Intended learning outcomes (ILOs)
• List at least four bacterial phyla
• Identify and differentiate between the bacterial phyla described here
• Discuss and explain examples from each of the bacterial phyla described here
• Discuss the impact certain bacterial species have on human health
Bacterial Phyla
Acidobacteria, Actinobacteria, Aquificae, Armatimonadetes, Bacteroidetes, Caldiserica, Chlamydiae, Chlorobi,
Chloroflexi, Chrysiogenetes, Coprothermobacterota, Cyanobacteria, Deferribacteres, Deinococcus-Thermus,
Dictyoglomi, Elusimicrobia, Fibrobacteres, Firmicutes, Fusobacteria, Gemmatimonadetes, Lentisphaerae,
Nitrospirae, Planctomycetes, Proteobacteria, Spirochaetes, Synergistetes, Tenericutes, Thermodesulfobacteria,
Thermotogae, Verrucomicrobi
Actinobacteria
→ Members of the phylum Actinobacteria are Gram-positive and known for their high guanine and cytosine
(GC) content in their DNA.
→ While they can be isolated from aquatic environments, they are the one of dominant bacterial phyla in the
soil.
→ In the soil the Actinobacteria display a filamentous morphology like that of filamentous fungi.
→ The bacteria form extensive mycelial networks that form symbiotic associations with plants – the bacterium
fixes nitrogen in exchange for plant produced sugars.
• Streptomyces
⤷ Streptomyces is the largest bacterial genus with over 500 described species.
⤷ Members of this genus are known for the complex secondary metabolism and produce more than two-
thirds of all our naturally produced antibiotics (neomycin, cypemycin, grisemycin, bottromycins and
chloramphenicol).
⤷ Interestingly, the Streptomycetes are the ones that produce that distinct "earthy" smell after rain.
⤷ The bacterium produces the volatile compound geosmin which becomes more pronounced after the
rains.
TJW Notes
, Bacteroidetes
→ The phylum Bacteroidetes is composed of Gram-negative, non-spore-forming, anaerobic or aerobic, rod-
shaped bacteria that are widely distributed in the environment
→ They ate a major member of the human gut microbiome reaching up to 1011 cells per gram of intestinal
material.
→ They perform metabolic conversions that are essential for the host, such as degradation of proteins or
complex sugar polymers.
→ They also modulate the host immune system through specific interactions.
→ Reduced abundance of the Bacteroidetes in the gut microbiome is associated with obesity.
→ However, the bacterial group appears to be enriched in patients suffering from irritable bowel syndrome
and is involved in type 1 and type 2 diabetes.
→ Bacteroides spp. are specifically were associated with adiposity, insulin resistance and an inflammatory
phenotype.
Firmicutes
→ The Firmicutes are a phylum of mostly Gram-positive bacteria that can be spherical or rod shaped.
→ In contrast to the Actinobacteria, the Firmicutes are the low-G+C group.
→ Many produce endospores, which are resistant to desiccation and can survive extreme conditions and are
therefore important human pathogens.
• Clostridium
⤷ Clostridium is a genus of Gram-positive bacteria.
⤷ They are obligate anaerobes and are rod shaped.
⤷ They are known for their characteristic bowling pin shaped endospores.
⤷ Clostridium species inhabit soils and the intestinal tract of animals,
including humans.
The main species responsible for disease in humans are:
1. Clostridium botulinum
2. Clostridium perfringens
3. Clostridium tetanus
1. Clostridium botulinum:
→ Clostridium botulinum produces the botulinum toxin which can cause botulism.
→ The toxin prevents the release of acetylcholine inhibiting muscle contraction.
→ If the respiratory muscles are targeted it can lead to respiratory failure and death.
→ Interestingly, the toxin has found application in the medical field.
→ Botox (botulinum toxin) and is commonly used in cosmetic surgery to paralyze facial muscles to
reduce the signs of aging.
→ It is also used to in the treatment of chronic migraines.
TJW Notes
