Chapter 13 Microbial Life

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

 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 Microorganisms are diverse and widespread

Microbiology The study of organisms (microorganisms or microbes) too small to be seen without magnification This includes: 1. Bacteria 2. Viruses 3. Fungi 4. Protozoa 5. Algae 6. Helminthes

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 360 o 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 120 o C for minutes will destroy

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. adsorption 2. penetration 3. replication 4. assembly 5. maturation 6. release

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 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

100, 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

– 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 single-celled silica shell Euglenophyta single-celled photosynthesis Dinoflagellata flagella and can move usually photosynthetic sometimes phosphorescent plankton Chrysophyta silica in their cell wall found in fresh water Phaeophyta contains many familiar seaweeds. Rhodophyta red pigments contains many types of seaweed