Kingdom Prokaryotae

The kingdom Prokaryotae consists solely of bacteria and it is so named because bacteria, and only bacteria, have prokaryotic cells. They are organisms with very small cells and have no true nucleus. Their DNA is found in the nuclear region.

Bacteria are unicells, but occur together in vast numbers, either as entirely separate cells or clumped together in groups. They are ubiquitous and are biochemically very active and fast-growing.

Morphology

Bacteria cells are extremely small their characterisation shapes are often the most important visible clue to their identification.

Cell size: 0.1 - 2 µm (width) ; 1 - 5 µm (length) It's definitely way out smaller than your body cells.

Shape: There are 4 major shapes; spherical bacteria (coccus forms), rods (bacillus forms), various forms of spiral or curved rods, and filamentous bacteria.

Arrangement: may occur in singles, pairs, clusters, chains, etc.

Bacteria may contain other features like :

• Flagellum for movement
• Fimbriae for adhesion
• Pili for genetic transfer/conjugation
• Capsule to prevent desiccation
• endospore with heat-resistant properties for survival

The Gram Stain

The Gram stain is the most important microbiological stain. The Gram stain is one of the first steps in identifying prokaryotic cells. The staining technique distinguishes two types of bacteria, know today as Gram-positive (appears purple) and Gram-negative (appear red). The different staining properties of these two groups of bacteria are due to differences in the chemical composition of their walls.

Gram-positive bacteria have hardly any lipid along with the murein of the cell wall. These are bacteria which may form endospores. The Gram-positive bacteria include Bacillus, Clostridium, Staphylococcus and Streptococcus species. Gram-negative bacteria, on the other hand, have substantial amounts of lipid in their wall. They are not adversely affected by the antibacterial enzyme lysozyme, and are resistant to the antibiotic penicillin. Gram-negative bacteria include those of the Salmonella, Escherichia and Azotobacter.