Pectin , Chitin and Lignin

Pectin

pectin are derived from protopectin that occurs in the plant middle lamellae or in the plant primary cell wall in association with hemicellulose / Many fruits have a high pectin content and it also occurs in the cell wall of certain algae.The pectin carbohydrates are complex polysaccharides composed of galacturonic acid unit bound to one another in a long chain . They are thus poly galacturonic acid . Also sometimes traces of other sugars may also be present .

Fig:Pectin

The enzyme involved in the breakdown of pectin substances can be divided into three categories;

1. Pectinesterases
2. Enzymes that carry out the hydrolytic cleavage of the polymer
3. Polygalacturonase

Among the enzymes involved pectin ,esterases are involved in the splitting the ester bonds and remove the methyl groups and polygalacturonase also called trans eliminating enzyme breakdown chain.A wide range of bacteria and fungi are capable of degranulating such as Botrytis cinerea, bacteria such as Erwinia carnivore , pectinolytic activity is associated with plant pathogenicity. Some spores forming bacteria like Bacillus polymyxin and Bacillus merchants are very active in pectin degradation.

Chitin

Chitin is most polysaccharides in nature whose basic unit is an amino sugar The polysaccharide is structural constituent giving mechanical strength to an organism containing it chitin insoluble in water ,organic solvents concentrate alkali or dilute mineral acid but it can be solubilized and degradation either enzymatically or by treatment with concentrated acid.

In structure, chitin consists of a long chain of N-acetyl glucosamine unit in a linear arrangement. The pure compound contains 6.9 % nitrogen . The polymer is similar to cellulose with on of the hydroxyl group of each glucose in cellulose being replaced by acetylamino( NHCOCH3) units

vFig: chitin

Fig: chitin

Some chitin has a varying amount of chitosan associated with them . Chitosan is similar to chitin but it has lost the acetyl group (COCH3) so , that it is a long chain of glucosamine linked together as in the original chitin . Chitin is produced by members of both the plant and animal kingdom . In cell wall of many filamentous fungi , the considerable amount of polysaccharides are deposited and the polymer is important to the maintenance of the structural integrity and hence viability of this organism. The chitin component of the fungus hyphal wall can make up a large proportion of the total cellular material but growth condition age , temperature and pH alter the concentration . Chitin is found in the skeleton of no.of invertebrates animals. The chitin in insects in linked with proteins in a complex that stabilizes the chitin against enzymatic degradation.

Degradation of chitin

The breakdown of chitin involved the conversion of an insoluble product that penetrates the cells and carbs to provide energy and carbon or sometimes N2 for growth . The responsible and the common product that appears in culture during degradation are N-acetyl glucosamine and glucosamine.The transformation usually involved the following enzymes.

1. Chitinase : It catalyzes the depolymerization of a chain to yield oligomers moving several of the N-acetyl glucosamine units as the dimer
2. N-acetyl glucosaminidase(chitobiose): It hydrolyzes the oligomers and dimers of N-acetyl glucosamine chain to yield N-acetyl glucosamine (individual). The N-acetyl glucosamine ultimately generated is the converted to acetic acid and glucosamine and the ammonia is liberated from the latter compound . The glucosamine or a confirmed it is readily attacked and serves within a cell to supply carbon and energy.

The Actinomycetes of the genus Streptomyces and Nocardia are predominant chitin decomposes . Similarly Micromonospora actinopt ane's , Streosporagium also help in degradation of chitin . Fungi of the genera Trichoderma, Verticillium , Bacillus and Pseudomonas among the bacteria are chitin decomposers . In anaerobic condition, Clostridium is known to metabolize the compound.

Lignin

The 3rd most abundant constituent of plant tissue is commonly arginine . It is superseded in relative quantity only by cellulose and hemicellulose . Certain plant the woody species, in particular, contribute a large amount of login to the material to the degraded to the activity of soil microflora . In forest alone , vast quantities of lignin are continuously deposited on the soil as wood waste and these must destroy either by burying or biological means . Login occurs in the woody material of the vascular plant and is found in the plant . The cell wall in close association with cellulose and hemicellulose within the plant ,login is found in the secondary layer of the cell wall and also to some extend in the middle lamella . Login probably never occurs free , usually, it is combined with polysaccharides.

The login molecular any contain only three element carbon, nitrogen ,and oxygen but the structure is are aromatic rather than being of carbohydrates type as typified by cellulose and the hemicellulose . The basic unit in lignin seems to be a phenylpropane type of structure which may exist in 3 types.

Lignin is degraded very slowly . They are extremely resistance to microbial attack and represent the main source of slowly decaying organic matter in the soil . Lignin is attacked almost exclusively by fungi especially by white rot . Basidiomycetes and some member of Ascomycetes i.e Valeria are also capable of degrading lignin . Fungi release enzyme that split the polymer into constituent subunit which is then susceptible to further degradation of the variety of microorganisms i.e both fungi and bacteria compare to cellulose and hemicellulose the lignin is only slowly degraded by wood-decaying fungi and bacteria . In the breakdown of lignin monooxygenase , dioxygenase and phenol oxidases are involved . Basidiomycetes cause a various room of decay of wood on as roots . The cellulose and hemicellulose of the wood and leave lignin component undecayed . In what rots all component of wood are destroyed decay is performed by fungi that primarily attack lignin and other degraded lignin and cellulose. The phenol oxidases oxidize aromatic compound containing one phenol or two hydroxyls ,while leases.oxidize only these aromatic compound with more than one hydroxyl group. These enzymes are said to be able to cleave either linkage ,remove side chains and cause the loss of methoxyl group.

Lignin degrading microorganism

1. Bacteria: Artherbacter, Flavobacteria ,Micrococcus , Pseudomonas , Xanthomonas etc.
2. Fungi: Aspergillus , Fusarium , Pencillum etc.

Reference

Rangaswami, G and PT Bagyaraja. Agricultural Microbiology. 2nd. Prentice Hall of India, 1993.

Alexander, M. Introduction To Soil Microbiology . Academic Press, 1961.