Role of microorganisms in the fermentation process

1. Role of microorganisms in the fermentation process
Initially, it might be hard to imagine how microorganisms contribute to the
fermentation process. How can such small and microscopic cells unseen to the
naked eyes produce such high volumes of products? How such microorganisms
can produce such a rich diversity of fermentation products which are useful to
human beings?
The answer to the first question is simple enough. One tiny microscopic microbial
cell will not produce industrially significant volume of fermentation products.
However, when we talk about billions and billions of microbial cells in the
fermentation vat, the volume and concentration of fermentation products is
industrially and economically significant!
The diversity of fermentation products produced by the microorganisms is
attributed to the rich diversity of microorganisms which have diverse metabolisms
that can yield various types of fermentation products
Why microorganisms are the best choice for fermentation?
The success of using microorganisms for fermentation lies in their very
microscopic and metabolic characteristics. It is good being small!
1. High surface area to volume ratio
Microorganisms are very tiny creatures. Taking an example of a rod bacterium
(imagine a brick!), we can see that it has six free surfaces that surrounds the
bacterium. These six free surfaces interfaced with the surrounding environment
from where they obtained their nutrients or to where they throw away their
metabolic waste products.
With such a high number of free surface areas in a tiny volume of cell, it confers
upon the bacterial cell a very high surface area to volume ratio. This very high
surface area to volume ratio allows maximum or optimum surfaces for diffusions
or molecular exchanges to occur between the microbial cell and the environment.
No matter where the molecules are, they are easily accessible for diffusion into the
microbial cell.

2. Compare this with the elephant which is such a huge animal. This has a very low
ratio of surface area to volume ratio! If nutrients are to diffuse through the surface
area of the elephant it would not be enough to supply every cell of the elephant!
The efficient nutrient uptake coupled with the small size of the cell will allow for
rapid synthesis and reproduction of new cells. Microorganisms under ideal state
will double up within hours. Animals like elephants and human may take months
to reproduce themselves.
2. Mode of nutrients transportation
The nutrients which diffuse into the microbial can either use simple diffusion
process which is powered by the differences in the concentration gradients between
the environment and within the cell. For very small nutrient molecules, most would
diffuse by the mechanism of passive diffusion. Larger and complex molecules use
active or group transport which requires expansion or utilization of energy
Microbes easily reproduce asexually! There is no real need to have a opposite
partner cells, get married and reproduce. They will just as easily split their cells
into two daughter cells which will later grow into larger cells and repeat the cycle..
3. Genetic adaptability
Microorganisms generally show the ability to adapt to new environment. They can
get easily adapted to living under different environmental conditions and also
adapting to new sources of carbon or substrate. This ability is the result of various
genetic adaptations which selects "successful" strains through mutation and genetic
recombination. Some of the bacteria are even equipped with plasmids which can
synthesize new enzymes that help the microorganisms exploit the new
environment. The very short generation times and the high population generation
will aid the selection and recombination process.
4. Metabolic diversity
The unique things about microbes are their metabolic diversity shown by various
members of the microorganisms. They have the ability to use different energy
sources and to use different type’s terminal electron acceptors

3. Their ability to use different substrates is also correlated with the microbe’s ability
to produce a diversity of fermentation products
There are numerous examples for fermented food
Fish sauce
In production of fish sauce, eviscerated fish is mixed with salt and placed in
fermented tanks to allow liquefaction for about six months. The collected liquid is
further ripened for few more months. Halophillic microbes are involved in this
fermentation process. Streptococcus, Micrococcus and Bacillus species
predominate. This product is dark colored with a distinct aroma.
Sauerkraut
This refers to fermented cabbage. Normal microflora in cabbage is involved in the
fermentation process under anaerobic conditions. Leuconostoc mesenteroides and
Lactobacillus plantarum is involved. Temperature is a crucial factor in the control
of fermentation. If the temperature is below 21 degrees Celcius, Lactobacilli
outgrow. L. mesenteroides require a lower temperature below 21 0C. Acidity
created by Lactobacilli prevents the growth of L. mesenteroides.
Pickels
Pickels consist of vegetables like cucumber, onions, chilies etc. Lactic acid
bacteria such as Leuconostoc mesenteroides, P. cerevisiae, L. brevis, and L.
plantarum are involved in the fermentation process these bacteria also take part in
fermentation of olives.
Soy sauce
In production of soy sauce, a mixture of soybean and wheat flour is inoculated with
Aspergillus oryzae and Aspergillus soyae. These fungi digest complex starch and
produce sugars which facilitate the growth of bacteria. Anaerobic bacteria carry
out fermentation to produce soy sauce.
Beer and Ale

4. Malted beverages are produced by brewing. Mainly the yeasts are involved in the
process. Yeasts convert fermentable sugars to ethanol and carbon dioxide. As
yeasts do not produce enough amylases to hydrolyze starch in barley grains, they
are germinated prior to brewing. Hops which are added for bitterness have an
inhibitory effect on gram positive bacteria. Saccharomyces carlsbergensis is the
principle organism used. This species is subjected to various genetic modifications
to increase the efficiency of the fermentation. In addition to ethanol and carbon
dioxide, yeasts produce a small amount of glycerol, acetic acid and aromatic esters.
Ale is a top fermented beverage with Saccharomyces cerevisiae.
Wine
Wine is made from grape juice in large scale. Yests; Saccharomyces cerevisiae
var. ellipsoideus is the culture used in wine fermentation. High temperature is not
suitable for this fermentation as yeasts die while low temperature allows the
growth of lactic acid bacteria.