Lecture 16 Flashcards
What bacteria are found in soil?
proteobacteria dominate, acidobacteria, actinobacteria
Rhizosphere
volume of soil around plant roots influenced by materials released from roots. zone of chemical, biological, and physical influence generated by root growth and activity
Rhizoplane
surface of root, including soil particles
Mycorrhizal symbiosis
fungal symbiosis helps plants acquire phosphate and nitrogen from the soil
Rhizobial symbiosis
Bacterial symbiosis helps plants acquire nitrogen from the atmosphere
Lineages of proteobacterium
gram -, alphaproteobacterium, betaproteobacterium, gammaproteobacterium, deltaproteobacterium, epsilonproteobacterium
Class alphaproteobacteria
7 orders, 20 families, gram -, live in environments typically low in nutrients (oligotrophic), most abundant bacteria in oceans
Rhizobia
microbial genera able to form nitrogen fixing nodules with legumes, free in soil but cannot fix nitrogen under aerobic conditions
Atmosphere composition (nitrogen fixation)
nitrogen (most abundant), nitrogen fixation = conversion of N2 in ammonia, carried out by only some soil bacteria
Legume-rhizobia symbiosis
nitrogen is limiting in some soils
1. rhizophere communication - legume <> rhizobia
2. Endosymbiosis - rhizobia enter inside plant cells
3. Legumes: fabales (fabaceae) inhabit nitrogen poor soils
Biological nitrogen fixation - fossil fuel free
- rhizobia contain nitrogenase, fixation of N2 demanding, inhibited by oxygen, free rhizobia do not fix N in soil, nodules provide microaerobic environment
Global nitrogen fertilizer production (Haber)
N2 + 3H2 <> 2NH3
2% of global ff comsumption, sustains 1/3 of global pop. 1/2 nitrogen in human body from N fertilizer
Nitrogen fertilizer run off
20% of N is lost as run off in lakes + rivers, eutrophication leads to oxygen depletion
Flavonoids
Secreted by legume roots into the soil when nitrogen levels are low
Nodulation factor
produced by rhizobia to gain entry into legume roots (LCO)
Legume Rhizobium communication (3 steps)
- plant roots exude flavonoids into the soil when N levels low
- Rhizobia perceive flavonoids indicates that a root is nearby
- Rhizobia in turn produce nod factor (LCO)
Root nodule formation by rhizobium
- perception of nod factor by plant triggers changes in root hairs to allow rhizobia to enter
- plant builds infection thread to guide rhizobia into inner tissues
- surrounded by peribacteroid membrane, units now called symbiosomes. then nitrogen fixation
Nodules (leghemoglobin)
of nodules depend on soil and light, red due to leghemoglobin
Protein secretion in bacteria
7 systems:
type 1 and iv gram -/+
types 2, 3, 4 are unique to gram -
translocation
movement of proteins from cytoplasm to or across plasma membrane
posttranslational
co-transitional (translocation)
-using signal peptides to deliver pre-protein secretion system
-Using signal recognition particle proteins to bind protein as its leaving ribosome to deliver to secretion
secretion
movement of proteins from the cytoplasm to external environment
General secretion (type 1)
across plasma membrane
sec - unfolded proteins with SP across
Tat - Folded proteins with twin arginine signal sequence
YidC - folding and translocating plasma membrane proteins
Sec/Tat-dependent
type 2/5: deliver proteins across OM after sec or tat
Sec/tat independant
Type 3: injection of virulence factors to host
Type 4: protein and Dna transport to host
Type 6: bacterium-bacterium translocation
Sec Pathway
translocates proteins from cyto into plas mem
secY. secE, secG form a channel in mem, secA translocates preprotein
Tat system
protein translocation system in bacteria, translocate folded proteins with twin arginine residues
Type 3 secretion system
needle like, bridges pm and om of gram - bacteria, protein into host cell
Type 4 secretion system
secrete proteins in Gram pos, neg and archaea, secrete DNA protein complexes
Agrobacterium
protebacterium, formation of tumor like growths
agrobacterium host interaction
through natural wound, signal transduction system by plant chemicals (transfers DNA to plant), Ti plamid
Ti plasmid
virulence region encodes DNA delivery system, left and right borders cleaved and cargo transported, T- DNA contains enzymes for plant hormone biosynthesis
Agrobacterium virulence genes
21 genes found in 6 seperate operons on Ti plasmid, Vir genes induced by plant chemicals, type 4 built and transferred into plant cell
Steps: how agrobacterium transfers DNA
- T-DNA excision
- Movement of T-DNA out of bacterium
- Nuclear import and integration of T-DNA
- Expression of T-DNA and pathogenicity
