ACC Deaminase-producing Bacteria Research Articles

Assessing the role of ACC deaminase-producing bacteria in alleviating salinity stress and enhancing zinc uptake in plants by altering the root architecture of French bean (Phaseolus vulgaris) plants.

The consortium inoculation with strains R1 and R4 modified the root system to boost seedling growth, increase the zinc content of French bean pods, and reduce salinity stress. The present study demonstrated the effect of two 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase-producing plant growth-promoting rhizobacteria (Pantoea agglomerans R1 and Pseudomonas fragi R4) alone and consortia on the root system development, French bean growth, and zinc content as well as salinity stress tolerance. Both the strains were characterized for ACC utilization activity (426.23 and 380.54nmol α-ketobutyrate mg protein-1h-1), indole acetic acid (IAA) production, phosphate solubilization, ammonia, hydrogen cyanide (HCN), and siderophore production. The strains exhibited zinc solubilization in both plate and broth assays with zinc oxide and zinc carbonate as zinc sources as validated by atomic absorption spectroscopy (AAS). Single or combined inoculations with the selected strains significantly modulated the architectural and morphological traits of the root system of French bean plants. Furthermore, the application of R1and R4 consortia has enhanced zinc content in roots (60.83mgkg-1), shoots (15.41mgkg-1), and pods (30.04mgkg-1) of French bean plants grown in ZnCO3 amended soil. In another set of pot experiments, the consortium bacterization has significantly enhanced length as well as fresh and dry biomass of roots and shoots of the French bean plant under saline stress conditions. Additionally, inoculation with ACC-degrading rhizobacterial strains has increased chlorophyll and carotenoid contents, osmoprotectant content, and antioxidative enzyme (catalase and peroxidase) activity in comparison to their counterparts exposed to salt treatments only. Current findings suggested ACC deaminase-producing rhizobacterial strains hold the potential to improve root architecture which in turn promotes plant growth under salt-stressed conditions as well as enhances micronutrient concentration in host plants.

Root 1-aminocyclopropane-l-carboxylic acid (ACC) and rhizosphere ACC deaminase-producing bacteria affect apple root architecture under soil compaction stress

Root 1-aminocyclopropane-l-carboxylic acid (ACC) and rhizosphere ACC deaminase-producing bacteria affect apple root architecture under soil compaction stress

Possible mechanisms for the equilibrium of ACC and role of ACC deaminase-producing bacteria.

Plant growth-promoting rhizobacteria (PGPR) actively colonize the plant rhizosphere, which not only stimulates plants' growth and development but also mitigates the adverse effects of abiotic stressors. Besides other techniques and approaches used for the alleviation of abiotic stress conditions, the utilization of PGPR with multiplant growth-promoting traits is desirable because the application of PGPR is pragmatic, sustainable, and environmentally friendly. In the past four decades, numerous ACC deaminase-producing PGPR have been reported for the improvement of crop plants' growth and development under different abiotic stress conditions. Since 1-aminocyclopropane-1-carboxylate (ACC) deaminase producing PGPR regulates ethylene production by utilizing the exuded ACC, which is an immediate precursor of ethylene biosynthesis. However, little is known about the basic mechanism involved in the acquisition of ACC by ACC deaminase-producing bacteria since the enzyme ACC deaminase is localized inside the bacterial cells and ACC is exuded into the rhizosphere from plant roots. In the present article, we proposed candidate attractants involved in the transfer of ACC into ACC deaminase-producing bacteria. Additionally, we discussed the importance and relation of these candidate attractants with ACC deaminase under abiotic stress conditions. KEY POINTS: • The ethylene precursor, ACC, exude from plant tissues under abiotic stresses • ACC deaminase activity of PGPR localized in the cytoplasm and periplasm of bacteria • Proposed candidate attractants for the transfer and equilibrium of exuded ACC.

Role of ACC deaminase producing bacteria for abiotic stress management and sustainable agriculture production.

Plants are immobile and are exposed to various biotic and abiotic stresses, including heat, cold, drought, flooding, nutrient deficiency, heavy metal exposure, phytopathogens, and pest attacks. The stressors significantly affect agricultural productivity when exceed a certain threshold. It has been reported that most of the stressed plants are reported to have increased ethylene synthesis from its precursor 1-aminocyclopropane-1-carboxylic acid (ACC). Ethylene is a plant hormone that plays a vital role in the regulation of various physiological processes, such as respiration, nitrogen fixation, and photosynthesis. The increment in the plant hormone ethylene would reduce plant growth and development, and if the ethylene level increased beyond the limit, it could also result in plant death. Therefore, plant growth-promoting bacteria (PGPB) possessing ACC deaminase activity play an essential role in the management of biotic and abiotic stresses by hydrolysing 1-aminocyclopropane-1-carboxylic acid using ACC deaminase. In this review, the importance of ACC deaminase-producing bacteria in promoting plant growth under various abiotic stressors is discussed.

Pseudomonas 1-Aminocyclopropane-1-carboxylate (ACC) Deaminase and Its Role in Beneficial Plant-Microbe Interactions.

The expression of the enzyme 1-aminocylopropane-1-carboxylate (ACC) deaminase, and the consequent modulation of plant ACC and ethylene concentrations, is one of the most important features of plant-associated bacteria. By decreasing plant ACC and ethylene concentrations, ACC deaminase-producing bacteria can overcome some of the deleterious effects of inhibitory levels of ACC and ethylene in various aspects of plant-microbe interactions, as well as plant growth and development (especially under stressful conditions). As a result, the acdS gene, encoding ACC deaminase, is often prevalent and positively selected in the microbiome of plants. Several members of the genus Pseudomonas are widely prevalent in the microbiome of plants worldwide. Due to its adaptation to a plant-associated lifestyle many Pseudomonas strains are of great interest for the development of novel sustainable agricultural and biotechnological solutions, especially those presenting ACC deaminase activity. This manuscript discusses several aspects of ACC deaminase and its role in the increased plant growth promotion, plant protection against abiotic and biotic stress and promotion of the rhizobial nodulation process by Pseudomonas. Knowledge regarding the properties and actions of ACC deaminase-producing Pseudomonas is key for a better understanding of plant-microbe interactions and the selection of highly effective strains for various applications in agriculture and biotechnology.

Lowered Cd toxicity, uptake and expression of metal transporter genes in maize plant by ACC deaminase-producing bacteria Achromobacter sp.

In this study, an ACC deaminase-producing bacterial strain Achromobacter sp. A1 was isolated from maize rhizosphere soil, characterized and evaluated for the effects on cadmium (Cd) immobilization in solution/rhizosphere, physiological characteristics and the tissue Cd contents in maize and the molecular mechanisms involved by hydroponic and pot experiments. ACC deaminase activity of strain A1 was significantly enhanced by Cd addition and Cd concentration decreased (55.54–63.62%) in solution supplemented with various Cd concentrations. Strain A1 significantly increased the maize dry weights (30.77–105%) and chlorophyll content (7.46–14.46%), decreased MDA content (25.16–36.87%) and ethylene production (20.93–35.86%) in hydroponic experiment. Strain A1 significantly reduced the above-ground tissue Cd uptake by 12.64–33.68% and 42–48% in hydroponic and pot experiments, reduced the DTPA-extractable Cd content and elevated invertase, urease and catalase activity in rhizosphere soils. In addition, the expression levels of Cd transporter genes HMA3 and Nramp5 were significantly reduced in root and shoot after strain A1 inoculation. These results indicate that strain A1 has great potential for application as a novel and environmentally friendly inoculant to immobilize Cd and reduce maize Cd uptake in Cd-contaminated environments, and will improve the understanding of the relative molecular mechanisms underlying the response to strain A1 in maize plant.

Ecological and physiological characterization of ACC deaminase-producing bacteria isolated from specific sites in Yogyakarta, Indonesia

The decrease of plant growth and productivity may be due to environmental stresses that induce excessive ethylene synthesis. ACC (1-aminocyclopropane-1-carboxylate) deaminase-producing bacteria are known to decrease plant ethylene levels by converting the ethylene precursor, ACC to ammonia and α-ketobutyrate. This study was aimed to understanding ecological and physiological characters of ACC deaminase-producing bacteria. The bacterial strains used were Sphingobacterium multivorum BK1, Bacillus mycoides CB2, Pantoea dispersa CK4, Pantoea agglomerans KD6.2, Enterobacter ludwigii KW3, Bacillus aryabhattai TW7, Pseudomonas monteilii KS12, Pseudomonas putida KS16.2, Pseudomonas putida PIR 3C, Stenotrophomonas maltophilia PIR5, Lysinibacillus pakistanensis PIC5, Bacillus aryabhattai PIC11, and Roultella terrigena PCM8. It was observed that all bacterial strains demonstrated optimal growth at pH 6-8, temperature 25–30°C, and oxygen requirement of aerobic to facultative anaerobic. All of strains have Phosphate Solubilizing Index between 1,1–3,04 and IAA (Indole-3-Acetic Acid) production level between 0,11-10,33 ppm.hour-1. In terms of antagonistic properties, all bacterial strains were found incapable of inhibiting Xanthomonas oryzae pv. oryzae and Ralstonia solanacearum growth. All bacterial strains were capable of using glucose, sucrose, cellulose and mannitol as the source of carbon and energy. In addition, all bacterial strains also demonstrated Cr6+ tolerance ofs 100–300 mg.L-1.

ACC deaminase plays a major role in Pseudomonas fluorescens YsS6 ability to promote the nodulation of Alpha- and Betaproteobacteria rhizobial strains.

Ethylene acts as a major regulator of the nodulation process of leguminous plants. Several rhizobial strains possess the ability to modulate plant ethylene levels through the expression of the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase; however, rhizobia present low enzymatic activities. One possible alternative to this problem resides on the use of free-living bacteria, such as Pseudomonas, presenting high levels of ACC deaminase activity that may be used as adjuvants in the nodulation process by decreasing inhibitory ethylene levels. Nevertheless, not much is understood about the specific role of ACC deaminase in the possible role of free-living bacteria as nodulation adjuvants. Therefore, this work aims to study the effect of ACC deaminase in the plant growth-promoting bacterium, Pseudomonas fluorescens YsS6, ability to facilitate alpha- and beta-rhizobia nodulation. The ACC deaminase-producing P. fluorescens YsS6 and its ACC deaminase mutant were used in co-inoculation assays to evaluate their impact in the nodulation process of alpha- (Rhizobium tropici CIAT899) and beta-rhizobia (Cupriavidus taiwanensis STM894) representatives, in Phaseolus vulgaris and Mimosa pudica plants, respectively. The results obtained indicate that the wild-type P. fluorescens YsS6, but not its mutant defective in ACC deaminase production, increase the nodulation abilities of both alpha- and beta-rhizobia, resulting in an increased leguminous plant growth. Moreover, this is the first report of the positive effect of free-living bacteria in the nodulation process of beta-rhizobia. The modulation of inhibitory ethylene levels by free-living ACC deaminase-producing bacteria plays an important role in facilitating the nodulation process of alpha- and beta-rhizobia.

Plant Growth Promotion Under Water: Decrease of Waterlogging-Induced ACC and Ethylene Levels by ACC Deaminase-Producing Bacteria.

Some plant growth-promoting bacteria encode for 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which facilitates plant growth and development by lowering the level of stress ethylene under waterlogged conditions. The substrate ACC is the immediate precursor for ethylene synthesis in plants; while bacterial ACC deaminase hydrolyzes this compound into α-ketobutyrate and ammonia to mitigate the adverse effects of the stress caused by ethylene exposure. Here, the structure and function of ACC deaminase, ethylene biosynthesis and waterlogging response, waterlogging and its consequences, role of bacterial ACC deaminase under waterlogged conditions, and effect of this enzyme on terrestrial and riparian plants are discussed.

ACC deaminase-producing bacteria mediated drought and salt tolerance in Capsicum annuum

ABSTRACTInfluence of drought and salt stress on different morphological and physiological growth parameters in Capsicum annuum inoculated with our isolates was estimated during the present study. Bulkhorderia cepacia was reported to possess the maximal, whereas Citrobacter feurendii the least plant growth promoting efficacy under salt and drought stress. ACC Deaminase activity of purified B. cepacia, C. feurendii and Serratia marcescens was 12.8 ± 0.44, 12.3 ± 0.56 and 11.7 ± 0.53 μM αKB mg−1 min−1 respectively. Under drought stress, B. cepacia showed maximum tolerance as it produced 4.893 ± 0.06 mg/mg protein of exopolysaccharide followed by C. feurendii and S. marcescens that produced 4.23 ± 0.03 and 3.46 ± 0.05 mg/mg protein, respectively. Chlorophyll “a” concentration was recorded 5.7 gm L−1 in B. cepacia inoculated plant (without stress) and was sustained till 2.9 gm L−1 even under the highest tested drought period. Chlorophyll “a” concentration in the B. cepacia inoculated plant under the highest tested NaCl concentration was 3.2 gm L−1. Thus, bacterial inoculation mitigates the effects of salinity by the proliferation of root system, increasing plant biomass proving to be potential bioinoculum for alleviating abiotic stress.

Rhizosphere Sampling Protocols for Microbiome (16S/18S/ITS rRNA) Library Preparation and Enrichment for the Isolation of Drought Tolerance-Promoting Microbes.

Natural plant microbiomes are abundant and have a remarkably robust composition, both as epiphytes on the plant surface and as endophytes within plant tissues. Microbes in the former "habitat" face limited nutrients and harsh environmental conditions, while those in the latter likely lead a more sheltered existence. The most populous and diverse of these microbiomes are associated with the zone around the plant roots, commonly referred to as the rhizosphere. A majority of recent studies characterize these plant-associated microbiomes by community profiling of bacteria and fungi, using amplicon-based marker genes and next-generation sequencing (NGS). Here, we collate a group of protocols that incorporate current best practices and optimized methodologies for sampling, handling of samples, and rRNA library preparation for variable regions of V5-V6 and V9 of the bacterial 16S ribosomal RNA (rRNA) gene, and the ITS2 region joining the 5.8S and 28S regions of the fungal rRNA gene. Samples collected for such culture-independent analyses can also be used for the actual isolation of microbes of interest, perhaps even those identified by the libraries described above. One group of microbes that holds promise for mediating plant stress incurred by drought are bacteria that are capable of reducing or eliminating the plant's perception of the stress through degradation of the gaseous plant hormone ethylene, which is abundantly produced in response to drought stimuli. This is accomplished by some types of soil bacteria that can produce the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which is the immediate precursor to ethylene. Here we provide a high-throughput protocol for screening of ACC deaminase-producing bacteria for the applied purpose of mitigating the impact of plant drought stress.

Erratum to: Changes in volatiles in carrots inoculated with ACC deaminase-producing bacteria isolated from organic crops

Erratum to: Changes in volatiles in carrots inoculated with ACC deaminase-producing bacteria isolated from organic crops

Changes in volatiles in carrots inoculated with ACC deaminase-producing bacteria isolated from organic crops

Bacterial ACC deaminase is one of the key tools to ameliorate plant stress by lowering ethylene level in plants. The effects of ACC deaminase-producing bacteria on the volatile profiles in plants have not been examined to date. To address this, we performed metabolic profiling of volatiles in carrots following inoculation of the bacteria producing ACC deaminase. We isolated ACC deaminase-producing bacteria from the inner part of the fruits and vegetables grown on organic farms by culturing on ACC-containing media, and screened them with PCR for the acdS gene, mungbean growth assay, and in vitro ACC deaminase activity. The isolated endophytes were evaluated for their ability to alter volatile profiles in carrots. Eleven bacterial strains possessing the activity to cleave ACC were selected among the 60 isolates grown on the medium containing ACC as a sole N source. Three of them that belonged to Pseudomonas could reduce the levels of (E)-2-hexenal and the other green leaf volatiles (GLVs) and terpenoids in the carrot leaves following inoculation of the seeds. The isolated endophytes with ACC deaminase activity could alter the composition of volatiles in plants, probably through lowering ethylene level in the plant.

Bacterial biosynthesis of 1-aminocyclopropane-1-caboxylate (ACC) deaminase, a useful trait to elongation and endophytic colonization of the roots of rice under constant flooded conditions.

This study was conducted to investigate the role of 1-aminocyclopropane-1-carboxylate (ACC) deaminase in Pseudomonas fluorescens strain REN1 and its ability to reduce ethylenelevels produced during stress, endophytically colonize and promote the elongation of the roots of rice seedlings under gnotobiotic conditions. We isolated 80 bacteria from inside roots of rice plants grown in the farmers' fields in Guilan, Iran. All of the isolates were characterized for plant growth promoting (PGP) traits. In addition, the colonization assay of these isolates on rice seedlings was carried outto screen for competent endophytes. The best bacterial isolate, based on ACC deaminase production, was identified and used for further study. 16S rDNA sequence analysisrevealed that the endophyte was closely related to Pseudomonas fluorescens. The results of this study showed ACC deaminase containing P. fluorescens REN1 increased in vitro root elongation and endophytically colonized the root of rice seedlings significantly, as compared to control under constant flooded conditions. The trait of low amount of indole-3-acetic acid (IAA) production (<15μgmL(-1)) and the high production of ACC deaminase by bacteria may be main factors in colonizing rice seedling roots compared to other PGP traits (siderophore production and phosphate solubilization) in this study. Endophytic IAA and ACC deaminase-producing bacteria may be preferential selections by rice seedlings. Therefore, it may be suggested that the utilization of ACC as a nutrient gives the isolates advantages in more endophytic colonization and increase of root length of rice seedlings.

Characterization of 1-Aminocyclopropane-1-Carboxylate (ACC) Deaminase-Containing Pseudomonas spp. in the Rhizosphere of Salt-Stressed Canola

AbstractWhen exposed to biotic or abiotic stress conditions, plants produce ethylene from its immediate precursor 1-aminocyclopropane-1-carboxylate (ACC), leading to retarded root growth and senescence. Many plant growth-promoting rhizobacteria contain the enzyme ACC deaminase and this enzyme can cleave ACC to form α-ketobutyrate and ammonium, thereby lowering levels of ethylene. The aim of this study was to isolate and characterize ACC deaminase-producing bacteria from the rhizosphere of salt-stressed canola (Brassica napus L.). Out of 105 random bacterial isolates, 15 were able to utilize ACC as the sole source of nitrogen. These 15 isolates were also positive for indole acetic acid (IAA) production. Phylogenetic analysis based on partial 16S rDNA sequences showed that all isolates belonged to fluorescent Pseudomonas spp. In the canola rhizosphere investigated in this study, Pseudomonas fluorescens was the dominant ACC deaminase-producing species. Cluster analysis based on BOX-A1R-based repetitive extragenic palindromic-polymerase chain reaction (BOX-PCR) patterns suggested a high degree of genetic variability in ACC deaminase-producing P. fluorescens strains. The presence of indigenous ACC-degrading bacteria in the rhizosphere of canola grown in saline soils indicates that these bacteria may contribute to salinity tolerance.

Plant Growth-Promoting Bacteria Facilitate the Growth of Barley and Oats in Salt-Impacted Soil: Implications for Phytoremediation of Saline Soils

Plant growth-promoting bacteria (PGPB) strains that contain the enzyme 1-amino- cyclopropane-1-carboxylate (ACC) deaminase can lower stress ethylene levels and improve plant growth. In this study, ACC deaminase-producing bacteria were isolated from a salt-impacted (∼50 dS/m) farm field, and their ability to promote plant growth of barley and oats in saline soil was investigated in pouch assays (1% NaCl), greenhouse trials (9.4 dS/m), and field trials (6–24 dS/m). A mix of previously isolated PGPB strains UW3 (Pseudomonas sp.) and UW4 (P. sp.) was also tested for comparison. Rhizobacterial isolate CMH3 (P. corrugata) and UW3+UW4 partially alleviated plant salt stress in growth pouch assays. In greenhouse trials, CMH3 enhanced root biomass of barley and oats by 200% and 50%, respectively. UW3+UW4, CMH3 and isolate CMH2 also enhanced barley and oat shoot growth by 100%–150%. In field tests, shoot biomass of oats tripled when treated with UW3+UW4 and doubled with CHM3 compared with that of untreated plants. PGPB treatment did not affect salt uptake on a per mass basis; higher plant biomass led to greater salt uptake, resulting in decreased soil salinity. This study demonstrates a method for improving plant growth in marginal saline soils. Associated implications for salt remediation are discussed.

Evidence for the involvement of ACC deaminase from Pseudomonas putida UW4 in the biocontrol of pine wilt disease caused by Bursaphelenchus xylophilus

Pine wilt disease, caused by the nematode Bursaphelenchus xylophilus, is responsible for devastation of pine forests worldwide. Until now, there are no effective ways of dealing with this serious threat. The use of 1-aminocyclopropane-1-carboxylate (ACC) deaminase (encoded by the acdS gene)-producing plant growth-promoting bacteria has been shown to be a useful strategy to reduce the damage due to biotic and abiotic stresses. Pinus pinaster seedlings inoculated with the ACC deaminase-producing bacterium Pseudomonas putida strain UW4 showed an increased root and shoot development and reduction of B. xylophilus induced symptoms. In contrast, a P. putida UW4 acdS mutant was unable to promote pine seedling growth or to decrease B. xylophilus induced symptoms. This is the first report on the use of ACC deaminase-producing bacteria as a potential biological control agent for a tree disease, thus suggesting that the inoculation of pine seedlings grown in a tree nursery might constitute a novel strategy to obtain B. xylophilus resistant pine trees.

Improved growth performance of the mangrove Avicennia marina seedlings using a 1-aminocyclopropane-1-carboxylic acid deaminase-producing isolate of Pseudoalteromonas maricaloris

Out of 62 bacterial isolates obtained from the mangrove Avicenniamarina rhizosphere that grows along the Abu Dhabi coast, United Arab Emirates (UAE), an isolate of Pseudoalteromonas maricaloris (Wild type strain) (WT) produced relatively high levels of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase in vitro. Application of this WT strain under greenhouse conditions to A. marina seedlings significantly (P < 0.05), reduced endogenous levels of ACC in the roots and shoots, and significantly (P < 0.05) increased the levels of in planta endogenous plant growth regulators (PGRs) including indole-3-acetic acid (IAA), indole-3-pyruvic acid (IPYA), putrescine (Put), spermidine (Spd) and spermine (Spm) in roots and shoots compared with control mangrove seedlings. WT application has also significantly (P < 0.05) increased photosynthetic pigment contents, photosynthetic carbon assimilation, plant water use efficiency and promoted mangrove seedlings growth characteristics including increased dry weight and length of roots and shoots, total leaf area and the number of the side branches compared with control mangrove seedlings. In comparison, an ACC deaminase non-producing mutant strain (NPM) failed to reduce endogenous levels of ACC in the roots and shoots and also failed to increase endogenous PGRs and photosynthetic pigments and did not promote seedling growth. Both WT and NPM strains were incapable of producing in vitro detectable levels of IAA, IPYA, Gibberellic acid (GA3), zeatin (Z), Put, Spd and Spm in the culture filtrates. This study demonstrated for the first time the ability of ACC deaminase-producing bacteria to promote mangrove growth under greenhouse conditions. P. maricaloris has potential as biological inoculants to promote the growth of mangrove seedlings in afforestation programs in nutrient impoverished sediments in hyper-saline coastal areas in the UAE.

Interactions between Pseudomonas putida UW4 and Gigaspora rosea BEG9 and their consequences for the growth of cucumber under salt-stress conditions

After the determination of the toxic but nonlethal concentration of NaCl for cucumber, we examined the interaction between an ACC (1-aminocyclopropane-1-carboxylate) deaminase producing bacterial strain and an arbuscular mycorrhizal fungus (AMF) and their effects on cucumber growth under salinity. In the first experiment, cucumber seedlings were exposed to 0.1, 50, 100 or 200 mmol l(-1) NaCl, and plant biomass and leaf area were measured. While seeds exposed to 200 mmol l(-1) NaCl did not germinate, plant growth and leaf size were reduced by 50 or 100 mmol l(-1) salt. The latter salt cancentration caused plant death in 1 month. In the second experiment, seeds were inoculated with the ACC deaminase-producing strain Pseudomonas putida UW4 (AcdS(+)), its mutant unable to produce the enzyme (AcdS(-)), or the AMF Gigaspora rosea BEG9, individually or in combination and exposed to 75 mmol l(-1) salt. Plant morphometric and root architectural parameters, mycorrhizal and bacterial colonization and the influence of each micro-organism on the photosynthetic efficiency were evaluated. The AcdS(+) strain or the AMF, inoculated alone, increased plant growth, affected root architecture and improved photosynthetic activity. Mycorrhizal colonization was inhibited by each bacterial strain. Salinity negatively affects cucumber growth and health, but root colonization by ACC deaminase-producing bacteria or arbuscular mycorrhizal fungi can improve plant tolerance to such stressful condition. Arbuscular mycorrhizal fungus and bacterial ACC deaminase may ameliorate plant growth under stressful conditions. It was previously shown that, under optimal growth conditions, Ps. putida UW4 AcdS(+) increases root colonization by Gi. rosea resulting in synergistic effects on cucumber growth. These results suggest that while in optimal conditions ACC deaminase is mainly involved in the bacteria/fungus interactions, while under stressful conditions this enzyme plays a role in plant/bacterium interactions. This finding is relevant from an ecological and an applicative point of view.

Prospective Use of 1-Aminocyclopropane-1-Carboxylate Deaminase-Producing Bacteria for Plant Growth Promotion and Defense against Biotic and Abiotic Stresses in Peat-Soil-Agriculture

The 1-aminocyclopropane-1-carboxylate (ACC) deaminase (EC4.1.99.4) is an enzyme produced by some soil bacteria to degrade ACC (the immediate precursor of ethylene) to reduce ethylene biosynthesis in higher plants. Increased concentrations of ethylene in plant tissues, which are triggered by various biotic and abiotic stresses, inhibits plant growth and weakens the plant defense against the stressors. Various findings on the successful use of ACC deaminase producing bacteria for plant growth under unfavorable soil conditions are inspiring their use in tropical peat-soil-agriculture, which possesses bio-physical constraints. It has been proven that inoculation of plants with ACC deaminase producing bacteria decreased ethylene inhibition generated by unfavorable environmental conditions, such as nutrient shortage, flooding, drought, high salts, and the presence of heavy metals and organic pollutants. Understanding the mechanisms by which ACC deaminase-producing bacteria act to reduce plant stress and the fitness of bacterial traits with the properties and constraints of peat-soils becomes a key to utilize these bacteria in improving crop productivity. The bacteria may ameliorate plant stress as well as promote plant growth under seasonal bio-physical changes of peat-soils that are usually encountered in the field.