Questions and Answers
Which organelle is typically lacking in plant pathogenic bacteria?
Mitochondria
Which type of bacteria may be mistakenly referred to as ray fungi due to their filamentous structure?
Streptomyces
What is the typical shape of Streptomyces bacteria?
Filamentous branched
Which type of bacterial motility structure helps in bacterial movement?
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What is the characteristic feature of mycoplasma bacteria?
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Which staining method is commonly used for the classification of bacteria based on their cell wall composition?
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What is one characteristic that differentiates gram positive bacteria from gram negative bacteria based on the text?
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Which type of bacteria retains the crystal violet stain in the Gram staining process?
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What is a distinguishing feature of the cell wall structure of gram negative bacteria?
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Which of the following statements is true about gram positive bacteria according to the text?
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What is the role of safranin in the Gram staining process?
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Which factor contributes to the ability of bacteria to retain crystal violet stain or not?
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What is the primary function of the slime layer in plant pathogenic bacteria?
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Which of the following statements about flagella in plant pathogenic bacteria is correct?
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What is the primary purpose of Gram staining in bacterial classification?
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Which of the following is NOT a component of the slime layer in plant pathogenic bacteria?
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What is the term used to describe bacteria that lack flagella?
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Which of the following steps is NOT part of the Gram staining procedure?
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Study Notes
Bacteria Characteristics
- Bacteria are the second most important organisms that cause plant diseases.
- They are prokaryotic, single-celled, and mostly achlorophyllous organisms with a cell wall and no membrane-bound organelles.
- Most bacterial species are saprophytes, living on dead organic matter.
- There are about 200 bacterial species that are plant pathogenic.
Morphology
- Bacteria can be rod-shaped (bacilli), spherical (cocci), spiral (spirilli), coma-shaped (vibrios), or thread-like (filamentous).
- Streptomyces has a filamentous, branched hypha-like structure, while Mycoplasma has no definite shape due to the lack of a cell wall.
Size and Appearance
- Rod-shaped bacteria range from 0.6 to 3.5 µm in length and from 0.5 to 1 µm in diameter.
- Single bacteria appear as hyaline or yellowish white under a compound microscope.
- Colonies of most bacteria have a whitish or greyish appearance, but some develop yellow, red, or other colors.
Gram Staining
- Gram-positive bacteria retain the crystal violet stain after rinsing, while Gram-negative bacteria do not.
- Gram-positive bacteria have a thicker, homogeneous cell wall, lower lipid content, and teichoic acid present.
- Gram-negative bacteria have a thinner, usually three-layered cell wall, higher lipid content, and no teichoic acid.
Cell Structure
- A bacterium has a thin, rigid cell wall, a distinct three-layered cytoplasmic membrane, and a slime layer made up of viscous gummy material.
- The slime layer has bacterial immunological properties and is mostly composed of polysaccharides.
Flagella
- Most plant pathogenic bacteria have delicate, thread-like flagella that are usually longer than the cell.
- The arrangement of flagella on the bacterial cell is an important taxonomic character for bacterial classification.
- Flagella can be arranged in different ways, such as Monotrichous, Lophotrichous, Amphitrichous, Peritrichous, or Atrichous.
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