All living things are composed of cells, of which there are two basic types, the prokaryotic
cell and the eucaryotic cell .The parts of the cell are described briefly beginning from the outside.

Cell wall: Procaryotic cell walls contain glycopeptides; these are absent in eucaryotic cells. Cell walls of eucaryotic cells contain chitin, cellulose and other sugar polymers. These provide rigidity where cell walls are present.

Cell membrane: Composed of a double layer of phospholipids, the cell membrane
completely surrounds the cell. It is not a passive barrier, but enables the cell to actively
select the metabolites it wants to accumulate and to excrete waste products.
Ribosomes are the sites of protein synthesis. They consist of two sub-units. Procaryotic
ribosomes are 70S and have two sub-units: 30S (small) and a 50S (large) sub-units.
Eucaryotic ribosomes are 80S and have sub-units of 40S (small) and a 60S (large). (The
unit S means Svedberg units, a measure of the rate of sedimentation of a particle in an
ultracentrifuge, where the sedimentation rate is proportional to the size of the particle.
Svedberg units are not additive–two sub-units together can have Svedberg values that do
not add up to that of the entire ribosome). The prokaryotic 30S sub-unit is constructed from
a 16S RNA molecule and 21 polypeptide chains, while the 50S sub-unit is constructed
from two RNA molecules, 5S and 23S respectively and 34 polypeptide chains.
Mitochondria are membrane-enclosed structures where in aerobic eucaryotic cells the
processes of respiration and oxidative phosphorylation occur in energy release.
Procaryotic cells lack mitochondria and the processes of energy release take place in the
cell membrane.
Nuclear membrane surrounds the nucleus in eukaryotic cells, but is absent in procaryotic
cells. In procaryotic cells only one single circular macromolecule of DNA constitutes the
hereditary apparatus or genome. Eucaryotic cells have DNA spread in several
Nucleolus is a structure within the eucaryotic nucleus for the synthesis of ribosomal RNA.
Ribosomal proteins synthesized in the cytoplasm are transported into the nucleolus and
combine with the ribosomal RNA to form the small and large sub-units of the eucaryotic
ribosome. They are then exported into the cytoplasm where they unite to form the intact

Bacteria are described in two compendia, Bergey’s Manual of Determinative Bacteriology
and Bergey’s Manual of Systematic Bacteriology. The first manual (on Determinative

Bacteriology) is designed to facilitate the identification of a bacterium whose identity  is 
unknown. It was first published in 1923 and the current edition, published in 1994 is the
ninth. The companion volume (on Systematic Bacteriology) records the accepted published
descriptions of bacteria, and classifies them into taxonomic groups. The first edition was
produced in four volumes and published between 1984 and 1989. The bacterial
classification in the latest (second) edition of Bergey’s Manual of Sytematic Bacteriology is
based on 16S RNA sequences, following the work of Carl Woese, and organizes the
Domain Bacteria into 18 groups (or phyla; singular, phylum) It is to be published in five
volumes. Volume 1 which deals with the Archae and the deeply branching and
phototrophic bacteria was published in 2001; Volume 2 published in 2005, deals with the
Proteobacteria and has three parts while Volume 3 was published in 2006 and deals with
the low G+C Gram-positive bacteria. The last two volumes, Volume 4 (the high C + C
Gram-positive bacteria) and Volume 5 (The Plenctomyces, Spirochaetes, Fibrobacteres,
Bacteriodetes and Fusobacteria) will be published in 2007. The manuals are named after Dr
D H Bergey who was the first Chairman of the Board set up by the then Society of
American Bacteriologists (now American Society for Microbiology) to publish the books.
The publication of Bergey Manuals is now managed by the Bergey’s Manual Trust.

Of the 18 phyla in the bacteria, the Aquiflex is evolutionarily the most
primitive, while the most advanced is the Proteobacteria. The bacterial phyla used in
industrial microbiology and biotechnology are found in the Proteobacteria, the
Firmicutes and the Actinobacteria.

The Proteobacteria:
The Proteobacteria are a major group of bacteria. Due to the diversity of types of bacteria
in the group, it is named after Proteus, the Greek god, who could change his shape.
Proteobacteria include a wide variety of pathogens, such as Escherichia, Salmonella, Vibrio
and Helicobacter, as well as free-living bacteria some of which can fix nitrogen. The group
also includes the purple bacteria, so-called because of their reddish pigmentation, and

which use energy from sun light in photosynthesis.
All Proteobacteria are Gram-negative, with an outer membrane mainly composed of
lipopolysaccharides. Many move about using flagella, but some are non-motile or rely on
bacterial gliding. There is also a wide variety in the types of metabolism. Most members
are facultatively or obligately anaerobic and heterotrophic, but there are numerous

Proteobacteria are divided into five groups: (alpha), (beta), (gamma), (delta), 
(epsilon). The only organisms of current industrial importance in the Proteobacteria are
Acetobacter and  Gluconobacter, which are acetic acid bacteria and belong to the
Alphaproteobacteria. An organism also belonging to the Alphaproteobacteria, and
which has the potential to become important industrially is Zymomonas. It produces

copious amounts of alcohol, but its use industrially is not yet widespread.

The Acetic Acid Bacteria:
The acetic acid bacteria are Acetobacter(peritrichously flagellated) and Gluconobacter

(polarly flagellated). They have the following properties:
i. They carry out incomplete oxidation of alcohol leading to the production of acetic
acid, and are used in the manufacture of vinegar.
ii. Gluconobacter lacks the complete citric acid cycle and can not oxidize acetic acid;
Acetobacter on the on the other hand, has all the citric acid enzymes and can oxidize
acetic acid further to Carbon dioxide.
iii. They stand acid conditions of pH 5.0 or lower.
iv. Their property of ‘under-oxidizing’sugars is exploited in the following:
a. The production of glucoronic acid from glucose, galactonic acid from
galactose and arabonic acid from arabinose;
b. The production of sorbose from sorbitol by acetic acid bacteria,
an important stage in the manufacture of ascorbic acid (also known as
Vitamin C)
v. Acetic acid bacteria are able to produce pure cellulose when grown in an unshaken
culture. This is yet to be exploited industrially, but the need for cellulose of the purity of the bacterial product may arise one day.

The Firmicutes:
The Firmicutes are a division of bacteria, all of which are Gram-positive, in contrast to the
Proteobacteria which are all Gram-negative. A few, the mycoplasmas, lack cell walls
altogether and so do not respond to Gram staining, but still lack the second membrane

found in other Gram-negative forms; consequently they are regarded as Gram-positive.

Originally the Firmicutes were taken to include all Gram-positive bacteria, but more
recently they tend to be restricted to a core group of related forms, called the low G+C
group in contrast to the Actinobacteria, which have high G+C ratios. The G+C ratio is an
important taxonomic characteristic used in classifying bacteria. It is the ratio of Guanine
and Cytosine to Guanine, Cytosine, Adenine, and Thymine in the cell. Thus the GC ratio
= G+C divided by G+C+A+T x 100. It is used to classify Gram-positive bacteria: low G+C
Gram-positive bacteria (ie those with G+C less than 50%) are placed in the Fermicutes,
while those with 50% or more are in Actinobacteria. Fermicutes contain many bacteria of
industrial importance and are divided into three major groups: i. spore-forming, ii. nonspore forming, and iii) wall-less (this group contains pathogens and no industrial

Spore forming firmicutes:

Spore-forming Firmicutes form internal spores, unlike the Actinobacteria where the
spore-forming members produce external ones. The group is divided into two: Bacillus
spp, which are aerobic and Clostridium spp which are anaerobic. Bacillus spp are
sometimes used in enzyme production. Some species are well liked by mankind because
of their ability to kill insects. Bacillus papilliae infects and kills the larvae of the beetles in
the family Scarabaeidae while B. thuringiensisis used against mosquitoes . The
genes for the toxin produced by B. thuringiensis are also being engineered into plants to
make them resistant to insect pests . Clostridia on the other hand are mainly
pathogens of humans and animals.

Non-spore forming firmicutes:
The Lactic Acid Bacteria: The non-spore forming low G+C members of the firmicutes
group are very important in industry as they contain the lactic acid bacteria.
The lactic acid bacteria are rods or cocci placed in the following genera:Enterococcus,
Lactobacillus, Lactococcus, Leuconostoc, Pediococcus and Streptococcus and are among some of
the most widely studied bacteria because of their important in the production of some
foods, and industrial and pharmaceutical products. They lack porphyrins and

cytochromes, do not carry out electron transport phosphorylation and hence obtain energy by substrate level phosphorylation. They grow anaerobically but are not killed by
oxygen as is the case with many anaerobes: they will grow with or without oxygen. They
obtain their energy from sugars and are found in environments where sugar is present.
They have limited synthetic ability and hence are fastidious, requiring, when cultivated,
the addition of amino acids, vitamins and nucleotides.
Lactic acid bacteria are divided into two major groups: The homofermentative group,
which produce lactic acid as the sole product of the fermentation of sugars, and the
heterofermentative, which besides lactic acid also produce ethanol, as well as CO. The
difference between the two is as a result of the absence of the enzyme aldolase in the
heterofermenters. Aldolase is a key enzyme in the E-M-P pathway and spits hexose
glucose into three-sugar moieties. Homofermentative lactic acid bacteria convert the D-glyceraldehyde 3-phosphate to lactic acid. Heterofermentative lactic acid bacteria receive
five-carbon xylulose 5 phosphate from the Pentose pathway. The five carbon xylulose is
split into glyceraldehyde 3-phosphate (3-carbon), which leads to lactic acid, and the two carbon acetyl phosphate which leads to ethanol.

Use of Lactic Acid Bacteria for Industrial Purposes:
The desirable characteristics of lactic acid bacteria as industrial microorganisms include
a. their ability to rapidly and completely ferment cheap raw materials,
b. their minimal requirement of nitrogenous substances,
c. they produce high yields of the much preferred stereo specific lactic acid
d. ability to grow under conditions of low pH and high temperature, and
e. ability to produce low amounts of cell mass as well as negligible amounts of other


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Cited By Kamal Singh Khadka/ Shailendra Parajuli Msc Microbiology/ Biotechnology
Assistant Professor In PU, RE-COST, PNC, LA, NA.
Pokhara, Nepal.




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