## 1 Introduction  
Soil is the soul of infinite life forms ranging from miniscule microbes to macro-invertebrates. The latter groups are represented by earthworms, termites and ants, which are distinguished by their capacity to excavate the soil and produce a great impact on soil physical properties by creating organomineral structures, such as macro-voids, nests, mounds, galleries and caverns. These organisms have been described as \"ecological engineers\" of the soil [1]. Earthworms play a pivotal role in decomposition, nutrient cycling and maintenance of soil structure in the terrestrial ecosystem [2]. The gut of the earthworm constitutes an anoxic and organic substrate-rich microzone which provides a unique opportunity to the ingested heterotrophic soil bacteria for anaerobiosis [3]. The earthworm's alimentary tract provides a compelling environment to the gut associated microorganisms, and microorganisms experience a continuous change in the pH, salinity, nutrient levels and gases like oxygen, nitrogen, hydrogen etc. which can influence the production of extracellular polymeric substances (EPS) or biofilm by gut-inhabiting microorganisms [4]. EPS are a complex blend of high molecular weight microbial biopolymeric secretory by-products. These biopolymers mostly consist of proteins, polysaccharides, uronic acids, humic substances, lipids, and nucleic acids [5]. Synthesis of EPS and their composition are regulated by a variety of environmental conditions especially the nutrient level including the availability of carbon and nitrogen in the growth medium [6]. These EPS show unique physiological and physicochemical properties which make them suitable for several clinical, industrial and environmental applications [7; 8]. Biopolymers have been recognized by many researchers as potential alternatives to conventional chemical polymers because of their ease of biodegradability, high efficiency, and non-toxic nature [9]. Microbial EPS offer an array of promises for their applications in foods, drug delivery, oil recovery, water purification, and metal removal in mining and industrial waste treatments, and also in downstream processes in fermentation and pharmaceutical industries [10]. In wastewater treatment and downstream processing industries, flocculating agents are used in the process of removing colloids, suspended solids and cell debris comprising main constituents of wastewater [11]. Synthetic polymers like acrylamide, acrylic acid and mixtures of their derivatives are oft-used flocculants for such treatments [12]. However, reports on some of these synthetic flocculants show their neurotoxic and carcinogenic effects, including disorders like neuropathies, ataxia, numbness of hands and feet, muscle weakness, and in some cases cerebellar alterations even at a sub-chronic concentration [13]. Hence, it is important to develop non-toxic, environmental-friendly, cost-effective and highly efficient flocculating agents for wastewater treatment. In this scenario, bioflocculants endowed with attributes of biodegradability, non-toxicity and eco-friendly nature are gaining importance [14]. EPS produced by microorganisms could be a promising alternative to the chemically synthesized flocculants [11]. Recently the extensive usage of various heavy metal (e.g., Cu, Zn, Cd, Cr, Pb, Ni, Co) compounds in different industries has led to their increase in ecosystems [15]. Heavy metals are nonbiodegradable in nature, and as a result they persist in the environment for longer periods of time. Conventional treatment processes for the remediation of heavy metal ions include coagulation, chemical precipitation, electrodialysis, evaporative recovery, floatation, flocculation, ion exchange, nanofiltration, reverse osmosis and ultrafiltration [16]. Although effective, these methods are often highly expensive and result in the production of a huge amount of ineradicable toxic slurries which again pollutes the environment.