Bacterial IAA Research Articles

Roles of β-Indole Acetic Acid (IAA) Producing Endophytic Bacteria on the Recovery of Plant Growth and Survival Ability of Sugarcane Infected White Leaf Disease (SWLD).

β-Indole acetic acid is produced in the rhizosphere by endophytic bacteria and promotes plant growth. Effects of bacterial IAA producers (BIPs) on plant growth and recovery of sugarcane seedlings infected with phytoplasma causing white leaf disease (SWLD) were examined. Fifty-five endophytic bacteria isolated from rice roots were collected from the Mekong River Delta, Vietnam. Seven isolates showed β-Indole acetic acid production in culture medium supplemented with tryptophan. Interestingly, two of them (BC17 and BTII2) produced the highest β-Indole acetic acid after 4days of culture. Based on 16S rRNA sequences and phylogenetic analysis, the BC17 and BTII2 isolates were identified as Delftia lacustris and Rahnella aquatilis, respectively. Plant growth induced by the BC17 and BTII2 isolates showed statistically significant differences in height, root length and fresh weight of rice seedlings compared with non-treatment as the control. Treatment of two bacterial isolates in SWLD infected sugarcane plants also showed differences in height of sugarcane seedlings, while gradual symptoms of exposure decreased plant mortality compared to non-treatment as the control. BIPs were shown to be efficient biofertilizer inoculants that promoted plant growth and also ameliorated damage caused by phytoplasma-associated diseases at the sugarcane seedling stage.

Bacterial Modulation of the Plant Ethylene Signaling Pathway Improves Tolerance to Salt Stress in Lettuce (Lactuca sativa L.)

Salinity has extensive adverse effects on plant growth and the development of new agronomic strategies to improve crop salt tolerance is becoming necessary. Currently, the use of plant growth promoting rhizobacteria (PGPR) to mitigate abiotic stress in crops is of increasing interest. The most analyzed mechanism is based on ACC deaminase activity, an enzyme that decreases the ethylene synthesis, an important phytohormone in plant stress response. We aimed to identify other PGPR mediated mechanisms involved in the regulation of salt stress in plant. We used three PGPR strains (ESL001, ESL007, SH31), of which only ESL007 demonstrated ACC deaminase activity, to evaluate their effect on lettuce plants under salt stress (100 mM NaCl). We measured growth and biochemical parameters (e.g., proline content, lipid peroxidation and ROS degradation), as well as expression levels of genes involved in ethylene signaling (CTR1, EBF1) and transcription factors induced by ethylene (ERF5, ERF13). All bacterial strains enhanced growth on salt-stressed lettuce plants and modulated the proline levels. Strains ESL007 and SH31 triggered a higher catalase and ascorbate-peroxidase activity, compared to non-stressed plants. Differential expression of ethylene-related genes in inoculated plants subjected to salinity was observed. We gained consistent evidence for the existence of alternative mechanisms to ethylene modulation, which probably rely on bacterial IAA production and other chemical signals. These mechanisms modify the expression of genes associated with ethylene signaling and regulation, complementarily to the ACC deaminase model to diminish abiotic stress responses.

Indole-3-acetic acid biosynthesis and its regulation in plant-associated bacteria.

Numerous studies have reported the stimulation of plant growth following inoculation with an IAA-producing PGPB. However, the specific mode of IAA production by the PGPB is rarely elucidated. In part, this is due to the overwhelming complexity of IAA biosynthesis and regulation. The promiscuity of the enzymes implicated in IAA biosynthesis adds another element of complexity when attempting to decipher their role in IAA biosynthesis. To date, the majority of research on IAA biosynthesis describes three separate pathways classified in terms of their intermediates-indole acetonitrile (IAN), indole acetamide (IAM), and indole pyruvic acid (IPA). Each of these pathways is mediated by a set of enzymes, many of which are traditionally assumed to exist for that specific catalytic role. This lends the possibility of missing other, novel, enzymes that may also incidentally serve that function. Some of these pathways are constitutively expressed, while others are inducible. Some enzymes involved in IAA biosynthesis are known to be regulated by IAA or by IAA precursors, as well as by a multitude of environmental cues. This review aims to provide an update to our current understanding of the biosynthesis and regulation of IAA in bacteria. KEY POINTS: • IAA produced by PGPB improves bacterial stress tolerance and promotes plant growth. • Bacterial IAA biosynthesis is convoluted; multiple interdependent pathways. • Biosynthesis of IAA is regulated by IAA, IAA-precursors, and environmental factors.

Microbial IAA: Spectral Analysis and Application to Modulate Growth of Triticum aestivum

Plant growth promoting rhizobacteria (PGPR) play an essential part in transformation, solubilization, and mobilization of nutrients procured from the soil. Plant-microbe interaction can be termed as an eco-friendly approach which not only improves plant growth but helps in sustaining the soil and prevents environmental degradation from agrochemicals. PGPR improve plant growth through various mechanisms. One of the mechanisms involved is phytohormone production by the bacterial strains. In the current study, spectral analysis of thirteen already isolated and identified auxin-producing microbial strains (AAL1, AB8, A7B, A5C, A3E, A11E, AL2, A9G, A12G, A13G, AM10, P4, and S6) was carried out. Fourier transform infrared spectroscopy (FTIR) of the bacterial IAA exhibited close structural similarity between bacterial IAA and standard IAA. The growth-enhancing capability of strains was verified through the application of these strains on Triticum aestivum seedlings and enhancement of growth was statistically analyzed which indicated remarkable improvement in growth and metabolism both under laboratory and field conditions. Several bacterial isolates also proved to be very effective in improving biochemical parameters of plants. The current study suggested that the application of IAA-producing PGPR as biofertilizer is effective in enhancing plant growth as well as plant yield.

Chlorophytum comosum–bacteria interactions for airborne benzene remediation: Effect of native endophytic Enterobacter sp. EN2 inoculation and blue-red LED light

This study was performed to determine the effect of plant–endophytic Enterobacter sp. EN2 interactions and blue-red LED light conditions on gaseous benzene removal by plants. It was found that under consecutive benzene fumigation for three cycles (18 days), inoculation of the strain EN2 into sterilized and non-sterilized native C. comosum resulted in significantly increased gaseous benzene removal compared to that in non-inoculated groups under the same light conditions (P < 0.05). Remarkably, EN2 colonization in inoculated plants under LED conditions was higher than under fluorescence conditions as the EN2 could grow better under LED conditions. Strain EN2 possesses NADPH that is used to facilitate benzene degradation and modulate plant growth under benzene stress by bacterial IAA production and ACC deaminase activity; higher IAA and lower ethylene levels were found in inoculated plants compared to non-inoculated ones. These contributed to better benzene removal efficiency. Interestingly, under fumigation for 16 cycles (67 days), there was no difference in gaseous benzene removal between inoculated plants and non-inoculated plants under the same light conditions at initial benzene concentrations of 5 ppm. This is probably due to EN2 reaching maximum growth under all treatments. However, C. comosum exhibited better benzene removal under LED conditions than under fluorescence conditions during 16 cycles, possibly due to better photosynthetic performance and plant growth, leading to more NADPH, and eventually enhanced benzene removal efficiency. Hence, the most efficient acceleration of benzene removal was provided by inoculation of strain EN2 onto C. comosum under blue-red LED light conditions.

Phytostimulatory effect of indole-3-acetic acid by Enterobacter cloacae SN19 isolated from Teramnus labialis (L. f.) Spreng rhizosphere

Abstract A total of 30 morphologically distinct bacterial cultures were isolated from rhizosphere of wild tropical leguminous plant, Teramnus labialis (L. f.) Spreng. These isolates were screened for different plant growth promoting (PGP) traits amongst which a bacterial isolate designated as SN19 identified as Enterobacter cloacae (JQ904624) exhibited maximum IAA production (382.23 µg ml −1 in 0.1% L -tryptophan supplemented medium) along with other PGP traits. The production of IAA was confirmed by TLC and LC–MS/MS analysis. Biological potency of the bacterial IAA was determined using wheat coleoptile bioassay and in vitro root induction of Pluchea lanceolata shoot explants. The seed bacterization and bioinoculation of groundnut ( Arachis hypogaea ), rice ( Oryza sativa ), wheat ( Triticum aestivum ), mung ( Vigna radiata ) and maize ( Zea mays ) using this siderophorogenic IAA producer resulted in enhanced seed germination rate and plant vigour under in vivo condition. Thus, our findings indicate that the bacterium Enterobacter cloacae SN19 can serve as a promising plant growth promoting microbial inoculant.

Studies on the factors modulating indole-3-acetic acid production in endophytic bacterial isolates from Piper nigrum and molecular analysis of ipdc gene.

The study mainly aimed quantitative analysis of IAA produced by endophytic bacteria under various conditions including the presence of extract from Piper nigrum. Analysis of genetic basis of IAA production was also conducted by studying the presence and diversity of the ipdc gene among the selected isolates. Five endophytic bacteria isolated previously from P. nigrum were used for the study. The effect of temperature, pH, agitation, tryptophan concentration and plant extract on modulating IAA production of selected isolates was analysed by colorimetric method. Comparative and quantitative analysis of IAA production by colorimetric isolates under optimal culture condition was analysed by HPTLC method. Presence of ipdc gene and thereby biosynthetic basis of IAA production among the selected isolates were studied by PCR-based amplification and subsequent insilico analysis of sequence obtained. Among the selected bacterial isolates from P. nigrum, isolate PnB 8 (Klebsiella pneumoniae) was found to have the maximum yield of IAA under various conditions optimized and was confirmed by colorimetric, HPLC and HPTLC analysis. Very interestingly, the study showed stimulating effect of phytochemicals from P. nigrum on IAA production by endophytic bacteria isolated from same plant. This study is unique because of the selection of endophytes from same source for comparative and quantitative analysis of IAA production under various conditions. Study on stimulatory effect of phytochemicals on bacterial IAA production as explained in the study is a novel approach. Studies on molecular basis of IAA production which was confirmed by sequence analysis of ipdc gene make the study scientifically attractive. Even though microbial production of IAA is well known, current report on detailed optimization, effect of plant extract and molecular confirmation of IAA biosynthesis is comparatively novel in its approach.

Interactions of bacterial cytokinins and IAA in the rhizosphere may alter phytostimulatory efficiency of rhizobacteria

Phytohormones from rhizobacterial origin have been linked to their phytostimulation potential. However, while studying the efficacy of plant growth promoting bacteria, focus has always been on a single hormone. The role of plant hormones often overlay and they mutually modulate their effect. In current study focus was on the role of two hormones (cytokinins and indole acetic acid) in phytostimulation by rhizobacteria. Endogenous rhizosphere bacteria were isolated and screened for the presence of phytohormones. Bacterial strains from three different genera (Pseudomonas, Bacillus and Azospirillum) were screened positive for cytokinins and IAA. Phytohormones were simultaneously determined in SPE purified bacterial extract by ultra performance liquid chromatography (UPLC) coupled to a tandem mass spectrometer through electrospray interface. Cytokinins and IAA were determined in positive and negative mode, respectively with MRM scan. Zeatin, zeatin riboside and dihydrozeatin riboside were detected and quantified in the selected strains. Significant positive correlation between cytokinins and IAA in bacterial culture and plant endogenous hormones (r = 0.933 and r = 0.983; P = 0.01, respectively) was observed. However, strains with high IAA to cytokinins ratio could hardly enhance in-planta cytokinins, indicating antagonistic relation between the two hormones. Significant correlation of cytokinin with shoot length (r = 0.797; P = 0.01), fresh weight (r = 0.685; P = 0.01) and dry weight (r = 0.704; P = 0.01) was reported under axenic conditions. Bacterial IAA was correlated negatively to root length (r = 0.853; P = 0.01) and positively correlated to the number of roots (r = 0.964; P = 0.01). In natural conditions maximum increase in spike length (33%), number of tillers (71%) and weight of seeds (39%) was documented at final harvest in bacterially inoculated plants.

Beziehungen zwischen Pflanzen und epiphytischen Bakterien hinsichtlich ihres Auxinstoffwechsels: XI. Der Einfluß von IES-bildenden, IES-abbauenden und IES-neutralen Bakterien auf den Auxingehalt der Maispflanze im Vergleich zur Wirkung von Zucker-, Aminosäure- oder Vitaminapplikationen

Summary This investigation was undertaken to decide whether epiphytic bacteria increase the auxin content of their host plant only by giving off IAA, or also by supplying other metabolites, which could affect the auxin content directly or indirectly. 29 different but not identified bacteria strains were isolated from shoots, roots, and from the hydroculture medium of corn plants. The production of IAA from tryptophan and the degradation of IAA by these epiphytic bacteria of corn plants has been investigated. 5 strains were able to produce IAA from tryptophan without being able to destroy it, 6 strains could destroy IAA but not produce it, 13 strains had both properties, and 5 strains behaved indifferent to IAA. More extractable and diffusible auxin was received from sterilized corn plants which were artificially reinfected with epihphytic IAA-producing bacteria strains than from sterile corn plants. Reinfection with strains unable to produce IAA was ineffective, this comes true in the cases of both IAA-indifferent strains and of IAA-destroying ones. This result underlines the causal connection between bacterial IAA production and auxin increase in the host plant. Simultaneous reinfection of the sterile plant material with both an IAA-producing and an IAA-destroying strain did not affect the auxin content. An application of tryptophan increased the auxin content of corn plants which were artificially reinfected with IAA-producing bacteria strains, whereas it was ineffective in the case of plants having been reinfected with IAA-destroying or IAA-indifferent strains. This result, too, corroborates the significance of bacterial IAA production for the bacteria-mediated increase of the auxin level. Application of glucose, glutamic acid, and tyrosine did not result in any influence on the auxin content of sterile, nonsterile or reinfected plants, neither by being converted into a metabolite influencing auxin metabolism, nor by stimulating bacterial growth. Obviously another factor, possibly tryptophan, limits the bacterial effect on the auxin content of the plant. Application of thiamine, riboflavine, and pyridoxal-5’-phsophate did not affect the auxin content of sterile plants. Therefore these potential bacterial metabolites are without significance for the bacteria-induced auxin increase. Application of niacide, on the other hand, considerably increased the auxin content of sterile plants. But the results of another investigation (M anteuffel , S iegl 1973) prove niacide not to be a bacterial metabolite influencing the auxin content under our experimental conditions. The results of the present investigation confirm the supposition that the IAA production by epiphytic bacteria is physiologically significant in enhancing the auxin level in the host plant.

Interactions between Plants and Epiphytic Bacteria Regarding Their Auxin Metabolism

AbstractUsing hydrocultured pea plants, 109 bacterial strains (42 from shoots) were isolated from shoots, roots, and from the hydroculture medium. 58 different strains (26 from shoots) were able to produce IAA from tryptophan, 15 different strains (7 from shoots) were able lo destroy IAA. (Included are 13 strains possessing both properties.) As far as they could be identified, the IAA‐producing and ‐destroying strains belong to Pseudomonas (by far dominating), Achromobacter, Alcaligenses, Bacillus, and Flavobacterium. The IAA‐destroying activity strongly depends on the physiological state of the bacteria and the milieu conditions. Bacterial IAA production (but not IAA‐degradation) is supposed to be important for the plant.