Agriculture Reference
In-Depth Information
thermophile as defined by Brock (
1978
) is “an organism capable of living at tem-
peratures at or near the maximum for the taxonomic group of which it is part.” Cel-
lular structure and activities are affected by various factors including temperature.
Thermophilic microbes have developed special attributes in their structural make-up
in terms of its major components, including proteins, nucleic acids and lipids, which
allow them to prevail and thrive at high temperatures. A significant increase in the
proportion of nonpolar, hydrophobic amino acids (isoleucine, leucine, methionine,
phenylalanine, and valine) indicates the role of hydrophobicity for stabilization of
thermophilic proteins (Lieph et al.
2006
). A reduction in the glycine content and
extensive ionic interactions that form a network over the surface of the molecule as-
sists the compacted protein to resist unfolding at high temperature (Ladenstein and
Antranikian
1998
). A higher content of arginine and a reduction in the total num-
ber of thermally unstable residues, such as Cys, Lys, Met, Asn and Gln (Cicicopol
et al.
1994
), have been associated with thermostable proteins. An increase in ion-
pair content, or a change from monomeric to oligomeric structure (Cicicopol et al.
1994
) a decrease in the length of surface loops that connect elements of secondary
structure (Thompson and Eisenberg
1999
), additional networks of hydrogen bonds
(Jaenicke and Bohm
1998
), an increase in disulfide bond formation (Beeby et al.
2005
), and an exchange of amino acids to increase helix propensity of residues in
alpha-helices and the presence of noncovalent, ionic bonds called salt bridges on
a protein's surface, are some of the known factors that have been shown to play a
major role in maintaining the biologically active structure of thermophilic proteins
(Das and Gerstein
2000
).
6.2.1
A Brief Classification of Thermophilic Bacilli
The thermophilic
Bacilli
are a phenotypically diverse group, that are Gram-positive
and/or Gram-variable, aerobic or facultative anaerobic, endospore-forming, rod-
shaped bacteria. This group has undergone considerable reclassification, as the ad-
vancement in molecular biology has resulted in a shift in the identification pattern,
from the basis of phenotypic characterization towards nucleotide sequence analysis
of conserved genes, particularly, by 16s rRNA gene analysis. According to Ludwig
et al. (
2007
) and Logan et al. (
2009
), the thermophilic
Bacilli
are categorised under
the phylum
Firmicutes
and class
Bacilli
which is further subdivided into order
Bacil-
lales
and
Lactobacillales
. The order
Bacillales
consists of nine families, namely: (I)
Bacillaceae, (II) Alicyclobacillaceae, (III)
Listeriaceae
, (IV)
Paenibacillaceae
, (V)
Pasteuriaceae, (VI)
Planococcaceae
, (VII)
Sporolactobacillaceae
, (VIII)
Staphylo-
coccaceae
, (IX)
Thermoactinomycetaceae
. The order
Lactobacillales
is composed
of six families, including: (I)
Lactobacillaceae
, (II)
Aerococcaceae
, (III)
Carnobac-
teriaceae
, (IV)
Enterococcaceae
, (V)
Leuconostocaceae
and (VI)
Streptococcaceae
.
The genus
Bacillus,
Paenibacillus
and
Streptococcus
are extensively studied due to
their vast occurrence and their ability to utilize diverse carbon compounds as energy
source (Cihan et al.
2012
).
Bacillus
and related genera have been shown to produce
a variety of enzymes with industrial importance owing to their versatility and perfor-
mance over a broad pH and temperature range (Cihan et al.
2012
).
