Environmental Microbiology of Aquatic and Waste Systems

4.1 Taxonomy of Microorganisms in Aquatic Environments 51

Table 4.3 Some properties used for bacterial classification and
identification

S. No. Property

1. Nutritional type
   (i) Autotrophy
   (ii) Heterotrophy


2. Energy release
   (i) Lithotrophy
   (ii) Organotrophy


3. Cell wall: Gram reaction
   (i) Gram negative
   (ii) Gram positive


4. Cell morphology
   (i) Cell shapes
   (ii) Cell aggregation
   (iii) Flagellation – motility
   (iv) Spore formation and location
   (v) Special staining, e.g., Ziehl–Nielsen


5. Physiological properties
   (i) Utilization of various sugars
   (ii) Utilization of various polysaccharides
   (iii) Utilization of various nitrogenous
   substrates
   (iv) Oxygen requirement
   (v) Temperature requirements
   (vi) pH requirement
   (vii) Production of special enzymes, e.g.,
   catalase, coagulase, optochin, oxidase


6. Antigenic properties


7. Molecular (nucleic acid) methods
   (i) G + C composition
   (ii) DNA:DNA hybridization
   (iii) Ribotyping
   (iv) Fluorescent in­situ hybridization (FISH)


8. Chemical analysis (Chemotaxonomy)
   (i) Lipid analysis
   (ii) Protein analysis

(b) Source of reducing equivalent

During the generation of energy in the cell,

electrons are transferred from one compound to

another. An organism is said to be organ­

otrophic when it uses organic compounds as a

source of electrons. When the source of elec­

trons is inorganic, it is said to be lithotrophic.

(c) Source of energy

Some organisms derive energy for the genera­

tion of ATP used for the biosynthesis of new

compounds and other cellular activities from

sunlight; such organisms are phototrophic.

When the generation of ATP occurs through

energy obtained from chemical reactions, the

organism is said to be chemotrophic.

The carbon source utilized, the source of

reducing equivalent, and the source of energy

determine the nutritional type of bacteria, and a

wide variety of combinations of these three is

possible. Table 4.4 gives a selection of the

possible permutations.

2. Cell wall: Gram reaction
   The Gram stain was devised by the German doctor,
   Christian Gram in 1884 and divides bacteria into
   two groups: Gram positive and Gram negative. On
   account of the greater thickness of peptidoglycan in
   the Gram positive wall (see Fig. 4.2), the iodine­
   crystal violet stain in the Gram stain is retained when
   decolorized with dilute acid, whereas it is removed
   in the Gram negative cell wall. The Gram stain also
   divides all bacteria into two groups regarding their
   susceptibility to the classical antibiotic penicillin:
   Gram­positive bacteria, being susceptible, while
   Gram negative bacteria are not (Fig. 4. 3 ).


3. Cell morphology
   (a) Individual cell shapes
   Cell shapes in bacteria are limited and are
   spheres (coccus– cocci, plural), rods, spiral, or
   comma or vibrio (see Fig. 4.4).

Table 4.4 Nutritional types of living things

S/No Nutritional type Energy source Carbon source Reducing equivalent Example
1 Photoautotrophs Light CO 2 Organotrophic Plants, Cyanobacteria
2 Photoautotrophs Light CO 2 Lithotrophic Sulfur bacteria e.g.,
H 2 S → S Beggitoa sp.
3 Chemoautotrophs Chemotrophic CO 2 Oxidation of sulfur Thiobacillus oxidans
4 Photoheterotrophs Light Organic compounds Organotrophic Purple non­sulfur bacteria
5 Chemoheterotrophs Chemotrophic Organic compounds Organotrophic Animals, fungi, protozoa,
most bacteria