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Microbial-derived natural bioproducts for a sustainable environment 59

3.2.2.4 Characteristics

3.2.2.4.1 EPS biodegradability
Owing to its composition, it is easily degraded by the microbial isolates. It is also
used as a source of carbon and energy (Zhang and Bishop, 2003). Methods used to
extract EPS also govern the type and biodegradability of the generated EPS. Some
of the components are not easily degraded, which pass out untreated while sacchar-
ides and proteins get utilized and break down easily.

3.2.2.4.2 Amphiphilic nature of EPS
It has both apolar (hydrophobic regions in carbohydrates, aromatics, and aliphatic
groups in proteins) and charged (phosphoric, carboxyl, hydroxyl, and phenolic
groups) groups (Flemming and Leis, 2002). Presence of these groups make it
amphoteric and also defines the composition of a particular EPS. Hydrophobic areas
are helpful for adsorption of pollutants; similarly, the charged anionic groups can
also aid in the sorption of different elements (Sheng et al., 2010).
3.2.2.4.3 Adsorption capacity
As discussed in the earlier section about the amphoteric nature of EPS, there are
many groups which can serve as the adsorption sites for organic matter and metals.
These polar groups give EPS a high-binding capacity forming highly strengthened
complexes with elements and compounds (Flemming and Leis, 2002; Joshi and
Juwarkar, 2009). It is negatively charged so it easily attracts positively charged
groups of organic contaminants and aids their removal, such as benzene (Sp¨ ath
et al., 1998) and phenanthrene (Liu et al., 2001).

3.2.2.5 Parameters governing EPS production

The certain parameters whose variations can bring significant changes in EPS pro-
duction are described in the following:
1. Nutrient content: The biodegradability of EPS allows its usage as a source of energy
under nutrient shortage conditions. The accessibility of carbon and nitrogen in the culture
medium is the most important factor for the biosynthesis of EPS by the microbial cells.
The carbohydrates, such as fructose, glucose, and sucrose, are utilized by the microorgan-
isms as their source of carbon and energy, whereas amino acids and ammonium salts as
their nitrogen sources, which considerably affects the EPS production (Czaczyk and
Myszka, 2007). The production of EPS is influenced by both nitrogen content and the
type of N-sources. Total EPS vary considerably with a change in the concentration of
nitrogen. It was found that a low supply of phosphorus promotes the production of EPS. It
was reported that an EPS with high protein-to-carbohydrates ratio is produced when sup-
plied with a substrate having C:N ratio (Liu and Fang, 2003).
2. Effect of pH and temperature: Temperature and pH have a significant effect on the EPS
growth in the microbial culture. pH values help to regulate the morphological variations
of the cells, for example, acute pH profiles of the culture medium, that is, pH between 2.0
and 4.0 or pH $ 10 inhibits the microbial growth and the synthesis of extracellular poly-
mers (Stredansky and Conti, 1999). The optimum pH range for the production of EPS in a
medium lies between 5.5 and 6.5 (Lee et al., 1999).