Microbial Ecology and Symbiosis

For this class, what does one species need to be for microbial symbiosis?

At least one microbial species, but there other can be bacteria, fungi, archaea, other eukaryotes (ex: amoeba)…still debatable about viruses though (because they are not cellular life)

How many groups need to be in a symbiotic species?

At least two partners (but one partner could even be a “group” of microbes)

What is the definition of symbiosis?

A partnership between organisms of different species or groups

Are all microbial symbiotic associations good/positive?

No, they can be positive or negative

Do symbiotic relationships always remain the same?

Nope, they can change and evolve over time

What are the five symbiotic relationships?

1. mutualism

2. synergism

3. commensalism

4. amensalism

5. parasitism

What is mutualism? How do the species interact? How can we be 100% sure it is mutualism?

Mutualism is when each partner benefits (+/+)

Its defining factor is that the partners will have a noticeable negative outcome if they separate or can even fail to grow independently (by growth=decrease in size, low energy acquisition, etc.)

How would you describe the relationship between normal microbial flora and a “host” organism?

Mutualism

In the context of our gut microbes, they get food/energy from us, and we get their help to digest food/they take up space to prevent pathogenic species from growing→there will be a reduction in fitness if separated (we lose the ability to properly digest some food)

True or false: there needs to be a reduction in fitness when the partners separate for it to be considered mutualism?

True (doesnt always have to be death)

How many bacterial species are in the honeybee gut microbiome?

9

How would you describe the two partners in the honeybee mutualism example?

partner 1: the honeybee

partner 2: the group of 9 bacterial species

Describe how the honeybee and the bacteria in its microbiome have a mutualistic relationship? (aka describe how they benefit each other and then what would happen when they separate)

How the bacteria help the honeybee: the bacteria help the bees in digestion and fermentation of plant cell components (nutritional support) and can also help with immunity support

How the honeybee help the bacteria: the bee provides substrates for catabolism for the bacteria (nutritional support) and a protective environment

What happens when they separate: the bees show nutritional depravation, weight gain, immune dysfunction, and overall reduced fitness. As for the bacteria, they have reduced population growth and increased predation (both experience a reduction in fitness→mutualism)

What is synergism? How can we tell it is not mutualism?

Synergism is when there is optional cooperation where partners benefit BUT they can grow independently

We can tell it is not mutualism because the partners can be easily separated with little evidence of severe reduction in overall fitness

How would you describe the relationship between normal flora species and other normal flora species?

Synergistic

In the lower GI tract of humans, many bacteria will ferment the sugars we consume and release H2 and CO2 (bacteria waste). Methanogens (archaea) can use H2 and CO2 as substrates for metabolism

The bacteria provide substrates (h2 and CO2) for the archaeal metabolism while the archaea use bacterial waste (removing down prevents waste build up). They can live separately though

The bacteria and archaea in the lower GI tract are synergistic, but what is their relationship with the human host?

Mutualistic (bactera/archaea will have a population reduction without the human and the human will lose proper nutrient uptake without the bacteria)

What is commensalism?

When one or more partners benefit from the other but the other partner will not benefit nor be harmed (+/0)

What is the most complicated symbiotic relationship? Why?

Commensalism because often the more we look into the relationship, we are likely to recategorize it to something else

What is an example of commensalism we used in class (think wetland ecosystems)

H2S is common in many wetland ecosystems but is toxic to many bacteria. Beggiatoa can oxidize H2S, removing it from the local environment. The Beggiatoa are not affected positive or negatively by its neighbors)

Beggiatoa’s effect on others: removes H2S to make environment more conducive for growth

Other bacteria’s effect on Beggiatoa: none

What are the two subcategories of amensalism?

Antibiosis and competition

What is antibiosis vs competition

Antibiosis is when one partner releases a compound (toxin/substrate) that harms the other

Competition is when partners compete for the same limited resource and harm happens through resource scarcity not substance attack

Why can we say amensalism is the opposite of commensalism?

Because amensalism is when one partner is harmed but the other partner is neither harmed nor benefited (ex: a microbe release a toxin as a natural metabolic product that harms the other partner, but this partner does not effect the microbe)

Is antibiosis when one partner directly harms the other?

No, one partner is BROADLY releasing a toxin (producing it as a natural byproduct and not in response to the presence of a specific microbe=nonspecific harm)

what is ammensalism? is it specific?

when partner 1 is harming the partner 2 (nonspecifically) but partner 1 is not affected by partner 2 (0/-). (you can also think of it is as partner 1 benefits from the harm of partner 2, but this is not parasitism because partner 1 is not specifically attacking partner 2). it is a nonspecific relationship, meaning the organism(s) being harmed are not a specific target of the other. rather the partner is releasing broad acting toxins or antibiotics (partner 1 naturally releases toxins as part of a normal process and not in response to partner 2’s presence)

Describe the relationship between Streptomycens and soil?

It is ammensalistic (specififically antibiosis because it releases toxins)

Streptomycens will secrete an antimicrobial/antieukaryotic compounds into the soil (nonspecifically), and these compounds will kill neighbors that may be competing for the same nutrients, especially since Streptomycens can grow in high population and acquire organic material for itself

*Streptomycens is benefitting from the death of neighbors to acquire more products, but the streptomycens is not producing this toxin specifically for the neighbors

What is parasitism? is specific or nonspecific?

When one or more partners benefits from harming the other but this relationship is SPECIFIC, meaning the organism being harmed is usually the specific target of the other OR cause cellular specific harmful behavior once introduced to the other

*it will sense whether a specific cell type or neighbor is near and CHANGE its behavior to harm the other

How is Legionella an example of parasitism? Where are Legionella usuallh fond?

Legionella are usually found in bacterial freshwater biofilms and have a high amino acid content in their EPS. Amoebas like to prey on these bacteria for nutrition, but when consumed, the Legionella change gene expression to express proteins that specifically prevent the amoeba from disgesting it (SPECIFIC ATTACK) and will take amino acids from the amoeba (disrupting cellular activity)

The Legionella will also replicate in the amoeba using its specific amoeba cell environment (its amino acids) for survival while the amoeba will have reduced fitness

What are Legionella parasitic to in humans?

Human lung macrophages (white blood cells) (usually Legionella are inhaled from freshwater environment)

True or false: parasitic relationship cannot look like a microbe changing her gene expression around a specific target?

False: a microbe has to change its normal gene expression to find a specific target

How do we describe legionella parasites (look at the individual bacteria)

Legionella can use its own metabolic activity but cannot synthesize amino acids as well on its own (needs host cell)

When are coral animals sessile? Motile?

as adults→sessile

early juvenile stage→larvae

Lifepsan of coral

years to decades

Lifespan of bleached coral

weeks to months

Coral microbiome

Algae, bacteria, fungi, archaea, viruses (phage)

What is Coral holobiont:

use to describe coral plus the microbiome symbionts