Prelim 3 Biog1440 Flashcards
Symbiosis
The living together between organisms
-Interactions and possible co-evolution with associates microbes that allows some biological exchanges
Mutualism
Ex. bees and flowers
Species A, benefits
Species B, benefits
Commensalism
Ex. barnacles sticking and feeding out of whales
Species A, benefits
Species B, neutral
Parasitism
Ex. parasites
Species A, benefits
Species B, costs
Endosymbionts
microbes that reside within the body or cells of an organism
ex. wolbachia is a reproductive aprastie of insects and nematodes
ex. mitochondria and chloroplast
Lynn Margulis endosymbiosis theory
The eukaryotic cell could arise from a symbiotic union of primitive prokaryotic cells. This states that you start with two microbes and they engage in such a tight symbiosis that it leads to a eukaryotic cell.
Symbiogenesis
Mitochondria and chloroplasts evolved from certain bacteria engulfed by primitive cells
Microbiota
The ecological community of microorganisms associated with a host
ex. the skin microbiota
- The gut microbiota is not endosymbiotic, because the gut lumen is not “inside the body”
Rhizobacteria
They occupy the rhizosphere. Could either:
- Stay on the surface of the root.
- They are endophytic. They live between the cells of host plant tissues and form root nodules
Rhizobacteria depend on…
Nutrients secreted by plant cells, in return, they help to enhance plant growth by
- Producing chemicals (or some nutrients) that stimulate plant growth
- Producing antibiotics that eliminate bad microbes and protect the plant from disease/infection
- Absorbing toxic metals or increasing nutrient availability
The nitrogen cycle
Transforms nitrogen gas into nitrogen containing compounds that can be uptaken by the roots of the plants
- Nitrifying bacteria generate NO3- from NH4+
- The nitrifying bacteria takes the ammonium and generates nitrate. Nitrate will be the favored form of nitrogen that will be absorbed by the root alongside some ammonia.
Nitrogen fixing bacteria
Use nitrogen and generate ammonia (NH3) that will become ammonium (NH4+)
Ammonifying bacteria
Some additional bacteria can also generate some ammonium from a different source. They use decomposition products from the soil and generate some ammonium
Denitrifying bacteria
Takes nitrate and actually generates nitrogen (N2). So they do not help with the growth of the plant but would oppose it.
Rhizobia
Endosymbionts of legumes. Along a legume’s roots are swellings called nodules, composed of plant cells colonized
Nodules
Root tissue but mostly filled with some of the Rhizobia bacteria
Relationship between rhizobia and plants
The plant obains fixed nitrogen from Rhizobium, and Rhizobium obtains sugar and anaerobic environment
Development of nitrogen-fixing root nodules
Chemical dialogue between root cells (flavonoids) and Rhizobia (Nod factors)
To initiate the dialogue once a plant wants or needs to engage in symbiosis with Rhizobia, it will secrete some compounds called flavanoids (which are pigments) and those pigments will be synthesized and diffuse in the ground. If there is Rhizobia in the ground, they will bind and recognize the flavanoids. In response, they will produce proteins, NOD factors, that diffuse back towards the root. When the root receives some of those bacterial derived NOD factors, the roots will modulate the activity, their shape, and somehow follow the trail of the NOD factor a finds a microbe to internalize it
Where does Rhizobia attach?
The root hair which causes them to deform, grow, find and attach to microbes so it will enter those threads and colonize the roots. They grow within the root to develop these nodules.
Microbes in the human microbiota include species from each major domain:
- Bacteria ex. proteobacteria, cyanobacteria
- Archaea ex. crenarchaeota “extremophile”
- Eukarya ex. Fungi, yeast, plants, animals
Microbiota cannot be
Cultured
New solutions to microbiota investigation
Next generation sequencing: does NOT require culturing
Metagenomics: sequence-based analysis of genome of entire microbial communities, does not require culturing
Principal Component Analysis (PCA) Graph
Regroups together the different type of microbial community that look more alike
Microbiota is most abundant in the
GI tract. The large intestine is the preferred site. Over 70% if all bacteria are in the colon.