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microbial ecology chapter 30.
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so this is basically a review of biology
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when you learned about
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ecology and all the different levels and
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the relationships and like
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symbiotic relationships and the trophic
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levels and food chains and food webs
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but we're just going to be applying it
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to microbes now
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so if you remember ecology is the study
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of relationships of organisms to each
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other
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and to their environment so
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one individual is our lowest level
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of ecological organization a group of
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that same individuals
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so a group of elk make up a population
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then you have a group of elk plus a
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group of
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mountain lions plus a group of rabbits
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plus a population of trees and bushes
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and so all of these different living
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populations
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make up a community and then once you
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add in all of your abiotic factors
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into the next level like the atmosphere
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and the water
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and the temperature with your living
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things that's now your ecosystem
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and then all the different ecosystems in
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the world they can combine and make
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biomes and then all the biomes of the
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world make up the biosphere
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ecosystems vary within the biosphere in
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biodiversity and biomass
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biodiversity is the number of species
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present
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and their evenness of distribution so
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how are they distributed in the
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ecosystem
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are they clumped are they scattered are
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they randomly distributed
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the biomass is going to be the weight of
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all the organisms present
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in the ecosystem microorganisms play a
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major role in most ecosystems if not all
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the role of an organism plays in an
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ecosystem
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is called its ecological niche and you
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can pronounce that however you like
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niche niche i don't care the environment
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immediately surrounding the
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microorganism
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is called the micro environment the
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macro environment may be more easily
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measured
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and is very different from the micro
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environment
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organisms are categorized according to
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the trophic level
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so trophic just means food
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there's three general trophic levels
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primary producers
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consumers and decomposers and we'll
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quickly
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remind you of what those are
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primary producers are autotrophs that
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convert carbon dioxide to organic
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materials
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and they include two types photo
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autotrophs
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photo means light so these are getting
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their energy from the sunlight
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organisms that are photoautotrophs are
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plants algae
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cyanobacteria and inoxygenic phototrophs
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chemoautotrophs on the other hand are
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not using light to make their own food
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they're using chemicals
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in their environment so they oxidize
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inorganic compounds to make their own
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energy
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and they still are serving as a primary
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producer in their food chain
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examples of these guys are going to be
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like the bacteria that live
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in the deep deep ocean where no light
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penetrates
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then we have our consumers consumers are
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heterotrophs that rely on the primary
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producers
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you have herbivores that eat primary
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producers
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and so they don't eat meat these guys
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are called primary consumers
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secondary consumers are going to be
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carnivores that eat those
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herbivores carnivores that eat other
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carnivores are called tertiary consumers
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and the chain of consumption is called
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the food chain
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an interaction between food chains in an
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ecosystem
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so the overlapping of different food
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chains is called a food web
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then we have decomposers decomposers are
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heterotrophs that digest the remains of
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primary producers and consumers
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the complete breakdown of organic
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molecules to inorganic molecules is
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called mineralization
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decomposers are typically going to be
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fungus and bacterial species
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microbes often grow in communities
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attached to some type of solid surface
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or at an air water interface they
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usually grow in biofilms or what we call
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microbial mats
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a microbial mat is a thick dense
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organized structure composed of very
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distinctive layers
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frequently you have green pink and black
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the green layer is typically composed of
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various species
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of cyanobacteria and they're green
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because they have chloroplast
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because they're producers they're
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creating their own food
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using the energy from the sunlight the
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pink layer consists of purple sulfur
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bacteria
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which are heterotrophs the black layer
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is formed by iron molecules reacting
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with hydrogen sulfide
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hydrogen sulfide produced by bacteria
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are called sulfate reducers
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when bacteria grow in groups and build
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up
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on like your teeth for example that
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would be an example of a biofilm
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this is an example of a food chain
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in an ocean made up of microorganisms
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so you have the phytoplankton which are
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your producers that are creating the
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energy for the rest of the chain
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and then you have your heterotrophs like
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your bacterioplankton
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your flagellated microplankton your
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ciliate protozoans
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and your zooplankton
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deep lakes and oceans have
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characteristic zones each zone is going
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to have different amounts of sunlight
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so it's going to have different
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organisms that can live there
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the zones are influenced by microbial
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populations as well
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the upper zone has sufficient light
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penetration to support your
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photosynthetic
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organisms the organic material produced
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by these organisms
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descends and is metabolized by the
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heterotrophs
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marine environments range from deep seas
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to
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shallow coastal regions nutrients are
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scarce in the deep sea regions because
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there's not much light penetration
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so the only producers you have down
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there are your chemo autotrophs
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the nutrients are very abundant though
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in shallow coastal regions
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where sunlight does penetrate easily
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seawater contains high salt
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concentrations which supports halophilic
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microorganisms ocean waters are usually
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oligotrophic which means they're
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nutrient poor
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this limits the growth of microorganisms
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the ecology of inshore areas are not as
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stable as the deep sea
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they can be dramatically affected by
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nutrient-rich runoff
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so the consequence is going to be
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populations of algae and cyanobacteria
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are going to be huge which reduces the
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amount of oxygen
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in the water for the other organisms and
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that's creating hypoxic
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regions which are also called dead zones
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in lakes and streams the types and
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numbers of organisms living there
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depends on multiple factors like light
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concentration of dissolved oxygen
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nutrients and the temperature of the
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water
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some unique aquatic environments include
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like the great salt lakes
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water and these lakes evaporate leaving
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very high concentrations of salt
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much higher than seawater so extreme
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halophiles
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live in the great salt lakes iron
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springs contain large quantities
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of ferrous ions these are habitats for
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galileo species and sulfur springs
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support the growth of both
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photosynthetic and non-photosynthetic
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sulfur bacteria
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microbes are also found in terrestrial
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habitats
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human interest in microbiology of the
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soil stems from the ability of microbes
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to synthesize a variety of useful
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chemicals
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500 different antibiotic substances are
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produced
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by the streptomyces species 50 have a
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useful application in medicine
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agriculture and industry soil microbes
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are being tested for their ability
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to be able to degrade toxic chemicals as
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well
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so soil is composed of pulverized rock
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decaying organic material
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air and water it teams with microbial
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life including bacteria
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fungi algae and protozoa other life
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includes insects worms and plant roots
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the soil environment can fluctuate
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abruptly and dramatically depending on
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the location
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soil has multiple layers called horizons
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each horizon has distinctive
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characteristics the topsoil is known as
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the a horizon
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it's dark nutrient rich it supports
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plant growth
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and the depth can vary from location to
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location so it may be a couple inches
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thick
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or it may even be a foot thick the
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subsoil is known as the b horizon
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this is where you have the accumulation
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of clay salts and nutrients that are
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leached from the topsoil
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which means they flow down
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the sea horizon is partially weathered
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bedrock
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and the bedrock hard solid bedrock is
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the r horizon
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it's the lowest layer and it's not
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weathered
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microorganisms of the soil density and
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composition of microbial flora of soil
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is affected by environmental conditions
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wet soils are unfavorable for growth due
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to lack of air
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during drought water availability drops
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and many organisms
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decrease many organisms produce survival
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forms such as endospores and cysts
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to survive for long periods of time in
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the soil until the environmental
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conditions improve
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other environmental influences include
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acidity
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temperature and nutrient supply
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prokaryotes are the most
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numerous soil inhabitants their
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physiological diversity
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allows for the colonization of all types
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of soil
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of soil microbes gram-positive or more
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abundant than gram-negative
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the most common gram positive in the
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soil are bacillus species
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they produce endospores that allow for
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survival for long periods of time
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fungi are usually found in the top
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portions of soil due to their aerobic
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nature
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meaning they have to have oxygen fungi
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are crucial in decomposing plant matter
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some fungi are free living in the soil
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others develop symbiotic
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relationships with certain plant roots
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so mycorrhizae is an example of a
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symbiotic relationship
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between a fungus and a plant it enhances
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the competitiveness of plants
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by being able to uptake certain
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nutrients that the fungus is providing
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the plant
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there's two common mycorrhizal
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relationships
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endomycorase the fungus penetrates the
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root cells
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they grow within the cell and it's the
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most common relationship
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in plants in ecto mycorrhizae
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so ecto meaning outside the fungus grows
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outside the plant cells forming a sheath
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around the root
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they are mainly associated with certain
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types of trees
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symbiotic nitrogen fixers are really
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important
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in the world being able to fix that
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locked up nitrogen
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in the soil and making it usable for
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plants
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which then makes it usable for us and
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other animals
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is really important
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organisms collectively are called
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rhizobia
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the most agriculturally important
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nitrogen fixers
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they tend to be associated with
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leguminous plants like beans and peas
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the association between plants and
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rhizobia involves chemical communication
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between the partners
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so in this chart here you can see the
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crop
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and then the microbial species
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that is in association with it
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microorganisms also have important
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relationships with
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herbivores so herbivores rely
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on plants in order to eat well
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plants aren't necessarily easy to digest
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in your stomach so in ruminants such as
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cows and sheep
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the compartment is called the rumen the
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rumen is located in front of the true
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stomach
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in non-ruminants like horses it's called
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the cecum
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the cecum lies between the small and the
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large intestine
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microbes that inhabit these compartments
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digest the cellulose
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in the hemi cellulose to compounds that
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can be used as nutrients for the animal
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cellulose and hemicellulose are major
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components of plants
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that otherwise without the microbes
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couldn't easily be broken down
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so in the cow and in other ruminants
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like sheep
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the rumen is found right here and that's
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where the microbes are doing their magic
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and then in your non-ruminants like
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horses
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the cecum is right here in between the
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small intestine
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and the colon which is the large
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intestine
