’s atmosphere resulted in the formation of complex organic molecules, such as amino acids, sugars, fatty acids, and nitrogen bases which constituted the building blocks of life, i.e., proteins, carbohydrates, lipids, and nucleic acids, respectively. Since time amounting to billions of years, metal ions have been known to be associated with living systems—they were incorporated into various cellular macromolecules and became essential to the latter’s functionality. It is in the last century that the extent of influence of the metals on biological macromolecules has been appreciated. Metals are involved in more than 40% of enzymatic reactions and the metal-binding proteins are known to contribute toward almost all biological pathways (Monosson, 2012). Analysis of all chemical elements in the periodic table reveals that only a few of them are utilized by biological systems (Da Silva & Williams, 2001). There is an indication of the predominance of 11 elements in all biological systems. Four of them (O^{2 −}, H⁺, C, and N^{3 −}) constitute the majority of the total number of atoms present in living organisms. The other seven elements like Na⁺, K⁺, Ca^{2 +}, Mg^{2 +}, P^{3 −}, S^{2 −}, and Cl⁻ are considered to be crucial for the basic components of organic structure. Elements like V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, B, Si, Se, F, I, As, Br, and Sn are found in some and not in all living organisms. Most of these elements are required for enzymatic activities or structural integrity (Petukh & Alexov, 2014).

The heavy metals comprise the greatest number of elements. Microbes are in close association with metals since long time. Anthropogenic activities over last few decades have resulted in release of heavy metals into the environment. They are generally toxic to microbial cells and therefore the latter has evolved various metabolic responses to combat the toxicity of metals. However, microbial responses differ with different elements. Microbial interactions with heavy metals have led to metal immobilization or remediation through sequestration, accumulation, or precipitation. Sometimes, metal misincorporation can help to explain mechanisms of metal toxicity in biological systems. For example, cells grown with supplementation of Pb, U, Ru, Rh (each 50 nM), and Cr (200 nM) showed more than tenfold enhancement in the intracellular concentrations of specifically bound Pb and U in a marine heterotrophic archaebacteria, Pyrococcus furiosus (Cvetkovic et al., 2010). Further analysis of cytoplasmic proteins in P. furiosus revealed the association of Pb in metalloprotease and pyrophosphatase and that of U with iron protein ferritin and glycolytic Mg²⁺-dependent enzyme enolase suggesting that the metal assimilation by organisms depends on their natural environment of their existence (Cvetkovic et al., 2010).

Microbes like other living organisms, are made up of four major biological macromolecules which include carbohydrate, lipid, proteins, and nucleic acids. These bind metal ions specifically or nonspecifically to stabilize or maintain the structure of macromolecules (Petukh & Alexov, 2014). But, in case, the metals are toxic to microbes, they employ several mechanisms mediated by their cellular constituents like proteins, enzymes, polysaccharides to defend against metal toxicity. Microbial macromolecules have demonstrated tremendous potential for metal remediation through metal sequestration/compartmentalization/biotransformation/precipitation and contribute toward metal decontamination. Although extensive studies on the environmental impact of heavy metals exist in relation to their toxicity, there is still a lack of appreciation of the imperative roles played by microbial macromolecules in transformation/reduction of metal toxicity in the environment. This article seeks to emphasize the role of important biological macromolecules including carbohydrates, proteins, and nucleic acids of microbes with respect to their potential in metal bioremediation.

2: Carbohydrates

2.1: Extracellular polymeric substances

The extracellular polymeric substances (EPSs) primarily comprising of polysaccharides are the most studied components among the carbohydrates in context of metal bioremediation. Polysaccharides are polymeric carbohydrate structures of simple sugars (monosaccharides) linked together by glycosidic bonds. E...