GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

6. MICROBIAL GROWTH

6.3. MICROBIAL NUTRITION

6.3.1. Major and minor bioelements

Only a small number of elements from the periodic table are required by microorganisms in relatively high concentrations (≥10⁴ M). These are the ten major biological elements listed in Table 6.2.

Class="center">Table 6.2

Ten major bioelements, their sources, and some Functions

In addition to the ten major bioelements, microorganisms require minor bioelements (Table 6.3). Tables 6.2 and 6.3 show the sources of these elements as well as their metabolic functions.

Growth media used to cultivate microorganisms must meet the following minimum requirements: they must contain all the elements required for cell construction, and in a form that microorganisms can readily assimilate.

In nature, most biological elements occur as salts, and microorganisms take them up as cations and anions. A great diversity of compounds utilized by microorganisms is observed only for the first five elements (sulfur, nitrogen, oxygen, hydrogen, carbon).

Thus, sulfur is generally taken up as sulfates, reduced to sulfide, and then utilized in biosynthetic processes. However, certain groups of Bacteria require reduced sulfur compounds. For instance, some methanogenic bacteria grow only in the presence of hydrogen sulfide. Thiobacilli and some phototrophic bacteria use sulfides, elemental sulfur, or thiosulfate as electron Donors.

Nitrogen is required in large quantities, as it constitutes about 10% of cellular dry weight. In nature, nitrogen occurs as ammonia, nitrate, nitrite, nitrogen-containing organic compounds, and molecular nitrogen. The preferred nitrogen source for microorganisms is ammonia, which can be utilized by virtually all organisms. Nitrate is first reduced to ammonia and only then used in biosynthetic processes.

Table 6.3

Minor bioelements, their sources, and cellular functions

Nitrite is a product of nitrate-nitrite Respiration and the METABOLIC ACTIVITY OF Nitrosomonas and closely related genera. Furthermore, nitrite can be oxidized to nitrate by Nitrobacter bacteria. A number of bacteria are capable of fixing molecular nitrogen and reducing it to ammonia. This ability is found exclusively in prokaryotes. Finally, many microorganisms use Organic compounds as a nitrogen source.

Carbon, hydrogen, and oxygen can be utilized by Microorganisms in the form of both organic and Inorganic Compounds (СО₂, Н_2, Н₂S, NН₂, О₂, NO₂, SО₄²). It should be noted that none of the organic compounds produced by The activity of various organisms accumulate indefinitely on Earth. Microorganisms play a crucial role in their decomposition. The vast diversity of microbial metabolic processes led to the formulation of the so-called "doctrine of microbial infallibility," which states that virtually any naturally occurring carbon compound can be utilized by some microorganism.

The METABOLISM of compounds containing carbon, hydrogen, or oxygen is of great importance not only because these elements are essential cell components, but also because these compounds serve as substrates for energy generation in microorganisms.