Classification of Microbes: Purposes and Uses
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Briefly describe different ways to classify microbes. Classification is helpful to understand their physiochemical and pathological characteristics and to identify microbes.
Classification of Microbes: Purposes and Uses
- 1. BRS 1 Classification of Microbes Classification is helpful to understand their physiochemical and pathological characteristics and to identify microbes. DOI: 10.13140/RG.2.2.20981.08161 Dr. Bhoj Raj Singh Ex. Principal Scientist (Microbiology) ICAR-IVRI, Izatnagar-243 122, India Ex. Director CCS-National Institute of Animal Health, Baghpat-250 609, India Also available from https://www.researchgate.net/publication/389172761_Classifications_of_mi crobes_002_to_50_m
- 2. BRS 2 Microbes • Organisms not visible with naked eyes when in singularity. • Their size varies from 20 nanometres to 50 microns. • Microbes are classified either based on their structure (anatomy) or based on their physiological/ biochemical functions. • Structurally microbes may be acellular (non-cellular), unicellular, multicellular, prokaryotic (no nucleus in cells) and eukaryotes (nucleus contains genetic material. • Physiologically microbes may be divided in many different ways.
- 3. BRS 3 Non-Cellular microbes Two types • Viruses (parasites in eukaryotic cells) and Bacteriophages (parasites in prokaryotic cells) • Prions: Ill defined, infectious abnormally folded proteins that cause a group of fatal neurodegenerative diseases known as transmissible spongiform encephalopathy (TSEs).
- 4. BRS 4 Viruses: Enveloped and Non-enveloped • Enveloped viruses (covered with lipid bilayer membrane originated from host embedded with viral surface proteins, Influenza virus, HIV (human immunodeficiency virus), Herpes simplex virus, Ebola virus, and Dengue virus, often narrow host range and more susceptible to disinfectants, heat and soap). – dsDNA (Pox, Herpese, Iridovirus, Ranavirus) – ssDNA virus (Circovirus) – dsRNA (Rubella virus, Rotavirus) – ssRNA • ssRNA-Negative strand, non-segmented genome (Paramyxoviruses, Measles, Mumps, Parainfluenza and Respiratory Syncytial Viruses, Buniyavirus, rabies, measles, Nipah, and Ebola). • ssRNA-Negative strand, segmented genome (Orthomyxoviruses, Influenza viruses). • ssRNA-Positive strand (Coronavirus, Dengue, West Nile, Hepatitis C and Hepatitis A virus)
- 5. BRS 5 • Non-enveloped or naked viruses (More virulent, wide host range, more resistant to pH change, heat, detergents and disinfectants, poliovirus, adenovirus, rotavirus, norovirus, human papillomavirus (HPV), coxsackievirus, and rhinovirus) – dsDNA (Adenovirus) – ssDNA (Human Parvovirus causing fifth disease, Parvovirus, Microviridae family of bacteriophages). – dsRNA (Reoviruses, Rotavirus) – ssRNA (usually positive sense, Polivirus, Coxsackievirus, Echovirus, and Norovirus)
- 6. BRS 6 Unicellular microbes • Prokaryotes – Bacteria (Peptidoglycan in cell wall, cell membranes composed of lipid bilayer, lipids have fatty acids, single replicon origin and RNA polymerase, initiator tRNA formyl-methionine) Escherichia coli, Staphylococcus aureus. – Archea (No peptidoglycan cell wall, membranes made of lipid bilayeror monolayer, lipids are isoprene (C5H8) lipids, multiple replicon origins and RNA polymerases, initiator tRNA methionine) Halobacterium salinarum, Methanopyrus kandleri • Eukaryotes – Protozoa (causes of malaria, toxoplasmosis, leishmaniasis, the Chagas disease, sleepiness disease, amebiasis, giardiasis, and trichomoniasis) – Algae (Chlamydomonas, Chlorella) – Fungi (Candida, baker’s yeasts)
- 7. BRS 7 Multicellular Microbes • Bacteria (Myxobacteria form complex fruiting bodies and exhibit social behaviour, Magnetotactic bacteria form chains and are able to navigate using Earth's magnetic field, Cyanobacteria form chains and colonies, producing oxygen through photosynthesis). • Protozoa: Brown algae type kelp. • Algae (Microscopic plants:): Spirogyra. • Fungi: Most of the disease causing fungi like ringworms (Tinea Capitis, Tinea Corporis, and Onychomycosis), lung infections (aspergillosis, cryptococcosis, blastomycosis, coccidioidomycosis or Valley fever, and histoplasmosis) • Microscopic animals: Mites causing mange and scabies.
- 8. BRS 8 Physiological Classification • Based on Requirement of Carbon Source • Autotrophs: Obtain carbon from inorganic sources like CO2 (e.g., photosynthetic bacteria, cyanobacteria). • Heterotrophs: Obtain carbon from organic compounds (e.g., most bacteria, fungi). » Parasites » Saprophytes » Symbiotic » Free-living
- 9. BRS 9 Based on Requirement of Energy Source • Phototrophs: Use light as energy source (photosynthetic bacteria, algae) – Oxygenic phototrophs: Produces oxygen (Green algae, Diatoms, Cyanobacteria) – An-Oxygenic phototrophs (Purple sulfur bacteria, Green sulfur bacteria) • Chemotrophs: Obtain energy from chemical compounds – Chemoorganotrophs: Utilize organic compounds as energy source (most bacteria) – Chemolithotrophs: Utilize inorganic compounds as energy source (bacteria in extreme environments, Hydrogenovibrio crunogenus) – Chemoheterotrophs (or chemotrophic heterotrophs) are unable to fix carbon to form their own organic compounds (Fungi and animals). • Chemolithoheterotrophs, utilizing inorganic electron sources such as sulphur. • Chemoorganoheterotrophs, utilizing organic electron sources such as carbohydrates, lipids, and proteins.
- 10. BRS 10 Based on Oxygen Requirement • Aerobes: Require oxygen for growth (Bacillus spp.) • Obligate aerobes: Can only grow in the presence of oxygen (Mycobacterium tuberculosis). • Facultative anaerobes: Can grow with or without oxygen (Escherichia coli) • Anaerobes: Cannot grow in the presence of oxygen (Clostridium spp.) • Obligate anaerobes: Killed by oxygen (Actinomyces, Bacteroides, Clostridium, Fusobacterium, Peptostreptococcus, Porphyromonas, Prevotella, Propionibacterium, and Veillonella) • Aerotolerant anaerobes: Can tolerate oxygen but do not use it (Lactobacillus rhamnosus, Parabacteroides distasonis, Actinomyces neuii, and Streptococcus pyogenes) • Microaerophiles: Require low oxygen concentrations for growth (Campylobacter, Brucella)
- 11. BRS 11 Based on Growth Temperature Preference • Psychrophiles: Grow best at low temperatures (Pseudomonas, Moraxella, Psychrobacter, Flavobacterium, Polaromonas, Psychroflexus, Polaribacter, Moritella, Vibrio spp.) • Mesophiles: Grow best at moderate temperatures (most human pathogens) • Thermophiles: Grow best at high temperatures (Clostridium thermosacchrolyticum, Bacillus stearothermophilus, Thermoplasma acidophilum, Thermus aquaticus) • Hyperthermophiles: Thrive in extreme heat (Pyrodictium occultum, Pyrococcus abyssi)
- 12. BRS 12 Based on Tolerance to Salt in Growth Environment • Non-halophiles: Requires absence of salt for optimum growth (Vibrio choleare). • Slight halophiles: Grow best at salt concentrations between 0.2 - 0.5 M, (most of the bacteria). • Moderate halophiles: Optimal growth occurs at salt concentrations between 0.5 – 2.5 M (Some of Bacillus and Staphylococcus sp.) • Borderline halophiles: Optimal growth occurs at salt concentrations between 1.5 – 4 M. • Extreme halophiles: Require very high salt concentrations for growth; grow typically between 2.5 - 5.2 (Halobacteriaceae family of Archea Halobacterium, Halomonas smyrnensis, Halobacillus halophilus). • Extremely Halotolerant: Staphylococcus aureus. •
- 13. BRS 13 Based on Acidity Requirements for Growth • Acidophiles: Grow in acidic environments like volcanic areas, sulfur springs, and acidic mine drainage, Thiobacillus thiooxidans, Acidithiobacillus ferrooxidans, Picrophilus, Ferroplasma acidiphilum, and Thermoplasma acidophilus. • Neutrophiles: Grow at neutral pH, most of the common microbes • Alkalophiles: Grow in alkaline environments, soda lakes, salt lakes, and certain desert soils, Bacillus alcalophilus, Alkalibacterium tumefaciens, Natronobacterium magadii, and Halomonas sp. To survive in adverse environment bacteria produce exopolysaccharides (EPS) to defend against extreme conditions of salt concentrations, pH, low nutrient availability, and high temperatures prevalent in their habitats.
- 14. BRS 14 Classification based on Transmission of Microbes • Contagious: Spread through direct or indirect contact (Chicken pox, HIV/AIDS, Measles). • Airborne: Transmitted through small respiratory droplets expelled when someone with disease sneezes, coughs, laughs, or otherwise exhales in some way (Flu, COVID-19). • Soil borne: Transmitted through soil containing pathogens (Tetanus, Botulism, Gangrene, Ascariasis, Hookworms). • Foodborne: Spread through consumption of contaminated foods (Paratyphoid, Listeriosis, Shigellosis, Toxoplasmosis, foodpoisoning). • Waterborne: Spread through consumption or contacting dirty water (Typhoid, E. coli infections, Hepatitis A, Giardiasis, Norovirus). • Nosocomial: Acquired in hospitals through use of contaminated equipment, touching contaminated surfaces, touch of doctors and nurses (Legionellosis, Staphylococcus and Pseudomonas infections, Flu, COVID) • Vector borne: Transmitted through the bite or sting of an infected arthropod, such as a mosquito, tick, flea, or fly (Malaria, Dengue, Yellow fever, Lyme disease, Plague, Sleeping sickness)
- 15. BRS 15 Difference Between Prokaryotic and Eukaryotic Organisms Character Prokaryotic Cells Eukaryotic cells Nucleus Absent Present Organelles like mitochondria, endoplasmic reticulum, and Golgi apparatus Absent Present DNA in nucleus organized in chromosomes Circular Linear Reproduction Binary Mitosis/ Meiosis Cellular organization (majority) Unicellular Multicellular Ribosomes’ size 70s (30s and 50s) 80s (40s and 60s) Locomotive is powered by force of Proton ATPs
- 16. BRS 16 Difference Between Archaea and Bacteria Charcateristic Bacteria (Eubacteria) Archaea (Archaea bacteria) Cell Wall Composition Contains peptidoglycans (murein) polysaccharides, glycoproteins, pure protein, or pseudopeptidoglycan Cell membrane is made of Lipid bilayer made of fatty acids Lipid bilayer made of isoprene lipids RNA polymerase Single Multiple Disease causation May cause Do not cause Introns in DNA Absent Present Formation of endospores May be No Growth environment Wide range Extremophiles Asexual reproduction Binary fission Binary fission, fragmentation, or budding Nutrition A wide range, mostly heterotrophs Mostly autotrophs Effect of antibiotics Yes No Initiator amino acid in peptide synthesis Formyl-methionine Methionine Replication initiation Usually single origin/chromosome, initiator protein DnaA Multiple origin/chromosome, initiator protein complexes Orc/Cdc6
- 17. BRS 17 Seven Major Types of Bacteria • Firmicutes: Low G + C Gram-positive spore forming bacteria, Bacillus, Clostridia, Erysipelotichaceae, Thermolithbacteria, Negativicutes. • Proeobacteria: Gram-negative bacteria, the second largest phylum of hydrogenogenic CO oxidizers, which are composed of mesophilic and neutrophilic bacteria, Escherichia coli, Salmonella, Citrobacter. • Actinobacteria: Gram-positive bacteria with > 50% of G + C content in their DNA are filamentous bacteria, Actinomyces, Nocardia, Micrococcus, Rhodococcus. • Bacteroidetes: Gram-negative anaerobic nonspore-forming bacteria, Chitinophaga, Cytophaga, Flavobacterium. • Verrucominobacteria: Thermoacidophilic methanotrophs, widespread in the environment and have important role in biogeochemical Carbon cycle. • Fusobacteria: Non-sporeforming Gram-negative anaerobic rods that metabolise peptone or carbohydrates to produce butyrate as the main metabolic end product with lower levels of lactate, propionate and acetate, Fusobacterium • Cyanobacteria: oxygenic photoautotrophic Gram-negative bacteria.
- 18. BRS 18 Hope the ppt may be of good use for microbiologists Thank you for attention