Bacterial delignification of paddy straw
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Date
2015
Authors
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Publisher
CCSHAU
Abstract
India is the second largest producer of paddy in the world after China and produces 98 million
ton of paddy with roughly 130 million ton of straw. Field burning is the major practice for removing
paddy straw which results in nutrient losses, increases the air pollution and consequently affects public
health. Lignin is one of the most abundant aromatic natural substances present in the biosphere. It is a
polymer composed of phenylpropanoid units, associated with cellulose and hemicelluloses in plant cell.
In biological treatment systems, a wide variety of microorganisms including fungi, actinomycetes and
bacteria have been used in lignin biodegradation. Now a day, the ligninolytic bacteria gaining
importance, because of wider tolerance of temperature, pH and oxygen limitation than fungi. In the
present study, a total of 30 bacterial isolates were obtained from soil and different ecological niches.
Out of these, 15 isolates were screened for ligninolytic activity on LB media containing dyes (aniline
blue, phenol red and guaiacol).The zone index varied from 2.7 to 3.7 with bacterial isolate DS2
showing the maximum zone of clearance (3.7) on LB media containing aniline dye. Only eight
bacterial isolates were selected for measuring the ligninolytic enzyme activity in MSM broth
containing 1.0% lignin. The activity of laccase varied from 2.34 – 3.56 U/ml, manganese peroxidase
(MnP) ranged from 1.48- 4.12 U/ml and lignin peroxidase (LiP) varied from 2.37- 5.99 U/ml. The
bacterial isolate, LS1 had both the highest laccase (3.56 U/ml) as well as lignin peroxidase (5.99 U/ml)
activity. However, maximum manganese peroxidase activity was observed in PS1 (4.12 U/ml). All
bacterial isolates (except PS1) produced maximum lignin peroxidase enzymes activity as compared to
other enzyme. Five selected ligninolytic bacterial isolates were used for the delignification of paddy
straw with different conditions like temperatures (25, 30 and 35°C), pH (5.0, 6.0 and 7.0) and
incubation period (7, 14 and 21 days) under stationary condition. Optimum temperature for
delignification was found to be 30°C and pH 6.0 for DS2 and LS1 whereas pH 7.0 for CS3, CS4 and
PS1) after 21 days of incubation. The maximum lignin reduction (32%) was observed by isolate DS2
followed by LS1 (30%), therefore, DS2 and LS1 were scored as best isolates for delignification of
paddy straw.
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Keywords
Aromatic compounds, Enzymes, Bacteria, Crop residues, Rice, Cellulose, Fungi, Polysaccharides, Selection, Inorganic compounds