Poly-B-hydroxybutyrate (PHB): A Biodegradable Polymer of Microbial Origin - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 49

the idea about PHB productivity profile of bacterium ( Figure 1 and 2) (Sayyed et al.,
2009, Sayyed and Gangurde, 2010).

Carbon Source
Excess of carbon sources is required for efficient synthesis of PHA (Lee, 1996). Lee
(1996) and Haywood et al. (1991) reported accumulation of PHB in P. olovarans from
a carbon source containing 6-14 C atoms. Fluorescent pseudomonads have been re-
ported to utilize the organic acids like acetic acid and lactic acid effectively for the
accumulation of PHB (Bitar and Underhill, 1990). Although, PHB accumulation was
evident in pH range, 5.5-9, the level increased towards neutral pH with an abrupt
decline beyond 8. Maximum PHB levels have also been reported around neutral pH
(Byrom, 1994). Rapske (1962) observed that optimum pH for growth and PHB pro-
duction by A. eutrophus was 6.9.
The PHB accumulation is directly proportional to the Carbon: Nitrogen ratio
(Macrae and Wilkinson, 1958). The hydroxyl acid monomer units depend on the
carbon source utilized. Bacteria such as Alcaligenes eutrophus utilize various C4
and C5 sources to produce polymers with monomer compositions of 3HB, 4HB,
3-hydroxyvalerate (HV), and 5HV (Anderson and Dawes, 1990). The C1-C9 alcohols
and C2-C10 monocarboxylic acid have also been tested as nutrient sources and pro-
ceed useful for PHB production and found that PHB could be obtained with the odd
number of carbon sources.
On the other hand, PHB can be produced using renewable carbon sources such as
sugars and plant oils. Various waste materials are also considered as carbon sources
such as whey (Ahn et al., 2000; Wong and lee, 1998), molasses (Page, 1992; Page
et al., 1997; Zhang et al., 1994) and starch (Hassan et al., 1998; Yu, 2001). Table 3
shows the microorganisms producing PHB from different substrates.

table 3. Microorganisms producing polymers of Polyhydroxybutyrate from different substrates and
biowastes.

Substrate Polyhydroxybutyrate (PHB)

Gram-Positive Reference Gram-Negative Reference

Glucose Bacillus Valappil et al., 2007;

Porwal et al., 2008;
Kumar et al., 2009;
Yuksekdag and Beyatli,
2004;
Valappil et al., 2007

Azotobacter
Comamonas
Escherichia
Pseudomonas
Ralstonia
Vibrio

Page and Cornish, 1993;
Lee et al., 2004;
Nikel et al., 2006,
Bertrand et al., 1990;
Nurbas and Kutsal, 2004
Chien et al., 2007

Streptococcus
Streptomyces

Fructose Bacillus Kumar et al., 2009 Comamonas

Ralstonia

Lee et al., 2004
Young et al., 1994

Sucrose Bacillus Kumar et al., 2009

Valappil et al., 2007
Anil et al., 2007
Yuksekdag and Beyatli,
2004

Alcaligenes
Comamonas
Vibrio

Shi et al., 2007
Lee et al., 2004
Chien et al., 2007

Streptococcus