Diversity of Microbes

Option F.1

Assessment statementsF.1.1 Outline the classification of living organisms into three domains.F.1.2 Explain the reasons for the reclassification of living organisms into three domains.F.1.3 Distinguish between the characteristics of the three domains.F.1.4 Outline the wide diversity of habitat in the Archaea, as exemplified by methanogens,

thermophiles and halophiles.F.1.5 Outline the diversity of Eubacteria, including shape and cell wall structure.F.1.6 State, with one example, that some bacteria form aggregates that show

characteristics not seen in individual bacteria.F.1.7 Compare the structure of the cell walls of Gram-positive and Gram-negative

Eubacteria.F.1.8 Outline the diversity of structure in viruses including: naked capsid versus enveloped

capsid; DNA versus RNA; and single stranded versus double stranded DNA or RNA.F.1.9 Outline the diversity of microscopic eukaryotes, as illustrated by Saccharomyces,

Amoeba, Plasmodium, Paramecium, Euglena and Chlorella.

The five kingdoms• Established in 1959 by Robert

Whittaker• Bacteria: single-celled organisms with

no organized nucleus and no membrane-bound organelles

• Protista: single-celled organisms with an organized nucleus and organelles each surround by a membrane

• Fungi: multicellular organisms which obtain their food using extracellular digestion and have cell walls of chitin

• Plants: multicellular organisms which obtain their food by photosynthesis and have cell walls of cellulose

• Animals: multicellular organisms which obtain their food by feeding on other organisms and have no cell wall

Five kingdoms grouped into two categories

• Prokaryotes: bacteria which lack an organized nucleus and no membrane-bound organelles

• Eukaryotes: all of the other kingdoms which have an organized nucleus and membrane-bound organelles

The three domains• Attempt by Carl Woese to improve the accuracy of the classification system based

on studies of rRNA

• Bacteria: or Eubacteria (true bacteria); prokaryotes lacking an organized nucleus and membrane-bound organelles.

• Archaea: formerly Archaebacteria or ‘ancient’ bacteria. Also prokaryotes; most live in extreme environments. NOT BACTERIA.

• Eukarya: single-celled and multicellular organisms which all have their DNA contained in a nucleus; plants, animals, protists, and fungi.

Reasons for reclassification into three domains

• rRNA is a molecule common to all organisms

• Performs same function in all organisms

• Coded for by DNA• By looking at variation in the

sequence of rRNA, evolutionary relationships became apparent

• Eubacteria and Archaea have different molecules making up their cell walls

• E and A have different molecular structure of their cell membranes

• E and A have different sequences of nucleotides in their rRNA

Characteristics of the three domains

Histones IntronsSize of

Ribosomes

Cell membrane

lipids

Peptidoglycan in cell wall

Organelles

Eukarya Present Present 80S Unbranched hydrocarbons Absent Present

ArchaeaHistone-

like proteins

Present in some

70SSome

branched hydrocarbons

Absent Absent

Eubacteria Absent Absent 70S Unbranched hydrocarbons Present Absent

Diversity of habitat of Archaea

• Methanogens – use carbon dioxide to make methane; obligate anaerobes; live in guts of termites and cattle, Siberian tundra, swamps rice fields, and in large intestines of dogs, pigs, and humans

• Thermophiles – live in sulfur hot springs where the pH is very acidic and temperatures are up to 90°C; some live in hydrothermal vents up to 105°C

• Halophiles – live in the Dead Sea, the Great Salt lake, and evaporated salt water ponds

Diversity of Bacteria

Indigenous microbiota

Streptococcus mutans is the primary bacterium involved in plaque formation

and initiation of dental caries.

While E. coli is a consistent resident of the small intestine. Some strains of E. coli are pathogens that cause intestinal infections, urinary tract infections

and neonatal meningitis.

Diversity of Bacteria• Aggregation

– Vibrio fischeri emit light when in large groups, but not alone

– Bioluminescence caused by turning on of gene by increased amount of signal molecule

– Exist in light organs of squid– Bacteria senses high density based upon

amt. of signal present called quorum sensing

• Variety of cell wall– Gram +

• Stain purple– Gram –

• Stain pink

TED Talks Microbes: Bonnie Bassler on how bacteria “talk”

Comparison of gram+ and gram- bacteria

Cell wall structureGram+ bacteria

(stain purple)

Gram– bacteria

(stain pink)

Complexity Simple Complex

Amount of peptidoglycan

(protective sugar network)

Large amount Small amount

Peptidoglycan placement

In outer layer of bacteriaCovered by outer

membrane (protects from antibiotics)

Outer membrane AbsentPresent with

lipopolysaccharides (toxic to host) attached

Diversity of structure of viruses• Are viruses alive?• Not cellular• Cannot reproduce without a

host• Basic structure

– Nucleic acid • DNA (double- or single-stranded)• RNA (double- or single-stranded)

– Several enzymes– Protein coat (capsid)

• May be naked or enveloped by membrane

Diversity of microscopic eukaryotes

Organism Nutrition Locomotion Cell wall Chloroplasts Cilia or flagella

Saccharomyces

Amoeba

Plasmodium

Paramecium

Euglena

Chlorella

Saccharomyces • Fungi• May respire aerobically or

anaerobically• Ferments carbohydrates in flour

or malt and gain energy from this digestion

• Carbon dioxide gas (in bread) and ethanol (in beer) are by-products

• Secrete enzymes outside their cells and absorb the produces of digestion back into the cell

• Have chitin in cell wall

Amoeba

• Fluid state of cytoplasm enables it to change its shape easily• Pseudopodia wrap around a prey in order to trap it in a food

vacuole for intracellular digestion

Plasmodium• Parasitic heterotroph• Mosquitoes carry and infect humans causing malaria

Paramecium• Ciliated autotroph• Contains chlorophyll a and b• Intracellular digestion• Food taken into oral groove and passes to gullet

Euglena

• Both autotrophic and heterotrophic

• Contains chlorophyll• Has eyespot which

facilitates movement towards light

• Can absorb food from outside the cell

• Has flagellum

Chlorella• Single-celled green algae• Non-motile• Cell wall of cellulose• Thought to be beneficial as a dietary supplement