Bacteria and VirusesBacteria and Viruses

Bacteria are very successful because of their rapid growth rates and their

metabolic versatility

Outline of TodayOutline of Today’’s lectures lecture

I. Monera – Prokaryotic Organisms

* Key Concepts• Characteristics• Growth and reproduction• Classification

• Archaebacteria• Eubacteria

• Roles of Prokaryotic Organisms

II. Viruses

* Key Concepts• Size• Disease caused by viruses

Key Concepts:Key Concepts:

� The simplest forms of life are bacteria

� Bacteria are the only prokaryotes

� Bacteria reproduce by binary fission

� The first living organisms on earth were

bacteria (4 billion years!)

� Different lineages of organisms arose from

bacteria

Characteristics of BacteriaCharacteristics of Bacteria

� Metabolic Diversity

� Photoautotrophic

�Chemoautotrophic

�Heterotrophs

� Sizes and Shapes

� 1 - 10 micrometers

�Coccus

�Bacillus

� Spirillum

� Structures

�Cell walls

�Membrane

�Ribosomes

�DNA in cytoplasm

One circular DNA

� Flagella

�Capsule

A BacteriumA Bacterium

How Small Are Bacteria?How Small Are Bacteria?

Bacillus cells on the tip of a pin

Magnified

14,000 times

Bacterial Growth and ReproductionBacterial Growth and Reproduction

�Increase in number of cells

�Binary fission

Bacterial ClassificationBacterial Classification

� Taxonomy

� Gene sequencing and comparative biochemistry

ArchaebacteriaArchaebacteria

They can thrive in hot thermal vents where They can thrive in hot thermal vents where

temperatures are far too hot for the survival of other temperatures are far too hot for the survival of other

life forms.life forms.

They can tolerate the absence of oxygen and, not They can tolerate the absence of oxygen and, not

only survive, but flourish. Also, they can live in only survive, but flourish. Also, they can live in

acidic soils, hot springs, coalmines, salt lakes, etc.acidic soils, hot springs, coalmines, salt lakes, etc.

They can even process inorganic molecules asThey can even process inorganic molecules as

an energy source.an energy source.

These bacteria are capable of living in some These bacteria are capable of living in some

of the most extreme environments on earth.of the most extreme environments on earth.

EubacteriaEubacteria

� Photoautotrophic

�Cyanobacteria

� Ponds and freshwater

� Chemoautotrophic

� Environment

�Cycling of N2 , S2

� Chemoheterotrophic

�Most bacteria

�Pathogenic

�Endospores

Roles of Prokaryotic OrganismsRoles of Prokaryotic Organisms

� Photosynthesis - Cyanobacteria

� Decomposers - saprobes- feed on dead organisms

� Nitrogen fixation: N2 to NH3 - plants can use

ammonia (Atmosphere 78% N2 molecules)

� Pathogenicity-be able to cause disease : Clostridium

tetani Tetanus, Clostridium botulium Botulism,

Black Death – plague, Tuberculosis, Streptococcus

pneumonia

� Produce vitamins: Escherichia coli ( E. coli) V K

� Commercial uses: Beer and Wine (sugar to alcohol),

Cheese and Yogurt

Viruses (Viruses (Key Concepts):Key Concepts):

�Viruses are non-cellular

�Viruses are nonliving infectious agents

�Viruses consist of either DNA or RNA

surrounded by a protein coat

�Some may have an envelope and spikes

�Viruses cannot reproduce on their own but

must use a host cell’s machinery

�Enveloped or non-enveloped

Viruses Size: 0.05-0.2 µm

VirusesViruses

� Enveloped or non-enveloped

� Spiked

Enveloped Virus

Viral Multiplication CyclesViral Multiplication Cycles

� 5 Steps

�Attachment

�Penetration

�Replication

�Assembly

�Release

� Lytic pathway

�Host cell lysis

� Lysogenic pathway

�Viral DNA integrates into

bacterial chromosome

SmallpoxSmallpox

Herpes simplex lesion of lower lip, second day after onset

Measles

HIV, a retrovirus

In ConclusionIn Conclusion

� After the origin of life, a divergence occurred

leading to Eubacteria and common ancestors of

Archaebacteria and Eukaryotic cells

� All bacteria are prokaryotes

� Bacteria have 3 basic shapes: cocci, bacilli, and

spirilla

In ConclusionIn Conclusion

�Many bacteria have external structures

that increase their survival and

pathogenicity

�Bacteria reproduce by binary fission

In ConclusionIn Conclusion

� Viruses are nonliving infectious agents

� Viruses consist of either DNA or RNA

surrounded by a protein coat

� Some may have an envelope and spikes

� Viruses cannot reproduce on their own but must

use a host cell’s machinery

� There are five steps in the multiplication cycle of

a virus

In ConclusionIn Conclusion

�There are two pathways common in the

multiplication of bacteriophages: lytic and

lysogenic