Evidence for gluconic acid production by Enterobacter intermedium as an efficient strategy to avoid protozoan grazing

The effect of pure gluconic acid and of gluconic-acid-producing bacteria on the activity of three protozoan species, Colpoda steinii (a ciliate), Vahlkampfia sp. (an amoeba) and Neobodo designis (a flagellate), was determined in vitro and in soil microcosms. Pure gluconic acid was shown to mediate disappearance of active cells, due to encystment and/or death of protozoa, at 0.15 mM in saline medium. Similarly, the presence of gluconic acid inhibited excystment of the three protozoa tested. Enterobacter intermedium 60-2G (Wt), a gluconic acid-producing rhizobacterium, elicited the same effects on protozoa when co-cultured in the presence of 5 g L⁻¹ glucose. However, the effect was not observed when glucose was omitted from the medium. Similarly, a pqqA isogenic mutant strain, unable to produce gluconic acid from glucose, exhibited a reduced effect on protozoan activity. Rhizosphere-microcosm studies performed with wheat (Triticum aestivum L.) confirmed the reduced ability of the pqqA mutant to limit protozoa reproduction compared to the Wt strain. Since the sodium salt of gluconic acid did not cause any significant stress to protozoa and considering that addition of 50 mM Tris-Cl (pH 7.2) abolished the deleterious effect of gluconic acid, acidification of the medium appeared as the key factor that induced encystment/death of protozoa. We propose that production and excretion of gluconic acid should be considered an efficient mechanism evolved by bacteria to escape, tolerate or defend themselves against protozoan grazing in rhizosphere environments.     

Interactions between mycorrhizal fungi and mycorrhizosphere bacteria during mineral weathering: Budget analysis and bacterial quantification

The impact of ectomycorrhizal fungi or rhizosphere bacteria on tree seedling growth and nutrient uptake is well known. However, few studies have combined those microorganisms in one experiment to clarify their relative contribution and interactions in nutrient acquisition. Here, we monitored the respective contributions of pine roots, two ubiquitous forest ectomycorrhizal fungi Scleroderma citrinum and Laccaria bicolor, and two S. citrinum-mycorrhizosphere bacterial strains of Burkholderia glathei and Collimonas sp., on mineral weathering, nutrient uptake, and plant growth. Pinus sylvestris plants were grown on quartz–biotite substrate and inoculated or not with combinations of mycorrhizal fungi and/or bacterial strains. Magnesium and potassium fluxes were measured and nutrient budgets were calculated. Both ectomycorrhizal fungi significantly increased Mg plant uptake. No significant effects of the two bacterial strains were detected on the K and Mg budgets, but co-inoculating the mycorrhizal fungus S. citrinum and the efficient mineral-weathering B. glathei bacterial strain significantly improved the Mg budget. Similarly, co-inoculating S. citrinum with the Collimonas sp. bacterial strain significantly improved the pine biomass compared to non-inoculated pine plants. In order to better understand this process, we monitored the survival of the inoculated bacterial strains in the quartz–biotite substrate, the pine rhizosphere, and the mycorrhizal niche. The results showed that the two bacterial strains harboured different colonization behaviours both of which depended on the presence of the ectomycorrhizal partner. The populations of the Burkholderia strain were maintained in all these environments with a significantly higher density in the mycorrhizal niche, especially of S. citrinum. In contrast the population of the Collimonas strain reached the detection level except in the treatment inoculated with S. citrinum. These results highlight the need for taking into account the ecology of the microorganisms, and more specifically the fungal–bacterial interactions, when studying mineral weathering and plant nutrition.     

Effect of Bacillus subtilis on granite weathering: A laboratory experiment

We performed a comparative experiment to investigate: (1) how the ubiquitous soil bacterium Bacillus subtilis weathers granite; and (2) which granite-forming minerals weather more rapidly via biological processes. Batch system experiments (granite specimen in a 500 ml solution including NaCl, glucose, yeast extract and bacteria B. subtilis at 27 °C) were carried out for 30 days. Granite surfaces were observed by SEM before and after the experiment. B. subtilis had a strong influence on granite weathering by forming pits. There were 2.4 times as many pits and micropores were 2.3 times wider in granite exposed to B. subtilis when compared with bacteria-free samples. B. subtilis appear to preferentially select an optimum place to adhere to the mineral and dissolve essential elements from the mineral to live. Plagioclase was more vulnerable to bacterial weathering than biotite among the granite composing minerals.     

Long term impact of mineral amendment on the distribution of the mineral weathering associated bacterial communities from the beech Scleroderma citrinum ectomycorrhizosphere

Liming is a known forest management procedure used to amend nutrient-poor soils such as soils of acidic forests to rectify cation deficiencies and to restore soil pH. However, although this procedure is well known for its beneficial effect on the forest trees, its relative impact on the functional and taxonomic diversity of the soil bacterial communities has been poorly investigated. In this study, we characterized the ability of the soil bacteria to weather soil minerals and to hydrolyze chitin. A collection of 80 bacterial strains was isolated from the Scleroderma citrinum ectomycorrhizosphere and the adjacent bulk soil in two stands of mature beeches (Fagus sylvatica) developed on very acidic soil and presenting two levels of calcium (Ca) availability: a control plot as well as a plot amended with Ca in 1973. All the bacterial isolates were identified by partial 16S rRNA gene sequence analysis as members of the genera Burkholderia, Bacillus, Dyella, Kitasatospora, Micrococcus, Paenibacillus, Pseudomonas, and Rhodanobacter. Using a microplate assay for quantifying the production of protons and the quantity of iron released from biotite, we demonstrated that the bacterial strains from the amended plot harbored a significant higher mineral weathering potential that the ones isolated from the control plot. Notably, the weathering efficacy of the ectomycorrhizosphere bacterial isolates was significantly greater than that of the bulk soil isolates in the control treatment but not in the amended plot. These data reveal that forest management, here mineral amendment, can strongly affect the structure of bacterial communities even over the long term.     

Seasons differently impact the structure of mineral weathering bacterial communities in beech and spruce stands

Bacterial communities play an essential role in the sustainability of forest ecosystems by releasing from soil minerals the nutritive cations required not only for their own nutrition but also for that of trees. If it is admitted that the nutritional needs of trees vary during seasons, the seasonal dynamics of the mineral weathering bacterial communities colonizing the tree rhizosphere remain unknown. In this study, we characterized the mineral weathering efficacy of bacterial strains, from the rhizosphere and the adjacent bulk soil at four different seasons under two different tree species, the evergreen spruce and the deciduous beech, using a microplate assay that measures the quantity of iron released from biotite. We showed that the functional and taxonomic structures of the mineral weathering bacterial communities varied significantly with the tree species as well as with the season. Notably, the Burkholderia strains from the beech stand appeared more efficient to weather biotite that the one from the spruce stand. The mineral weathering efficacy of the bulk soil isolates did not vary during seasons under the beech stand whereas it was significantly higher for the spring and summer isolates from the spruce stand. The weathering efficacy of the rhizosphere isolates was significantly higher for the autumn isolates compared to the isolates sampled in the other seasons under the beech stand and in summer compared to the other seasons under spruce. These results suggest that seasonal differences do occur in forest soil bacterial communities and that evergreen and deciduous trees do not follow the same dynamic.     

Impact of glucose on microbial community of a soil containing pyrite cinders: Role of bacteria in arsenic mobilization under submerged condition

Arsenic transformation and mobilization in a pyrite cinder-polluted soil were studied under submerged conditions both in the presence and absence of glucose. The presence of the carbon source enhanced bacterial activity and a reduction in the redox potential, resulting in release of higher amounts of arsenic iron and manganese in the aqueous phase. Since arsenic solubilization was not concomitant to that of iron, desorption rather than dissolution was found to be the main mechanism controlling its release from pyrite cinders. Arsenate was reduced to arsenite whose presence increased during the time course of the experiment. Denaturing gradient gel electrophoresis analysis of 16S rRNA genes of the total bacterial community revealed that the addition of glucose stimulated uncultivable populations of Flavobacterium and Paenibacillus. The isolation technique enabled the characterisation of nineteen arsenic-resistant bacteria, mostly related to the facultative aerobic genera Bacillus, Paenibacillus, Staphylococcus and to Rhodococcus and Micromonospora. Most of them contained putative arsenate reductase and/or arsenite efflux pump as indicated by the presence of ArsC and/or ArsB genes. Four strains showed the ability to reduce arsenate by an intracellular detoxification mechanism, and one strain was able to oxidize arsenite, indicating that bacteria with the ability to oxidize or reduce arsenic are ubiquitous in soils. The findings confirm that bacterial activity was responsible for the arsenic reduction causing the solubilization of the metalloid from pyrite cinders to aqueous phases. Reducing conditions, such as those present in flooded soils in the presence of readily utilizable carbon sources could induce arsenic mobilization.     

Isolation and characterization of phosphate-solubilizing bacteria from betel nut (Areca catechu) and their effects on plant growth and phosphorus mobilization in tropical soils

Phosphate-solubilizing bacteria (PSB) were isolated and characterized from the rhizosphere and bulk soils of Areca catechu plants. A long history of phosphate fertilizer use has elicited a direct effect on the incidence of soil PSB. Their abundance and ability to solubilize insoluble phosphate were significantly greater (P?<?0.0001) in soils with low available phosphorus (P) content than in other soil types. Three efficient PSB strains, namely, ASL12, ASG34, and ADH302, were identified as Acinetobacter pittii, Escherichia coli, and Enterobacter cloacae by characterizing 16S rRNA sequences and biochemical characteristics; they produced gluconic acid at concentrations of 7862.4, 4306.5, and 2663.8 mg L^?1, respectively. The highest amount of solubilized P was determined in Pikovskaya (PVK) medium for the bacterial strain ASL12. The secretion of gluconic acid was related to the available P of rhizosphere soils and P solubilization. Under shaded conditions, the application of these three strains significantly improved plant height, shoot and root dry weight, and nutrient uptake of A. catechu seedlings. A further increase in P solubilization was observed by co-inoculating the three strains and also applying tricalcium phosphate (TCP) or aluminum phosphate (AP). A significant (P?<?0.05) correlation was also observed between P-solubilization activity and A. catechu plant growth in pot experiments. Thus, the three strains can be potentially applied as inoculants in tropical and aluminum-rich soils.     

Changes in weathering effectiveness and community of culturable mineral-weathering bacteria along a soil profile

Bacteria play important roles in mineral weathering, element mobilization, and soil formation. However, little is known about the mineral-weathering bacteria in subsurface soil environments. In this study, a total of 360 bacterial isolates were isolated from the different horizons of a soil profile and characterized for their mineral-weathering abilities and diversity along the soil profile. Among the 360 isolates, 226 isolates were found to have the ability to weather biotite. The average of released Fe, Si, and Al were significantly higher by the isolates from deeper horizons than from upper horizons. Although the proportion of the highly effective Fe solubilizers was not significantly different among the different horizons, the proportion of the highly effective Si and Al solubilizers was significantly higher in the deeper horizons than in the upper horizons. Furthermore, the element-releasing patterns of the mineral-weathering bacteria were different among the different horizons. Most of mineral-weathering bacteria from the soil profile could significantly lower the culture medium pH in the mineral-weathering process. The diversity of the mineral-weathering bacteria was higher in the upper horizons than in the deeper horizons. The weathering bacteria belonged to 12 bacterial genera, among which Burkholderia, Bacillus, and Lysinibacillus were the dominant and high-efficient weathering bacteria. The results showed the depth-related changes in the weathering capacity and community structures of the culturable mineral-weathering bacteria and suggested the possible roles of the bacteria in the mineral-weathering and element mobilization along the soil profile.     

一株高效溶解钾长石芽孢杆菌的分离鉴定与生物学特性研究

从风化的钾质粗面岩表面分离筛选到1株高效风化钾长石的芽孢杆菌E31菌株,通过菌株的生理生化特征并结合菌株16S r DNA序列分析,E31菌株被鉴定为苏云金芽孢杆菌(Bacillus thuringiensis)。同时对E31菌株溶解钾长石的效应与机制以及生物学特性进行了研究。结果表明,E31菌株能风化钾长石并释放出其中的元素,28℃振荡培养不同时间,接菌处理发酵液中可溶性K、Fe、Ca、Al含量分别比对照提高了19.6%~25.6%、1~12.5倍、10.4%~47.2%和1.2~4.5倍。在钾长石存在条件下接菌处理发酵液pH为3.62~3.80,发酵液中葡萄糖酸含量达61~1 794 mg/L,发酵液细胞数量达(8.7~16.1)×10~6 cfu/ml,表明菌株可以通过代谢产生的有机酸来加速对钾长石的分解作用。另外,E31菌株能够合成生长素和铁载体,E31菌株对温度、pH和盐浓度具有较强的耐受性。     

Genetic diversity and potential for promotion of plant growth detected in nodule endophytic bacteria of soybean grown in Heilongjiang province of China

A total of 98 non-symbiotic endophytic bacterial strains isolated from soybean root nodules were classified into eight rDNA types in ARDRA analysis and 21 BOX types in BOX-PCR. The phylogenetic analysis of 16S rDNA identified these strains as Pantoea, Serratia, Acinetobacter, Bacillus, Agrobacterium, and Burkholderia. Limited genetic diversity was revealed among these bacteria since most of the strains (85.7%) were found in three very similar rDNA types corresponding to Pantoea agglomerans, and many strains shared the same BOX-PCR patterns. The inoculation of nodule endophytes had no significant effects on the growth and nodulation of soybean, but most of the strains produced indoleacetic acid (IAA), could solubilize mineral phosphate, and could fix nitrogen, implying that they are a valuable pool for discovering plant growth promoting bacteria. Our results demonstrated that the nodule endophytes were common in soybean and their diversity was affected by the plant's character and the soil conditions. The 99% similarities found in the nifH genes of Bradyrhizobium japonicum and of the endophytic Bacillus strains strongly indicated that horizontal transfer of symbiotic genes happened between the symbiotic bacteria and the endophytes.     

Phosphate-solubilizing Pseudomonas putida can influence the rhizobia-legume symbiosis

Allfalfa and soybean are the most important leguminous plants in the agricultural system of the semiarid pampas of Argentina. The possible action of phosphate solubilizing bacteria on the leguminous-rhizobia symbiosis was studied since in this region the available phosphorus distribution is not uniform. The strains used were Sinorhizobium meliloti 3DOh13, a good solubilizer of iron and phosphorus for alfalfa, Bradyrhizobium japonicum TIIIB for soybean and two phosphorus-solubilizing strains of Pseudomonas putida (SP21 and SP22) for growth promotion treatments. Modification of shoot and root system dry weights occured in soybean but not in alfalfa in presence of Pseudomonas strains.     

Cadmium-tolerant plant growth-promoting bacteria associated with the roots of Indian mustard (Brassica juncea L. Czern.)

Eleven cadmium-tolerant bacterial strains were isolated from the root zone of Indian mustard (Brassica juncea L. Czern.) seedlings grown in Cd-supplemented soils as well as sewage sludge and mining waste highly contaminated with Cd. The bacteria also showed increased tolerance to other metals including Zn, Cu, Ni and Co. The isolated strains included Variovorax paradoxus, Rhodococcus sp. and Flavobacterium sp., and were capable of stimulating root elongation of B. juncea seedlings either in the presence or absence of toxic Cd concentrations. Some of the strains produced indoles or siderophores, but none possessed C₂H₂-reduction activity. All the strains, except Flavobacterium sp. strain 5P-3, contained the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which hydrolyses ACC (the immediate precursor of plant hormone ethylene) to NH₃ and α-ketobutyrate. V. paradoxus utilized ACC as a sole source of N or energy. A positive correlation between the in vitro ACC deaminase activity of the bacteria and their stimulating effect on root elongation suggested that utilization of ACC is an important bacterial trait determining root growth promotion. The isolated bacteria offer promise as inoculants to improve growth of the metal accumulating plant B. juncea in the presence of toxic Cd concentrations and for the development of plant-inoculant systems useful for phytoremediation of polluted soils.     

Plant growth promoting properties of a strain of Enterobacter ludwigii isolated from Lolium perenne rhizosphere

The capability of native bacterial strains isolated from Lolium perenne rhizosphere to behave as plant growth promoting bacteria and /or biocontrol agents was investigated. One strain (BNM 0357) over 13 isolates from the root tips of L. perenne resulted proved to be nitrogenase positive (ARA test) and an IAA producer. Conventional tests and the API 20E diagnostic kit indicated that BNM 0357 behaves to the Enterobacteriaceae family and to the Enterobacter genus. Molecular identification by 16S rRNA sequence analysis indicated that BNM 0357 had the highest similarity to Enterobacter ludwigii (EN-119). Isolate BNM 0357 had the capability to solubilize calcium triphosphate and to antagonize Fusarium solani mycelial growth and spore germination. Strain BNM 0357 also showed the ability to improve the development of the root system of L. perenne. This study disclosed features of E. ludwigii BNM 0357 that deserve further studies aimed at confirming its putative importance as a PGPR.     

Inoculation of root microorganisms for sustainable wheat-rice and wheat-black gram rotations in India

The scarcity of non-renewable resources such as soils and fertilizers and the consequences of climate change can dramatically influence the food security of future generations. Mutualistic root microorganisms such as plant growth-promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungi (AMF) can improve plant fitness. We tested the growth response of wheat (Triticum aestivum [L.]), rice (Oriza sativa [L.]) and black gram (Vigna mungo [L.], Hepper) to an inoculation of AMF and PGPR alone or in combination over two years at seven locations in a region extending from the Himalayan foothills to the Indo-Gangetic plain. The AMF applied consisted of a consortium of different strains, the PGPR of two fluorescent Pseudomonas strains (Pseudomonas jessenii, R62; Pseudomonas synxantha, R81), derived from wheat rhizosphere from one test region. We found that dual inoculation of wheat with PGPR and AMF increased grain yield by 41% as compared to un-inoculated controls. Yield responses to the inoculants were highest at locations with previously low yields. AMF or PGPR alone augmented wheat grain yield by 29% and 31%, respectively. The bio-inoculants were effective both at Zero and at farmers’ practice fertilization level (70 kg N ha⁻¹, 11 kg P ha⁻¹ in mineral form to wheat crop). Also raw protein (nitrogen × 5.7) and mineral nutrient concentration of wheat grains (phosphorus, potassium, copper, iron, zinc, manganese) were higher after inoculation (+6% to +53%). Phosphorus use efficiency of wheat grains [kg P grain kg⁻¹ P fertilizer] was increased by 95%. AMF and PGPR application also improved soil quality as indicated by increased soil enzyme activities of alkaline and acid phosphatase, urease and dehydrogenase. Effects on rice and black gram yields were far less pronounced over two cropping seasons, suggesting that AMF and PGPR isolated from the target crop were more efficient. We conclude that mutualistic root microorganisms have a high potential for contributing to food security and for improving nutrition status in southern countries, while safeguarding natural resources such as P stocks.     

Solubilization of zinc phosphate by a strain of Pseudomonas fluorescens isolated from a forest soil

 A strain of Pseudomonas fluorescens, able to solubilize zinc phosphate, was isolated from a forest soil. Colonies of the microorganism produced clear haloes on solid medium incorporating zinc phosphate, but only when glucose was provided as the carbon source. Solubilization of zinc phosphate occurred by both an increase in the H⁺ concentration of the medium, probably a consequence of ammonia assimilation, and the production of gluconic acid. High concentrations of gluconic acid were produced when P. fluorescens 3a was cultured in the presence of zinc phosphate. Although under some conditions gluconic acid is purportedly able to solubilize metals by the formation of chelates, no evidence of zinc chelation was obtained in our experiments. Furthermore, the increased Zn²⁺ concentration caused by the solubilization process resulted in the manifestation of toxic effects on the culture. A sample of the culture, sonicated to disrupt cells, still possessed the ability to produce gluconic acid from glucose, in the presence and absence of zinc phosphate. The lack of gluconic acid overproduction in cultures of P. fluorescens 3a which were not amended with zinc phosphate suggests that at least some of the glucose oxidation required for the zinc solubilization occurred as a result of the toxic stress caused by the high Zn²⁺ concentration. Received: 16 December 1997     

Dispersal patterns and behaviour of the nematode Phasmarhabditis hermaphrodita in mineral soils and organic media

The commercially available parasitic nematode Phasmarhabditis hermaphrodita is an effective biocontrol agent for slugs and particularly Deroceras reticulatum, a widespread pest species. Use of the nematode is currently limited by cost and it may be that by developing a fuller understanding of the ecology and behaviour of this nematode, more cost effective application strategies can be developed. We investigated the ability of two strains of P. hermaphrodita (one newly isolated and one that had been maintained in vitro for >15 years) to move through mineral soils and organic media. Active dispersal of both strains was found to be greatest in organic media (bark chips and leaf litter, and to a lesser extent peat) and the nematode was capable of growth and reproduction in leaf litter. Conversely, active dispersal was poor in mineral soils. Nematodes moved further in a clay loam compared with a sandy loam, and moved more at a bulk density of 1.0 vs. 1.2 Mg m⁻³. However, P. hermaphrodita was capable of moving greater distances in mineral soils by using the earthworm Lumbricus terrestris as a phoretic host. Our data suggest that P. hermaphrodita is a facultative parasite that is adapted to living in leaf litter and organic material where slugs frequently rest. The implications of these findings for using the nematode as a biological control agent for slugs are discussed.     

Characterization of brushite as a re-crystallization product formed during bacterial solubilization of hydroxyapatite in batch cultures

Two strains of bacteria (Burkholderia sp., strain FeGL01, and Burkholderia caribiensis, strain FeGL03) were isolated from a Brazilian high phosphorus iron ore. The capacity of both strains to solubilize hydroxyapatite, Ca₅(PO₄)₃(OH), was assessed in plate and batch cultures. In batch cultures, the concentration of solution-P showed two kinetics: an initial one, characterized by a continuously increasing kinetics and a second one, characterized by oscillatory kinetics. To understand the nature of these oscillations, phosphatic residues in the spent broth were collected before, during and after the oscillations, and characterized using scanning electron microscopy (SEM), energy-dispersive X-ray chemical microanalyses (EDX) and X-ray diffraction (XRD). From these studies, it was found that drops in P concentration were related to the formation of an intermediate phosphate in the residues, identified as brushite, CaHPO₄·2H₂O. Later increase of available P in the solution was found to be a consequence of re-dissolution of brushite crystals previously formed. Re-crystallization of brushite was also detected in plate cultures after 12-14 days of incubation     

The Role of Iron Bacteria on Weathering and Attenuation Processes at Acidic Environments

The present research reproduces the chemical and microbiological reactions that occur naturally when a metal sulfide is discharged onto a natural soil, with special emphasis on iron cycle. The role of indigenous microbiota from an extremely acidic site on both weathering and attenuation processes related to the iron mobilization has been studied and the iron cycle has been reproduced at laboratory scale. In the first stage, the weathering phase, a residual sulfide mineral was bioleached using a mixed culture of iron-oxidizing bacteria isolated from the own substrate. The acid liquor obtained (pH 2), with a high metal concentration (160 mM in total iron), was filtered and neutralized. Solids obtained from the two sources (from the weathering process and after the neutralization stage) were characterized by X-ray and scanning electron microscope/energy dispersive X-ray spectroscopy, resulting ferric iron precipitates such as jarosites, goethites, and ferrihydrites with different crystalline properties. The contribution of ferric iron-reducing bacteria on the attenuation of high-content iron effluents was also studied. Mixed cultures of ferric iron-reducing bacteria, isolated from those acidic substrates, were active in reducing soluble ferric iron (60 mM in concentration), and a 66% of bioreduction was reached after 15 days. Dissimilatory ferric iron reduction has been achieved with adapted cultures at pH values from 7 to 4.     

Growth promotion of plants by plant growth-promoting rhizobacteria under greenhouse and two different field soil conditions

This study was conducted with sugar beet in greenhouse and field at two soil type with different organic matter (containing 2.4 and 15.9% OM, referred as the low- and high-OM soil) conditions in order to investigate seed inoculation of sugar beet, with five N₂-fixing and two phosphate solubilizing bacteria in comparison to control and mineral fertilizers (N and P) application. Three bacterial strains dissolved P; all bacterial strains fixed N₂ and significantly increased growth of sugar beet. In the greenhouse, inoculations with PGPR increased sugar beet root weight by 2.8-46.7% depending on the species. Leaf, root and sugar yield were increased by the bacterial inoculation by 15.5-20.8, 12.3-16.1, and 9.8-14.7%, respectively, in the experiment of low- and high-OM soil. Plant growth responses were variable and dependent on the inoculants strain, soil organic matter content, growing stage, harvest date and growth parameter evaluated. The effect of PGPR was greater at early growth stages than at the later. Effective Bacillus species, such as OSU-142, RC07 and M-13, Paenibacillus polymyxa RC05, Pseudomonas putida RC06 and Rhodobacter capsulatus RC04 may be used in organic and sustainable agriculture.