Bacterial Endospores, Shape and Size

Bacterial Endospore

• Endospores are dormant bodies produced by bacterial genera like Bacillus and Clostridium.
• These bacteria have a two-phase life cycle, alternating between a vegetative cell and an endospore.
• The cells form an endospore, through a process called sporulation, when exposed to certain environmental signals.
• The vegetative cell is the metabolically active and growing phase.
• Spores in a resting stage can withstand extreme conditions and survive long-term.
• Spore resistance results from low water content.
• Spore resistance results from low spore wall permeability.
• Spore resistance results from low metabolic activity, as the spore is dormant.
• Spore resistance results from a high content of calcium and dipicolinic acid.

Bacterial Shape, Arrangement and Sizes

• Most bacteria are monomorphic, maintaining a single shape determined by heredity.
• Some bacteria, like Corynebacterium spp., are genetically pleomorphic, meaning their shapes can vary.
• Bacteria have one of three general shapes depending on the configuration of the cell wall.
• Spherical or ball-shaped bacteria are called coccus.
• Cocci can be perfect spheres but may also be oval, bean-shaped, or pointed.
• Cylindrical cells (longer than wide) is termed a rod, or bacillus.
• Short and plump rods are called coccobacillus.
• Spiral-shaped cells are referred to as either a vibrio, spirillum, or spirochete.
• A vibrio is gently curved or comma-shaped.
• A spirillum is a rigid helix, twisted twice or more along its axis.
• A spirochete is a more flexible helix resembling a spring.

Bacterial Sizes

• Bacteria range from 0.2-2 µm in diameter and 2-8 µm in length.

Bacterial Arrangement

• Cocci exhibit distinct arrangements based on their planes of division.
• Division in one plane produces diplococcus or streptococcus.
• Diplococci are cocci arranged in pairs.
• Streptococci are cocci arranged in chains.
• Division in two planes results in a tetrad arrangement (cocci arranged in squares of 4).
• Division in three planes produces a sarcina arrangement (cocci in cubes of 8-64 cells).
• Division in several planes creates a staphylococcus arrangement (cocci in irregular, grape-like clusters).
• Bacilli divide in one plane, forming diplobacillus, streptobacillus, or palisades.
• Diplobacilli are bacilli arranged in pairs.
• Streptobacilli are bacilli arranged in chains.
• Palisades are bacilli arranged like a fence of stakes.

Nutrition of Bacteria

• Bacteria are composed of 70-80% water and 20-30% dry weight.
• Macromolecules, like proteins, carbohydrates, lipids, DNA, and RNA, make up 96% of the dry weight.
• Monomers, with 3-3.5%, comprises amino acids, sugars, and nucleotides.
• Inorganic ions ~1% of the dry weight.
• Microbial nutrition is how microbes take in chemical compounds from the environment for life, which are known as nutrients.
• An essential nutrient is a substance, element, or compound organisms must get from outside their cells.
• Macronutrients are used in relatively large quantities as components of carbohydrates, lipid, protein, and nucleic acid synthesis, aiding in cell structure and metabolism.
• Macronutrients include carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, sulfur, calcium, iron, sodium, chlorine, and magnesium, represented as C HOPKIN'S Ca Fe, Na Cl Mg.
• Micronutrients (trace elements) are required in very small amounts to maintain protein structure and enzyme function, including zinc, copper, molybdenum, manganese, cobalt, nickel, and selenium ions (Zn, Cu, Mo, Mn, Co, Ni, Se).
• Growth factors are organic compounds a cell needs for growth but cannot synthesize, such as amino acids, purines, pyrimidines, and vitamins.
• Carbon sources are CO2 from sediments/soils for bacterial cells and organic compounds from living things.
• Nitrogen as N₂ gas is from the air and also from soil and water, for bacterial cell usage.
• Oxygen gas (O₂) is in the air and comes from photosynthesis bacterial cells.
• Hydrogen is in water (H₂O) and in organic compounds from the vents that bacterial cells need.
• Posphorus is in rocks and mineral deposits with soil for bacterial cells as phosphates.
• Sulfur is in soil as SO4-, SH and in mineral deposits for bacterial cells to live.
• Essential element for the structure of respiratory proteins is iron for bacteria.
• Cl- is a micronutrient that aids membrane transport

Growth Factors

• Organic compounds (not elements).
• Required in small amounts by cells to fulfill specific roles in biosynthesis.
• Absence prevents the growth of microorganisms.
• Growth factors include amino acids, purines/pyrimidines, and vitamins.
• Organisms with complex nutritional requirements that need many growth factors are fastidious.
• Neisseria gonorrhoeae which requires blood or hemoglobin and several amino acids and vitamins to grow is an example of a fastidious organism.
• E. coli does not need additional growth factors in its culture medium because it can synthesize all essential growth factors (they are non-fastidious).
• Auxotrophs are mutant strains of bacteria requiring a growth factor not needed by the parent strain.
• A strain of E. coli requiring tryptophan is a tryptophan auxotroph.

Nutritional and Metabolic Patterns

• Metabolic patterns are categorized based on how an organism obtains energy, reducing power, and carbon.
• Chemotrophs obtain energy from chemical compounds.
• Phototrophs obtain energy from light.
• Lithotrophs obtain reducing equivalents from inorganic compounds.
• Organotrophs obtain reducing equivalents from organic compounds.
• Autotrophs obtain carbon from carbon dioxide (CO2) and can synthesize organic molecules from inorganic nutrients.
• Heterotrophs obtain carbon from organic compounds and cannot synthesize organic molecules from inorganic nutrients.

Factors Affecting Microbial Growth

• The process of microbial growth depends on the source of energy.
• Also, the process depends on the carbon and electron source.
• The process also depends on the physical (environmental) and nutritional requirements.
• Physical requirements include air (molecular oxygen).
• Physical requirements include pH.
• Physical requirements include temperature.
• Physical requirements include water.
• Physical requirements include miscellaneous factors.

Effect of Oxygen

• A common method to test an organism's oxygen sensitivity is to use a thioglycolate broth.
• The broth has a low percentage of agar to allow motile bacteria to move throughout the medium.
• Thioglycolate has strong reducing properties, binding free oxygen.
• Fresh oxygen is available only at the top of the tube.
• Bacterial density will increase in the area where oxygen is best used for growth.
• Obligate aerobes grow only with oxygen and obtain energy through aerobic respiration; Pseudomonas spp.
• Obligate anaerobes grow only without oxygen and are inhibited/killed by its presence, obtaining energy through anaerobic respiration/fermentation; Clostridium spp. are examples.
• Facultative anaerobes grow with/without oxygen, but generally better with oxygen like E. coli.
• Aerotolerant anaerobes, like obligate anaerobes, cannot use oxygen but can grow in its presence they are obligate fermenters; Lactobacillus spp.
• Microaerophiles are organisms that need a low concentration of oxygen for growth, but higher concentrations are inhibitory, for example, Helicobacter pylori.
• Toxic forms of oxygen, like singlet oxygen, superoxide free radicals, and hydrogen peroxide, can harm organisms.
• Oxygen-tolerant bacteria produce enzymes such as superoxide dismutase (SOD).
• SOD converts the superoxide free radical into molecular oxygen (O₂) and hydrogen peroxide (H2O2) which neutralizes it.
• Catalase and peroxidase are used to neutralize hydrogen peroxide.

Effect of pH

• Microorganisms are in groups based on their optimum pH requirements.
• Neutrophiles grow best at pH 5-8, like Escherichia coli, Staphylococci, and Salmonella spp.
• Acidophiles grow best at pH below 5.5, for example, Lactobacillus acidophilus.
• Alkaliphiles grow best at pH above 8.5, for instance, Vibrio cholera, the pathogenic agent of cholera.

Peptic Ulcer

• This is a painful sore on the stomach lining.
• Peptic ulcers (until the 1980s) were thought to be caused by spicy foods, stress, and excess acids.
• Peptic ulcers are discovered to be caused by Helicobacter pylori bacterium.
• H. pylori bacteria can survive the low pH of the stomach.
• H. pylori achieves a microenvironment with a nearly neutral pH.
• H. pylori achieves pH balance by producing large amounts of the enzyme urease.
• Urease breaks down urea to form NH4+ and CO2.
• The ammonium ion raises the pH of the surrounding environment.

Effect of Temperature

• Bacteria have a minimum, optimum, and maximum growth temperature.
• Psychrophiles (cold-loving bacteria) have an optimum growth temperature range of -5°C and 15°C, typically in Arctic and Antarctic regions.
• Mesophiles grow best at moderate temperatures, with an optimum between 25°C and 45°C; common soil and body bacteria.
• Thermophiles (heat-loving bacteria) have an optimum growth temperature between 45°C and 70°C, commonly in hot springs.
• Hyperthermophiles grow at very high temperatures, with an optimum between 70°C and 110°C, members of Archaea, found near hydrothermal vents.
• Fungi grow best at 20 – 25°C.
• Special cell walls of temperature extremophiles withstand extreme temperatures.
• Special membranes of temperature extremophiles withstand extreme temperatures.
• Psychrophiles have polyunsaturated fatty acids in their cell membranes, increasing fluidity and helping adaptation to a cool environment (unsaturated fatty acids remain liquid at low temperatures).
• Thermophiles have highly saturated fatty acids in their cell membranes stable at high temperatures.
• Special enzymes of temperature extremophiles withstand extreme temperatures.

Effect of Water

• The water requirements of microorganisms are described in terms of the water activity (aw) of the food or environment.
• Water activity (aw) is a measure of the amount of freely available water within a food.
• The aw of pure water is 1.00 and the aw of completely dehydrated food is 0.00, thus, higher aw will have more microorganisms.
• Bacteria need water activity of at least 0.91 and fungi at least 0.7.
• Pathogenic/spoilage bacteria do not grow in water activity of less than 0.85.
• The water activity is altered to prevent microbial growth via the addition of solutes, ions, freezing, or drying.

Miscellaneous Factors

• Halophiles are organisms that thrive in high salt concentrations.
• Halophiles are mild (1-6%), moderate (6-15%), or extreme (15-30%) based on halotolerance.
• Halophiles require sodium chloride (salt) for growth.
• Halotolerant organisms don't require salt but can grow under saline conditions.
• Osmotolerants can grow in solutions with high solute (sugar) concentration.
• Osmophilic require solutions with high solute (sugar) concentration for growth.
• Most bacteria cannot tolerate low surface tension with exceptions.
• E. coli found in the intestine, tolerate bile lowering the surface tension.
• Barophiles optimally grow at pressures greater than atmospheric pressure.
• Barophilic bacteria live in deep-sea environments, growing rapidly at low temperatures and high pressures (often exceeding 380 atm).

Microbial Growth

• When microbes are given the required environmental factors and nutrients, they become active and grow.
• Microbial growth is measured via the increase in population by measuring cell number and mass.
• Bacteria division is asexual and goes through binary fission where one cell becomes two.
• Bacteria reproduction also occurs through multiple fission, budding, and the production of spores.

Stages of Cell Division

• A parent cell is first present at the beginning of the cell cycle.
• Chromosome replication and cell enlargement occurs.
• The parent cell duplicates the chromosome, synthesizes new structures, and enlarges.
• Chromosome division and septation happens as the chromosomes attach to the cytoskeleton and are separated.
• The cell lays down a septum, walling off the new cells, and other components are equally distributed.
• The septum is synthesized completely, forming two separate cell chambers, to complete cell compartments.
• The new daughter cells are independent units with some will separate into chains/pairs.

Growth Curve

• Growth curve can be used for bacteria growth in the lab.
• Bacteria allowed to grow in a closed system/batch culture (no food, no wastes).
• The predictable pattern results in a growth curve.
• A growth curve can be composed of four phases: lag, exponential or log, stationary, and death or decline.
• Generation time for an organism can be found from the growth curve: the time it takes for a complete fission cycle.
• In bacteria, each new fission cycle or generation increases the population by a factor of two which doubles it.

Normal Growth Curve of Bacteria

• Consists of distinct graph stages: lag, logarithmic, stationary, decline phases.
• Lag phase is an adaptation period for the bacteria with no cell division.
• Cells synthesize RNA/enzymes/essential metabolites that are missing from their new environment in this phase.
• Exponential or log phase is when cells have accumulated their needs for cell division.
• Predictable doublings in the population as conditions that are optimal will result in results if conditions are not ideal.
• Stationary phase occurs when the bacterial population has little to no nutrients and an excess of waste which inhibits growth or lack of space, causing the cells to enter the stationary phase.
• At the end of the death/decline pahse the majority of cells die.
• The cell culture becomes sterile, except for spore-forming bacteria.