Microbiology Essentials: Bacteria, Protozoa, Algae, and Fungi

Bacteria

Bacteria possess a capsule composed of glucidic substances (uronic acid) or D-glutamine. This structure protects against leukocyte phagocytosis, regulates substance exchange, and facilitates adhesion to specific host tissues.

Cell Wall

The cell wall is composed of peptidoglycan (murein), specifically N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAGA) linked by B(1-4) bonds. It protects against osmotic pressure, lysozyme, and penicillin antibiotics.

• Gram-positive: Thick, lipid-rich wall containing 90% peptidoglycan and teichoic acid.
• Gram-negative: Thin-walled, complex structure with 10% peptidoglycan and an outer membrane containing lipoproteins.

Plasma Membrane and Mesosomes

The plasma membrane limits and shapes the cell while regulating substance exchange. Mesosomes contain enzymes and are involved in DNA duplication, respiration, growth regulation, photosynthesis, and nitrogen assimilation.

Internal Structures

• Hyaloplasm: A colloidal structure occupying half the internal volume.
• Ribosomes: Composed of proteins and rRNA; they synthesize proteins and are 70S (50S + 30S) in size.
• Bacterial DNA: A circular, double-helix molecule located in the nucleoid, linked to mesosomes. It lacks histone proteins and contains the genetic information for bacterial operation.
• Inclusions: Reserve granules.
• Flagella: Provide mobility and are classified as monotrichous, lophotrichous, amphitrichous, or peritrichous. They are composed of flagellin.
• Fimbriae (Pili): Shorter and thinner than flagella; they facilitate attachment, molecular exchange, and genetic material transfer.

Protozoa

Protozoa are unicellular, heterotrophic, eukaryotic organisms. They reproduce via asexual methods (budding, bipartition, sporulation) or sexual methods (fusion of nuclei). They inhabit water-rich environments, live in symbiosis, or act as parasites. They move using cilia, flagella, or pseudopods.

Algae

Algae are eukaryotic, photosynthetic organisms with a cell wall and chloroplasts. They primarily inhabit aquatic environments. Reproduction is varied, including asexual cell division and sexual reproduction. They are essential components of marine phytoplankton.

Fungi

Molds

Molds are small, filamentous structures (hyphae) that are heterotrophic, symbiotic, parasitic, or saprophytic. Reproduction occurs via asexual spores or sexual methods like somatogamy and conjugation.

Yeasts

Yeasts are unicellular. They reproduce asexually via budding and sexually through the fusion of two haploid cells of opposite signs to form a zygote, which then multiplies by mitosis.