Phosphate uptake kinetics by Acinetobacter isolates

Acinetobacter isolates from activated sludge treatment plants of forest industry were used as model organisms for polyphosphate accumulating bacteria to study excess phosphate uptake by the overplus phenomenon as well as luxury uptake of phosphate during growth. The initial, rapid phosphate uptake by the phosphorus-starved Acinetobacter isolates (the overplus phenomenon) followed the Michaelis-Menten model (maximum initial phosphate uptake rate 29 mg P g(-1) dry mass (DM) h(-1), half-saturation constant for excess phosphate uptake 17 mg P L(-1)). During the rapid uptake no growth was observed, but most cells contained polyphosphate granules. Also growth and luxury uptake of phosphate could be modeled with the Michaelis-Menten equation (maximum phosphate uptake rate 3.7-12 mg P g(-1) DM h(-1), half-saturation constant for growth 0.47-6.0 mg P L(-1), maximum specific growth rate 0.15-0.55 h(-1)). (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 304-309, 1997.     

Highly efficient uptake of phosphorus in epiphytic bromeliads

Background and Aims

Vascular epiphytes which can be abundant in tree crowns of tropical forests have to cope with low and highly intermittent water and nutrient supply from rainwater, throughfall and stem flow. Phosphorus rather than nitrogen has been suggested as the most limiting nutrient element, but, unlike nitrogen, this element has received little attention in physiological studies. This motivated the present report, in which phosphate uptake kinetics by leaves and roots, the subsequent distribution within plants and the metabolic fate of phosphate were studied as a step towards an improved understanding of physiological adaptations to the conditions of tree canopies.

Methods

Radioactively labelled [³²P]phosphate was used to study uptake kinetics and plant distribution of phosphorus absorbed from bromeliad tanks. The metabolism of low molecular phosphorus metabolites was analysed by thin-layer chromatography followed by autoradiography.

Key Results

Uptake of phosphate from tanks is an ATP-dependent process. The kinetics of phosphorus uptake suggest that epiphytes possess effective phosphate transporters. The K_m value of 1·05 µm determined for leaves of the bromeliad Aechmea fasciata is comparable with values obtained for the high affinity phosphate transporters in roots of terrestrial plants. In this species, young leaves are the main sink for phosphate absorbed from tank water. Within these leaves, phosphate is then allocated from the basal uptake zone into distal sections of the leaves. More than 80 % of the phosphate incorporated into leaves is not used in metabolism but stored as phytin.

Conclusions

Tank epiphytes are adapted to low and intermittent nutrient supply by different mechanisms. They possess an effective mechanism to take up phosphate, minimizing dilution and loss of phosphorus captured in the tank. Available phosphorus is taken up from the tank solution almost quantitatively, and the surplus not needed for current metabolism is accumulated in reserves, i.e. plants show luxury consumption. Young, developing leaves are preferentially supplied with this nutrient element. Taken together, these features allow epiphytes the efficient use of scarce and variable nutrient supplies.Key words: Epiphytic bromeliads, phosphorus uptake, forest canopies, luxury consumption, phytotelms, plant nutrition, Aechmea fasciata     

PHOTOSYNTHETIC CAPACITY AND LUXURY UPTAKE OF CARBON DURING PHOSPHATE LIMITATION IN PEDIASTRUM DUPLEX (CHLOROPHYCEAE)1

When cells of Pediastrum duplex Meyen experience phosphorus depletion, their capacity for carbon fixation declines, but sizes and carbon contents of the cells increase several-fold, an apparent instance of “luxury uptake” of carbon. Maximum rates of uptake of phosphate increase during the same period, and are consequently correlated with the enlarged surface area of the cells. Thus the disadvantage of increased cell volume, which may accelerate sinking speed in nature, is offset by the increased capacity of the cells for nutrient uptake.     

Effect of auxin producing and phosphate solubilizing bacteria on mobility of soil phosphorus,growth rate,and P acquisition by wheat plants

Microorganisms capable of mobilizing phosphate promote plant growth, this activity being frequently accompanied by production of plant hormones auxins. However, the extent of contribution of these characteristics to promotion of plant growth remains unclear. Paenibacillus illinoisensis IB 1087 and Pseudomonas extremaustralis IB-Ki-13-1A strains were selected for their capacity to mobilize phosphates and to synthesize auxins in vitro. The effects of inoculating these bacteria on the content of mobile phosphorus in the soil as well as on the phosphorus and hormone content in wheat plants were studied and the observed responses were related to the changes in plant growth. Inoculation of bacteria into the soil increased P concentration in the plants suggesting their increased capacity for the efficient acquisition of phosphorus compounds, while concentration of mobile phosphorus in the soil was increased by its inoculation with bacteria only in the absence of plants. The treatment increased plants mass (to greater extent in the case of P. illinoisensis) in accordance with the increased level of auxins in the treated plant. Increased mass accumulation did not correlate with the potential ability of bacteria strains for production of auxins or phosphate mobilization in vitro. Our data indicate importance of increased auxin content in the plants for the stimulation of root growth and capacity for P uptake as influenced by growth-promoting bacteria.     

Luxury consumption and specific utilization rates of three macroelements in two Taraxacum microspecies of contrasting mineral ecology

Plants of Taraxacum sellandii Dahlst., a microspecies adapted to fertile, and Taraxacum nordstedtii Dahlst., adapted to infertile soils, were cultured hydroponically, either on a complete nutrient solution or on one deprived of nitrogen, phosphorus, or potassium ions. For all four treatments, the growth and internal mineral concentration of the plants was monitored. For plants cultured on a complete nutrient solution, the uptake rates of nitrate, phosphate, and potassium ions were determined. Luxury consumption of the three macronutrients was computed as the excess of ion absorption over the ion uptake rates minimally required to sustain maximum growth. In these calculations the critical N, P, or K⁺ concentrations, earlier derived, were used as parameters describing the mineral status minimally required to allow maximum growth. Efficiency in use of the three macroelements at various levels of mineral accumulation was also computed. Finally, the response to phosphate starvation as related to phosphate uptake capacity and the accumulation of P was investigated.
The physiological properies investigated provide a causal background for the superior adaptation of T. nordstedtii as compared to T. sellandii to infertile sites. Taraxacum nordstedtii had a higher relative luxury consumption of NO₃^–, H₂PO^-₄, and K⁺, a higher efficiency in N and P use at N– and (severe) P-deficiency, respectively; and, after phosphate starvation, a relatively high preservation of phosphate uptake capacity and an enlargement of P storage. In combination with the low potential growth, luxury consumption will be particularly effective in T. nordstedtii in preventing or minimizing mineral deficiency. The distribution of minerals between cytoplasm and vacuoles as a factor in mineral use efficiency is discussed.     

Relationship between Energy-dependent Phosphate Uptake and the Electrical Membrane Potential in Lemna gibba G1

High rates of phosphate uptake into phosphate-starved Lemna gibba L. G1 were correlated with a high membrane potential (pd = −220 millivolts). In plants maintaining a low pd (−110 millivolts), the uptake rate was only 20% of that of high-pd plants. At the onset of phosphate transport, the membrane of high-pd plants was transiently depolarized. This effect was much smaller in low-pd plants. Light stimulated phosphate uptake and the repolarization upon phosphate-induced depolarization, especially in plants grown without sucrose. The phosphate uptake rate was optimal at pH 6 and decreased with increasing pH, corresponding to the phosphate-induced pd changes. Phosphate starvation stimulated the uptake and increased the phosphate-induced depolarization, thus indicating that phosphate uptake depends on the intracellular phosphate level. It is suggested that uptake of monovalent phosphate in Lemna gibba proceeds by an H⁺ cotransport dependent on the proton electrochemical potential difference and, hence, on the activity of an H⁺ -extrusion pump.     

Relationship between Nitrite Reduction and Active Phosphate Uptake in the Phosphate-Accumulating Denitrifier Pseudomonas sp. Strain JR 12

Phosphate uptake by the phosphate-accumulating denitrifier Pseudomonas sp. JR12 was examined with different combinations of electron and carbon donors and electron acceptors. Phosphate uptake in acetate-supplemented cells took place with either oxygen or nitrate but did not take place when nitrite served as the final electron acceptor. Furthermore, nitrite reduction rates by this denitrifier were shown to be significantly reduced in the presence of phosphate. Phosphate uptake assays in the presence of the H⁺-ATPase inhibitor N,N′-dicyclohexylcarbodiimide (DCCD), in the presence of the uncoupler carbonyl cyanide 3-chlorophenylhydrazone (CCCP), or with osmotic shock-treated cells indicated that phosphate transport over the cytoplasmic membrane of this bacterium was mediated by primary and secondary transport systems. By examining the redox transitions of whole cells at 553 nm we found that phosphate addition caused a significant oxidation of a c-type cytochrome. Based on these findings, we propose that this c-type cytochrome serves as an intermediate in the electron transfer to both nitrite reductase and the site responsible for active phosphate transport. In previous studies with this bacterium we found that the oxidation state of this c-type cytochrome was significantly higher in acetate-supplemented, nitrite-respiring cells (incapable of phosphate uptake) than in phosphate-accumulating cells incubated with different combinations of electron donors and acceptors. Based on the latter finding and results obtained in the present study it is suggested that phosphate uptake in this bacterium is subjected to a redox control of the active phosphate transport site. By means of this mechanism an explanation is provided for the observed absence of phosphate uptake in the presence of nitrite and inhibition of nitrite reduction by phosphate in this organism. The implications of these findings regarding denitrifying, phosphate removal wastewater plants is discussed.     

Iron and phosphate uptake explains the calcifuge–calcicole behavior of the terricolous lichens Cladonia furcata subsp. furcata and C. rangiformis

Mechanisms causing the calcifuge–calcicole behavior of lichens are largely unexplored. Studying the case examples of two closely related terricolous lichens, the calcifuge Cladonia furcata subsp. furcata and the calcicole C. rangiformis, we found that preference for acidic or calcareous soils in these lichens is related to iron and phosphate uptake as in vascular plants. In laboratory studies, the calcicole species was more efficient in the intracellular uptake of Fe³⁺ and phosphate at pH 8 than the calcifuge species. At pH 3, intracellular uptake of Fe²⁺ in the calcicole species significantly exceeded that in the calcifuge species suggesting that calcicole lichens suffer from toxicity symptoms by excess Fe²⁺ at acidic sites. Though these observations parallel findings from calcifuge and calcicole vascular plants, mechanisms leading to the different iron and phosphate uptake characteristics in the studied calcifuge and calcicole lichens may differ from those in vascular plants and should be the topic of future research. A role of the depside atranorin in facilitating iron uptake by reducing Fe³⁺ in the apoplast is hypothesized.     

Novel phosphate solubilizing bacteria ‘Pantoea cypripedii PS1’ along with Enterobacter aerogenes PS16 and Rhizobium ciceri enhance the growth of chickpea (Cicer arietinum L.)

Phosphate solubilizing bacteria (PSB) are known to convert the insoluble forms of phosphate to soluble one and make them available for plant uptake. The present study aimed to isolate PSB from the rhizosphere of chickpea (Cicer arietinum L. cv. GPF2) and examine their effect on the growth and seed number. The isolated PSB were analyzed for phosphate solubilization, indole acetic acid and siderophore production. PSB were characterized for phenotypic and biochemical properties, BIOLOG and whole-cell fatty acid methyl ester profile and found to be closely related to Pantoea cypripedii and Enterobacter aerogenes based on 16s rRNA gene sequencing. A high increase in growth of C. arietinum was observed when innoculated with PSB in tricalcium phosphate amended soils. A higher uptake in total P (53 %) of plants was observed when inoculated with mixture of P. cypripedii and E. aerogenes along with Rhizobium ciceri as compared to respective control plants which significantly increased the seed number (98.3 %) and seed weight (46.1 %). This study demonstrated the ability of novel PSB P. cypripedii along with E. aerogenes and R. ciceri to promote chickpea growth.     

In Situ Characterization of Nitrospira-Like Nitrite-Oxidizing Bacteria Active in Wastewater Treatment Plants

Uncultivated Nitrospira-like bacteria in different biofilm and activated-sludge samples were investigated by cultivation-independent molecular approaches. Initially, the phylogenetic affiliation of Nitrospira-like bacteria in a nitrifying biofilm was determined by 16S rRNA gene sequence analysis. Subsequently, a phylogenetic consensus tree of the Nitrospira phylum including all publicly available sequences was constructed. This analysis revealed that the genus Nitrospira consists of at least four distinct sublineages. Based on these data, two 16S rRNA-directed oligonucleotide probes specific for the phylum and genus Nitrospira, respectively, were developed and evaluated for suitability for fluorescence in situ hybridization (FISH). The probes were used to investigate the in situ architecture of cell aggregates of Nitrospira-like nitrite oxidizers in wastewater treatment plants by FISH, confocal laser scanning microscopy, and computer-aided three-dimensional visualization. Cavities and a network of cell-free channels inside the Nitrospira microcolonies were detected that were water permeable, as demonstrated by fluorescein staining. The uptake of different carbon sources by Nitrospira-like bacteria within their natural habitat under different incubation conditions was studied by combined FISH and microautoradiography. Under aerobic conditions, the Nitrospira-like bacteria in bioreactor samples took up inorganic carbon (as HCO₃⁻ or as CO₂) and pyruvate but not acetate, butyrate, and propionate, suggesting that these bacteria can grow mixotrophically in the presence of pyruvate. In contrast, no uptake by the Nitrospira-like bacteria of any of the carbon sources tested was observed under anoxic or anaerobic conditions.     

Phosphate-solubilizing activity of aerobic methylobacteria

Phosphate-solubilizing activity was found in 14 strains of plant-associated aerobic methylobacteria belonging to the genera Methylophilus, Methylobacillus, Methylovorus, Methylopila, Methylobacterium, Delftia, and Ancyclobacter. The growth of methylobacteria on medium with methanol as the carbon and energy source and insoluble tricalcium phosphate as the phosphorus source was accompanied by a decrease in pH due to the accumulation of up to 7 mM formic acid as a methanol oxidation intermediate and by release of 120–280 μM phosphate ions, which can be used by both bacteria and plants. Phosphate-solubilizing activity is a newly revealed role of methylobacteria in phytosymbiosis.     

Screening of plant growth promoting traits in heavy metals resistant bacteria: Prospects in phytoremediation

Phytoremediation is considered as a novel environmental friendly technology, which uses plants to remove or immobilize heavy metals. The use of metal-resistant plant growth-promoting bacteria (PGPB) constitutes an important technology for enhancing biomass production as well as tolerance of the plants to heavy metals. In this study, we isolated twenty seven (NF1-NF27) chromium resistant bacteria. The bacteria were tested for heavy metals (Cr, Zn, Cu, Ni, Pb and Co) resistance, Cr(VI) reduction and PGPB characters (phosphate solubilization, production of IAA and siderophores). The results showed that the bacterial isolates resist to heavy metals and reduce Cr(VI), with varying capabilities. 37.14% of the isolates have the capacity of solubilizing phosphate, 28.57% are able to produce siderophores and all isolates have the ability to produce IAA. Isolate NF2 that showed high heavy metal resistance and plant growth promotion characteristics was identified by 16S rDNA sequence analysis as a strain of Cellulosimicrobium sp.. Pot culture experiments conducted under greenhouse conditions showed that this strain was able to promote plant growth of alfalfa in control and in heavy metals (Cr, Zn and Cu) spiked soils and increased metal uptake by the plants. Thus, the potential of Cellulosimicrobium sp. for both bioremediation and plant growth promotion has significance in the management of environmental pollution.     

Simulated herbivory effects on rhizosphere organisms in pea (Pisum sativum) depended on phosphate

The effects of simulated aboveground herbivory and phosphate addition to soil on rhizosphere organisms (arbuscular mychorrhiza (AM), Rhizobium spp., bacteria, protozoa and nematodes) were studied in a 2 by 2 factorial designed pot experiment with Pea plants (Pisum sativum). Measurements were performed on 24 day old plants that were still in the nutrient acquisition phase before flowering. AM colonization and bacterial feeding nematodes were stimulated by high simulated her- bivory especially when plants were phosphate deficient. Total number of nematodes was higher with phosphate deficiency. Furthermore, non-significant peak values in soil respiration, total number of nematodes, and bacterial number were observed in phosphate deficient plants with high simulated herbivory. In phosphate amended plants, fast-growing protozoa and bacterial feeding nematodes decreased at high simulated herbivory. These results support the hypothesis that the plant regulates abundances of both AM and free-living rhizosphere organisms and thereby the amount of plant-available nutrients, according to demand via root exudation. Rhizobium spp. was significantly stimulated by phosphate addition but not affected by simulated herbivory. Metabolites produced by rhizosphere bacteria from plants exposed to high simulated herbivory in phosphate amended soil stimulated seed performance. Possible interactions between protozoa and nematodes in relation to production and composition of bacteria in the rhizosphere are discussed.     

Luxury uptake of phosphorus by microalgae in waste stabilisation ponds: current understanding and future direction

There is a need to improve phosphorus removal for the tens of thousands of small communities around the world that currently rely on waste stabilisation ponds for their wastewater treatment. We now know that microalgae in pond systems are capable of accumulating phosphorus within their cells as polyphosphate in a process known as luxury uptake, but this knowledge has not yet been applied to engineer a new process to improve phosphorus removal. This paper summarises the current understanding of this mechanism, discusses the key factors influencing polyphosphate accumulation and provides future direction for research in this field. There have only been a limited number of studies that have focussed on luxury uptake of polyphosphate by microalgae in high phosphorus concentration environments such as those found in waste stabilisation pond systems. However, from this review it has been shown that the environmental factors which influence polyphosphate storage are the phosphate concentration, light intensity and temperature. Currently we are limited to a black box understanding of the bulk population and as a result future research needs to focus on a systematic evaluation of different microalgal genera under a wide range of environmental, biological and process variables in order to reveal the conditions needed to reliably trigger this phenomenon. This will then provide the basis for developing a new algal biotechnology optimised for luxury uptake of polyphosphate. While there are still several key questions that need to be answered there is potential for this to lead to a process which could be as significant to pond systems as the development of enhanced biological phosphorus removal was for the activated sludge process.     

Effect of co-inoculation of methylotrophic Methylobacterium oryzae with Azospirillum brasilense and Burkholderia pyrrocinia on the growth and nutrient uptake of tomato, red pepper and rice

The present greenhouse study was undertaken to evaluate the effects of co-inoculating methylotrophic Methylobacterium oryzae CBMB20 along with nitrogen-fixing Azospirillum brasilense CW903 or a phosphate solubilizing bacterium Burkholderia pyrrocinia CBPB-HOD on the growth and nutrient uptake of tomato, red pepper and rice. Seed inoculation and soil/foliar application of the bacterial strains alone or under dual inoculation increased the plant growth in terms of shoot or root length and increased the nutrient uptake in the plants studied compared to uninoculated control plants. Co-inoculation of M. oryzae CBMB20 with A. brasilense CW903 or B. pyrrocinia CBPB-HOD improved the N and P concentration of plants, while the results varied among the plant species tested. Also, co-inoculation of the bacterial strains increased the activity of nitrogenase, urease and phosphatase enzymes in soil when compared to uninoculated control or individual inoculations. Though the inoculation effects were analyzed at an early stage of plant growth, the results conclusively suggest that M. oryzae being compatible with other microorganisms in the rhizosphere can potentially be used as individual inoculant or co-inoculated with other plant growth promoting bacteria to increase the production in sustainable agricultural systems.     

Effects of sulphate and pH on the plant-availability of phosphate adsorbed on goethite

The adsorption of phosphate on metal (hydr)oxides may be influenced by the pH and by the adsorption of other ions. In this study, the influence of sulphate and pH on phosphate adsorption on goethite and the availability to plants of adsorbed phosphate was examined. Maize plants were grown on suspensions of goethite with adsorbed phosphate, containing the same total amount of phosphate and either 0.11 mM or 2.01 mM sulphate at pH 3.7, 4.6 or 5.5. The uptake of phosphorus by the plants increased with the larger sulphate concentration and decreasing pH. Mean P uptake in the treatment with 2.01 mM sulphate and pH 3.7 was 55 µmol plant^-1, whereas in the treatment with 0.11 mM sulphate and pH 5.5 it was 2 µmol plant^-1. Batch adsorption experiments using³² P and speciation modelling of ion adsorption showed that in the presence of sulphate, the phosphate concentration in solution strongly increased with decreasing pH, due to competitive adsorption between sulphate and phosphate on goethite. Modelled phosphate concentrations in solution in the uptake experiment were all below 0.6 µM and correlated well with the observed P uptake. This correlation indicates that the strong influence of the sulphate concentration and pH on the plant-availability of adsorbed phosphate results from the competition between sulphate and phosphate for adsorption on goethite.     

Mutant of Arabidopsis deficient in xylem loading of phosphate

A mutant of Arabidopsis thaliana deficient in the accumulation of inorganic phosphate has been isolated by screening directly for plants with altered quantities of total leaf phosphate. The mutant plants accumulate approximately 5% as much inorganic phosphate, and 24 to 44% as much total phosphate, as wild-type plants in aerial portions of the plant. Growth of the mutant is reduced, relative to wild type, and it exhibits other symptoms normally associated with phosphate deficiency. The phosphate deficiency is caused by a single nuclear recessive mutation at a locus designated pho1. The rate of phosphate uptake into the roots was similar between mutant and wild-type plants over a wide range of external phosphate concentrations. In contrast, when plants were grown in media containing 200 micromolar phosphate or less, phosphate transfer to the shoots of the mutant was reduced to 3 to 10% of the wild-type levels. The defect in phosphate transfer to the shoots could be overcome by providing higher levels of phosphate. Transfer of sulfate to the shoots was essentially normal in the mutant, indicating that the pho1 lesion was not a general defect in anion transport. Movement of phosphate through the xylem of the shoots was not impaired. The results suggest that the mutant is deficient in activity of a protein required to load phosphate into the xylem.     

Carbonic Anhydrase-Dependent Inorganic Carbon Uptake by the Red Macroalga, Chondrus crispus

The rate of photosynthetic carbon uptake of Chondrus crispus Stack-house plants, at various CO₂ concentrations and pretreated with carbonic anhydrase (CA) inhibitors, was determined using an air-suspension, differential infra-red gas analyzer technique. It was found that the CA inhibitors, acetazolamide, dextran-bound acetazolamide (DBI, which does not permeate cell membranes), and subtilisin (a protease that attacks the cell surface) inhibit photosynthetic carbon uptake in C. crispus. Inhibition was greatest at low CO₂ concentrations, and decreased at CO₂ saturation. Acetazolamide inhibited carbon uptake to a greater extent than DBI. The data support the conclusion that C. crispus plants utilize HCO₃⁻ for photosynthesis, and that both cell-surface and internal CA are involved in the photosynthetic uptake of inorganic carbon.     

OsARF16 Is Involved in Cytokinin-Mediated Inhibition of Phosphate Transport and Phosphate Signaling in Rice (Oryza sativa L.)

Background

Plant responses to phytohormone stimuli are the most important biological features for plants to survive in a complex environment. Cytokinin regulates growth and nutrient homeostasis, such as the phosphate (Pi) starvation response and Pi uptake in plants. However, the mechanisms underlying how cytokinin participates in Pi uptake and Pi signaling are largely unknown. In this study, we found that OsARF16 is required for the cytokinin response and is involved in the negative regulation of Pi uptake and Pi signaling by cytokinin.

Principal Findings

The mutant osarf16 showed an obvious resistance to exogenous cytokinin treatment and the expression level of the OsARF16 gene was considerably up-regulated by cytokinin. Cytokinin (6-BA) application suppressed Pi uptake and the Pi starvation response in wild-type Nipponbare (NIP) and all these responses were compromised in the osarf16 mutant. Our data showed that cytokinin inhibits the transport of Pi from the roots to the shoots and that OsARF16 is involved in this process. The Pi content in the osarf16 mutant was much higher than in NIP under 6-BA treatment. The expressions of PHOSPHATE TRANSPORTER1 (PHT1) genes, phosphate (Pi) starvation-induced (PSI) genes and purple PAPase genes were higher in the osarf16 mutant than in NIP under cytokinin treatment.

Conclusion

Our results revealed a new biological function for OsARF16 in the cytokinin-mediated inhibition of Pi uptake and Pi signaling in rice.     

Multifarious beneficial traits and plant growth promoting potential of Serratia marcescens KiSII and Enterobacter sp. RNF 267 isolated from the rhizosphere of coconut palms (Cocos nucifera L.)

Two plant growth promoting bacteria designated as KiSII and RNF 267 isolated from the rhizosphere of coconut palms were identified as Serratia marcescens and Enterobacter sp. based on their phenotypic features, BIOLOG studies and 16S rRNA gene sequence analysis. Both bacteria exhibited phosphate solubilization, ammonification, and production of indole acetic acid, ??-1, 3 glucanase activities and 1-aminocyclopropane-1-carboxylate-deaminase activity. They could also tolerate a range of pH conditions, low temperature and salinity (NaCl). In addition, S. marcescens KiSII exhibited N- fixation potential, chitinase activity, siderophore production and antibiotics production. Seed bacterization with these bacteria increased the growth parameters of test plants such as paddy and cowpea over uninoculated control in green house assay. In coconut seedlings, significant increase in growth and nutrient uptake accompanied with higher populations of plant beneficial microorganisms in their rhizospheres were recorded on inoculation with both the PGPRs. The present study clearly revealed that PGPRs can aid in production of healthy and vigorous seedlings of coconut palm which are hardy perennial crops. They offer a scope to be developed into novel PGPR based bioinoculants for production of elite seedlings that can benefit the coconut farming community and the coconut based ecology.