Growth stimulation in bean (Phaseolus vulgaris L.) by Trichoderma

Trichoderma species are commonly used as biological control agents against phytopathogenic fungi and some strains are able to produce metabolites that enhance plant growth. In the current study we evaluated the production of potential growth-promoting metabolites, rhizosphere competence and endophytism for 101 isolates of Trichoderma from Colombia, and assessed the relationship of these factors to the enhancement of early stages of growth on bean seedlings. Twenty percent of these Trichoderma strains were able to produce soluble forms of phosphate from phosphoric rock. Only 8% of the assessed strains showed consistent ability to produce siderophores to convert ferric iron to soluble forms by chelation. Sixty percent of isolates produced indole-3-acetic acid (IAA) or auxin analogues. The production of any of these metabolites was a characteristic of specific strains, as the ability to produce these metabolites varied greatly within species. Moreover, the production of these substances did not correlate with enhanced growth on bean seedlings, measured as the combined increase in length of roots and aerial parts in the V3 stage of growth. Seven Trichoderma isolates significantly improved the growth of bean seedlings. However, metabolite production varied widely in these seven strains, and some isolates did not produce any of the assessed growth-promoting metabolites. Results indicated that growth was enhanced in the presence of rhizosphere competent and endophytic strains of Trichoderma, and these characteristics were strain-specific and not characteristic for species.     

Plant growth-promoting activities of fluorescent pseudomonads,isolated from the Iranian soils

Fluorescent pseudomonads are among the most influencing plant growth-promoting rhizobacteria in plants rhizosphere. In this research work the plant growth-promoting activities of 40 different strains of Pseudomonas fluorescens and Pseudomonas putida, previously isolated from the rhizosphere of wheat (Triticum aestivum L.) and canola (Brassica napus L.) and maintained in the microbial collection of Soil and Water Research Institute, Tehran, Iran, were evaluated. The ability of bacteria to produce auxin and siderophores and utilizing P sources with little solubility was determined. Four strains of Wp1 (P. putida), Cfp10 (Pseudomonas sp.), Wp150 (P. putida), and Wp159 (P. putida) were able to grow in the DF medium with ACC. Thirty percent of bacterial isolates from canola rhizosphere and 33% of bacterial isolates from wheat rhizosphere were able to produce HCN. The results indicate that most of the bacteria, tested in the experiment, have plant growth-promoting activities. This is the first time that such PGPR species are isolated from the Iranian soils. With respect to their great biological capacities they can be used for wheat and canola inoculation in different parts of the world, which is of very important agricultural implications.     

Isolation,Selection and Characterization of Root-Associated Rock Phosphate Solubilizing Bacteria in Moroccan Wheat (Triticum aestivum L.)

Abstract

Phosphorus (P) is the most important macronutrient next to nitrogen for the growth and development of plants. But often unavailable for plants because of its high reactivity with many soil constituents. Thus, the use of phosphate solubilizing bacteria (PSBs) as biofertilizers seems to be an effective way to resolve the soluble phosphorus availability in soil. The present study was conducted to isolate and characterize rock PSB associated with the rhizosphere of wheat (Triticum aestivum L.) from fourteen different wheat-growing sites of Meknes region in Morocco. A total of one hundred ninety-eight (198) rock PSBs were isolated employing NBRIP medium amended with rock phosphate (RP), out of which five strains (A17, A81, B26, B106, and B107) were selected for their strong ability to dissolve RP and were tested in vitro for plant growth-promoting (PGP) traits including production of indole acetic acid (IAA), siderophores, hydrogen cyanide (HCN), and antifungal activity, as well as their response to the effect of extrinsic and intrinsic stress. The 16S rRNA gene sequencing and phylogenetic analysis identified these isolates belong to four genera, Pantoea, Pseudomonas, Serratia, and Enterobacter. The phosphate solubilization index (SI) of selected isolates ranged between 2.3 and 2.7, and the amount of solubilized phosphorus in the liquid medium varied from 59.1 to 90.2 µg mL^?1. HPLC analysis revealed that all the selected isolates produced multiple organic acids (oxalic, citric, gluconic succinic, and fumaric acids) from glucose under aerobic conditions. Except for the A81 strain, all selected isolates were able to produce IAA ranging between 2.9 and 21.2 µg mL^?1. The isolates A17, B26, and B107 showed the ability to produce siderophores ranging from 79.3 to 20.8% siderophore units. Only two strains (A17 and B26) were able to produce HCN. All selected isolates showed good resistance against different environmental stresses like 10–50?°C temperature, 0.5–2?g L^?1 salt concentration and 4.5–9?pH range, and against different antibiotics. The antagonistic effect showed that among the five selected strains, only two strains (B26 and A17) were able to suppress the growth of tested fungi. This study clearly indicates that our selected rock PSBs can be used as biofertilizers for grain crops after studying their interaction with the host crop and field evaluation.     

Isolation and characterization of plant growth-promoting rhizobacteria from wheat roots by wheat germ agglutinin labeled with fluorescein isothiocyanate

Thirty-two isolates were obtained from wheat rhizosphere by wheat germ agglutinin (WGA) labeled with fluorescein isothiocyanate (FITC). Most isolates were able to produce indole acetic acid (65.6%) and siderophores (59.3%), as well as exhibited phosphate solubilization (96.8%). Fourteen isolates displayed three plant growth-promoting traits. Among these strains, two phosphate-dissolving ones, WS29 and WS31, were evaluated for their beneficial effects on the early growth of wheat (Triticum aestivum Wan33). Strain WS29 and WS31 significantly promoted the development of lateral roots by 34.9% and 27.6%, as well as increased the root dry weight by 25.0% and 25.6%, respectively, compared to those of the control. Based on 16S rRNA gene sequence comparisons and phylogenetic positions, both isolates were determined to belong to the genus Bacillus. The proportion of isolates showing the properties of plant growth-promoting rhizobacteria (PGPR) was higher than in previous reports. The efficiency of the isolation of PGPR strains was also greatly increased by WGA labeled with FITC. The present study indicated that WGA could be used as an effective tool for isolating PGPR strains with high affinity to host plants from wheat roots. The proposed approach could facilitate research on biofertilizers or biocontrol agents.     

Plant growth-promoting potential of endophytic bacteria isolated from roots of coastal sand dune plants

Endophytic bacteria associated with the roots of coastal sand dune plants were isolated, taxonomically characterized, and tested for their plant growth-promoting activities. Ninety-one endophytic bacterial isolates were collected and assigned to 17 different genera of 6 major bacterial phyla based on partial 16S rDNA sequence analyses. Gammaproteobacteria represented the majority of the isolates (65.9%), and members of Pseudomonas constituted 49.5% of the total isolates. When testing for antagonism towards plant pathogenic fungi, 25 strains were antagonistic towards Rhizoctonia solani, 57 strains were antagonistic towards Pythium ultimum, 53 strains were antagonistic towards Fusarium oxysporum, and 41 strains were antagonistic towards Botrytis cinerea. Seven strains were shown to produce indole acetic acid (IAA), 33 to produce siderophores, 23 to produce protease, 37 to produce pectinase, and 38 to produce chitinase. The broadest spectra of activities were observed among the Pseudomonas strains, indicating outstanding plant growth-promoting potential. The isolates from C. kobomugi and M. sibirica also exhibited good plant growth-promoting potential. The correlations among individual plant growth-promoting activities were examined using phi coefficients, and the resulting data indicated that the production of protease, pectinase, chitinase, and siderophores was highly related.     

Hydroxamate-siderophore production and utilization by marine eubacteria

Siderophore (iron-binding chelator) production was examined in 30 strains of open ocean bacteria from the generaVibrio, Alteromonas, Alcaligenes, Pseudomonas, andPhotobacterium. The results showed that hydroxamate-type siderophore production was widely distributed in various marine species, except for isolates ofAlteromonas macleodii andV. nereis. In all cases, the ability to produce siderophores was under the control of iron levels in the medium and satisfied the iron requirements of the siderophore bioassay organism. On the basis of chemical assay and bacterial bioassays, none of the examined isolates produced phenolate-type siderophores. Several isolates produces siderophores that were neither hydroxamatenor phenolate-type siderophores. Some strains such asAlteromonas communis produce siderophores that could be used by many other isolates. In contrast, the siderophore produced byAlcaligenes venustus had little cross-strain utilization. These findings suggest that the ability to produce siderophores may be common to open ocean bacteria.     

Biological control of bacterial spot disease and plant growth-promoting effects of lactic acid bacteria on pepper

In our previous studies, we observed the biological control effect of lactic acid bacteria strains (LABs) KLF01, KLC02 and KPD03 against different plant pathogenic bacteria in vitro against Ralstonia solanacearum, and strains KLF01 and KLC02 against Pectobacterium carotovorum under greenhouse and field experiments, respectively. In this study, we observed the efficacy of these bacteria against bacterial spot pathogen (Xanthomonas campestris pv. vesicatoria) and their plant growth-promoting activities in pepper (Capsicum annuum L. var. annuum), under greenhouse and field conditions. LABs significantly (P < 0.05) reduced bacterial spot on pepper plants in comparison to untreated plants in both the greenhouse and the field experiments. The plant growth-promoting effect of LABs on pepper varied; some strains had a significant effect on growth promotion (P < 0.05) compared with untreated plants, while some showed no significant effect in the greenhouse and field experiments. Additionally, LABs were able to colonise roots, produce indole-3-acetic acid (IAA), siderophores and solubilise phosphate. These findings indicate that application of LABs could provide a promising alternative for the management of bacterial spot disease in pepper plants and could therefore be used as a healthy plant growth-promoting agent.     

Potential role of rhizobia to enhance chickpea-growth and yield in low fertility-soils of Tunisia

Plant growth-promoting rhizobacteria are bacteria that improve plant growth and reduce plant pathogen damages. In this study, 100 nodule bacteria were isolated from chickpea, screened for their plant growth-promoting (PGP) traits and then characterised by PCR-RFLP of 16 S rDNA. Results showed that most of the slow-growing isolates fixed nitrogen but those exhibiting fast-growth did not. Fourteen isolates solubilized inorganic phosphorus, 16 strains produced siderophores, and 17 strains produced indole acetic acid. Co-culture experiments identified three strains having an inhibitory effect against Fusarium oxysporum, the primary pathogenic fungus for chickpea in Tunisia. Rhizobia with PGP traits were assigned to Mesorhizobium ciceri, Mesorhizobium mediterraneum, Sinorhizobium meliloti and Agrobacterium tumefaciens. We noted that PGP activities were differentially distributed between M. ciceri and M. mediterraneum. The region of Mateur in northern Tunisia, with clay–silty soil, was the origin of 53% of PGP isolates. Interestingly, we found that S. meliloti and A. tumefaciens strains did not behave as parasitic nodule-bacteria but as PGP rhizobacteria useful for chickpea nutrition and health. In fact, S. meliloti strains could solubilize phosphorus, produce siderophore and auxin. The A. tumefaciens strains could perform the previous PGP traits and inhibit pathogen growth also. Finally, one candidate strain of M. ciceri (LL10)—selected for its highest symbiotic nitrogen fixation and phosphorus solubilization—was used for field experiment. The LL10 inoculation increased grain yield more than three-fold. These finding showed the potential role of rhizobia to be used as biofertilizers and biopesticides, representing low-cost and environment-friendly inputs for sustainable agriculture.

     

The effect of plant growth-promoting rhizobacteria on the growth of rice (Oryza sativa L.) cropped in southern Brazilian fields

Background and Aims

Several strains of rhizobacteria may be found in the rhizospheric soil, on the root surface or in association with rice plants. These bacteria are able to colonize plant root systems and promote plant growth and crop yield through a variety of mechanisms. The objectives of this study were to isolate, identify, and characterize putative plant growth-promoting rhizobacteria (PGPR) associated with rice cropped in different areas of southern Brazil.

Methods

Bacterial strains were selectively isolated based on their growth on three selective semi-solid nitrogen-free media. Bacteria were identified at the genus level by PCR-RFLP 16S rRNA gene analysis and partial sequencing methodologies. Bacterial isolates were evaluated for their ability to produce indolic compounds and siderophores and to solubilize phosphate. In vitro biological nitrogen fixation and the ability to produce 1-aminocyclopropane-1-carboxylate deaminase were evaluated for each bacterial isolate used in the inoculation experiments.

Results

In total, 336 bacterial strains were isolated representing 31 different bacterial genera. Strains belonging to the genera Agrobacterium, Burkholderia, Enterobacter, and Pseudomonas were the most prominent isolates. Siderophore and indolic compounds producers were widely found among isolates, but 101 isolates were able to solubilize phosphate. Under gnotobiotic conditions, eight isolates were able to stimulate the growth of rice plants. Five of these eight isolates were also field tested in rice plants subjected to different nitrogen fertilization rates.

Conclusions

The results showed that the condition of half-fertilization plus separate inoculation with the isolates AC32 (Herbaspirillum sp.), AG15 (Burkholderia sp.), CA21 (Pseudacidovorax sp.), and UR51 (Azospirillum sp.) achieved rice growth similar to those achieved by full-fertilization without inoculation, thus highlighting the potential of these strains for formulating new bioinoculants for rice crops.     

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.     

烤烟根际烟碱降解细菌的多样性及其促生特性分析

【背景】挖掘兼具烟碱降解和植物根际促生细菌(Plant Growth-Promoting Rhizobacteria,PGPR)功能的细菌资源,有助于保护土壤质量,实现绿色种植。【目的】分析烤烟根际细菌多样性,筛选可降解高浓度烟碱的PGPR。【方法】采用纯培养法在选择性培养基上分离烟碱降解细菌。通过BOXA1R-PCR分析技术、16SrRNA基因测序及系统发育树构建,对菌株的遗传多样性和分类学地位进行分析。进一步评价了菌株的吲哚乙酸(Indole-3-Acetic Acid,IAA)活性、溶磷能力、病原菌拮抗能力等PGPR指标,以筛选出高效PGPR,最后通过盆栽试验验证其促生效果。【结果】分离得到58株烟碱降解细菌,根据BOXA1R-PCR指纹图谱选取11株菌进行16S rRNA基因序列测定,结果表明,58株菌分别属于芽孢杆菌属(Bacillus)、假单胞菌属(Pseudomonas)、拉乌尔菌属(Raoultella)和短波单胞菌属(Brevundimonas)4个属,以芽孢杆菌属(Bacillus)为优势菌属。58株细菌中48.28%的菌株可产IAA,27.59%具备溶磷能力,37.93%具备纤维素降解能力,G2-13、G2-3及HT2-8因促生与抗病特性突出而被筛选为目标功能菌。盆栽试验结果表明,G2-13菌株对幼苗生长的促进作用明显,可使株高与地上部鲜重分别增加33.05%与53.32%。【结论】烤烟根际存在较为丰富多样的烟碱降解细菌,它们在种植业上具有潜在的应用价值。     

Growth Enhancement of Chickpea in Saline Soils Using Plant Growth-Promoting Rhizobacteria

Bacterial isolates with the ability to tolerate salinity and plant growth-promoting features were isolated from the saline areas of Gujarat, India, that is, Bhavnagar and Khambat. A total of 176 strains of rhizobacteria were isolated out of which 62 bacterial strains were able to tolerate 1 M NaCl. These were then further studied for their potential plant growth-promoting rhizobacteria characteristics like phosphate solubilization, siderophore production, and IAA production. Twenty-eight isolates of the 62 strains showed good tricalcium phosphate solubilization in solid medium in the range of 9–22 mm and 15 isolates showed good phosphate solubilization in liquid medium in the range of 9–45 μg/ml. Siderophore production was checked in all 15 isolates, and 13 were screened out that produced the hydroxamate type of siderophore in the range of 11–50 mM. Among the 13 isolates, 10 were able to produce indole acetic acid in the range of 10–26 μg/ml after 72 h of incubation. Pot trials were carried out on chickpea under 300 mM NaCl stress using the best five isolates. Plants inoculated with MSC1 or MSC4 isolates showed an increase in the parameters that evaluate plant growth when compared to uninoculated controls. Strains MSC1 and MSC4 were identified as Pseudomonas putida and Pseudomonas pseudoalcaligens, respectively, according to sequence analysis of the 16S rRNA gene.     

烟草根际可培养微生物多样性及防病促生菌的筛选

[背景] 根际微生物在植物根部生态系统中扮演着重要角色,影响着植物的营养吸收和健康生长。[目的] 了解常年不发病烟田烤烟品种K326根际可培养微生物的多样性,筛选具有防病促生功能的菌株,为烟草病害绿色防控提供资源。[方法] 采用传统培养方法对烟草根际土壤中的细菌和真菌进行分离鉴定,评价菌株的促生特性及病原菌拮抗能力,并进一步验证典型菌株对盆栽烟苗的促生效果。[结果] 共获得261株微生物菌株,包括160株细菌和101株真菌。经分子鉴定,细菌中以变形菌门（Proteobacteria）和厚壁菌门（Firmicutes）为主要类群;真菌中以子囊菌门（Ascomycota）和毛霉菌门（Mucoromycota）为主要类群。在属水平上,细菌以假单胞菌属（Pseudomonas）和芽孢杆菌属（Bacillus）为主,真菌以曲霉属（Aspergillus）和青霉属（Penicillium）为主。从不同种水平上进一步选择44株细菌为代表菌株,发现它们均具有不同程度的吲哚-3-乙酸（Indole-3-Acetic Acid,IAA）产生能力,9株能够溶解有机磷,16株能够溶解无机磷,13株产生铁载体,14株产生生1-氨基环丙烷-1-羧酸（1-Aminocyclopropane-1-Carboxylate,ACC）脱氨酶。从160株细菌中筛选得到抑制青枯病菌和黑胫病菌的菌株数目分别为25、26株。经盆栽试验发现韩国假单胞菌（P. koreensis） HCH2-3、浅黄绿假单胞菌（P. lurida） FGD5-2和贝莱斯芽孢杆菌（B. velezensis） EM-1对烟苗呈现不同程度的促生作用,其中3株菌联合施加对烟苗的促生效果最明显。[结论] 烟草根际存在着丰富多样的具有防病促生潜力的微生物,并且合成菌群或功能互补的菌株联合施用是未来微生物菌剂研发的重要方向。     

缓解花生连作障碍的根际促生菌分离及功能鉴定

[目的] 长期连作障碍严重降低花生生产的产量及品质,根际促生菌可有效降解土壤中自毒化感物质、抑制植物病原菌生长及促进植物生长,从而有效缓解连作障碍问题。筛选优化具有缓解花生连作障碍能力的多功能根际益生微生物,验证其益生作用能力,为根际促生菌株在连作障碍中的应用提供理论依据及技术支持。[方法] 采集连作12年地块花生根际土壤,利用以酚酸为唯一碳源的筛选培养基获得具有酚酸自毒化感物质降解及利用能力的根际促生菌,通过16S rRNA基因测序进行系统发育分析,确定根际促生菌菌株的分类地位,并验证其对植物病原菌生长抑制能力及解磷、解钾、产植物激素吲哚乙酸能力。[结果] 从连作12年的花生发病土壤中获得7株可高效降解酚酸类自毒物质且降解底物多样的根际微生物菌株,经16S rRNA测序比对分别为克雷伯氏菌B02 （Klebsiella sp.B02）、克雷伯氏菌B07 （Klebsiella sp.B07）、克雷伯氏菌B15 （Klebsiella sp.B15）、芽孢杆菌B28 （Bacillus sp.B28）、不动杆菌P09 （Acinetobacter sp.P09）、布鲁氏杆菌VA05 （Brucella sp.VA05）、芽孢杆菌CA04 （Bacillus sp.CA04）。促生实验表明,7株高效降解菌株均可以合成吲哚乙酸,3株具有固氮能力,4株菌具有解有机磷及无机磷的能力,2株菌具有解钾的能力。拮抗实验表明,2株菌可以抑制多种植物病原菌的生长,均为芽孢杆菌属。选取Bacillus sp.B28初步验证对花生种子萌发及幼苗生长的影响,结果表明根际促生菌可显著缓解酚酸对花生种子发芽的抑制,并明显促进花生幼苗的生长。[结论] 获得多株具有降解酚酸类自毒化感物质、抑制植物病原菌生长及促进植物生长的多功能花生根际促生菌,更好地为根际促生菌在连作障碍治理中的有效应用提供菌株及技术支持。     

Detection and differentiation of microbial siderophores by isoelectric focusing and chrome azurol S overlay

Siderophores are microbial, low molecular weight iron-chelating compounds. Fluorescent Pseudomonads produce different, strain-specific fluorescent siderophores (pyoverdines) as well as non-fluorescent siderophores in response to low iron conditions. We present an isoelectric focusing method applicable to unpurified as well as to purified pyoverdine samples where the fluorescent siderophores are visualized under UV illumination. Siderophores from different Pseudomonas sp., amongst which are P. aeruginosa, P. fluorescens and P. putida, including egg yolk, rhizospheric and clinical isolates as well as some derived Tn5 mutants were separated by this technique. Different patterns could be observed for strains known to produce different siderophores. The application of the chrome azurol S assay as a gel overlay further allows immediate detection of non-fluorescent siderophores or possibly degradation products with residual siderophore activity. The method was also applied to other microbial siderophores such as deferrioxamine B.     

Phosphate solubilization potential and stress tolerance of rhizobacteria from rice soil in Northern Thailand

Plant growth-promoting rhizobacteria (PGPR) are known to influence plant growth by various direct or indirect mechanisms. A total of 216 phosphate-solubilizing bacterial isolates were isolated from different rice rhizospheric soil in Northern Thailand. These isolate were screened in vitro for their plant growth-promoting activities such as solubilization of inorganic phosphate, ammonia (NH₃), catalase and cell wall-degrading enzyme activity. It was found that 100% solubilized inorganic phosphate, 77.77% produced NH₃ and most of the isolates were positive for catalase. In addition, some strains also produced cell wall-degrading enzymes such as protease (7%), chitinase (1%), cellulase (3%) and β-glucanase (3%), as evidenced by phenotypic biochemical test and quantitative assay using spectrophotometry. The isolates could exhibit more than two or three plant growth-promoting (PGP) traits, which may promote plant growth directly or indirectly or synergistically. Part of this study focused on the effect of NaCl, temperature, and pH on a specific the bacterial isolate Acinetobacter CR 1.8. Strain CR 1.8 was able to grow on up to 25% NaCl, between 25 and 55°C, and at pH 5–9. Maximum solubilization of tricalcium phosphate and aluminium phosphate was obtained at neutral pH, and 37°C. Strain CR 1.8 had protease activity but no cellulase, β-glucanase and cellulase activities.     

Endophytic bacteria from Datura metel for plant growth promotion and bioprotection against Fusarium wilt in tomato

Nine non-pathogenic bacterial isolates, recovered from Datura metel organs and able to colonise the internal stem tissues of tomato cultivar Rio Grande, were screened for their ability to suppress tomato Fusarium wilt disease caused by Fusarium oxysporum f. sp. lycopersici (FOL), and to enhance plant growth. S33 and S85 isolates tested were found to be the most effective in decreasing Fusarium wilt severity by 94–95% compared to FOL-inoculated and untreated control. A significant enhancement of growth parameters was recorded on tomato plants inoculated or not with FOL. Both isolates were characterised and identified using 16S rDNA sequencing genes as Stenotrophomonas sp. str. S33 (KR818084) and Pseudomonas sp. str. S85 (KR818087). Screened in vitro for their antifungal activity towards FOL, these isolates led to 38.7% and 22.5% decrease in pathogen radial growth and to the formation of an inhibition zone of 12.75 and 8.37?mm respectively. Stenotrophomonas sp. str. S33 and Pseudomonas sp. str. S85 were found to be chitinase-, protease- and pectinase-producing strains but unable to produce hydrogen cyanide. Production of indole-3-acetic acid-like compounds, phosphate solubilising ability and pectinase activity were investigated for elucidating their plant growth-promoting traits and their endophytic colonisation ability.     

Actinomycetes isolated from medicinal plant rhizosphere soils: diversity and screening of antifungal compounds,indole-3-acetic acid and siderophore production

A total of 445 actinomycete isolates were obtained from 16 medicinal plant rhizosphere soils. Morphological and chemotaxonomic studies indicated that 89% of the isolates belonged to the genus Streptomyces, 11% were non-Streptomycetes: Actinomadura sp., Microbispora sp., Micromonospora sp., Nocardia sp, Nonomurea sp. and three isolates were unclassified. The highest number and diversity of actinomycetes were isolated from Curcuma mangga rhizosphere soil. Twenty-three Streptomyces isolates showed activity against at least one of the five phytopathogenic fungi: Alternaria brassicicola, Collectotrichum gloeosporioides, Fusarium oxysporum, Penicillium digitatum and Sclerotium rolfsii. Thirty-six actinomycete isolates showed abilities to produce indole-3-acetic acid (IAA) and 75 isolates produced siderophores on chrome azurol S (CAS) agar. Streptomyces CMU-PA101 and Streptomyces CMU-SK126 had high ability to produced antifungal compounds, IAA and siderophores.     

Rhizosphere bacteria affect growth and metal uptake of heavy metal accumulating willows

A variety of plants growing on metalliferous soils accumulate metals in their harvestable parts and have the potential to be used for phytoremediation of heavy metal polluted land. There is increasing evidence that rhizosphere bacteria contribute to the metal extraction process, but the mechanisms of this plant–microbe interaction are not yet understood. In this study ten rhizosphere isolates obtained from heavy metal accumulating willows affiliating with Pseudomonas, Janthinobacterium, Serratia, Flavobacterium, Streptomyces and Agromyces were analysed for their effect on plant growth, Zn and Cd uptake. In plate assays Zn, Cd and Pb resistances and the ability of the bacteria to produce indole-3-acetic acid (IAA), 1-amino-cyclopropane-1-carboxylic acid deaminase (ACC deaminase) and siderophores were determined. The isolates showed resistance to high Zn concentrations, indicating an adaptation to high concentrations of mobile Zn in the rhizosphere of Salix caprea. Four siderophore producers, two IAA producers and one strain producing both siderophores and IAA were identified. None of the analysed strains produced ACC deaminase. Metal mobilization by bacterial metabolites was assessed by extracting Zn and Cd from soil with supernatants of liquid cultures. Strain Agromyces AR33 almost doubled Zn and Cd extractability, probably by the relase of Zn and Cd specific ligands. The remaining strains, immobilized both metals. When Salix caprea plantlets were grown in γ-sterilized, Zn/Cd/Pb contaminated soil and inoculated with the Zn resistant isolates, Streptomyces AR17 enhanced Zn and Cd uptake. Agromyces AR33 tendentiously promoted plant growth and thereby increased the total amount of Zn and Cd extracted from soil. The IAA producing strains did not affect plant growth, and the siderophore producers did not enhance Zn and Cd accumulation. Apparently other mechanisms than the production of IAA, ACC deaminase and siderophores were involved in the observed plant–microbe interactions.     

三种蓝莓根际细菌的分离及其对蓝莓苗生长发育的影响

【目的】从3种蓝莓根际土壤中分离细菌,探究蓝莓根际土壤细菌多样性,并筛选具有产酸、促生长、抑菌性能的菌株,为蓝莓专用微生物肥料的研究提供优质菌株资源和理论基础。【方法】选用5种培养基分离3种蓝莓根际土壤细菌,并进行16S rRNA基因测序和系统发育分析。筛选产酸、产吲哚-3-乙酸（indole-3-acetic acid,IAA）和铁载体、固氮、溶磷和抑制灰葡萄孢生长的菌株,挑选最适菌株制备菌剂进行蓝莓苗盆栽实验验证促生能力,并检测菌剂对蓝莓元素吸收和根际土壤肥力的影响。【结果】从3种蓝莓根际土壤分离得到124株细菌,挑选70株代表性菌株进行16S rRNA基因测序,分布于3个门21个属,其中芽孢杆菌属（Bacillus）、假单胞菌属（Pseudomonas）、链霉菌属（Streptomyces）和红球菌属（Rhodococcus）为优势分离菌群。代表性菌株中,21.4%的菌株能产酸,21.4%的菌株产吲哚-3-乙酸,47.1%的菌株具有固氮潜力,65.7%的菌株具有解磷能力,14.3%的菌株能产铁载体。少量菌株同时具有产酸、产IAA、固氮、解磷和抑菌等能力。选取具有产酸和多种促生特征的菌株绿针假单胞菌CSM-70和双鱼假单胞菌CSM-129进行盆栽蓝莓苗处理,发现2株菌均能显著促进蓝莓苗的生长发育并调控根际土壤pH,其中菌株CSM-70处理还显著促进了蓝莓叶片氮、磷元素的吸收,提升了土壤速效钾、碱解氮的含量。【结论】蓝莓根际细菌多样性高且蕴藏着丰富的促生长菌株,绿针假单胞菌CSM-70和双鱼假单胞菌CSM-129能够促进蓝莓苗生长、调控根际土壤pH和肥力,并促进植株养分吸收,具有蓝莓专用微生物菌剂研制与应用的潜力。