CHAPTER 1

• Microbiology is the study of organisms and agents too small to be seen by the naked eye (<1mm)
• A typical bacterium is 0.002 mm or 2 µm and weighs 10−12 g
• Viruses are even smaller, ranging from 0.02 µm to 0.4 µm
• The new definition of Microbiology includes organisms that can exist as single cells, contain a nucleic acid genome, and are capable of replicating that genome
• Microbiology includes microorganisms like Epulopiscium and Thiomargarita, as well as viruses
• Bacteria can be classified based on their shape as cocci (spherical), bacilli (rod-shaped), spirilla (spiral-shaped), or vibrio (comma-shaped).
• Gram-positive bacteria have thick peptidoglycan cell walls, while gram-negative bacteria have thin peptidoglycan cell walls with an outer membrane containing lipopolysaccharides (LPS).
• The most common method used to identify bacteria is the Gram stain.
• Mycoplasmas lack a cell wall altogether.
• Archaea are prokaryotes found in extreme environments such as hot springs, salt lakes, and deep sea hydrothermal vents.
• Capsules are polysaccharide layers surrounding bacterial cells that protect them against phagocytosis by host immune system cells.
• Cocci bacteria include Staphylococcus, Streptococcus, Enterococcus, Listeria monocytogenes, Clostridioides difficile, Bacillus anthracis, Mycobacterium tuberculosis, Corynebacterium diphtheriae, Propionibacterium acnes, and Neisseria meningitidis.
• Archaea differ from bacteria in terms of ribosomal RNA sequences and the presence of ether linkages between fatty acids instead of ester bonds.
• Flagella are long filaments attached to the surface of some bacteria that allow them to move through liquid environments.
• Viruses are not considered living organisms because they cannot reproduce without a host cell.
• Pili are short hairlike structures found on many bacteria that facilitate attachment to surfaces and transfer genetic material between cells.
• Microorganisms are Earth’s life support system, influencing nearly every moment of our lives
• Microbes are in our water, food, and even on and in us
• Microbiology allows us to explore the invisible microbial world, evolving at a breathtaking pace
• Fluorescence microscopy uses lasers to map the three-dimensional structure of cells, like the image showing human cells infected with Listeria monocytogenes
• Listeria, a foodborne bacterial pathogen, can hijack cellular systems, causing actin to polymerize and propel the cell within the host cytoplasm, aiding its spread and survival
• Research on Listeria provides insights into the biology of this pathogen and the ever-changing microbial world
• Microbiology was born of the microscope, and microscopy is foundational to microbiology
• Microbiologists have developed methods for visualizing microorganisms, essential to microbiology
• A microbial culture is a collection of cells grown in or on a nutrient medium, aiding in the study of microbial basis of disease and biochemical diversity
• All cells have a permeability barrier called the cytoplasmic membrane, ribosomes for protein synthesis, and some have a cell wall for structural strength
• There are two fundamental cell types: prokaryotic cells found in Bacteria and Archaea, and eukaryotic cells found in the Eukarya group, which includes plants, animals, and diverse microbial eukaryotes
• Prokaryotic cells and eukaryotic cells both possess a DNA genome, which is the full set of genes in a cell
• A gene is a segment of DNA that encodes a protein or an RNA molecule
• In eukaryotic cells, DNA is present as several linear molecules within the membrane-enclosed nucleus, while the genomes of Bacteria and Archaea are typically closed circular chromosomes that form the nucleoid, a mass visible in the electron microscope but not enclosed by a membrane
• Most prokaryotic cells have only a single chromosome, but many also contain one or more small circles of DNA distinct from that of the chromosome, called plasmids
• Plasmids typically contain genes that are not essential but often confer some special property on the cell, such as unique metabolism or antibiotic resistance
• The genomes of Bacteria and Archaea typically contain between 500 and 10,000 genes encoded by 0.5 to 10 million base pairs of DNA, while eukaryotic cells typically have larger and less streamlined genomes
• Cell size is influenced fundamentally by cell structure:

  • Eukaryotic cells can actively transport molecules and macromolecules within the cytoplasm due to their complex intracellular structure and organelles
  • Prokaryotic cells rely on diffusion for transport through the cytoplasm, limiting their size
• Diffusion is fast at small distances, but the rate of diffusion increases as the square of the distance traveled, affecting cell size
• Chance mutations in DNA cause new cells to have new properties, promoting evolution
• Phylogenetic trees built from DNA sequences capture evolutionary relationships between species
• Some cells can form new cell structures such as a spore
• Cells interact with each other by chemical messengers for communication
• Information from DNA is converted into proteins, which do work and convert nutrients from the environment into new cells for growth