Question

Write an essay on structure & nutrition of bacteria ?

Answer 1

Structure of Bacterium cell :

Structure of bacterium cell is simple & primitive. They are different & undeveloped structures than plant cells. Following structures are found under electron mocroscope-

(a) Cell wall & capsule – Every bacterium is bounded by a cell wall which is similar to the exoskeleton of insects, In most of the bacteria, a jelly like extra layer is found outside the cell wall which is called as slime layer. In some bacteria, it is very thick & called as capsule. The slime layer consists of carbohydrates, amino acids & gum. The cell wall of bacteria is made up of peptidoglycane like muramic acid and diaminopimelic acid.

(b) Cytoplasm – It is bounded by a cell membrane. The cytoplasm is homogenous which contain fat gobules & glycogen particles. It is without definite nucleus but nuclear suvstance (DNA) is suspended in the cytoplasm. Such nucleus is called as incipient nucleus. The cytoplasm bears gas vacuoles & ribosomes but membrane bounded orgenelles such as plastids, mitochondria etc are absent.

Some species of bacteria bear a special chlorophyll called bacteria-chlorophyll, hence they perform photosynthesis. The inpushing of the cell membrance are called as Mesosomes which contain respiratory enzymes.

(C) Flagella – Bacteria may be flagellated or non-flagellated. The flagellated bacteria are motile. The number & position of flagella in motile bacteria is variable and on this basis, the motile bacteria are of five types viz-

1. Atrichous: They are without flagella.
   Example – Micrococcus
2. Monotrichous: One flagellum at one end.
   Example – Vibrio
3. Lophotrichous – More than one flagella at one end.
   Example – Thiospiriluim
4. Amphitrichous – One or more flagella at both the ends.
   Example – Nitrosomonas, spiriluim etc
5. Peritrichous – Flagella on all over the sides of bac-teria.

Example – Bacillus typhus nutrition:

On the basis of nutrition bacteria are of two types-

1. Autotrophic bacteria – A few species of bacteria are autotrophs. Some are chemosynthetie and some are photosynthetic like plants.

(a) Photosynthetic bacteria – Some species have bacte- ribchlorophyll or chlorobium chlorophyll pigments which are a compound of magnesium and are found in chromotophores not in plastids. They do not synthesize carbohydrates using CO₂ & H₂O like plants but they perform photosynthesis using  CO₂ + H₂S & product is sulphur instead to  O₂
CO₂ + 2H₂S -----> (CH₂O)_n+ 2S + H₂O

Examples: Chromatum, Chlorobuim, chlorobacterium etc.

(b) Chemosynthetie bacteria – Some bacteria convert CO₂ into carbohydrates using various types of chemical re-actions. They are without chlorophyll, hence sun light is not required. They perform oxidation of some sub-stances to get energy such as Sulphur & its compound, Ammonia, Nitrates, Iron, Hydrogen, CO, Methane etc. Such as Sulphur bacteria, Iron bacteria etc.

(i) Sulphur bacteria – The obtain energy by oxida¬tion of sulphur & its compounds.

Examples: Beggiatoa, Thiothrix, Thobacillus etc.
2H₂S +O₂ → 2S + H₂O + 122.2 kcal
2S + 2H₂O+ 3O₂ → 2H₂SO₄+ 284.4 kcal

(ii) Iron bacteria – They obtain energy by oxidizing ferrous compounds into ferric compounds.

Examples: Gallionella, Leptothrix, Fembacillus etc.
4 FeCO₃ + O₂ + 6 H₂O→ 4 FeCOH₃ + 4 CO₂

(iii) Hydrogen bacteria – They convert molecular hydrogen into water to get energy.

Example: Bacillus pentatrofera
2H₂ + O₂ → 2H₂ O + 137 kcal energy
2H₂+ CO₂  → 115 kcal → C₆ H₁₂ O₆ + H₂O

(iv) Nitrifying bacteria – They obtain energy from nitrogen compounds such as-

1. Oxidizing ammonia into nitrates
   Example: Nitrosomonas, Nitrosococcus etc.
   2NH₃ + 3O → 2HNO₂ + 2H₂O + 158 kcal.
2. Coverting nitrites into nitrates
   Example: Nitrobacter, Bactoderma etc.
   2 HNO₂ + O₂ → 2HNO₃ + 38 kcal energy.

(v) Carbon bacteria – Some bacteria obtain energy by oxidizing carbon-mono-oxide.

Example – Oligacarbophil etc.
2CO + O₂ → 2CO₂ + energy.

(vi) Methane bacteria – They obtain energy by oxidizing methane.

Example – Methanomonas etc.
CH₄ + 2O → CO₂ + 2H₂O + energy.

2. Heterotrophic bacteria-

Most of the bacteria are parasitic. They absorb complex organic compounds by making them soluble with the help of enzymes. They are of three types-

(a) Saprophytes – They lead their life on dead complex organic compounds.

Example – Bacillus

(b) Symbionts – They establish permanant relationship with other plants or animals and are mutually benefited.

Example – Rhizobuim bacteria in the nodules of roots of legume plants.

(c) Parasites – They are pathogens and live inside / outside the body of host plant / animal.

Example – Corynibacterium, Xanthomonas.