Environmental Micro Exam 3

What is mutualism?

both organisms benefit

What is an example of mutualism?

lichens

What is synergism?

both organisms benefit

What is the difference between mutualism and synergism?

in mutualistic relationships, both organisms benefit, in synergistic relationships, both organisms cannot survive without the other but both benefit

What are some examples of synergism?

secondary fermentation, nitrification, and methanogenesis

What is commensalism?

one organism benefits and one is neutral or unharmed

What is an example of commensalism?

sake production

What is neutralism?

both organisms are neutral

What is an example of neutralism?

lactobacillus and streptococcus in yogurt starter cultures

What is predation?

one organism benefits and one organism is harmed

What is an example of predation?

vapiprovibrio chlorellavorus

What is amensalism?

one organism is neutral or benefits and one organism is harmed

What is an example of amensalism?

antibiotic production

What is competition?

both organisms are harmed

What is an example of competition?

aspergillus flavis atoxigenic strains

What makes up the mutualistic relationship of lichens?

fungi and alga (cyanobacteria)

Where are lichens seen?

They grow on rocks, trees, roofs, and soil

What does the alga/cyanobacteria provide the organism?

it provides the organic matter that feeds the fungi

What does the fungi provide the organism?

provides a solid anchor to protect the alga from erosion by rain or wind, it also provides acids that free inorganic nutrients needed by photosynthetic partner

Why are lichens considered primary producers?

They perform photosynthesis and fix CO2 into organic carbon

How is lichen morphology determined?

fungal morphology

What are the four main types of lichen morphology?

* Fruticose
* Foliose
* Crustose
* Gelatinous

Fruticose Lichen

* shrub-like appearance
* 3D
* vertical growth pattern

Foliose Lichen

* lobed “leaf-like” appearance
* loosely attached to substrate

Crustose Lichen

* tightly attached to substrate
* dusty/crusty growth
* Endolithic - immersed in rock
* Endophloidic - immersed in plant tissue
* Leprose - loose and powdery with no layering

Gelatinous Lichen

* primarily composed of cyanobacteria
* gel-like appearance from polysaccharide mucilageon exterior of cyanobacterial cells
* looks gross
* makes outside gooey

Example of Gelatinous Lichen

Collema coccophorum

* tar jelly lichen
* photobiont: Nostoc (cyano)
* grows on soils and sand

Example of crustose lichen

Dimelaena oreina

* Golden Moonglow Lichen
* Grows on vertical siliceous rock
* Common in North and South American deserts
* Photobiont: Trexbouxia (unicellular green alga)

Example of Foliose Lichen

Imshaugia placecorodia

* American Starburst Lichen
* Photobiont: trexbouxia
* grows only on pine bark

Example of Fruticose Lichen

Cladonia rangiferina

* reindeer lichen
* photobiont: asterochloris
* source of bioactive compounds (tested as antimicrobials)
* cold tolerant (found on alpine tundra and boreal forests)
* used in many research studies as model lichen

Role of Bacteria in Lichen System

Recent evidence suggests that bacteria contributes to:

* Supply of N, P, and S
* Resistance against biotic/abiotic stressors
* Support of photosynthesis
* Degradation of lichen thallus (to recycle nutrients)
* Breakdown of toxic metabolites (like heavy metals)

What are the syntrophic partners?

* Primary degrader: responsible for mineralization of large compounds to small metabolites
* Consumer: removes degraders waste products

Commensalism: Sake Production

* Aspergillus oryzae is added to rice and ferments for 5-7 days
* During this time it produces amylases, glucoamylases, and proteases
* converts starch to sugar
* S. cerevisiae (yeast) is then added and ferments for 7 days
* S. cerevisiae benefits and aspergillus is unaffected

Neutralism

* rare in microbial communities
* can occur when different populations consume separate limiting nutrients and don’t produce any by-products that affect each other

What are the requirements for predation?

* motility


* ability to breakdown complex macromolecules

What are the difference modes of bacterial predation?

* facultative or obligate
* individual or social
* cell-to-cell contact or remote

Facultative or obligate

* nutrient acquisition
* they can or they MUST feed on other organisms

Individual or social

* bacterial wolf-packs


* one cell breaks down prey or multiple cells work together to break down prey

cell-to-cell contact or remote

* diffusion
* must be touching or cells must produce extracellular enzymes that break down prey

What are the two forms of cell-to-cell contact?

epibiotic or endobiotic

Epibiotic

* lives on the surface of the host

Example of epibiotic predator:

* Vampirococcus
* Gram -
* Freshwater (anoxic lakes in spain)
* motile
* attaches to surface of Chromatium minus

via “cytoplasmic bridges

Endobiotic

* enter prey and divide inside the cell

Example of endobiotic predator:

* Daptobacter
* cytoplasm
* first identified gammaproteobacterium capable of predation
* Bdellovibrio
* periplasm

Bacterial Wolf-Pack Lifestyle

* Myxococcus xanthus
* Gram – soil bacterium with a complex life cycle
* Form complex fruiting bodies during starvation
* Produce spores for dissemination
* Social behavior- most cells die during spore formation
* Most lyse to feed sporulating cells

Wolf-Pack Hypothesis

* M. xanthus cells move as swarms toward prey cells


* Increases density of hydrolytic enzymes needed to lyse prey
* Facultatively multi-cellular

Mycotoxin

toxin produced by mold

Aflatoxin

Toxins produced by Aspergillus flavus

* Four types: B1, B2, G1, G2
* Fluoresce blue or green (B or G) under UV light


* Problematic contaminant of food supply in developing counties
* Stockpiled as chemical weapon by Iraqi government in the 1980s

Ammensalism: Antibiotic Production

* Eleftheria terrae
* produces newly discovered antibiotic teixobactin
* Teixobactin
* Effective against G+ bacteria
* Binds to peptidoglycan precursors
* Kills MRSA, M. tuberculosis, and B. anthracis

What is competition?

Two or more microorganisms competing for the same resources or space

Example of competition

* Aspergillus flavis atoxigenic strains
* Alfa-Guard® reduces aflatoxin levels by up to 85%

What are biofilms?

* microbial megacommunities
* can form on any water-associated surface
* attach to the surface via production of extracellular polymer matrix

What are the biofilm development stages?

1. Reversible attachment
2. Irreversible attachment
3. First maturation phase
4. second maturation phase
5. Dispersal phase

Why are biofilms important?

* protection against abiotic stress
* protection against grazing
* increased resistance to antimicrobial agents
* Why? It’s more difficult for microbes to penetrate through whole biofilm

What are some examples of biofilms and humans?

* dental plaque
* waste water treatment
* pipelines
* nosocomial infection on medical implants

What’s the problem with biofilms and pipelines?

* MIC or microbially influenced corrosion
* it’s considered a contributing factor to pipeline failure and leaks

What is the blame for the biofilm-pipeline issue?

* metal reducers (shewanella, geobacter)
* sulfur reducers (deltaproteobacteria, firmicutes)
* fermenters (acid by-products)

What is quorum sensing?

* regulation of gene expression by diffusible molecules
* abundance of signaling molecules usually correlates with population density
* autoinducers

What are autoinducers?

extracellular signaling molecules

What must a good signaling molecule be able to do?

1. Must be small
2. Must be able to be released via passive diffusion or active transport
3. Must be recognized by other cells and induce a response

What are some ecological benefits to quorum sensing?

* coordination of gene expression and/or behavior among members of a bacterial community
* avoidance of host immune or defense responses
* signaling between a host and a bacterium

How does signaling work in gram - bacteria?

* AHLs aka N-acyl homoserine lactones
* most well studied signaling molecule for G-
* Made up of:
* Homoserine Lactone Ring
* Fatty acyl side chain
* Length and modification of side chain determines signal

How does Aliivibrio fischeri (gram -) work?

* bioluminescence is correlated with cell density in the host
* cells release in the AHL signal
* accumulates in host and initiates a signal that induces bioluminescence

The lux operon

* Two proteins involved in quorum sensing:
* AHL synthase
* AHL responsive regulatory protein

luxA

luciferase alpha subunit

luxB

luciferase beta subunit

luxC

encodes a fatty reductase that synthesizes the aldehyde substrate necessary for luciferase

luxD

involved in aldehyde synthesis (produces fatty acids)

luxE

involved in aldehyde synthesis

luxG

flavin reductase

How does signaling work in Gram + bacteria?

* Don’t use AHLs because of thick peptidoglycan layer that AHLs cannot penetrate
* They instead use gamma - butyrolactones or signaling peptides

How do gamma-butyrolactones work?

* Don’t activate expression like AHLs
* Instead, they alleviate repression of gene expression

Example of gamma-butyrolactones being used?

* factor in streptomyces griseus
* stimulates mycelium formation and streptomycin production
* Mechanism: regulates expression of AdpA
* In low levels: repressor (ArpA) bound to AdpA
* In high levels: repressor dissociates from AdpA

Peptide signaling

Two component regulatory system:


1. Histidine kinase sensor protein (in membrane)
2. Cytoplasmic response regulator protein
3. Autoinducing peptide

More common form of G+ signaling

How does Peptide Signaling work?

* sensor protein detects the peptide signal
* communicates the changes to response regulator
* response regulator then regulates changes in gene expression
* response to stimulus

What is quorum quenching?

* breakdown of AHLs to interfere with the signal
* Two types of enzymes:
* AHL lactonases
* AHL acylases

Why does quorum quenching occur?

* competitive advantage
* avoid detection by host immune system

What are the three types of interkingdom signaling?

1. Bacteria respond to host signals
2. Interference in bacterial signaling by host
3. Recognition and response to bacterial signals by host (immune system)

What is the holobiont?

the complex of all cellular components of an organism

Why do we use the invertebrate model?

* Experimental traceability
* easy to work with
* Simple microbial communities
* mechanisms easier to disentangle
* Features of the symbiosis are conserved among all animals
* broad application

Why are bacterial symbionts so important in the ocean?

* ocean in generally nutrient poor
* bacterial symbionts can harness chemical energy sources
* provide nutrients to themselves and host
* alternatives: defense (predators or pathogens)

Euprymna scolopes - The Hawaiian Bobtail Squid

* cephalopod
* 30-50 mm in lenth
* matures in 80 days
* nocturnal
* variety of camouflage mechanisms
* ink, burying, bioluminescence
* predator: Hawaiian Monk Seal

Euprymna - Aliivibrio Symbiosis

* mutualistic relationship
* horizontally transmitted between generations

Challenges to horizontal transmission:

* Host must be able to recruit, enrich, and harvest its microbial partner
* Stability
* role of immune system
* Partner must be able to tolerate multiple environments
* “Niche Switch”
* totally changes the environment where it lives
* macroenvironment - microenvironment

What are the benefits to the symbiosis between the Bobtail Squid and Aliivibrio?

* Animal host (E. scolopes)
* counter illumination during nocturnal activity
* control intensity - resemble moonlight
* Bacterial symbiont (A. fischeri)
* nutrient rich environment

The Diel Cycle

Dawn: squid bury themselves in sand

* expel \~95% of all symbionts
* repopulate

Night: active with peak population

What is the benefit of expulsion?

There is then a large population of this bacteria in the environment available to the baby squid when they hatch

What is symbiont specificity and how does it relate to the squid - aiilvibrio relationship?

* how many different species of symbionts does the host associate with
* ONLY A. fischeri colonize the light organ
* Only G- cells can accumulate in mucus
* Mucus acts as chemotaxis trigger for A. fischeri
* Prior to entering crypt, cells are exposed to two rounds of oxidative stressors
* Toxic concentrations of nitric oxide (NO)
* Halide peroxidase - hypophalous acid

Symbiont specific morphogenesis

1. Diverse population of bacteria outside of host, motile and nonmotile
2. Gram - population aggregates in mucus
3. Exposure to oxidative stressors
4. Cells that survive move into crypt


1. bacteria lose their flagella and can no longer move
5. Cells move into mature area of light organ

What is Darwin’s paradox?

How can such diverse ecosystems and environments be supported in clear, oligotrophic, or nutrient poor waters

* coral reefs are effective in recycling nutrients

What is the Island Mass Effect?

* Increase in phytoplankton biomass near island reef systems
* Supports rich ecological systems that otherwise lack new production

What did the Gove et al. study find?

* first to study IME at an ocean scale rather than single island or island chain scale
* Increase in coral abundance in systems with increased phytoplankton biomass
* spans multiple trophic levels

Coral - Microbe Symbiosis

* Host: cnidarian stony corals
* Symbiont: symbiodinium photosynthetic dinoflagellate
* zooxanthellae
* Foundation of coral reef ecosystems
* Reef-building coral
* broadcast spawning: release gametes into water
* male and female fuse to form larva
* larva settle and establish new coral colony

Is the symbiosis between coral and microbe horizontal or vertical?

* It’s both
* Vertical: symbiodinium cells present in egg prior to release
* Horizontal: free-living symbiodinium can be ingested by juvenile coral

What are the benefits of the relationship between coral and microbe?

* host: organic compounds
* symbiont: inorganic nutrients

What are the threats to the symbiosis of coral-microbe?

Coral Bleaching

What is coral bleaching?

* loss of color from coral due to expulsion or lysis of the symbiont
* exposes the limestone skeleton

What causes coral bleaching?

* stress
* the most common stressor is changes in temperature
* the smallest change in temperature (0.5 - 1.5 degrees above or below optimal) can result in this

What are the current predictions for coral reefs?

* loss of all Indian Ocean corals within a few years
* Global collapse of corals by 2050

What is vibrio sholloi?

* coral reef pathogen - oculina patagonica
* produces a toxin that inhibits zooxanthellae photosynthesis
* the infection only occurs at elevated temperatures
* it can be treated with antibiotics