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Chapter 13
Microbial Life
Characteristics of MicrobesProkaryotic cells
Smaller Lack special structures such as a nucleus and
organellesAll prokaryotic cells are microorganisms
Some microorganisms are eukaryoticViruses?
“Micro”organisms
Pathogens causing disease
Normal / indigenous floradecomposing 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. Bacteria2. Viruses3. Fungi4. Protozoa 5. Algae6. 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
Flagellarotates 360o
1-2 or many distributed over entire cell
Fimbriaeadhesion
Pilimade of pilin proteinfound only in Gram negative cellsFunctions
joins bacterial cells for DNA transfer (conjugation)
Adhesionto 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 proteindense area called the
nucleoid
Plasmids
small circular, double-stranded DNA
stable extrachromosomal DNA elements that carry nonessential genetic information
duplicated and passed on to offspringreplicate independently from
the chromosome
Endospores
resting, dormant cellsproduced by some G+ generaresistance 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 VirusesCapsids
All viruses possessConstructed 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 envelopemostly animal virusesacquired when virus leaves host cellProtects the nucleic acid when the
virion is outside the host cellspikes
exposed proteins on the outside of the envelope
essential for attachment of the virus to the host cell
Nakedcomposed only of a nucleocapsid
Envelopedsurrounded by an envelope
Nucleic acidsViral genome
either DNA or RNA but never bothNumber of genes varies for each type of virus
few to hundredsDNA viruses
usually double stranded (ds) may be single stranded (ss)circular or linear
RNA viruses usually single strandedmay be double strandedSegmented versus nonsegmented
6 Steps in Viral Replication
1. adsorption 2. penetration 3. replication 4. assembly5. maturation6. 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 StructureHyphae
MyceliumConidia / sporesSexual and asexual
reproductionCell wallsCell walls contain chitin Energy reserve is glycogen Nonmotile
Produce wind-blown sporesGrow toward food source
Fungal Organization
Yeasts Soft, uniform texture
and appearance Unicellular (bicellular)False hyphaeBeta-glycan cell wall
structure
Protozoa
Protozoa100,000 species
@ 25 are important pathogensSome spread by insect vectors
Vary in shape, lack a cell wall Most are unicellularColonies are rareObtain food by engulfing or ingesting
smaller organisms and plant materialMost are harmless, free-living in a moist
habitat
Protozoa
Exist as trophozoite motile feeding stage
cystDormant 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 DiversityDiatoms
single-celled silica shell
Euglenophyta single-celled photosynthesis
Dinoflagellata flagella and can moveusually photosyntheticsometimes
phosphorescentplankton
Chrysophyta silica in their cell wall found in fresh water
Phaeophyta contains many
familiar seaweeds.Rhodophyta
red pigmentscontains many types
of seaweed