Isolation and characterization of poly--hydroxybutyrate producing Bacillus sp. from soils
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Date
2008
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Publisher
CCSHAU
Abstract
Plastics and polymers are an integral part of our daily existence
because of their properties of durability and resistance to degradation.
Plastic wastes are considered to be severe environmental contaminants
causing waste disposal problems. Recently, the problems concerning global
environment and solid waste management have created much interest in the
development of biodegradable plastics with desired physical and chemical
properties. The PHB and other biodegradable polyesters are promising
candidates for the development of environment friendly, totally
biodegradable plastics. Polyhydroxy-alkanoates (PHAs) are intracellular
carbon and energy reserves that are accumulated by many bacteria when
surplus carbon is available, under certain nutrient limited conditions of
growth. Different biodegradable plastics have been developed by microbial
fermentations. However, limitations of these materials still exist due to high
cost of production. For minimization of cost for the production of
biodegradable plastics, the waste biological sludge generated at waste water
treatment plants is one of the substrate used for the production of PHB.
These compounds can be produced in large quantities from renewable
resources by well known fermentation processes and have potential to
replace petroleum derived thermoplastics.
A total of 115 bacterial isolates differing in their morphology were
isolated from various soils and were screened using Nile blue A and was
verified by using Sudan black B dye. Nine PHB producing bacilli were
selected depending upon their fluorescence on Nile blue A plates and PHB
production under minimal medium broth was studied. High PHB producing
Isolates ZTL-31, ZTL-32 and Sld-110 were selected for subsequent studies.
Conditions for higher PHB production were optimized for temperature,
time, aeration conditions and different carbon and nitrogen sources. Three
different carbon sources milk whey, sewage sludge, molasses were used.
Isolate No. Sld-110 produced highest amount of PHB (322.2 mg/g dry
weight of cells) when 1 % of molasses was used as carbon source at 27C
after 72 h under stationary conditions. Isolate Sld-110 produced up to 310.6
mg/g (w/w) PHB with ammonium phosphate as nitrogen source. However,
it produced 356.4 mg/g (w/w) PHB without nitrogen source in minimal
medium containing 1 % molasses at 27ºC after 72 h under stationary
conditions.
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Keywords
PHB, Bacillus, Milk whey, Molasses, Sewage sludge