Environmental Engineering Reference
In-Depth Information
less visible elemental cycles of metals, carrying
out oxidation/reduction of metals (e.g., manga-
nese and iron). Microorganisms are the primary
organisms responsible for degradation of a great
variety of natural organic compounds, includ-
ing cellulose, hemicellulose, lignin, and chitin,
which are the most abundant organic matter on
Earth (Mishra and Thakur
2012
). Due to their
versatility, microbes not only provide ecological
services but also play a major role in semiarti-
ficial systems such as sewage treatment plants,
landfills, and in toxic waste bioremediation. To
mention few examples in which microbes are re-
sponsible for degradation of toxic chemicals de-
rived from anthropogenic sources such as PAH,
PCBs (polychlorinated biphenyls), dioxins, pes-
ticides, etc (Jaiswal et al.
2011
). In most cases
these microbes are genuine members of natural
communities. Some organisms are obligatory de-
graders, frequently switching their metabolism
on degradation and consumption to acquire car-
bon and/or energy.
It also participates in bioremediation and puri-
fication of hazardous wastes in water. Biological
treatments are more effective as these methods
convert toxic chemicals to less toxic ones and
possess a significant degree of self-regulation
(Mishra et al.
2013
). Microorganisms have di-
verse capacities to biotransform and, in some
cases, completely destroy toxic chemicals from
our environment. Since these transformations
alter the chemistry of the hazardous chemicals,
they may also alter toxicity, environmental fate,
and bioaccumulation potential (Das et al.
2012
).
Several halogenated chemicals such as the chlo-
rinated aromatic compounds, which are major
contaminants, nitro aromatics and other conju-
gated hydrocarbons-polluted contaminated sites
could be reclaimed by use of the vanguard organ-
isms isolated from contaminated sites by enrich-
ment cultures.
Spingomonas paucimobilis
BPSI-
3 that was isolated from PCB contaminated soil
was observed to degrade halogenated PAHs and
biphenyls (Davison et al.
1999
). Head and Swan-
nell (
1994
) reported bioremediation of petroleum
hydrocarbon contaminates in marine habitats by
anaerobic hydrocarbon metabolism via bioaug-
mentation and stressed to reject the approach of
nutrient amendment as it can potentially exert
an oxygen demand due to biological ammonia
oxidation. Samanta et al. isolated
Ralstonia sp
.
SJ98 from pesticide-contaminated agricultural
soil using a chemotactic enrichment technique
(Samanta et al.
2000
).
In nature majority reactions result in mineral-
ization of the contaminant but sometime recalci-
trant formed during the process act as potent toxic
compound than the original xenobiotic chemical.
Pseudomonas putida
and
Burkholderia cepacia
have even been genetically engineered to cover a
wider range of contaminants though
Pseudomo-
nas sp.
possesses metabolic plasmids too. Lajoie
et al. (
1994
) studied the use of surfactant based
field application vectors for PCB degradation, as
single microbe barely possesses all the enzymes
for mineralization of a xenobiotic chemical. The
specificity of the pollutant and the microbe de-
grading it depends upon the enzymes involved in
the selective chemotaxis of the microbe toward
4.4.2
Microbes in Industrial Products
Many products useful to mankind are synthe-
sized at commercial level using microbes. Bev-
erages, antibiotics, alcohol, enzymes (glucose
oxidase, amylase, protease, lipase, cellulose, xy-
lanase, etc.), proteins, vaccines, steroids, amino
acids are the few important examples. Microbial
biochemicals are also used as biocontrol agents
as an alternative to insecticides, pesticides etc.
4.4.3
Biodegradation of Xenobiotics
Human kind is increasingly using pesticides such
as BHC, DDT, 2,4-D, 2,4,5-T for getting rid of
unwanted weeds, insect pests, or pathogenic
microorganisms. Removing chemicals from
the environment can be achieved easily and in
an environment-friendly manner by biological
methods that involve use of microbes and plants
to degrade xenobiotic compounds and thus de-
contamination of the polluted site.
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