Microbial diversity

Question 1

Bacterial phyla

Answer 1

80+ phyla can be distinguished based on 16s ribosomal RNA
Only 30 phyla have species successfully cultured
More than 90% of characterised genera and species come from four phyla – proteobacteria, actinobacteria, firmicutes, Bacteroidetes
Size of each bacterial phylum varies
Largest phylum is proteobacteria with 6 classes and 1300 species
Proteobacteria types include gamma, beta, delta, epsilon and zeta
For each there are more 16s rRNA gene sequences than type species with both decreasing from proteobacteria to zetraproteobacteria which has no type species
For the remaining phyla 16s rRNA gene sequences are between 1 and 10 to the sixth power while type species is low for some phyla and higher for others

Question 2

Proteobacteira phylum

Answer 2

Proteobacteria are:
- The largest and most metabolically diverse bacterial phylum
- Many different shapes
- Gram-negative
- 6 classes
- Majority of known medically, industrially and agriculturally significant bacteria including pathogens
- Horizontal gene flow important in shaping metabolic diversity

Question 3

Firmicutes phylum

Answer 3

Firmicutes are:
- Mostly gram-positive with some exceptions
- Live in the gut
- Endospore formers, lactic acid bacteria, other
- First colonisers in the intestine of newborns
- Genetic exchange common and non-selective
- Obligate aerobes or facultative anaerobes or strict anaerobes

Question 4

Endospores

Answer 4

Some bacteria produce intracellular spores a stripped-down dormant form to which the bacterium can reduce itself
- Survival structures
- Can survive in a metabolically inert state for decades
- Highly resistant to extreme temperatures, radiation and stresses
- Can only be killed by temp reached in autoclave (121 degrees c)
- Most resistant biological structures
- Germinate to become vegetative cells when appropriate nutrients become available

Question 5

Endospore formation

Answer 5

Process starts w replication of bacterial chromosome but then cells divide asymmetrically. Mother cell engulfs developing endospore then once development is complete it is released
Stage 0-1 = while replicating chromosome, nucleoid lengthens to from the axial filament (which signals sporulation)
Stage 2 = sporulation septum forms at a point about a quarter of cell length – polar septum. Large portion of cell is called mother cell, which is in charge of nourishing the developing endospore
Stage 3 = mother cell engulfs/phagocytes the developing endospore completely
Stage 4 = developing endospore is surrounded by 2 cell membranes, its own and the mother cells. A layer of murein, the cortex, is synthesised between the two membranes
Stage 5-6 = developing endospore becomes surrounded by additional layers, the exosporium. The developing endospore synthesises dipicolinic acid
Stage 7 = mother cell lyses, releasing mature endospore
Position of endospore in mother cell differs among bacterial species = useful in identification

Question 6

Endospore staining

Answer 6

1. Bacteria stained w malachite green dye
2. Bacteria treated w steam to allow dye to penetrate endospores coat
3. Slide rinsed w water
4. Counter stained w safranin

Question 7

Actinobacteria phylum

Answer 7

Actinobacteria are:
- Gram-positive
- Morphologically very diverse
- Widely distributed in the soil. Many responsible for breaking down wide range of plant and animal debris
- Major producers of antibiotics
- Some pathogenic

Question 8

Streptomyces

Answer 8

600+ species
Grow at filament tips, branch often
Results in compact, convoluted mycelium and colony
Primary soil microorganisms, responsible for earthy odour of soil
Alkaline/neutral soil more favourable
Found more in well drained than waterlogged soil
Produce many extracellular enzymes that help utilise polysaccharides, proteins, fats and other polymers
Produce 50% distinct antibiotics
Genomes typically quite large because many genes requires for antibiotic synthesis
60+ streptomycete used in human and veterinary medicine

Question 9

Cyanobacteria phylum

Answer 9

Cyanobacteria are:
- Gram-negative
- Photosynthetic
- Original producers of atmospheric o2
- Still contribute to about half of all o2 released into atmosphere
- Some have filamentous form, others unicellular
- Some produce toxins that affect the organisms that feed on them and the predators that then feed on them
- May be risk to humans in drinking water