lecture 7: development of microbial communities Flashcards
why has microbiology focused so much on pure cultures?
- microbio was established by studying disease causing organisms
- but these are a minority as most organisms live in communities of microbes
- using pure cultures allows us to see the things that are happening and we can attribute it to one microbe
limitations of pure culture
- how they are behaving in pure cultures might not be how these microbes behave in all environments
what are the different examples of microbial interactions within communities
- competition
- commensalism
- predation/parasitism
- mutualism
- co operation
- symbiosis
competition pros and cons
pros = good for natural selection, most fit is able to reproduce leading to the population being stronger
cons = bad for both of them, waste energy, hurt each other
direct competition
- direct/ interference
- physical fighting over resources
- same niche
indirect competition
- exploitative
- competition through consuming scarce resources, do not come into contact
co-operation
- organisms really chose to work together
- they can survive in the environment alone, but they chose to work together, as it is better off for the whole group
cheaters
- organisms that used to have a specific trait but they lost it because its to costly, but they still get the benefits from the trait
- this allows them to outcompete the organisms who still have the trait
mutualism
- both organisms benefit
commensalism
one organism benefits, the other organism is unharmed
parasitism/predation
one organism benefits, the other organism is harmed
symbiosis
-‘living together’
- two or more organisms from different species
- interactions can be positive, negative or neutral
what are the two major categories for ecology processes
stochastic and deterministic
stochastic
- processes occur at random
- no set rules, so predictions are not possible
- outcome will be impossible to determine
deterministic
- processes follow a consistent set of rules
- implies that given some input and parameters, the output will always be the same
- you can easily predict what will happen once you know the rules, and the conditions in the ecosystem
how do deterministic and stochastic processes relate to the colonisation process
- in a newly opened environment, the first cells to colonize are determined by what is found closest (deterministic)
- but the specific organism to colonize is random (stochastic)
- who takes over is determined by competition/cooperation outcomes
- as time passes and conditions change, new niches open allowing replacement of species
ecological successions
changes in species composition observed upon a disturbance that opens up niches for colonization
primary succession
environments are colonized for the first time (e.g. after volcanic eruption)
secondary succession
occur in established systems when a disturbance reduces diversity leading to a renewed succession thanks to newly available resources or removal of competition
what is a driving force of microbial community succession
gradients
- can be metabolic side effects (eg: less substrates, change in pH)
- or purposely generated metabolites (eg: antibiotics)
what are disturbances (as triggers of secondary successions)
disturbances = processes/events which affect the species composition. structure and functions within an ecosystem
- disturbances can have both positive and negative effects
- can be drivers of change and increase diversity
- can also collapse a community
how do communities respond to disturbances
resistance or resilience
resistance
staying essentially unchanged despite the presence of disturbances
resilience
returning to the reference state (or dynamic) after a temp disturbance
what determines at what point in a succession a microbe grows?
life history strategy = the general survival strategy used by a microbe to ensure species viability
- dictates the conditions under which a microbe can not only survive, but thrive
r strategist
- fast growers
- consumption and reproduction
K strategist
- slow growers
- optimal utilisation
- conservation of energy
r vs. k
r:
- dont compete well
- need lots of resources
- major “skill” is high reproduction
- do not depend on others
- have extreme population fluctuations
eg: pseudomonas
k:
- excel in competitive environments (low resources)
- efficient but slow growing
- stable population numbers
eg: streptomycetes
