Eubacteria: True Bacteria Characteristics

• The universal phylogenetic tree of life is constructed from the small subunit of rRNA gene sequence analysis.

Eubacteria

• Eubacteria are "true bacteria," relatively simple in structure.
• They are prokaryotic unicellular organisms.
• Eubacteria lack a nuclear membrane, mitochondria, Golgi bodies, and endoplasmic reticulum.
• They reproduce by asexual division.
• They are omnipresent, found in soil, air, and water.
• Eubacteria are unicellular prokaryotic microorganisms.
• The cell has a thick, rigid cell wall made of peptidoglycan outside the plasma membrane.
• They show great variation in nutrition, being autotrophic or heterotrophic (parasitic, saprophytic, or symbiotic).
• They lack true chlorophyll, but some photosynthetic types have bacteriochlorophyll.
• These bacteria lack a true nucleus (no nuclear membrane or nucleolus).
• They also lack mitochondria, Golgi apparatus, plastids, and endoplasmic reticulum.
• Both DNA and RNA are present in the bacterial cell.

Bacterial Cell Structure

• Bacterial cells are minute and studied with electron microscopes.
• Structures are either external or internal to the cell wall, with readily evident structures described as such:
• External structures include appendages like flagella and pili (fimbriae), and the glycocalyx (capsule or slime layer).
• A cell envelope has a cell wall and cell membrane
• Internal components include the cytoplasmic matrix, ribosomes, inclusions, nucleoid (chromosome), actin cytoskeleton, and endospore.

Bacterial Shapes

• Bacteria are classified based on cell shape, multi-cell aggregates, motility, spore formation, and reaction to Gram stain.
• The three main shapes are cocci (spherical), bacilli (rod-shaped), and spirochaetes (spiral or corkscrew-shaped).
• Vibrio cholera is comma-shaped.

Gram Staining

• Bacteria are classified by cell wall composition and ability to retain dyes during Gram's stain.
• Gram-positive bacteria have a purple appearance after Gram staining because they retain the crystal violet stain in the thick peptidoglycan layer.
• Staphylococcus, streptococcus, and some Listeria species are examples.
• Gram-negative bacteria lose the crystal violet stain and appear red due to the counterstain.
• The cell wall has a thin peptidoglycan layer.
• Gram's staining is used to distinguish bacteria named after Hans Christian Gram.

Nutritional Types of Bacteria

• Bacteria use mechanisms to get energy and nutrients for growth.
• Autotrophs get carbon from inorganic CO2:
  • Photoautotrophs use sunlight
  • Chemoautotrophs harvest energy from inorganic chemicals.
• Heterotrophs obtain carbon from organic molecules:
  • Photoheterotrophs get energy from sunlight
  • Chemoheterotrophs harvest energy from organic molecules.
• The sources of energy include light and oxidizing organic or inorganic molecules.
• Phototrophs use light as their energy source
• Chemotrophs get energy from chemical compound oxidation.
• Lithotrophs use reduced inorganic substances as electron source
• Organotrophs extract electrons from reduced organic compounds.
• Bacteria are classified into five nutritional classes based on primary sources of carbon, energy, and electrons: photolithoautotrophic or chemoorganoheterotrophic.
• Photolithoautotrophs use light energy.
• Photoorganoheterotrophs are common in polluted lakes and streams and can grow as photolithoautotrophs with molecular hydrogen.
• Chemolithoautotrophs oxidize reduced inorganic compounds.
• Chemolithoheterotrophs use reduced inorganic molecules for energy and organic sources for carbon.
• Chemoorganoheterotrophs use organic compounds for energy, hydrogen, electrons, and carbon, and most pathogenic microorganisms are of this type.

Reproduction of Bacteria

• Bacteria usually reproduce asexually through binary fission after growth and mass doubling.
• Asexual reproduction in bacteria can also be achived via conjugation
• During conjugation, two cells of different mating types come together, and genetic material is transferred from one to the other
• E. Coli is an example of bacterial reproductive techniques
• The population includes donor (F+) and recipient (F-) cells.
• F+ cells contain DNA transferable to F- cells.
• The F factor (fertility) is necessary for donation during conjugation, existing as a plasmid or part of the bacterial chromosome.
• Certain F genes encode sex pili, crucial for surface projection and binding to F- cells to establish a conjugation bridge.
• The F plasmid replicates, transferring DNA from donor to recipient via the bridge.
• F plasmids can carry genes for antibiotic resistance.