BIOLOGICAL BASIS OF PRODUCTIVITY IN INDUSTRIAL MICROBIOLOGY & BIOTECHNOLOGY(Contd..)
The Actinobacteria are the Firmicutes with G+C content of 50% or higher. They derive
their name from the fact that many members of the group have the tendency to form filaments or hyphae (actinis, Greek for ray or beam). The industrially important members of the group are the Actinomycetes and Corynebacterium. Corynebacterium spp are
important industrially as secreters of amino acids.
They have branching filamentous hyphae, which somewhat resemble the mycelia of the
fungi, among which they were originally classified. In fact they are unrelated to fungi, but
are regarded as bacteria for the following reasons. First they have petidoglycan in their
cell walls, and second they are about 1micrometer in diameter (never more than 1.5 ), whereas
fungi are at least twice that size in diameter.
As a group the actinomycetes are unsurpassed in their ability to produce secondary
metabolites which are of industrial importance, especially as pharmaceuticals. The best
known genus is Streptomyces, from which many antibiotics as well as non-anti-microbial
drugs have been obtained. The actinomycetes are primarily soil dwellers hence the
temptation to begin search for any bioactive microbial metabolite from soil.
Although plants and animals or their cell cultures are used in biotechnology,
microorganisms are used more often for reason which have been discussed. Fungi are
members of the Eucarya which are commonly used in industrial production.
The fungi are traditionally classified into the four groups given in Table 2.4, namely
Phycomycetes, Ascomycetes, Fungi Imprfecti, and Basidiomycetes. Among these the
following are those currently used in industrial microbiology
Rhizopus and Mucor are used for producing various enzymes
Yeasts are used for the production of ethanol and alcoholic beverages Claviceps purperea is used for the production of the ergot alkaloids.
Aspergillus is important because it produces the food toxin, aflatoxin, while Penicillium is which is well known for antibiotics production.
Agaricus produces the edible fruiting body or mushroom
Numerous useful products are made through the activity of fungi, but the above are only a selection.
CHARACTERISTICS IMPORTANT IN MICROBES USED IN INDUSTRIAL MICROBIOLOGY AND
Microorganisms which are used for industrial production must meet certain
requirements including those to be discussed below. It is important that these
characteristics be borne in mind when considering the candidacy of any microorganism
as an input in an industrial process.
i. The organism must be able to grow in a simple medium and should preferably not
require growth factors (i.e. pre-formed vitamins, nucleotides, and acids) outside
those which may be present in the industrial medium in which it is grown. It is
obvious that extraneous additional growth factors may increase the cost of the
fermentation and hence that of the finished product.
ii. The organism should be able to grow vigorously and rapidly in the medium in use.
A slow growing organism no matter how efficient it is, in terms of the production of
the target material, could be a liability. In the first place the slow rate of growth
exposes it, in comparison to other equally effective producers which are faster
growers, to a greater risk of contamination. Second, the rate of the turnover of the
production of the desired material is lower in a slower growing organism and
hence capital and personnel are tied up for longer periods, with consequent lower
iii. Not only should the organism grow rapidly, but it should also produce the desired
materials, whether they be cells or metabolic products, in as short a time as
possible, for reasons given above.
iv. Its end products should not include toxic and other undesirable materials,especially if these end products are for internal consumption.
v. The organism should have a reasonable genetic, and hence physiological stability.
An organism which mutates easily is an expensive risk. It could produce
undesired products if a mutation occurred unobserved. The result could be
reduced yield of the expected material, production of an entirely different product
or indeed a toxic material. None of these situations is a help towards achieving the
goal of the industry, which is the maximization of profits through the production
of goods with predictable properties to which the consumer is accustomed.
vi. The organism should lend itself to a suitable method of product harvest at the end
of the fermentation. If for example a yeast and a bacterium were equally suitable for
manufacturing a certain product, it would be better to use the yeast if the most appropriate recovery method was centrifugation. This is because while the bacterial diameter is approximately 1 , yeasts are approximately 5 . Assuming their densities are the same, yeasts would sediment 25 times more rapidly than bacteria.
The faster sedimentation would result in less expenditure in terms of
power, personnel supervision etc which could translate to higher profit.
vii. Wherever possible, organisms which have physiological requirements which
protect them against competition from contaminants should be used. An organism
with optimum productivity at high temperatures, low pH values or which is able to
elaborate agents inhibitory to competitors has a decided advantage over others.
Thus a thermophilic efficient producer would be preferred to a mesophilic one.
viii. The organism should be reasonably resistant to predators such as Bdellovibrio spp
or bacteriophages. It should therefore be part of the fundamental research of an
industrial establishment using a phage-susceptible organism to attempt to
produce phage-resistant but high yielding strains of the organism.
ix. Where practicable the organism should not be too highly demanding of oxygen as
aeration (through greater power demand for agitation of the fermentor impellers,
forced air injection etc) contributes about 20% of the cost of the finished product.
x. Lastly, the organism should be fairly easily amenable to genetic manipulation to enable establishment of strains with more acceptable properties.
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Cited By Kamal Singh Khadka
Msc Microbiology, TU
Assistant Professor in Pokhara University, Pokhara Bigyan Tatha Prabidi Campus(Previously RECOST), Nobel Academy, LA.