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Microbial-derived natural bioproducts for a sustainable environment 63

3.3.2 Bacterial synthesis of EPS

The EPS matrix as an extracellular material is mainly synthesized by the microbes.
Most of the biofilms having dry bacterial biomass ˃10% while 90% of the biomass
is responsible for making matrix usually called EPS. They are also named as intra-
cellular storage, slime, and capsular polysaccharides (CPS) because of their pres-
ence outside the cells, inside of microbial aggregates, or bound closely to the cell
surface, respectively (Sheng et al., 2010; Schmid et al., 2015). EPS mainly facilitate
in cell adherence to surfaces, although it defends cells against hurt from noxious
substances, cell drying and desiccation, cryoprotection, and engulfment by preda-
tory protozoa for growth at low temperature similarly as in conditions of nutrient
shortage and function as carbon or energy sources (Wingender et al., 1999; Nichols
et al., 2005).
Initially, EPS were known as “extracellular polysaccharides” because of the
higher content of polysaccharides present in the matrix; however, a common term
has given to represent various categories of macromolecules, such as nucleic acids,
proteins, lipids, and different biopolymers, such as humic substances, were identi-
fied as its constituents (Table 3.3)(Flemming and Wingender, 2010). EPS are gen-
erally high-molecular weight, biodegradable product of cellular lysis, and
hydrolysis from macromolecules. As they exist in very distinctive and complicated
chemical structure, their matrix size is in between 10 and 30 nm or thickness of
0.2 1.0 μm. Microbial forming polymeric substances have heterogeneous
chemical structure, EPS mainly expresses diverse properties, such as emulsifying,
gelling, thickening, and variety of applications in many industries, that is, paper
and pulp, food and pharmaceuticals, etc. (Nwodo et al., 2012). The primary
bacterial EPS was discovered in the mid-19th century, when an EPS in wine was
later known as dextran synthesized by Leuconostoc mesenteroides (Linker and
Jones, 1966). With the advancement in techniques, different exopolysaccharides,
such as alginate, cellulose, and xanthan, were revealed and numerous metabolic
pathways involved in the formation of biopolymer were also discovered (Pindar
and Bucke, 1975).
Several bacterial strains have been reported for the production of EPS using
waste as their carbon and energy source. Gupta and Thakur (2016) reported 0.83 g/
L of EPS produced by a thermotolerant bacterium Bacillus sp. ISTVK1 on sucrose
along with the removal of wastewater contaminant in the nutrient media. Buthelezi
et al. (2010) also reported 27.7 g/L of EPS production by using Klebsiella terrigena
R2 strain on ethanol and glycerol. As commercialization of EPS requires greater
production rates, the necessity for clean technology and minimization of production
rates has led to the consumption of other low-cost nutrient and carbon sources
from byproducts of agro-industry, such as molasses and corn-steep liquor, for sig-
nificant production of exopolysaccharides creating the product marketable. When
the carbon source was substituted with agro-substrates, molasses, rise in the produc-
tion rate of EPS have seen, that is, 4.8 g/L by Bacillus subtilis (Razack et al., 2013)
and 172.86 g/L by Gordonia polyisoprenivorans CCT 7137 (Fusconi et al., 2008)
(Table 3.4).