Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Chapter 32 – Microbial Interactions
Many Types of Microbial Interactions Exist
Microbial Interactions
- Symbiosis = an association of two or more different species of organisms
- Ectosymbiont
o Organism located on surface of another organism (usually larger)
- Endosymbiont
o Organism located within another organism
- Symbiont
o Physical contact between dissimilar organisms of similar size
Microbial Interactions – Further Examples
- Consortium
o Hosts that have more than one associated symbiont
o Relationships can be intermittent and cyclic or permanent
- Types of interactions include
o Mutualism, cooperation, predation, commensalism, parasitism, amensalism, and
competition
...
g
...
aphidicola – some of smallest genomes known
o extreme genomic stability
 no duplication, translocation, inversion, or horizontal transfer
o genes may be common among symbionts
- e
...
Protozoan-Termite Relationship
o Termite provides food for protozoan; protozoan digests cellulose in wood particles,
providing nutrients for termite
Zooxanthellae
- Marine invertebrates harbor zooxantheliae
o Dinoflagellates harbored by marine invertebrates
o Provide organic carbon to host
- Coral has pigments that protect algae from UV radiation
o Also provide N compounds, phosphates, and CO2 to endosymbionts
- Coral bleaching
o Caused by temp
...
g
...
g
...

The Rumen Ecosystem
- Ruminants
o Animals that have stomach divided into four compartments and chew a cud
- Rumen
o Upper part of the ruminant stomach
o Contains large, diverse population of microbes
Ruminants
- Ruminant and microbial community have a mutualistic relationship
o Specific interactions occur within the microbial community
- In cows, acetate, CO2 and H2 are used by methanogenic archaea to generate methane (CH4), a
greenhouse gas
...
g
...
nematophila and nematode host
o E
...
Akkermansia muscinphila and the host gut lining cells
Commensalism
- One organisms benefits and the other is neither harmed nor helped
- Commensal
o Organism that benefits
- Often syntrophic
- Can also involve modification of environment by one organism, making it more suited for
another organism
...


Predation
- Among microbes involves a predator species that attacks, usually killing its prey
- Bdellovibrio penetrates cell wall, grows outside plasma membrane
- Vampireococcus epibiotic mode of attacking prey
- Daptobacter penetrates prey then directly consumes the cytoplasmic contents
...

Parasitism
- One organism gains (parasite) and the other is harmed (host)
- Always some co-existence between host and parasite
- Successful parasites have evolved to co-exist in equilibrium with their hosts
o If balance upset, host or parasite may die
...
g
...

Another Parasitism Example – Lichens
- Lichens, an example of a controlled parasitism
o Association only occurs when organisms are nutritionally deprived
o Mycobiont – fungal partner
 Provides water, minerals, sheltered environment, and firm substratum for
growth
...

Genomic Reduction
- Outcome of long-term parasitic relationship
- Parasite loses unused genomic information
- Examples which can only now survive inside their host cells include
o Aphid endosymbiont Buchnera aphidicola
o Human pathogen Mycobacterium Leprae, Micoplasma genitalia, Encephalitozoon
cuniculi

Ammensalism: An Adverse Microbe-Microbe Interaction
• Negative impact of one organism on another based on release of a specific compound
• Some examples:
– antibiotic production by fungi and bacteria
– use of antibiotic-producing streptomycin by ants to control fungal parasites
– bacteriocin production by bacteria
– production of antibacterial peptides by insects and mammals
• e
...
, cecropins, defensins, and athelicidins
– production of organic acids during fermentation
Competition
• Occurs when two organisms try to acquire or use the same resource
• Two possible outcomes of competition
– one organism dominates
• competitive exclusion principal
– two organisms overlap too much in their resource use, and one
population is excluded
– two organisms share the resource
• both survive at lower population levels
Human-Microbe Interactions
• The human body is a diverse environment
– specific niches are present
– dynamic relationships exist
• Microbiome
– all the genes of the host and the microbiota
– goal is to determine the impact that microbial gene function has on human health
Human-Microbe Interactions – Microbial Terms
• Pathogenicity
– ability to produce pathological change or disease
• Pathogen
– any disease-producing microorganism
Human-Microbe Interactions – Germfree Animals
• Germfree animals
– born by cesarean section, raised in sterility
– can be used to study effects of microbes on animal health by
• comparing germfree animals to normal animals
• introducing a single microbe to the germfree animal and observing effects
– can be coupled with genomic studies for maximum benefit
Human-Microbe Interactions – The Microbiome
• Human Microbiome Project
– initiated in December 2007 by the National Institutes of Health (NIH)
• attempt to define ‘normal’ populations of microbes in and on human beings

–
–

as of 2014, whole metagenomic sequencing data for ~800 healthy human cohort
samples obtained; 16S sequence data from ~5,000 healthy human cohort samples
information gained may shed light on complex interactions between microbes and
humans in both healthy and diseased states

Normal Microbiota of the Human Body Adapt to Many Sites
Normal Microbiota of the Human Body
• Normal microbiota or microflora
– microbes regularly found at an anatomical site
• Relationship begins at birth
– varies with environment and food source
– Bifidobacteria
• found in breast fed babies
• protrophic – can synthesize all amino acids and growth factors from simple
carbohydrates
Microbial Diversity – Innate and Environmental Factors
Reasons to Study Normal Human Microbiota
• To gain insight into possible infections resulting from injury
• To understand causes and consequences of overgrowth of microbes normally absent from a
body site
• To increase awareness of role played by indigenous microbe in stimulating immune response
The Relationship between Normal Microbiota and the Host
• Usually mutually beneficial
– normal microbiota often prevent colonization by pathogens
– bacterial produces, e
...
, vitamins B and K are beneficial to the host
• Opportunistic pathogens
– members of normal microbiota that produce disease under certain circumstances
• Compromised host
– debilitated host with lowered resistance to infection
Skin
•
•
•

•

Commensal microbes include both resident and transient microbiota
Mechanically strong barrier
Inhospitable environment
– slightly acidic pH
– high concentration of NaCl
– many areas low in moisture
Inhibitory substances (e
...
lysozyme, cathelicidins)

Acne Vulgaris
• Caused in part by activities of Propionibacterium acnes
– sebum
• fluid secreted by oil glands
• accumulates, providing hospitable environment for P
...
epidermidis
– predominant bacteria present
– found just inside nostrils
• Nasopharynx may contain low numbers of potentially pathogenic microbes
– e
...
Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenza
Oropharynx
• Division of the pharynx lying between the soft palate and the upper edge of the epiglottis
– alpha-hemolytic streptococci
– diphtheroids
– Gram-negative cocci
– anaerobes in tonsillar crypts
Respiratory Tract
• No normal microbiota
• Microbes moved by:
– continuous stream of mucous generated by ciliated epithelial cells
– phagocytic action of alveolar macrophages
– lysozyme in mucus
Eye and External Ear
• Eye
– from birth throughout a human life, small numbers of bacterial commensals are found
on the conjunctiva of the eye
– the predominant bacterium is Staphylococcus epidermidis
• External ear
– similar to skin flora as well as fungi
Mouth
• Contains organisms that survive mechanical removal by adhering to gums and teeth
– contribute to formation of dental plaque, dental caries, gingivitis, and periodontal
disease
• Within hours of birth, the oral cavity is colonized by microorganisms from the surrounding
environment
Stomach
• Most microbes killed by acidic conditions
– some survive if pass through stomach very quickly
– some can survive if ingested in food particles
Small Intestine
• Divided into three areas
– duodenum
• contains few organisms
– Jejunum

–

ileum
• flora present becoming similar to that in colon
• pH becomes more alkaline

Large Intestine (Colon)
• Largest microbial population of body
– eliminated from body by peristalsis, desquamation, and movement of mucus
– replaced rapidly because of their high reproductive rate
– most of the microbes present are anaerobes
– Bacteroides thetaiontaomicron
• colonizes exfoliated host cells, food particles, and sloughed mucus
Genitourinary Tract
• Kidneys, ureter, and bladder
– normally free of microbes
• Distal portions of urethra
– few microbes found
• Female genital tract
– complex microbiota in a state of flux due to menstrual cycle
– acid-tolerant lactobacilli predominate
Human Microbiota by Body Site
Take Home Message
• This chapter is an interesting juxtaposition between two topics – microbe/organism interactions
and the more specific interactions between humans and the microbes in/on us
• Try to understand the main concepts and terms of the different types of relationships first
• Then, extrapolate that understanding forward to the normal human microbiome
• Last but not least, try to think about what might occur in the different human body areas if the
normal microbiome was disrupted or removed



---