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Plant Growth Promoting Rhizobacteria: Fundamentals and Applications (3.3…
Plant Growth Promoting Rhizobacteria:
Fundamentals and Applications
main groups of PGPR
Cyanobacteria
Actinobacteria
Bacteroidetes
Firmicutes
Proteobacteria
different direct and indirect mechanisms
(1) increased mineral nutrient solubilization and nitrogen fixation, making nutrients
available for the plant
(2) repression of soilborne pathogens (by the production of
hydrogen cyanide, siderophores, antibiotics, and/or competition for nutrients)
(3) improving plant stress tolerance to drought, salinity, and metal toxicity
(4) production of phytohormones such as indole-3-acetic acid (IAA)
have the enzyme
1-aminocyclopropane-1-carboxylate (ACC) deaminase
, which hydrolyses ACC, the immediate precursor of ethylene in plants
By lowering ethylene concentration in seedlings and thus
its inhibitory effect, these PGPR stimulate seedlings root length
2 группы (Bashan and Holguin (1998))
biocontrol-PGPB (plant growth promoting bacteria)
PGPB
также есть разделение на
extracellular
(ePGPR)
intracellular (iPGPR)
коммерческие мко
bioprotectants - suppression of plant disease
biofertilizers - improved nutrients acquisition
biostimulants - phytohormone
production
мко
Bacillus, Streptomyces, Pseudomonas,
Burkholderia, and Agrobacterium
2 Coinoculation of PGPR and Rhizobia: Improving Nodulation
increased plant nodulation
and N fixation
PGPR, in combination with efficient rhizobia, could improve the growth and nitrogen fixation by inducing the occupancy of introduced rhizobia in the nodules of the legume
3 Identification and Characterization of Beneficial Bacterial
Strains for Agriculture
four categories of schemes for identifying different bacterial strains
(1) traditional biochemical,
morphological, and physiological characters
(2) miniaturized versions of
traditional biochemical tests (e.g., API kits, VITEK cards, and Biolog plates)
(3) chemotaxonomic characters (such as polyacrylamide gel electrophoresis [PAGE], and fatty acid methyl ester [FAME] profiles)
(4) genomic characters (16S
rRNA gene sequencing, and DNA–DNA relatedness, and other techniques).
3.2 Phenotypic Features
Traditional phenotypic tests
colony morphology (color, dimensions, form)
microscopic appearance of the
cells
characteristics of the organism on
different growth substrates
growth range of microorganisms on different conditions
of salt, pH, and temperature
susceptibility toward different kinds of antimicrobial
agents
Biochemical tests in bacterial identification include
the relationship with oxygen, fermentation reactions, and nitrogen metabolism
3.3 Chemotaxonomic Characters
fatty acid methyl ester- FAME profiling
PAGE analysis of whole-cell proteins
polar lipid analysis
quinone content
cell wall diamino acid content
pyrolysis mass spectrometry
Fourier transform infrared spectroscopy
Raman spectroscopy
matrix-assisted
laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry
жирные кислоты - составные части липидов и липополисахаридов
FAME analysis is presently the only chemotaxonomic technique that is linked to a commercial database for identification purposes
Fatty acid profiles showing variability
in chain length
double-bond
position
substituent groups
Sodium dodecyl sulfate-PAGE of whole-cell proteins
requires standardized conditions of growth, combined with a rigorously standardized procedure for analysis, and normalization of the data for computer-assisted comparison of the results
Isoprenoid quinones
occur in the cytoplasmic membranes of most prokaryotes
play important roles in electron transport, oxidative phosphorylation, and,
possibly, active transport
2 структурные группы
naphthoquinones
phylloquinones
menaquinones
benzoquinones
The large variability of the side chains
differences in length, saturation, and hydrogenation
can be used to characterize
bacteria at different taxonomic levels
полярные липиды
has now been demonstrated for some novel genera among the Bacillaceae, although many polar lipids detected have not yet been structurally characterized.
3.4 Genetic Approaches
Different techniques
restriction fragment length polymorphism (RFLP)
plasmid profiling
ribotyping
amplified ribosomal DNA restriction analysis (ARDRA)
pulsed field gel electrophoresis (PFGE)
randomly amplified polymorphic
DNA (RAPD)
G+C пары
not more than 3% within a well-defined
species
not more than 10% within a well-defined genus
DNA–DNA hybridization or DNA–DNA reassociation technique
This technique considers the comparison between whole genome of two bacterial species
16S rRNA gene
sequence is deposited in databases
Ribosomal Database Project II (http://
rdp.cme.msu.edu/)
GenBank (
http://www.ncbi.nlm.nih.gov/
)
sequence comparing software packages such as
BLAST
and
CLUSTAL X
are used for alignment of 16S rRNA gene sequence
4 Prospective Biocontrol Agents of Plant Diseases
PGPR mechanisms
mechanisms of biological disease control
competition
production of metabolites
antibiotics
cell walldegrading
enzymes
siderophores
HCN
alteration of host defense mechanisms
Induced systemic resistance (ISR) or systemic acquired resistance (SAR)
activation of chemical and physical defenses of the plant
special
approach for improving the PGPR efficiency
use of mixtures containing
different genera or species
that presents additive or synergistic effects such as
nitrogen-fixing bacteria and mycorrhiza helper bacteria (MHB).
Another strategy is to use PGPR, mixed or alternated with fungicides, integrating biological and chemical control.
MHB (mycorrhiza helper bacteria)
assist mycorrhiza formation
significant functions
nutrient mobilization from soil minerals
fixation
of atmospheric nitrogen
plant protection against root pathogens
Pseudomonas fluorescens, P. monteilii, Bacillus coagulans, B. subtilis, Paenibacillus
brasilensis, Rhizobium leguminosarum, and Bradyrrhizobium japonicum.
5 Induced Systemic Resistance as a Mechanism of Disease
Suppression by Rhizobacteria
Induction of resistance promoted by PGPR
route of
salicylic acid with induction of PR-proteins (proteins related to the pathogenesis)
route of the jasmonic acid and ethylene
In addition to the PR-proteins, the plants produce other enzymes of the defense
peroxidases
катализирует образование лигнина
phenylalanine ammonia-lyase (PAL)
формирование фитоалексинов - phytoalexins
polyphenoloxidase
(PPO)
катализирует образование лигнина
production of enzymes
related to pathogenesis (PR-proteins)
largest property of the antagonistic strains
chitinases
lipoxygenases
peroxidases
this enzyme has been implicated in the oxidation of phenols, lignification, plant protection and elongation of plant cells
glucanases
phytoalexins
secondary metabolites, antibiotics, low molecular weight produced by plants in
response to physical stress, chemical, or biological
6 Bacterial Biofertilizers
can fix nitrogen, and solubilizing phosphorus
The mechanisms by which PGPR promote plant growth are not fully understood
but include among others
ability to produce or change the concentration of
plant hormones
asymbiotic N2 fixation
solubilization of mineral phosphate and other nutrients
solubilization of insoluble phosphates
P solubilization by microorganisms is directly related to production of siderophores, lytic enzymes, and phytohormones