Nutrition cultivation and isolation of bacteria
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INTRODUCTION
In a rather broader perspective the
‘bacteria’ are markedly distinguished by their inherent extreme
metabolic diversity
; whereas, a few of them may conveniently sustain themselves exclusively on
‘inorganic substances’
by strategically making use of such specific pathways which are practically
absent amongst the plant as well as animal kingdoms.
Based upon the aforesaid statement of facts one may individually explore and exploit the various
cardinal factor(s) that essentially govern the
nutrition, cultivation (growth), and isolation of bacteria,
actinomycetes
, fungi and viruses as enumerated under :
BACTERIA
The nutrition, cultivation (growth), and isolation of bacteria shall be dealt with in the sections
that follows :
Nutrition of Microorganisms (Bacteria)
Interestingly, the
microbial cell represents an extremely complex entity, which is essentially
comprised of approximately 70% of by its weight as water, and the remaining 30% by its weight as the
solid components. Besides, the
two major gaseous constituents viz., oxygen (O2) and hydrogen (H2) the
microbial cell
predominantly consists of four other major elements, namely : Carbon (C), nitrogen
(N)
, sulphur (S), and phosphorus (P). In fact, the six aforesaid constituents almost account for 95% of
the ensuing
cellular dry weight. The various other elements that also present but in relatively much
lesser quantum are : Na
+, K+, Ca2+, Mg2+, Mn2+, Co2+, Zn2+, Cu2+, Fe3+ and Mo4+. Based on these
critical observations and findings one may infer that the microorganisms significantly require an exceptionally
large number of elements for its adequate survival as well as growth (
i.e., cultivation).The following displays the various chemical composition of an
Escherichia coli cell.
It has been amply proved and established that
carbon represents an integral component of almost
all organic cell material ; and, hence, constitutes practically half of the ensuing dry cell weight.
Nitrogen
is more or less largely confined to the proteins, coenzymes, and the nucleic acids (DNA,
RNA).
Sulphur is a vital component of proteins and coenzymes ; whereas, phosphorus designates as
the major component of the nucleic acids.
It is, however, pertinent to mention here that as to date it is not possible to ascertain the precise
requirement of various elements
viz. C, N, S and O, by virtue of the fact that most bacteria predominantly
differ with regard to the actual chemical form wherein these elements are invariably consumed as
nutrients.
Cultivation (Growth) of Bacteria
The
cultivation (growth) of bacteria may be defined, as — ‘a systematic progressive increase
in the cellular components’
. Nevertheless, an appreciable enhancement in ‘mass’ exclusively may not
always reflect the element of growth because bacteria at certain specific instances may accumulate
enough mass without a corresponding increment in the actual
cell number. In the latest scenario the
terms
‘balanced growth’ has been introduced which essentially draws a line between the so called‘orderly growth’ and the ‘disorderly growth’.
Campbell defined
‘balanced growth’ as — ‘the two-fold increase of each biochemical unit of
the cells very much within the prevailing time period by a single division without having a
slightest change in the rate of growth’
. However, one may accomplish theoretically cultures with a
‘balanced growth’
having a more or less stable and constant chemical composition, but it is rather next
to impossible to achieve this.
Following are some of the cardinal aspects of
cultivation of bacteria, such as :
Binary Fission
It has been established beyond any reasonable doubt that the most abundantly available means of
bacterial cultivation (reproduction) is
binary fission, that is, one specific cell undergoes division to
give rise to the formation of
two cells.
Now, if one may start the process with a
single bacterium, the corresponding enhancement in
population is given by the following
geometric progression :
1 —
→ 2 —→ 22 —→ 23 —→ 2′ —→ 25 —→ 26 —→ 2n
where,
n = Number of generations.
Assuming that there is
no cell death at all, each succeding generation shall give rise to double its
population
. Thus, the total population ‘N’ at the end of a specific given time period may be expressed
as follows :
N = 1 × 2
n ...(a)
Furthermore, under normal experimental parameters, the actual number of organisms N
0 inoculated
at time
‘zero’ is not ‘1’ but most probably may range between several thousands. In such a situation,
the aforesaid ‘formula’ may now be given as follows :
N = N
0 × 2n ...(b)
Now, solving Eqn. (
b) for the value of ‘n’, we may have :
log
10 N = log10 N0 + n log10 2
or
n =
10 10 0
10
log N log N
log 2
−
...(
c)
Substituting the value of log
10 2 (i.e., 0.301) in Eqn. (c) above, we may ultimately simplify the
equation to :
n
= log10 N log10 N0
0.301
−
or
n = 3.3 (log10 N – log10 N0) ...(d)
Application of Eqn. (
d), one may calculate quite easily and conveniently the actual ‘number of
generations’
which have virtually occurred, based on the precise data with respect to the following
(