CHAPTER ONE
CHAPTER ONE
CHAPTER ONE
1.0
INTRODUCTION
Polyhydroxybutyrate (PHB) is one of the
polyhydroxyalkanoates (PHAs) which has biodegradable and biocompatible
properties. They are adopted in the biomed filed, in for example, medical in
plants and drug delivery carriers (Keshavarz and Roy, (2010).
Polyhydroxybutyrate was discovered and identified as
a granular component in bacterial cells. PHB can grow in a wide variety of
natural environmental and is the reserve polymer (intracellular granules) forum
in many types of bacteria in nature e.g. in soil, sea water, sewage sludge or
compost.
Polyhydroxybutyrate (PHAs) can be classified into
two groups depending on the numbe3r of carbon atoms in the monomer unit:
short-chain-length. (Scl-PHA) 3-5 carbon atom containing monomer and medium
chain-length (MclPHAs) 6-14 carbon atom containing monomers (Steribuchel and
Valentin, 1995).
The discovery if a polyester by Smet et al, (1983)
was the first report of accumulation of medium-chain-length (MCl-PHAs), i
constituents of 6-14 carbon atoms in axenic culture (Smet et al., 1983).
Currently, more than 140 hydroxyalkanoic acid have
been identified as constituent of polyhydroxyalkanoates (PHAs) representing a
versatile class of microbial polymer (Sterinbuchel and Valentin, 1995). Besides
linear and branched 3-40,5- ad 6-hydroxyalkaniates, various functionalized PHAs
constituents such as polyhydroxyalkanoates (PHAs) containing halogenated or
aromatic side chains have been described (Abe eta l., 1990).
The physical properties of the homopolymer of
hydroxybutyrate (PHB) are similar to those of poly propylene, for example
regarding melting point, crystrallinity, glass transition temperature etc, and
represent a stiff and brittle material (itocking and Marchessault,1994). The
properties are improved in copolymers containing up to 25 mol% 3-hydroxy
valerate (3HV), where toughness and flexibility are increased and the decrease
in crystrallinity and melting point advance the melt-processing of the polymer
without being degraded(Marchessault and 4u,2002)
Therefore, the poly (3HB-CO-3HV) copolymer gained
industrial interest and in the late 1980s, commercialization under the trade
name Biopol was initiated (Holmer etal., 1984). Biopol can be processed to
useful materials by various processes such, as extrusion, injection molding,
fiber spinning, coating or foaming. Because of the versatile applications as
themoplastie biopolymers, polyhydroxy allcanoates (PHAs) can also be used for
natural fiber composites or as binder in paints and for various application in
medicide and pharmary such as tissue engineering (Kessler et al., 1999)
Polyhydroxylbutyrate(PHB) is a commonly found substance
and readily biodegradable are robically and anaerobically. Microbes can use
polyhydroxylbutyrate (PHB) exists in the cytoplasmic fluid in the from of
crystalline granule about 0.5 Hm in diamete. Beta-hydroxybutyrate is connected
by ester linkage and from polyhydroxybutyrate (Andreson and Dawes, 1990). This
can be extracted from the cells as native granule or by solvent extraction (Doi
and lee, 1990) and processed in the way as polypropylene. S
These biopolymers were also found to increase the
resistance of bacteria (Tombolini and Nuti, 1989). Lemoigne, Grelet and croson
(1958) draw attention to the different amount of poly-beta – hydroxybutyrate
obtain by BacterimMegaterium on different media and maraca and
Wilkinson (1958) showed that more of the substance was formed as the glucose
concentration of the growth medium was increased; the subsequest depletion of
the product during the later stage of growth suggested a storage function. They
also showed that organism rich. In poly-beta-hydroxyrate had a slower rate of
autolysis than organisms poor in poly-beta-hydroxybutrate. It is probable;
therefore, that poly-beta-hydroxybutyrate act as a reserve carbon and energy
source – Tinelli(1955) found that the major part of the material was
metabolized at sporulation and deduced that the two processes were intimately
connected (Kato et al.,1992)
The bacterium capable of producing
polyhydroxybutyrate has been identified in more than twenty (20) bacterial
genera, including Azatobacter, Bacillus
Pollyhydroxyalkanoate is one such biodegradable
microbial polmer which is accumulated in bacteria as intracellular storage and
limited nitrogen source (Anderson and Dawes, 1990).
The polymer is known to occur as intracellular
granules in several genera of micro-organisms. The granules are syuthesized by
prokaryotes acids, sugars and other
carbon sources (Atking and kennedy, 1985). Polyhydroxybutrate is insoluble in
water, resistant to ultraviolet radiation and is impermeable to oxygen and is
very much suitable for use as food packaging material this polymer is readily
degraded in the soil and sewage and can be processed using the extrusion
technology that is currently used in making polyethylene or polypropylene
films(Byrom, 1987). The polyhydroxyalkanoate content and its composition are
influenced mainly by the strain of the micro-organisms (Halami, 2008). To
achieve a cost effective polyhydroxyalkanoate production, the availability of
an efficient bacterial strain is a prereguisite and is a focus of interest for
many investigation (Green spare et al., 1985).
The polyhydroxybutyrate production using inexpensive
carbon sources in the form of starch by the indigenous strain can be
advantageous as the complex starch substrates can be used directly without
involvement of any hydrolysis step (itahn et al., 1995).
Polyhydroxybutyrate (PHB) is used in food packaging,
plastic films, surgical sutures (stitching of the edges of a wound or
incision), contrived drug deliver e.t.c (kim et al., 1994). This bioplastic has
many applications in bone plates, nails,serews and in the treatment of
osteomyclitics (Itanzlikova et al., 1985).
(1)
AIMS AND OBJECTIVES OF THE RESEARCH
Isolation and biochemical identification of polyhydroxybutyrate
(PHB) producing bacteria from soil.
(2)Screaming
of polyhydroxybutyrate (PHB) producing bacteria isolated from soil.
(3) Polyhydrobutyrate (PHB) Production.
(4) Determination of effect of different nitrogen
sources on growth and polyhydroxybutyrate (PHB) production,
1.2 STATEMENT OF PROBLEM
The accumulation of these non-degradable
plastic in the environment is a menacing (treating) draw back increasing day by
day. Oil based polymers take many years to degrade which poses an environment
problem in some areas, and causes deleterious effects to wild life. To overcome
this, production of environmental friendly plastic have been discovered.
1.3 JUSTIFICATION
The continuous exhaustion of fossil
fuels led to the research for the production of bio-degradable plastic from
renewable sources the production of biodegradable polymers from renewable
resources is the need of the hour, in the face of these ecological facts.