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