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Microbial Life Chapter 13 Characteristics of Microbes Prokaryotic cells Smaller Lack special structures such as a nucleus and organelles All prokaryotic cells are microorganisms Some microorganisms are eukaryotic Viruses? “Micro”organisms Microorganisms are diverse and widespread Pathogens causing disease Normal / indigenous flora decomposing dead skin cells supplying essential vitamins, guarding against pathogenic organisms Saprobes In soil decompose dead organisms, sustaining chemical cycles Microbiology The study of organisms (microorganisms or microbes) too small to be seen without magnification This includes: 1. 2. 3. 4. 5. 6. Bacteria Viruses Fungi Protozoa Algae Helminthes Bacteria Bacteria – Single-celled organisms – Various shapes • Cocci • Bacilli • Spiral shapes – Cellular – Lack membrane-enclosed cellular structures – Widely distributed in nature Generalized structure of a prokaryotic cell Appendages Flagella rotates 360o 1-2 or many distributed over entire cell Fimbriae adhesion Pili made of pilin protein found only in Gram negative cells Functions joins bacterial cells for DNA transfer (conjugation) Adhesion to form biofilms and microcolonies The Cell Envelope External covering outside the cytoplasm Composed of few basic layers: glycocalyx cell wall Gram positive Gram negative cell membrane Maintains cell integrity Chromosome single, circular, double-stranded DNA molecule contains all the genetic information required by a cell DNA is tightly coiled around a protein dense area called the nucleoid Plasmids small circular, double-stranded DNA stable extrachromosomal DNA elements that carry nonessential genetic information duplicated and passed on to offspring replicate independently from the chromosome Endospores resting, dormant cells produced by some G+ genera resistance linked to high levels of calcium & certain acids longevity verges on immortality 25 to 250 million years pressurized steam at 120oC for 20-30 minutes will destroy Viruses Viruses – Acellular – Composed of nucleic acid and a few proteins – Requires electron microscope for viewing General Structure of Viruses Capsids All viruses possess Constructed from identical subunits called capsomers made of protein Structural types: helical Continuous helix of capsomers forming a cylindrical nucleocapsid icosahedral 20-sided with 12 corners vary in the number of capsomers General Structure of Viruses Viral envelope mostly animal viruses acquired when virus leaves host cell Protects the nucleic acid when the virion is outside the host cell spikes exposed proteins on the outside of the envelope essential for attachment of the virus to the host cell Naked composed only of a nucleocapsid Enveloped surrounded by an envelope Nucleic acids Viral genome either DNA or RNA but never both Number of genes varies for each type of virus few to hundreds DNA viruses usually double stranded (ds) may be single stranded (ss) circular or linear RNA viruses usually single stranded may be double stranded Segmented versus nonsegmented 6 Steps in Viral Replication 1. 2. 3. 4. 5. 6. adsorption penetration replication assembly maturation release Fungi Fungi – Yeasts and molds • Single-celled, microscopic – Mushrooms • Multicellular, macroscopic – Cell nucleus and other cellular structures – Absorb nutrients from their environment – Saprobes – Widely distributed in water and soil Thermal dimorphism grow as molds at 30°C and as yeasts at 37°C Fungal Organization - Mold Fungal Cell Structure Hyphae Mycelium Conidia / spores Sexual and asexual reproduction Cell walls contain chitin Energy reserve is glycogen Nonmotile Produce wind-blown spores Grow toward food source Fungal Organization Yeasts Soft, uniform texture and appearance Unicellular (bicellular) False hyphae Beta-glycan cell wall structure Protozoa Protozoa 100,000 species @ 25 are important pathogens Some spread by insect vectors Vary in shape, lack a cell wall Most are unicellular Colonies are rare Obtain food by engulfing or ingesting smaller organisms and plant material Most are harmless, free-living in a moist habitat Protozoa Exist as trophozoite motile feeding stage cyst Dormant resting stage when conditions are unfavorable for growth and feeding All reproduce asexually, mitosis or multiple fission Many also reproduce sexually Protozoan Classification Simple grouping is based on method of motility, reproduction, and life cycle Mastigophora primarily flagellar motility Sarcodina primarily ameba Ciliophora Cilia Apicomplexa motility is absent except male gametes Algae Algae – Unicellular to multicellular – Macroalgae – Microalgae – Have a nucleus and many membrane-enclosed cellular structures – Photosynthesize their own food – Widely distributed in fresh and salt water – Important source of food for other organisms Algae Diversity Diatoms Chrysophyta single-celled silica in their cell wall silica shell found in fresh water Euglenophyta single-celled photosynthesis Dinoflagellata Phaeophyta contains many familiar seaweeds. Rhodophyta flagella and can move red pigments usually photosynthetic contains many types of seaweed sometimes phosphorescent plankton
