1. How does modifying ethylene levels affect nodulation efficiency?
One way in which some strains of Rhizobium naturally increase the number of nodules
that they can form on the roots of a host legume is to limit the rise in ethylene that occurs
1. How might the inability of a Rhizobium strain to produce the poly-hydroxybutyrate affect nitrogen fixation?
Biological nitrogen fixation requires a large amount of energy in the form of ATP. Thus,
any mutation or genetic manipulation that increases the
1. Why is it unlikely that plants can be genetically engineered to fix nitrogen?
Nitrogen fixation is a very complicated process that requires the concerted efforts of a
large number of different proteins. An intact single DNA fragment containing all the
1. Briefly, how are compounds exuded from plant roots?
Plants exude compounds through a passive processes such as diffusion, ion channels, or
vesicle transport. It is thought that ABC transporters, driven by ATP hydrolysis, are
responsible for the exudati
1. How can some strains of cyanobacteria be genetically improved so they fix more
Scientists were able to genetically manipulate cyanobact so that it contained more
heterocysts and therefore fixed more nitrogen. The hetR gene, which encodes a se
1. What are the advantages of using alginate encapsulation and bentonite to deliver
Alginate bacterial inoculum is beneficial because it's chemically and physically uniform,
biodegradable, reproducible from batch-to-batch, requires l
1. How do PGPB facilitate plant uptake of inorganic phosphate from the soil?
Plants and bacteria typically solubilize inorganic phosphorus through the production and
secretion of small organic acids such as gluconic, citric, lactic, 2-ketogluconic, oxalic
1. How would you test whether or not a particular potential PGPB strain had
biocontrol activity against a particular phytopathogen?
Test each bacterial strain for the ability to prevent the proliferation of one or more
phytopathogens on agar plates. The p
1. What are bacterial siderophores and how do they affect plant growth?
Despite the abundance of iron on the earths surface, soil organisms such as plants and
microbes cannot readily assimilate enough iron to support their growth because the iron
1. Why should PGPB be used in agriculture instead of chemicals?
Chemicals contribute to pollution and global warming and accumulate in the
environment. PGPB have the potential to increase biomass, increase
nitrogen/phosphorous/iron content, incr
1. How do volatile organic compounds promote plant growth?
Volatile organic compounds stimulate plant growth by increasing plant leaf
surface area. They impact the expression of genes encoding flavonoid and
auxin synthesis, as well as cell-wall loosening
4. What sorts of changes might one need to make when patenting the
same invention in two different jurisdictions such as the USA and
The USA permits broad patents so that its possible to claim
chemicals/microbes that are similar but not identical t
1. How can foreign genes be integrated into the chromosomal DNA of a
Use transposition of mobile genetic elements or homologous recombination.
Modify naturally occurring transposons to contain the target gene and the
essential transposase gene,
1. How does the presence of IAA-producing bacteria affect metal
IAA positive PGPB have been found to facilitate the uptake of of metal
contaminants by plants and also protect plants from growth inhibition due to
the presence of metals in
1. Why are transgenic PGPB, including rhizobia, often found to be not
especially competitive with indigenous soil bacteria?
In general, PGPB that have been genetically modified are less able to survive
and proliferate in the environment than are the non-t
1. Why might it be advantageous to use endophytes rather than
rhizospheric bacteria in some phytoremediation protocols?
The majority of phytoremediation PGPB studies focus on endophytes.
Rhizospheric bacteria with degradative activity bind the surface of
1. How would you determine how a particular plant affects the
physiology/metabolism of PGPB with which it interacts?
You can identify changes in PGPB by treating the PGPB with plant root
exudates - this works especially well with rhizospheric PGPB. A bene
1. How would you prove that bacterial IAA contributes significantly to the
promotion of plant growth by a PGPB strain?
You can make a knockout mutant for the ipdC gene so that bacteria can no
longer synthesize IAA through the IPA pathway, and co
1. What are some of the ways in which ethylene affects plant growth and
It mediates plant responses and developmental stages, including seed
germination, tissue differentiation, root and shoot primordia formation, root
branching and elongatio
1. What is phytoremediation?
The use of plants (and bacteria) to sequester, stabilize or break down
environmental contaminants (usually either organics such as PCBs and PAHs,
or metals) that pollute soils.
A potentially clean, effective, and re
1. Having isolated a Pseudomonas gene encoding the enzyme indole-3pyruvic acid decarboxylase that is involved in the biosynthesis of IAA,
suggest a strategy for creating a mutant of the starting bacterium that
produces a decreased amount of IAA.
1. What are some of the ways in which PGPB can help to remediate salt
PGPB ameliorate salt stress by increasing growth promotion via IAA,
decreasing ethylene levels with ACC deaminase, induction of protective plant
stress proteins and metabolites,
1. What are the differences between ectomycorrhizal and arbuscular
Ectomycorrhiza colonize the outside of roots (extracellularly), where they
form a lattice-like network of branched hyphae. Theyre common in woody
plants and theyre culturable.
1. What are biosurfactants and how might they be used to improve
Biosurfactants can be produced by bacteria (sometimes PGPB), where they
are either secreted or remain attached to the cell membrane that reduce
1. What is trehalose and how does it protect plant against growth
inhibition caused by either drought or high salt?
Trehalose is an glucoside osmoprotectant that forms a gel phase as cells
dehydrate, replacing water and decreasing the damage done to cells
1. In the natural environment, how might the presence or absence of
antibiotic-producing PGPB in plant rhizospheres be affected by drought
A study of of PGPB producing phenazine-1-carboxylic acid was performed on
soil samples from 61 different
1. Describe a scheme for identifying Sphingomonas sp. proteins that are
involved in protecting plants against bacterial phyllosphere pathogens.
A suspension of Sphingomonas was mutagenized with a randomly-inserting
Tn5 mini-plasmid and bacteria with the i
1. Briefly describe the use of bacteriophages as biocontrol agents against
Cocktails of bacteriophage can be sprayed on plants as an alternative to
spraying copper or antibiotics, and if the phage target phytopathogenic
1. How does flooding in roots affect plant shoots and leaves?
The major negative impact of flooding on plants is the deprivation of oxygen
to the roots of plants. Soil microbes quickly consume all of the available
oxygen (anoxia) and and plants respond to
1. How would you select for biocontrol strains of P. fluorescens that
overproduce the antibiotic phenazine-1-carboxylate?
Use the bacterial spotting/zone of clearance method previously discussed.
2. What are siderophores and how do they prevent the prolif