Sustainable Agriculture through Plant Growth Promoting Rhizobacteria (PGPR)

1. Peran Mikroorganisme dalam Bidang Pertanian: Plant Growth Promoting Rhizobacteria (PGPR) Kuliah ke-15 Mikrobiologi 12/27/2016

2. INTRODUCTION • Indiscriminate use of chemical fertilizers adversely affects soil microorganism, fertility status of soil and environment • So, PGPRs are replacing agrochemicals for the plant growth promotion • Economically, environmentally beneficial for lower production cost and for sustainable agriculture 12/27/2016 4

3. RHIZOSPHERE AND PLANT GROWTH PROMOTING RHIZOBACTERIA • Term rhizosphere given by Hiltner (1904) and term PGPR given by Kloepper and Schroth (1981) • Rhizosphere is the narrow zone of soil specifically influenced by the root system • Populated by microorganisms and the bacteria called rhizobacteria • Three types: beneficial, deleterious & neutral groups • Beneficial free-living soil bacteria referred to as PGPR • Bacillus and Pseudomonas spp. are predominant among PGPR • 12/27/2016 5

4. PLANT GROWTH PROMOTING RHIZOBACTERIAL FORMS • 1. EXTRACELLULAR PGPR(ePGPR) • In rhizosphere, rhizoplane or between cells of root cortex • Includes Agrobacterium, Arthrobacter, Azotobacter, Azospirillum, Bacillus, Caulobacter, Chromobacterium, Erwinia, Pseudomonas and Serratia Flavobacterium, Micrococcous, • 2. INTRACELLULAR PGPR (iPGPR) • Inside specialized nodular structures of root cells. • Includes Allorhizobium, Bradyrhizobium , Mesorhizobium and Rhizobium, endophytes and Frankia 12/27/2016 6

5. PGPRMECHANISMS • 1.DIRECT MECHANISM • Providing plant with a compound synthesized by bacterium or facilitating uptake of nutrients from the environment • 2. INDIRECT MECHANISM • Reducing or preventing deleterious effects of phytopathogenic organisms by producing antagonistic substances or by inducing resistance 12/27/2016 7

6. Fig : The possible mode of action used by PGPR towards growth promotion in plants. The flow and location of nitrogen fixation, phosphorus solubilization, and siderophore production are shown (Vacheron, Desbrosses, Bouffaud, Touraine.,2013) MODE OF ACTION OFPGPR 8 12/27/2016

7. DIRECTMECHANISMS • 1. NITROGENFIXATION • Twomechanisms:- • a. SYMBIOTIC NITROGENFIXATION • Mutualistic relationship between a microbe and theplant. • Eg. Rhizobium, Bradyrhizobium, Sinorhizobium, Mesorhizobium andFrankia • b. NON-SYMBIOTIC NITROGENFIXATION • By free livingdiazotrophs • Eg. Azotobacter, Acetobacter, Azospirillum,, Diazotrophicus, Enterobacter, • Pseudomonas andcyanobacteria • Provides an integrated approach for disease management and maintains nitrogen level insoil. 9 12/27/2016

8. 2. PHOSPHATE SOLUBILIZATION • The main P solubilization mechanism includes: • Release of complex or mineral dissolving compounds • Liberation of extracellular enzymes • Release of P during substrate degradation • Includes genera Arthrobacter, Bacillus, Beijerinckia, Enterobacter, Erwinia, Flavobacterium, Microbacterium Pseudomonas, Rhizobium, Rhodococcus, and Serratia 12/27/2016 10

9. MOVEMENT OF PHOSPHORUS IN SOIL 11 12/27/2016 Source: Insight Microbiology;volume 1;issue 3,20

10. P SOLUBILIZATION BY P SOLUBILIZINGBACTERIA Source: Insight Microbiology;volume 1;issue 3, 2011 12 12/27/2016

11. 3. POTASSIUM SOLUBILIZATION • K is the third major essential macronutrient • PGPR solubilize K rock through production and secretion of organic acids. • They release K in accessible form from K bearing minerals in soils • Includes genera Acidothiobacillus Bacillus edaphicus, Bacillus ferrooxidans, mucilaginosus, Burkholderia, Paenibacillus sp. andPseudomonas 12/27/2016 13

12. 12/27/2016 • 4. SIDEROPHORE PRODUCTION • Siderophores are low molecular weight iron- • chelating compounds which provide a high affinity to coordinate ferric ions. • Kloeppar et al. (1980) were the first to demonstrate the importance of siderophore. • Direct benefit: Take up the labeled iron and chelating scarcely available iron • Indirect benefit: Enhanced chlorophyll level 14

13. IMPACT OF MICROBIALLY SECRETED SIDEROPHORES ON PLANTGROWTH Source: Insight Microbiology;volume 1;issue 3, 2011 15 12/27/2016

14. 5. PHYTOHORMONE PRODUCTION • a. Indole Acetic Acid (IAA) • Up to 80% of rhizobacteria can synthesize IAA • IAA stimulate cell proliferation, seed germination, resistance to stressful conditions and enhance uptake of minerals and nutrients • Pseudomonas, Rhizobium, Bradyrhizobium, Agrobacterium, Enterobacter and Klebsiella are IAA- producing PGPR 12/27/2016 16

15. b. Cytokinin andGibberellins • Includes genera Azotobacter sp., Rhizobium sp., Rhodospirillum rubrum, Pseudomonas fluorescens, Bacillus subtilis etc • Some strains of phytopathogens also synthesize cytokinins • PGPR produce lower cytokinin levels compared to phytopathogens • Thus, effect of PGPR on plant growth is stimulatory while that of pathogens is inhibitory. 17 12/27/2016

16. c.Ethylene • Lowering of ethylene production by inoculation of PGPR strains • induces:- • Improved nodule number • Improved nodule dry weight • Higher grain yield and straw yield • Increased nitrogen • Includes genera: Pseudomonas sp., Achromobacter, Agrobacterium, Azospirillum, Bacillus, Burkholderia, Enterobacter, Ralstonia, Serratia and Rhizobiumetc. 18 12/27/2016

17. INDIRECTMECHANISMS • 1. ANTIBIOTICS • One of the most powerful bio control mechanisms • Antibiotics produced:- • By psuedomonads: amphisin, (DAPG), oomycin A, phenazine, tensin,, and cyclic lipopeptides • By Bacillus, Streptomyces and Stenotrophomonas sp: oligomycin A and xanthobaccin • Drawback: some phytopathogens may specific antibiotics due to increased use. • 12/27/2016 developresistanceto 19

18. 2. LYTIC ENZYMES • PGPRs produce enzymes such as chitinases, dehydrogenase, β-glucanase, lipases, phosphatases, proteases etc. exhibiting hyperparasitic activity • Suppression of pathogenic fungi including Botrytis cinerea, Sclerotium rolfsii, Fusarium oxysporum, Phytophthora sp., Rhizoctonia solani, and Pythium ultimum 12/27/2016 20

19. 3. INDUCED AND SYSTEMIC RESISTANCE 21 12/27/2016

20. 4. EXO POLYSACCHARIDEPRODUCTION • Functions of EP-producing PGPR:- • Biofilm formation and rootcolonization. • Holding freephosphorous • Circulating essential nutrient to theplant • Protecting from foreign pathogens andstress • Shielding from desiccation • Plant defense response in plant–microbeinteractions 12/27/2016 22

21. BIOCONTROL PROPERTIES OF PGPRS • Bio control: Process through which a living organism limits the growth or propagation of undesired organisms or pathogens • Mechanism:- • Competition for nutrients • Production of antibiotics • Production of enzymes to degrade cell wall • Production of siderophores • Production of metabolites • Displacing pathogens 23 12/27/2016

22. APPLICATION OF PGPR AS BIOINOCULANT • Bio-fertilizers are defined as “substances that contain living microorganisms that when applied to seed, plant surfaces, or soil, colonize the plant and promote its growth by increasing the nutrient availability” • Mechanism:- • Increase efficiency of N-fixation • Ability to solubilize phosphate • Improve availability of Fe and Zn • Alter growth of roots and shoots by phytohormones • Eg: strains of Pseudomonas putida & Pseudomonas fluorescens 12/27/2016 24

23. ABIOTIC STRESS RESISTANCE THROUGH PGPR TEMPERATURES 1.EXTREME • High temperatures lead to increased drought • intensity; reduction in nodule number; infectious events; delay in nodulation • Heat-tolerant, actively nodulating and N2 fixing Rhizobium strains identified that play a key role in normal growth. 12/27/2016 25

24. 2. SOILACIDITY • Soil acidity affects plant growth and cause crop failures • Some strains of Rhizobium, Azorhizobium and Bradyrhizobium are low pH tolerant. • Tolerance to acidity by rhizobia correlated with the production of extracellular polysaccharide • 12/27/2016 26

25. HEAVY METAL RESISTANCE • Key pollutants to plants, ecosystem and humans. • Use of recombinant rhizobia plays a major role in phyto-remediation measures. • Microorganisms with high metal-binding capacity through metallothionins for enhancing the tolerance, sequestration of heavy metals widely exploited. 12/27/2016 27

26. SYNERGISTIC EFFECTS OF RHIZOBIAL CO- INOCULATION • Inconsistency of beneficial results, when single microbe used • Co-inoculation causes synergy by functioning as helper bacteria • Best combination of PGP bacteria, rhizobia and host genotype selected • Examples:- • Azospirillum: In leguminouscrops • A. lipoferum and R. leguminosarum pv. trifolii : Whiteclovers • Azotobacter • Bacillussp. • Psuedomonassp. • Enterobacter • Serratia • 12/27/2016 28

27. HARMFUL ASPECTS OFPGPR • Cyanide acts as a growth inhibitor for some plants • High levels of auxin inhibits root growth • Rhizobitoxine produced by Bradyrhizobium elkanii • may have a negative effect on nodulation • Rhizobitoxine can also induce foliar chlorosis in soybeans. • A select few bacterial species may inhibit growth. 12/27/2016 29

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29. FUTURE RESEARCH AND DEVELOPMENT STRATEGIES • Need of today’s world – higher yield and enhanced production in an eco-friendlymanner New concepts ofrhizo-engineering 1. Research in rhizosphere biology (molecular & biotechnological approaches) 2. Integrated management of soil microbialpopulations 3. Bioinoculants for high value crops like vegetables, fruits, andflowers 4. Application of multi strain bacterial consortium over singleinoculation 5. Addition of ice-nucleating plant growth promotingrhizobacteria 6. Comprehensive research on potassiumsolubilization 7. Biosafety data required for the registration ofPGPR 8. Non-phytotoxicPGPR 9. 10. PGPRs tolerant to adverse environmentalcondition 11. Cost effective PGPRproducts 12/27/2016 31

30. CONCLUSIONS • PGPRs are economically and environmentally beneficial for plant growth promotion • PGPRs may have a direct or an indirect mode of action • PGPRs may function as biofertilizer, bioinoculant, abiotic stress resistance inducers, co-inoculants and other growth promoting activities • New concepts and development strategies regarding PGPRs need to be constantly developed 12/27/2016 32

31. Thank You 33