Unit 2--Lecture 10 (Microbial Ecosystems) Flashcards
Ecosystem
The sum of the total of all organisms and abiotic factors in a particular environment
An ecosystem contains many different habitats
Microbes account for 50% of all biomass on earth
Habitat
Portion of an ecosystem where a community could reside
Species Richness
Total number of different species present
Species Abundance
Proportion of each species in an ecosystem
Microbial species richness and abundance are functions of the kinds and amounts of nutrients available in a habitat
Guilds
Metabolically related microbial populations
Sets of guilds form microbial communities that interact with microorganisms and abiotic factors in the ecosystem
Niche
Habitat shared by a guild
Supplies nutrients as well as conditions for growth
Biogeochemistry
The study of biologically mediated chemical transformations
A biogeochemical cycle defines he transformations of a key element by biological or chemical agents
—-typically proceeded by oxidation-reduction reactions
Environments and Microenvironments
Physiochemical conditions in a microenvironment are subject to rapid change, both spatially and temporally
Resources in natural environments are highly variable, and many microbes in nature face a feast-or-famine existence
Growth rates of microbes in nature are usually well below maximum growth rates defined in the laboratory
Competition and cooperation occur between microbes in natural systems
Biofilms
Assemblages of bacterial cells adhered to a surface and enclosed in an adhesive matrix excreted by the cells
The matrix is typically a mixture of polysaccharides
Biofilms trap nutrients for microbial growth and help prevent detachment of cells in flowing systems
Surfaces and Biofilms
Pseudomonas aeruginosa
Intracellular communication (quorum sensing) is critical in the development and maintenance of a biofilm
—-both intraspecies signaling and interspecies signaling likely occur in biofilms
Bacteria form biofilms for several reasons:
—-self-defense (physical forces that sweep away unattached cells, phagocytosis, penetration of toxins)
—-allows cells to remain in a favorable niche
—-allows bacterial cells to live in close association with one another
Soil
The loose outer material of Earth’s surface
Consists of four distinct layers:
—-O horizon: at the surface, with undecomposed plant material
—-A horizon: with most microbial growth, rich in organic material and nutrients
—-B horizon: the subsoil where organic material leached from the A horizon gathers, little microbial activity
—-C horizon: the base that is directly above the bedrock and forms from the bedrock
Soils are composed of:
Inorganic mineral matter (40% of soil volume)
Organic matter (5%)
Air and water (50%)
Living organisms (5%)
Soils
Soils are formed by interdependent physical, chemical, and biological processes
—-carbon dioxide is formed by respiring organisms that form carbonic acid that breaks down rock
—-physical processes such as freezing and thawing break apart rocks, allowing plant roots to penetrate and form an expanded rhizosphere
—-the rhizosphere, the area around plant roots where plants secrete sugars and other compounds, is rich in organic matter and microbial life
The Terrestrial Subsurface
The deep soil subsurface can extend for several hundred meters below the soil surface
—-archaea and bacteria
The deep subsurface is home to a group of organisms that may be the Archaea that are most closely related to eukaryotes, the Lokiarcheota
Freshwaters
Environments are highly variable
The balance between photosynthesis and respiration controls the oxygen and carbon cycles
Phytoplankton: oxygenic phototrophs suspended freely in water (include algae and Cyanobacteria)
Benthic species are attached to the bottom or sides of a lake or stream
Epilimnion: the warmer, less dense surface water
Hypolimnion: the cooler, denser water at the bottom of a lake or pond
Thermocline: separates the two
Freshwater (Rivers)
May be well mixed because of rapid water flow
Can still suffer from oxygen deficiencies due to high inputs of:
——organic matter from sewage
——agricultural and industrial pollution
Freshwaters: Biochemical Oxygen Demand (BOD)
The microbial oxygen-consuming capacity of a body of water
Increases with the influx of organic material (from sewage), then decreases over time
The Marine Environment
Compared to most freshwater environments, the open ocean is:
——saline
——low in nutrients, especially with respect to nitrogen, phosphorus, and iron
——cooler
Oxygen Minimum Zones (OMZs)
——regions of oxygen-depleted waters at intermediate depths
——high oxygen demand
——nutrient-rich areas
——high levels of denitrification and anammox
——OMZs are expanding
Major Marine Phototrophs
Most of the primary productivity in the ocean is due to photosynthesis by prochlorophytes
Prochlorococcus accounts for:
—— >40% of the biomass of marine phototrophs
—— ~50% of the net primary production
Trichodesmium: cyanobacterium, abundant phototroph
Ostreococcus: small phototrophic eukaryotes, important primary producers
Pelagic Bacteria, Archaea, and Viruses
The most abundant marine heterotroph is Pelagibacter, an oligotroph
Oligotroph: an organism that grows best at very low nutrient concentrations
Pelagibacter and other marine heterotrophs contain proteorhodopsin, a form of rhodopsin that allows cells to use light energy to drive ATP synthesis
Viruses are the most abundant microorganisms in the oceans
The Deep Sea
> 75% of all ocean water is deep sea, lying primarily between 1000 and 6000 m
Organisms that inhabit the deep sea must deal with:
——low temperature
——high pressure
——low nutrient levels
Deep-sea microbes are:
——piezophillic (pressure-loving) or piezotolerant
——often psychrophilic (cold-loving) or psychrotolerant, but can also be thermophilic or thermotolerant
Hydrothermal Vents
Thriving animal and microbial communities are associated with deep-sea hydrothermal vents
Chemolithotrophic bacteria predominate at vent
——utilize inorganic materials from the vents
Thermophiles and hyperthermophiles are present
