the evolution of microbial life: prokaryotes, protistajocha-biology.net/handouts/gralbio/prokaryotes...

The Evolution of Microbial Life: Prokaryotes, Protista

1

Earth was formed about 4.6 billion years ago.

Major Episodes in the History of Life

The Evolution of Life

Prokaryotes

(1) Evolved by 3.5 billion years ago

(1)

(3) Single-celled eukaryotes first evolved about 2.1 billion years ago.

(3) (4)

(4) Multicellular eukaryotes first evolved at least 1.2 billion years ago.

(5)

(5) Modern humans appeared about 200,000 years ago!

(2) Began oxygen production about 2.7 billion years ago

Lived alone for almost 2 billion years

Continue in great abundance today

(2)

Prokaryotes: Bacteria & Archaea Are the simplest, single celled, organisms living on Earth today…

the most abundant…

and the most diverse!

Domain

Domain

Domain

Kingdoms

It has been calculated that the

collective biomass of all

prokaryotes is at least 10 times

that of Eukaryotes


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Prokaryotes live deep within the Earth and in habitats too cold, too hot,

too salty, too acidic, or too alkaline for any eukaryote to survive.

Deep Sea chimneys (12,000 feet deep)

Temperature above 170F!

Head of a pin

Extremophile Archaea

Hot springs

Extremophile ArchaeaHalophiles

(Extremely salty

Environments)

Salt-producing ponds,

San Francisco bay, 5-8

times more salty than sea

water!

Main Prokaryotic characteristics

1) Prokaryotes lack nuclei

2) Have cell walls exterior to their

plasma membranes

3) Cell size: Much smaller than

Eukaryotes: Bacteria <1μm,

Eukaryotes >10 μm

4) DNA: No chromosomes in Prokaryotes

5) Cell division: Asexual by binary fission in bacteria, variable in Eukaryotes

6) Internal compartmentalization: Lack other membrane-enclosed organelles, only ribosomes

7) Metabolic diversity: Cellular respiration and synthesis of organic compounds can be done in different ways in prokaryotes


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Prokaryotic Nutrition

We can group all organisms in four major modes of nutrition based on…

Energy source (phototroph versus chemotroph) and

Carbon source (autotroph versus heterotroph)

Plants

Algae

Cyanobacteria

All

Eukaryotes

Prokaryotes

Prokaryotes

Prokaryotes

Photosynthesis

Cellular

Respiration

Binary fission

Prokaryotes reproduce by binary

fission at very high rates if conditions

are favorable.

Why are prokaryotes so diverse?

Two strains of Escherichia Coli are genetically

more different than you and a platypus!

Genetic variability ultimately depends on…

(1) How fast reproduction takes place More reproduction means more DNA replication,

which means high mutational rates (glitches while copying the DNA)

A few antibiotic resistant individuals in the

“population” can rapidly increase in a short

time and be transferred from one host to

another


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(2) Ways of shuffling the DNA between organisms

Conjugation

allows

prokaryotes to

directly exchange

DNA between

individuals (similar

to crossing over in

eukaryotes!)

Transduction

is when a virus

containing

bacterial DNA

passes it to

another

bacterium when

infecting it

Transformation is a process by which bacterial

cells “scavenge” DNA from their environment

(usually from bacteria that have died)

Many prokaryotes form endospores

Nutrient supply

Accumulation of metabolic wastes

Predation by other organisms

What prevents a prokaryotic colony to grow indefinitely?

Some prokaryotes

Form endospores, thick-coated, protective cells that are produced within

the cells when they are exposed to unfavorable conditions

Can survive very harsh conditions for extended periods, even centuries

Most endospores can survive in boiling water


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Main Prokaryotic Roles in Ecosystems Ch 5

Nitrogen fixation & Nitrification

Prokaryotes

ProkaryotesDecomposition

Is a chemical recycling

Prokaryotes and fungi are

the main decomposers in

all ecosystems

Prokaryotes

Nitrogen is needed for

proteins and nucleic

acids (DNA, RNA)

Prokaryotes are the

only living things that

can convert

atmospheric N2 to a

form that can be used

by other organisms,

such as NH3

(Ammonia)

Trichodesmium, also called sea sawdust, is a genus

of filamentous cyanobacteria (photosynthetic) that

also fixes nitrogen. They are found in nutrient poor

tropical and subtropical ocean waters


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Photosynthesis

Together with eukaryotic microscopic

algae (phytoplankton)…

Cyanobacteria (colonial blue-green

bacteria) are producers that release

more than 60% of the O2 present in out

atmosphere

Mutualistic symbionts

Are very important in the deep sea by producing bioluminescence in specific organs of many deep

sea organisms. This in turn is used for…

Avoiding predators

Attracting prey

Signaling potential mates

Herbivores that house bacteria in their digestive system that

help break down the cellulose

Bacteria in humans’ large intestine produce vitamins

Opportunistic pathogens

Some bacteria that are normal flora can also cause disease if the

person’s resistance is low, e.g. pneumonia

Harmful (Pathogenic) bacteria

Alteration of normal physiology: Bacteria cause

the destruction of the tissue, e.g. strep throat,

pneumonia, tuberculosis, leprosy

Bacteria produce endotoxins or exotoxins:

Endo: chemical components of cell wall

Exo: proteins secreted by bacteria

Leprosy

Human diseases:

botulism (toxins present in food or drinks)

tetanus and diphtheria (bacteria grow

inside the host)

Plant diseases: e.g. Apples: tree branches are killed, Citrus

plants (lemon, orange, etc.): cancer-like growths. Fruit

production is lowered


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24 13

What is a protist?

Whatever thing that is alive, is a eukaryote, and does not fit inside the other

groups!

they can be single celled (protozoa, algae) or multicellular (more than 180

feet in some seaweeds)

Kingdom Protista

ECOLOGICAL CLASSIFICATION

Plant-like: autotrophic

phytoplanktonSeaweeds

Animal-like: heterotrophic

(phagotrophic or ingestive)

protozoa

Fungus-like: heterotrophic

(absorptive)

Slime molds and water molds

24 14

Differences between Animal-like and Fungus-like

A fungus like protist (and real fungi cells

as well)

Has a rigid cell wall that prevent any

change in shape

Will move big molecules inside the

cell by means of absorption of pre

digested food (using exoenzymes)

An animal like protist or protozoa (and

real animal cells as well)

Has only a flexible cell membrane

Will move big molecules inside the

cell by means of phagocytosis

(endocytosis)

Food!

(bacterium)

phagocytosis

Food! (bacterium)

(1) exoenzymes (2) Extra

cellular

digestion

(3) Absorption to the cell

Both are heterotrophs (cannot make their own food)


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24 15

Algae: Plant-like Protists

Most algae have a cellulose cell wall. They

have chlorophyll inside chloroplasts and carry

on photosynthesis.

Plankton: small floating organisms

Phytoplankton photosynthetic algae that forms

the basis for most aquatic food chains.

Multicellular

(Seaweeds)

Green algae

Brown algae

Algae

Microscopic

(Phytoplankton)

Diatoms

Dinoflagellates

OthersRed

algae

1) Microscopic algae

Microscopic: Phytoplankton

DiatomsDiatoms the most common eukaryotic

producers in marine and

freshwater ecosystems

With a unique two-part, glass-like wall of

hydrated silica

Provides protection from predators

Can withstand pressure up to 1.4

million kg/m2

24 16

Dinoflagellates

Aquatic photoautotrophs that prefer warmer waters

(2nd) components of both marine and freshwater “net” phytoplankton

Shape is reinforced by internal plates of cellulose

Two flagella, make them spin as they move through the water

Mutualism with coral polyps

Dinoflagellates photosynthetic output

Is food for reef communities

Coral body

Polyp’s tentacles

with symbionts

Dinoflagellates

Corals provide

raw materials

algae need in

order to make

photosynthesisBioluminescence

ATP driven chemical reaction

Creates a glow when water is

agitated and dinoflagellates are

in great number

Red Tides

Rapid growth of some dinoflagellates and other

microbes

Is responsible for causing “red tides,” some

of which can be toxic to humans

Color appears red because of carotenoids Red tide


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24 17

Red algae(mostly

macroscopic)

2) Multicellular algae

Macroscopic: Seaweeds

Brown, red, and green seaweedsColor depends on the type

and amount of

photosynthetic pigments

Brown algae(biggest of all:

kelps)

Green algae

Economic importance

Some “red” species are important commercially

because they produce agar, used to grow bacteria

in a laboratory, and also carrageenin, which is

used in paint, cosmetics, and baking

Some “brown” species produce alginates, used

as stabilizers in frozen desserts, emulsifiers in

salad dressings, etc.

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Unicellular and Heterotrophs (ingestive or phagotrophic, like us!)

Most of them are free-living, some are parasites, some mutualists

Protozoa: Animal-like Protists

Some

Protozoa

FlagellatesMove by flagella

CiliatesMove by cilia

Paramecium

TintinnidsCiliates are the most structurally complex protozoan

AmoebozoansMove by pseudopods

Some are parasitesEntamoeba histolytica, is

spread by means of

contaminated water or

food: causes amebic

dysentery. 100,000 people

die worldwide every year

3rd most importance

disease for humans

Amoeba

Sporozoansall are parasites

Babesiosis (Babesia)

Malaria (Plasmodium)

Cryptosporidiosis

(Cryptosporidium)

Coccidian diseases

(Coccidian parasites infect

the intestinal tracts of

animals)


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The protozoa plasmodium causes malaria (1st disease in importance for humans)

Up to 300 million people become sick with malaria per year and 2 to 4 million die.

Malaria is transmitted by mosquitoes (vectors)

Sexual stage of the life cycle takes place in the mosquito.

Malaria in red blood cells

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Fungus-like Protists Fungus-like

Slime molds(myxomycota)

Water molds(Oomycota)

Heterotrophs (absorptive)

Spores for asexual reproduction

Were previously included in

Fungi

A “Giant amoeba”, whose

nucleus and organelles

have divided repeatedly

within a single large cell

Unicellular and

multicellular stages

•Water molds can be

saprophytes and

parasites in aquatic

and terrestrial

ecosystems

Parasitic water molds damage

fish and many crop plants

• An example is the Irish potato

famine in 1845 and 1847,

which destroyed the potato

crops.

Decomposers or

parasites

But these guys…

Are 2N (Fungi are

N=haploid)

Cell wall of cellulose

(Fungi is chitin)

Amoeboid reproductive

stage (different in fungi)

http://www.ucmp.berkeley.edu/chromista/saprolegnia2.jpg


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Oomycota - Peronosporales

Late blight of potato caused by Phytophthora infestans

Turns the stalk and stem to black slime

Phytophthora infestans - people preparing to

leave Ireland forever during the potato famine

1847

Irish famine of 1847

1 million people died

1 million (at least) had to leave

Ireland

Today

15% of losses in North America

70% in some areas of Russia

where pesticides are not available

the evolution of microbial life: prokaryotes, protistajocha-biology.net/handouts/gralbio/prokaryotes...

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