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Microbial-derived natural bioproducts for a sustainable environment 57

Sheng et al., 2010). In EPS, carbohydrates play the role of major component; how-
ever in some cases, their dominance is substituted by proteins or lipids (Flemming
and Wingender, 2001). Various factors govern the composition, such as growth
conditions, culture, extraction method, and analytical technique used (Sheng et al.,
2010). Owing to EPS, a hydrated gel, such as three-dimensional network, is created
binding the microorganisms that are highly favored by some sessile cells. EPS is
synthesized by both eukaryotic and prokaryotic organisms (Pseudomonas sp.,
Bacillus sp., Cupriavidus sp., Paracoccus sp.) and generally, its content in biofilms
varies from 55% to 90% of the total organic matter (Nielsen et al., 1997).
EPS helps in deciding the physiochemical characteristics of microbial aggre-
gates, such as structural framework, cell cell interaction, cell protection, adhesion,
biosorption of inorganic and organic elements, enzymatic interactions, dewatering,
and flocculation property (Wingender et al., 1999; Tian, 2008; Nicolaus et al.,
2010). They also serve as a source of energy under nutrient-limiting conditions and
form a net, such as protective barrier, against harmful compounds and/or stress con-
ditions (Sutherland, 2001a,b; Zhang and Bishop, 2003). The cellular material,
microbial biomolecules, and/or organic medium help in shaping the EPS matrix
that is viscous in nature (Wingender et al., 1999).

3.2.2.1 Definition of EPS
Quoting the previous literature, Geesey in 1982 defined it as “EPS of biological ori-
gin that participate in the formation of microbial aggregates.” With time, further
studies defined it in a more specific and certain manner in which saccharides were
accepted as a major constituent of EPS. However, some EPS preparations from acti-
vated sludge, pure bacterial culture, and trickling filter biofilms showed the domi-
nance of proteins and/or lipids (Nielsen et al., 1997; Dignac et al., 1998; Platt et al.,
1985). Wingender et al. (1999) used EPS as a generalized term for different macro-
molecule classes present inside a microbial aggregate which deleted confusions
regarding its composition. On the basis of the association between the cells, EPS is
of two types (Comte et al., 2006; Raszka et al., 2006):
1. Capsular EPS: This EPS is a part of the outer cellular membrane present in the microbial
pellet.
2. Slime EPS: Slime EPS is present in the supernatant formed after the digestion of the
microbial pellet. They are generally seen in the colloidal or the soluble form.

The state of matter constituting the EPS and its composition also differentiates it
in two forms (Laspidou and Rittmann, 2002; Tian, 2008). (1) Soluble EPS: The one
which is present in the loose form in the dissolved solution; for example, colloids
and slime. (2) Bound EPS: This is bound to the microbial cells; for example,
organic materials attached and condensed gels and sheets.
3.2.2.2 Distribution, structure, and characteristics of EPS

EPS is produced using different preparations, such as activated sludge and micro-
bial culture (as mentioned before) and accordingly the macromolecules involved