Microbes are classified into two primary groups: Bacteria and Archaea, each with distinct characteristics.
Life on Earth originated from microorganisms; however, it raises the question of how life emerged from non-living matter.
The early Earth was extremely hot with a hypoxic atmosphere, lacking oxygen necessary for modern life.
Biomolecules and macromolecules can spontaneously form under suitable conditions, driven by energy from ultraviolet radiation, lightning, and radioactivity.
When gases such as methane, carbon dioxide, nitrogen, and ammonia are subjected to various energy sources, they can form macromolecules, including fatty acids, sugars, and nucleic acids.
Self-replicating entities require:
A means of obtaining and using energy.
A mechanism for heredity to pass genetic information on to future generations.
Research suggests that early life forms were likely "naked" RNAs capable of self-replication, leading to the formation of the RNA World theory.
Clays and pyrite on early Earth may have facilitated the creation of organic compounds and films containing various macromolecules.
Experiments show that Montmorillonite clay can induce the formation of lipid vesicles, resembling early cells.
RNA oligonucleotides can also spontaneously form within these vesicles, hinting at the emergence of the first cells.
RNA-containing vesicles could have eventually become self-replicating.
As the Earth cooled, more complex macromolecules may have developed, leading to the formation of the first viable cell through a mixture of macromolecules and self-replicating RNA.
Natural selection favored cells with optimal catalytic rates, promoting the evolution of proteins and enzymes that surpassed RNA in efficiency.
Evidence suggests that microbial life existed on Earth around 3.5 billion years ago, found in sedimentary rocks that required liquid water, vital for life.
Stromatolites, consisting of microbial mats developed from bacteria, provide fossil evidence of early microbial life.
Early bacteria likely fixed atmospheric chemicals like methane and nitrogen for metabolic processes.
Cyanobacteria significantly influenced Earth's atmospheric composition through organic photosynthesis, contributing to the creation of the ozone layer and the availability of oxygen for aerobic organisms.
Early eukaryotic cells were simpler than modern eukaryotes and lacked complex organelles.
As early eukaryotic cells grew in size, they required more proteins, leading to the division of genes into chromosomes for efficient replication.
Mitochondria and chloroplasts may have derived from early aerobic and photosynthetic microbes incorporated into larger cells.
These organelles contain their own circular DNA and ribosomes similar to prokaryotic structures, and their incorporation represents a symbiotic relationship beneficial to both.
Phylogeny studies evolutionary relationships among species that reveal classification based on shared characteristics.
A phylogenetic tree constructed from rRNA comparisons demonstrates the relationship between Bacteria, Archaea, and Eukarya.
The tree presents three main domains representing all life:
Bacteria
Archaea
Eukarya
Notably, all prokaryotes (Bacteria and Archaea) are closely related, with Archaea being more similar to Eukarya.
Environmental conditions such as solutes and water, pH levels, temperature, oxygen concentration, and pressure significantly affect microbial growth.
In hypertonic environments, cells lose water, leading to plasmolysis.
In hypotonic environments, cells can absorb too much water and lysate; organisms adapt to changing osmolarity to survive.
Examples include halophiles, which thrive in high salt concentrations.
Microbes thrive in specific pH ranges:
Acidophiles: pH 0 to 5.5
Neutrophiles: pH 5.5 to 8.0
Alkalophiles: pH 8.0 to 11.5
Temperature impacts microbial growth; optimal temperatures vary by species.
Microbes are categorized based on their temperature preferences:
Psychrophiles (0-20°C)
Mesophiles (20-45°C, ideal growth is often at 37°C)
Thermophiles (45-80°C)
Hyperthermophiles (above 55°C)
Most bacteria thrive at normal atmospheric pressure; exceptions include:
Barotolerant prokaryotes that can tolerate higher pressures.
Barophilic prokaryotes that favor high-pressure environments.
Microbial oxygen tolerance varies:
Obligate aerobes require atmospheric oxygen.
Facultative anaerobes prefer oxygen but can grow without it.
Aerotolerant anaerobes grow better in an oxygen-free environment but can tolerate some oxygen.
Strict anaerobes cannot survive in oxygen.
Microaerophiles require reduced oxygen levels.
Fungi are heterotrophic eukaryotic organisms that were previously classified as primitive plants.
All fungi share certain traits, including microscopic stages in their life cycles and being eukaryotic.
Fungi, along with heterotrophic bacteria, are principal decomposers, breaking down organic matter to release nutrients back into the environment and supporting soil fertility.
Fungi can cause diseases in plants and animals, negatively impacting agriculture.
However, they also provide benefits, including food sources like mushrooms, yeast for baking and fermentation, and production of antibiotics such as penicillin.
Fungal cell walls are primarily made of chitin, which offers resistance to degradation compared to plant cellulose.
Fungi reproduce through both vegetative methods and spore production for dispersal, with spores formed as a survival strategy in adverse conditions.
Fungi secrete enzymes to break down complex organic materials, absorbing the resulting nutrients. They are primarily absorptive feeders, growing in or on their food sources.
Fungal growth is mainly restricted to moist environments as nutrient absorption occurs near the growing tips of hyphae, which are filamentous structures.
Fungi can be saprophytes, parasites, or form symbiotic relationships. They possess varying methods for nutrient acquisition, including predacious behaviors.
Certain fungi, like yeast, can reproduce both asexually and sexually, presenting diversity in reproductive strategies.
Mycoses are diseases triggered by fungi growing on or inside a host, while mycotoxicoses are due to exposure to fungal toxins.
Mycotoxins produced by fungi can lead to severe health issues in humans and animals, whose effects can be exacerbated by their persistence and stability even after cooking.
Examples of mycotoxin classes include:
Fumonisins linked to esophageal cancer through contaminated food.
Trichothecenes potentially used in chemical warfare.
Patulin, noted for antibacterial properties but toxic to animals and humans.
Medical mycology identifies three fungal groups that affect humans, namely obligately parasitic fungi, thermal dimorphic saprobes, and opportunistic saprobes.
Infections can be categorized into three main types:
Cutaneous infections affecting the skin’s outer layers.
Subcutaneous infections introduced through wounds.
Systemic infections stemming from true pathogenic fungi or opportunistic fungi in immunocompromised individuals.
Diseases like tinea (ringworm) are prevalent, caused by keratinolytic fungi including species from the Epidermophyton, Microsporum, and Trichophyton genera.
Conditions such as excessive moisture can lead to rapid fungal growth, causing candidiasis and other skin infections.
Conditions like chromoblastomycosis, entomophthoromycosis, mycetoma, and sporotrichosis can develop from various fungi entering the skin through wounds or bites.
Mycetoma and sporotrichosis involve tumor-like growths and can spread through lymphatic systems, leading to systemic infections and complications.
Systemic fungal infections can arise from specialized pathogens such as Histoplasma capsulatum and Coccidioides immitis or opportunistic saprobes related to compromised immune systems.
Histoplasmosis primarily infects the lungs and can spread via macrophages; symptoms may remain undetected initially.
Coccidioidomycosis shows flu-like symptoms and can lead to serious complications without treatment.
Blastomycosis presents as an asymptomatic lung infection in most individuals, while paracoccidiomycosis predominantly affects males and can have severe outcomes.
Opportunistic fungal infections have surged due to rising immunocompromised populations and include candidiasis and aspergillosis.
Candidiases can spread to various organs, complicating underlying health issues; Aspergillosis primarily affects individuals with pre-existing respiratory abnormalities.