1 - Planetary Health & Ecosystems Flashcards
Planetary health
The health of human civilisation and the state of the natural systems on which it depends
What is the health of humanity intrinsically linked to
The health of the environment
Anthropocene epoch
the time during which humans have had a substantial impact on our planet
One health
Collaborative approach to achieve optimal health and well-being outcomes, recognizing the interconnections between people, animals, plants and their shared environment
Role of microbes in planetary health
- Responsible for about half of all primary production
- Drive many important cycles on earth
- Important roles in health of animals plants and environments
Important cycles driven by microbes
- Generate oxygen
- Carbon cycling and sequestration
- Cycling of other nutrients
- Climate change / global warming
Ecosystem
- A complex of plants, animals and microbial communities and their physical environment
- Are dynamic and changing
Habitats
- Smaller parts of ecosystem
- May not be suited to all members of the ecosystem
- Contain multiple microenvironments
Examples of environments uniquely suited to microbes
- Hot springs
- Deep ocean thermal vents
- Acidic environments
Microenvironments
- The space immediately surrounding microbial cells and that they directly experience
- Conditions can change dramatically over small distances
Layers of soil
- O horizon: Plant material
- A horizon: Surface soil (high microbial activity)
- B horizon: Subsoil (Lower microbial activity)
- C horizon: Soil base (Ver low microbial activity
Microbial composition of a single soil particle
- Microbes in the outer zone consume all the O2 before it can diffuse to the centre
- Only anaerobic organisms live at the centre, then microaerophiles (low O2), then strict aerobes
- facultative anaerobes could be distributed throughout
Oxygen in liquid culture and colonies on agar
Poor diffusion and rapid consumption
Types of metabolic activities occurring in an ecosystem are a function of
- Species present
- Population sizes
- Physiological state
Rates at which metabolic activities occur are a function of
- Nutrient availability
- GRowth conditions
Why do microbes grow relatively slow in nature
- Resources and conditions are usually suboptimal
- Nutrients levels may be low
- Nutrients are not evenly distributed through the environment
- Microbes typically grow in mixed populations (in competition with other microbes)
Growth rates in nature vs in lab
- Growth rates in nature are well below maximal growth rates measured in labs
- E.g. E.coli in gut is about 12 hours, in lab 20 mins
Oligotrophic
- Low nutrient environments
- Therefore most organisms in nature are in state of growth arrest
Growth arrest
- Not actively growing, but also not dying
- Stressed by lack or nutrients or sub-optimal conditions
- Organisms must be able to survive starvation
Eutrophication
- Increase in nutrient availability
- Occurs in freshwater lakes as a result of water run off (causes algal bloom)
- Input of nutrients results in increased biological oxygen demand
Microbial strategies to cope with starvation
- May produce storage polymers, which they use when starving (e.g. polysaccharides)
- Decrease cell size (membrane lipids and ribosomes are recycled)
- Form endospores (Gram positive bacteria)
- Starvation proteins
- Enter viable but non-culturable (VBNC) state
Community
- Population of one species living in association with one or more other species
- Intense competition may occur, but also cooperation
Population
Group of microbes of same species residing at the same place at the same time
Microbiome
Comprises all of the genetic material within a microbiota (the entire collection of microorganisms in a specific niche, such as the human gut)
Two ways microbial diversity within communities can be expressed
- Species richness and species abundance
- Can change quickly over short timeframe
Species richness
Total number of different species present
How can species richness be measured
By culturing species in the lab or using molecular nucleic acid techniques to determine diversity of phylotypes
Species abundance
Proportion of each species within the community
What is richness and abundance functions of
- Prevailing conditions
- Types of nutrient available
Example of high species richness
- Undisturbed, organic-rich soils
- Lots of diverse nutrients (supports many different
species)
Example of low species richness
- Extreme environments
- Conditions only allow proliferation of select microbes
Examples of resources that govern microbial growth in nature
- Carbon
- Nitrogen (organic and inorganic)
- Other macronutrients (S, P, K)
- Electron donors and acceptors
Examples of conditions that govern microbial growth in nature
- Temperature
- Water potential (dry, moist, wet)
- pH
- Light
- Osmotic conditions
Two broad groups of soil
Mineral soils (Weathered rock, major group) and organic soil (derived from sedimentation in marshes and bogs)
Composition of soil
- Inorganic mineral matter (~40% by volume)
- Organic material (~5%)
- Air and water (~50%)
- Micro- and macro-organisms (~5%)
Factors limiting microbial growth
- Phosphorous
- Nitrogen
- oxygen
- Water availability
Rhizosphere
Soil surrounding plant roots that receives plant secretions
Where is microbial activity highest
Rhizosphere and surface layers (rich in organic material)
Examples of freshwater environments
- Lakes, streams, rivers, glaciers
- Resources and conditions vary widely
- o2 most important factor as does not dissolve well in water
Freshwater as microbial habitat
- Both O2 producing and O2 consuming organisms are present
- Balance between photosynthesis (O2 producing) and respiration (O2 consuming)
- Controls cycles of carbon, O2 and other nutrients
Main primary producers in freshwater
Oxygenic phototrophs
Oxygenic phototrophs
- Produce O2 and new organic material (fix carbon)
- Obtain energy from light, use water as an electron
donor - Includes algae and cyanobacteria
Layers of freshwater
- Epilimnion
- Thermocline
- Hypolimnion
Epilimnion
- Surface layer, warmer, less dense
- Higher in organic matter, oxygen
- Dominated by aerobic or facultative organisms
- Consume most organic nutrients and 02
Thermocline
Transition zone
Hypolimnion
- Bottom layer, cooler, denser
- o2 depleted, less organic nutrients
- Dominated by anaerobes
Why is running water harder to sample
Populations may be transient, therefore most studies focused on lakes
Major prokaryotic groups observed in freshwater (from largest to smallest)
- Proteobacteria
- Actinobacteria
- Bacteroidetes
- Cyanobacteria
Ocean vs freshwater as microbial habitat
- Nutrient levels in open ocean are comparatively lower (besides oxygen)
- Water temperature is generally cooler
- Total cell numbers typically 10-fold lower than in lakes
- Typically have smaller cells (due to nutrient poor environment, more energy efficient)
Ocean microbial communities varying according to water depth
- Phototrophic microbes use the sun’s energy in the top 200 m of the water column
- In deeper zones the microbes use organic and
inorganic chemicals for energy
Three seasonal microbial communities in ocean water
- Spring surface water bloom
- Summertime community in upper water column
- Deeper, more stable community
Primary production in oceans
Prochlorophytes
Prochlorophytes
- Tiny, photosynthetic prokaryotic phototrophs
- Type of cyanobacteria
- Contain chlorophylls alpha and beta but no phycobilin
- 4 strains with distinct ecotypes (each ecotype photosynthesises at different light intensities)
