Some Fundamentals of MICROBIOLOGY

Basic to the design of a biological treatment process or to the selection of the type of process to be used is an understanding of the form,structure, and biochemical activities of the important microorganisms (m.o.).

We will discuss the cytology and physiology of the m.o. commonly encountered in wastewater treatment.

BASIC CONCEPTS

In the past, m.o. were commonly grouped into 2 kingdoms: plants and animals.

Because of taxonomic difficulties, recent trend is to

group them into 3 kingdoms: protista, plants, and animals. Summary data on the characteristics of the mo in each kingdom are presented in Table 1.

Table 1. The 3 kingdoms of microorganisms

Kingdom Representative membersCharacterization AnimalRotifersCrustaceans Multicellular, with tissue differentiationPlantMossesFernsSeed plantsProtista:HigheraAlgaeProtozoaFungiSlime moldsUnicellular or multicellular, without tissue differentiationLowerb Blue-green algaeBacteria a Contain true nucleus (eucaryotic cells) b Contain no nuclear membrane (procaryotic cells)

Although the most significant differences among them are shown in the table, the 3 kingdoms are similar in that the cell is the basic unit of life for each, regardless of the complexity of the organism.

CELL STRUCTURE

In general, most living cells are quite similar. As shown in Figure 1, they have a cell wall, which may be either a rigid or a flexible membrane. If they are motile, they usually possess flagella or some hairlike appendages. The interior of the cell contains a colloidal suspension of proteins, carbohydrates and other complex organic compounds, called the cytoplasm. Each cell contains nucleic acid, the hereditary material that is vital to reproduction.

The cytoplasmic area contains ribonucleic acid (RNA), whose major role is in the synthesis of proteins. Also within the cell wall is the area of the nucleus, which is rich in deoxyribonucleic acid (DNA). DNA contains all the information necessary for the reproduction of all the cell components and may be considered to be the blueprint of the cell.

In some cells, the DNA is enclosed by a membrane and the nucleus is clearly defined (eucaryotic cells). In other cells, the nucleus is poorly defined (procaryotic cells). As shown in Table 1, bacteria and blue-green algae are examples of procaryotic cells.

Figure 1. Generalized schematic of bacterial cell

Energy and carbon sourcesTo continue to produce and function properly, an organism must have a source of energy and carbon for the synthesis of new cellular material.

Inorganic elements, such as nitrogen and phosphorous, and other trace elements, such as S, K, Ca, and Mg, are also vital to cell synthesis.

Two of the most common sources of cell carbon for m.o. are carbon dioxide and organic matter.

Autotrophic if an organism derives its cell carbon from carbon dioxide.

Heterotrophic if it uses organic carbon.

Energy is also needed in the synthesis of new cellular material. For autotrophic organisms, the energy can be supplied by the sun, as in photosynthesis, or by an inorganic oxidation-reduction reaction.

if the energy is supplied by the sun, the organism is called autotrophic photosynthetic.

If the energy is supplied by an inorganic oxidation-reduction reaction, it is called autotrophic chemosynthetic.

For heterotrophic organisms, the energy needed for cell synthesis is supplied by the oxidation or fermentation of organic matter. A classification of m.o. by sources of energy and cell carbon is presented in Table 2.

Table 2. General classification of m.o. by sources of energy and carbon

Classification Energy sourceCarbon sourceAutotrophic:Photosynthetic Light CO2Chemosynthetic Inorganic oxidation-reduction reactionCO2Heterotrophic:Organic oxidation-reduction reactionOrganic carbon

Aerobic and anaerobic metabolismOrganisms can also be classed according to their ability to use oxygen.Aerobic organisms can exist only when there is a supply of molecular oxygen.Anaerobic organisms can exist only in an environment that is devoid of oxygen.Facultative organisms have the ability to survive with or without oxygen.