Rhizosphere Isolates Research Articles

Genomic Investigation of a Rhizosphere Isolate, Streptomyces sp. JL1001, Associated with Polygonatum cyrtonema Hua.

In the present study, using genome mining, Streptomyces sp. JL1001, which possesses a leinamycin-type gene cluster, was identified from 14 strains of Streptomyces originating from the rhizosphere soil of Polygonatum cyrtonema Hua. The complete genome of Streptomyces sp. JL1001 was sequenced and analyzed. The genome of Streptomyces sp. JL1001 consists of a 7,943,495 bp chromosome with a 71.71% G+C content and 7315 protein-coding genes. We also identified 36 biosynthetic gene clusters (BGCs) for secondary metabolites in Streptomyces sp. JL1001. Twenty-seven BGCs had low (< 50%) or moderate (50-80%) similarity to other known secondary metabolite BGCs. In addition, a comparative analysis was conducted between the leinamycin-type gene cluster in Streptomyces sp. JL1001 and the biosynthetic gene clusters of leinamycin and largimycin. This study aims to provide a comprehensive analysis of the genomic features of rhizosphere Streptomyces sp. JL1001. It establishes the foundation for further investigation into experimental trials involving novel bioactive metabolites such as AT-less type I polyketides that have important potential applications in medicine and agriculture.

The Impact of Rhizospheric and Endophytic Bacteria on the Germination of Carajasia cangae: A Threatened Rubiaceae of the Amazon Cangas.

Carajasia cangae (Rubiaceae) is a narrow endemic species from the canga ecosystems of the Carajás National Forest that is facing extinction due to a limited range and habitat disturbance from hydroclimatological changes and mining activities. This study examines the influence of rhizospheric and endophytic bacteria on C. cangae seed germination to support conservation efforts. Soil samples, both rhizospheric and non-rhizospheric, as well as plant root tissues, were collected. Bacteria from these samples were subsequently isolated, cultured, and identified. DNA sequencing revealed the presence of 16 isolates (9 rhizospheric and 7 endophytic), representing 19 genera and 6 phyla: Proteobacteria, Actinobacteria, Acidobacteria, Firmicutes, Bacteroidetes, and Chloroflexi. The endophytic isolates of Bacillus and the rhizospheric isolates of Planococcus and Lysinibacillus reduced the median germination time and initiation time, while the rhizospheric isolates Serratia and Comamonas increased the germination time and decreased the germination percentage in comparison to the control sample. These findings emphasize the crucial role of endophytic bacteria in the germination of C. cangae and highlight isolates that could have beneficial effects in the following stages of plant growth. Understanding the impact of endophytic and rhizospheric bacterial isolates on seed germination can enhance conservation efforts by shortening the germination period of this species and thereby improving seedling production. Additionally, this knowledge will pave the way for future research on the role of bacteria in the establishment of C. cangae.

Assessment of Antifungal Potential of Rhizospheric Bacterial Isolates of Daucus carota against Rhizoctonia solani

Rhizoctonia solani is an important plant pathogen which is responsible for causing a number of plant diseases in a variety of cropping plants. The current studies were carried out to explore antifungal potential of bacteria isolated from rhizospheric region of Daucus carota against Rhizoctonia. Of the total 21 bacterial isolates isolated, only 3 isolates namely CVO-3, CVO-4 and CRY-O-2 were shown antifungal potential against Rhizoctonia. Besides having antifungal potential these isolates also have some plant growth promoting attributes that will be an extra benefit of using these isolates as a biofungicides against R. solani. Thus, these isolates could be used as biofungicides against Rhizoctonia to prevent a variety of plant diseases like sheath blight in Oryza sativa, stem canker and black scurf in Solanum tuberosum and seedling diseases in Brassica napus. The isolates CVO-3, CVO-4 and CRY-O-2 were also characterized biochemical level by using methods based on Determinative Bacteriology given in Bergey’s manual and at molecular level using 16S rRNA sequencing and sequences of 16S rDNA segment were submitted to NCBI in GenBank database with the accession numbers OR775574 (Lysinibacillus boronitolerans ss3cvo3), OR775575 (Lysinibacillus boronitolerans ss4cvo4) and OR708523 (Shouchella rhizosphaerae ss1cryo2). The present investigation is an approach towards the use of these bacterial isolates from carrot rhizosphere to control the activities in the rhizosphere of other cropping plants.

Production, characterization and application of lipases from endophytic and rhizospheric bacterial isolates

Production, characterization and application of lipases from endophytic and rhizospheric bacterial isolates

Antifungal potential of rhizospheric bacterial isolates of Daucus carota against brown spot fungus Cochliobolus miyabeanus

Cochliobolus miyabeanus is an important plant pathogen which causes a very common and widespread brown spot disease in rice, that may result in a severe reduction in the crop yield. The current studies were carried out to search out the antifungal potential of the bacterial isolates from the rhizospheric region of Daucus carota against brown spot fungus, C. miyabeanus. Isolation of rhizospheric bacterial isolates was done from carrot grown field of district Jaunpur in month of January, 2023. Experiment work has been done in Department of Biotechnology, Veer Bahadur Singh Purvanchal University, Jaunpur in 2023 from the month January to November. All bacterial isolates were tested for antifungal activity against brown spot fungi. Isolates were screened for their antifungal activities against brown spot fungus for further studying plant growth promoting, biochemical and morphological attributes. Isolates, CVO-7 and NBRI-O-2 showed efficient antifungal activity against test organism and also showed some plant growth promoting attributes that can further reduce the virulence of C. miyabeanus by enhancing availability of essential and trace elements for the plant. Both the isolates were characterized at a molecular level by using 16S rRNA gene sequencing and sequences of 16S rDNA segment were submitted to the NCBI GenBank database with the accession numbers OR775577 (Bacillus subtilis ss5cvo7) and OR775572 (Bacillus proteolyticus ss2nbrio2).

Enhancing potassium assimilation in soil for Zingiber officinale plant by rhizosphere bacterial isolate and optimization studies by response surface modeling

Rhizosphere bacteria have always proven their worth towards their associated plant in their defense mechanism and nutritional functions. This study was made to understand the impact of rhizosphere-associated bacterial isolate PGK01 in complimenting associated Zingiber officinale plants in their potassium nutritional requirements. The screening of the isolate suggested that it can solubilize potassium, which the plant shall use for its nutritional purposes. Molecular sequencing suggested that the strain belonged to Bacillus subtilis, whose sequence has been submitted to NCBI under the accession number OQ652138. In-situ analysis of the effect of bacteria on the growth parameters and yield of the plant indicated that in the presence of microbe, plants tend to grow more when compared to without the organism. The optimization studies conducted by response surface modeling suggested that only half of the potassium fertilizer is necessary when a plant is grown in the presence of isolate compared to the conventional method. The adequacy of the statistical model was verified by analyzing the Sequential Model Sum of Squares and Cook’s distance diagnostic, wherein the observation proved the significance of the mathematical model.

Antiproliferative and antimicrobial compounds from Streptomyces levis: supported by in vitro and in silico molecular docking approach

The present work describes the investigation of secondary metabolites produced by rhizospheric soil isolate Streptomyces levis with respect to partial purification, bioactivity, structural elucidation, and docking study. MIC (Minimum Inhibitory Concentration) of the fraction was found to be 16 µg/mL, 32 µg/mL, and 8 µg/mL against S. aureus, E. coli, and C. albicans respectively. The fraction exhibited an IC50 of 90.48 μg/mL and 59.10 µg/mL against L929 and HeLa cell lines respectively. Spectroscopic analysis showed abundant of Isofucosterol 3-O-[6-O-(9-Octadecanoyl)-b-D-glucopyranoside], and Viniferal. These compounds were docked against receptor molecules E6, E7, Caspase-3, and Bcl2. The in-silico results suggested that all the secondary metabolites showed higher docking scores than the standard compound 5-Fluorouracil. Molecular docking study and published literature suggested that Isofucosterol 3-O-[6-O-(9-Octadecanoyl)-b-D-glucopyranoside] inactivated viral oncoprotein E7 and arrested the cell cycle from entering in S phase. Viniferal induced apoptosis by inactivation of Bcl2.

Bio-Priming with Bacillus Isolates Suppresses Seed Infection and Improves the Germination of Garden Peas in the Presence of Fusarium Strains

Seed infection caused by Fusarium spp. is one of the major threats to the seed quality and yield of agricultural crops, including garden peas. The use of Bacillus spp. with multiple antagonistic and plant growth-promoting (PGP) abilities represents a potential disease control strategy. This study was performed to evaluate the biocontrol potential of new Bacillus spp. rhizosphere isolates against two Fusarium strains affecting garden peas. Six Bacillus isolates identified by 16S rDNA sequencing as B. velezensis (B42), B. subtilis (B43), B. mojavensis (B44, B46), B. amyloliquefaciens (B50), and B. halotolerans (B66) showed the highest in vitro inhibition of F. proliferatum PS1 and F. equiseti PS18 growth (over 40%). The selected Bacillus isolates possessed biosynthetic genes for endoglucanase (B42, B43, B50), surfactin (B43, B44, B46), fengycin (B44, B46), bacillomycin D (B42, B50), and iturin (B42), and were able to produce indole-3-acetic acid (IAA), siderophores, and cellulase. Two isolates, B. subtilis B43 and B. amyloliquefaciens B50, had the highest effect on final germination, shoot length, root length, shoot dry weight, root dry weight, and seedling vigor index of garden peas as compared to the control. Their individual or combined application reduced seed infection and increased seed germination in the presence of F. proliferatum PS1 and F. equiseti PS18, both after seed inoculation and seed bio-priming. The most promising results were obtained in the cases of the bacterial consortium, seed bio-priming, and the more pathogenic strain PS18. The novel Bacillus isolates may be potential biocontrol agents intended for the management of Fusarium seed-borne diseases.

Characterization of rhizospheric fungi and their in vitro antagonistic potential against myco-phytopathogens invading Macrotyloma uniflorum plants.

Microorganisms have become more resistant to pesticides, which increases their ability to invade and infect crops resulting in decreased crop productivity. The rhizosphere plays a crucial role in protecting plants from harmful invaders. The purpose of the study was to investigate the antagonistic efficiency of indigenous rhizospheric fungal isolates against phytopathogens of M. uniflorum plants so that they could be further used as potent Biocontrol agents. Thirty rhizospheric fungal isolates were collected from the roots of the Macrotyloma uniflorum plant and initially described morphologically for the present study. Further, in vitro tests were conducted to evaluate the antifungal activity of these strains against four myco-phytopathogens namely Macrophamina phaseolina, Phomopsis sp. PhSFX-1, Nigrospora oryzae, and Boeremia exigua. These pathogens are known to infect the same crop plant, M. uniflorum, and cause declines in crop productivity. Fifteen fungal strains out of the thirty fungal isolates showed some partial antagonistic activity against the myco-phytopathogens. The potent fungal isolates were further identified using molecular techniques, specifically based on the internal transcribed spacer (ITS) region sequencing. Penicillium mallochii, Cladosporium pseudocladosporioides, Aspergillus chevalieri, Epicoccum nigrum, Metarhizium anisopliae, and Mucor irregularis were among the strains that were identified. These potent fungal strains showed effective antagonistic activity against harmful phytopathogens. Current findings suggest that these strains may be taken into consideration as synthetic fungicides which are frequently employed to manage plant diseases alternatives.

The Potential of Clove Rhizospheric Bacteria to Produce Vanillin from Eugenol

Vanillin is one of the most important flavoring agents worldwide. Currently, consumers' awareness and concern for biovanillin production has been increasing. This study aimed to screen the potential of clove rhizospheric bacteria isolates producing vanillin through a biotransformation process of eugenol and to conduct the preliminary optimization of the biotransformation condition. Twenty-eight bacteria isolates were screened for their capability to transform eugenol into vanillin. BKL 15 isolate, which was identified as Lysinibacillus xylanilyticus, was selected as the highest vanillin producer among the isolates. The optimum molar yield of vanillin produced by the selected isolate was 4.99% (1.11 g/L) after 168 hours of biotransformation process in the medium consisting of TSB (30 g/L), eugenol (24 g/L), yeast extract (20 g/L), and concentration of casamino acid (20 g/L). Throughout the publications we have read, this is the first report of L. xylanolyticus that produces vanillin.

Suppression of Sugarcane Red Rot Disease through Its Rhizospheric Mycoflora

Red rot disease of sugarcane is so devastating in nature that it has been referred to as “cancer of sugarcane”. The sugar industry in India suffered losses more than 500 million US dollars every year due to red rot. So, there is a need to look over the management and control of the disease. Biological control method is an alternative method of chemical pesticides which are an innovative, cost effective and eco-friendly approach. Soil samples were collected from sugarcane rhizosphere of four different varieties viz., CoPk 05191 and CoLk 94184 (resistant to red rot) and CoJ 64 and Co 1148 (susceptible to red rot) planted at ICAR-Indian Institute of Sugarcane Research, Lucknow experimental farm. The samples were subjected for the isolation of rhizospheric mycoflora on Potato Dextrose Agar media and antagonistic activities of the isolates were tested against red rot pathogens (Cf 07, Cf 08 and Cf 09). Isolates showing more than 50 % inhibition with all the three pathotypes (Cf 07, Cf 08 and Cf 09) were selected for further study. Among the twelve selected isolates used for field experiment for the management of red rot, isolate T16 was found to be highly effective. The suppression of red rot offered by rhizospheric isolates is probably due to induced systemic resistance in sugarcane plants or by the enzymatic action of metabolites produced by the rhizospheric mycoflora. The different levels of red rot infected seed cane viz., 5%, 10%, 15%, 20%, 25%, 30%, 35% and 40% were treated with MHAT and planted along with healthy seed canes, infected seed canes, as a control to work out the losses caused by different level of red rot seed infection. The result revealed that a yield loss was recorded with the infected seed. The losses were directly proportionate with the level of red rot infected seed.

Cloning and transformation of CStr1 antibiotic gene from Streptomyces roseus for the management of brown leaf spot in rice incited by Helminthosporium oryzae

Rice seeds when treated with Streptomyces sp. showed significant increases in per cent germination, root length, shoot length and seedling vigour. Among the twenty isolates of Streptomyces sp. tested, the isolate CStr 1 was the most effective in promoting plant growth. The Streptomyces sp. isolate Str1 recorded a vigour index of 518.40. In the present investigation, out of the twenty rhizospheric actinomycetes isolates, all isolates were confirmed as Streptomyces at the genus level based on the PCR amplification of the DNA using genus specific primers which yielded an amplicon size of 620 bp. The partial sequence of DNA of seven isolates from rice rhizosphere showed 99-100 per cent similarity to Streptomyces sp in the NCBI database. The isolate Str 1 showed 100 per cent identity to S. roseus respectively in the NCBI database. Western blot analysis of leaf samples from rice plants showed that barley chitinase antiserum was able to recognize a protein with sizes of 42 kDa. The antibiotics identified as 4H-1-Benzopyran-4-one, 2-(3,4-dihydroxyphenyl)-6,8-di-?-D-glucopyranosyl-5,7-dihydroxy- (CAS) with molecular formula C27H30O16.. KEYWORDS :Antibiotic gene, chitinase, Helminthosporium oryzae, Streptomyces roseus, western blotting Rice

Molecular identification of fungal isolates from rhizospheric soil of medicinal plants

Further knowledge of the interactions between rhizospheric fungi and medicinal plants is needed to promote the manufacture of crude medications, as it has recently been clear how these fungi have a significant impact on the quality and quantity of crude pharmaceuticals through a specific fungus-host interaction. The present study was aimed to find out the diversities of fungi in the rhizospheric soil of medicinal plants particularly (Gingiber officinale, Calotropis gigantea, Endographis paniculata, Vigna mungo, Chrysopogon giganoids and Tinospora cordifolia) collected from CIMAP CSIR situated in Indian city Lucknow and from nearby Paikramau agriculture field Lucknow, U.P., India. The DNA of the rhizospheric fungal isolates was amplified through PCR for species level identification using a specific internal transcribed spacer primer (ITS1/ITS4). This study revealed that five different type of fungi identified surrounding the Rhizospheric region of the selected aforementioned plants such as Rhizopus oryzae, Fusarium incarnatum, Penicillium expansum, Aspergillus ochraceous and Aspergillus flavus further validated by sequencing the PCR findings and comparing them to other relevant sequences in GenBank (NCBI).

The influence of biostimulants on the rhizospheric microorganisms of scorzonera (Scorzonera hispanica L.)

Scorzonera (Scorzonera hispanica L.) is a particularly valuable species among little-known and rarely cultivated vegetables. It is a root vegetable of high dietary and nutritional values. The suitable microbiological activity of the soil favors the growth and development of scorzonera. Biostimulants can positively affect the communities of rhizospheric microorganisms of cultivated plants, including this important vegetable. The studies established the influence of biostimulants on the microbial communities in the scorzonera rhizosphere. Before setting up the field experiment, scorzonera seeds were dressed with fungicide Zaprawa Nasienna T 75 DS/WS or biostimulants Beta-Chikol, Bio-Algeen S-90, and Asahi SL. The laboratory microbiological analyses of scorzonera rhizosphere soil were conducted and determined the total population of bacteria and fungi. The obtained rhizosphere isolates of fungi Albifimbria, Clonostachys, Epicoccum, Penicillium, and Trichoderma sp. were tested to check the influence on fungi pathogenic to scorzonera (Fusarium culmorum, Fusarium oxysporum, Sclerotinia sclerotiorum, and Rhizoctonia solani). The experiments showed that biostimulants, especially Asahi SL and Beta-Chikol, favored the development of rhizobacteria populations (including Bacillus sp. and Pseudomonas sp.). All biostimulants (Beta-Chikol, in particular) and the fungicide decreased the population of rhizospheric fungi and limited the occurrence of polyphagous fungi in the rhizosphere of scorzonera. Biostimulant Beta-Chikol and fungicide Zaprawa Nasienna T 75 DS/WS were most effective in stimulating the development of antagonistic fungi. Clonostachys rosea, Trichoderma sp., and Albifimbria verrucaria predominated as antagonistic rhizospheric fungi.

Plant-Disease-Suppressive and Growth-Promoting Activities of Endophytic and Rhizobacterial Isolates Associated with Citrullus colocynthis.

This study was conducted to investigate the antagonistic potential of endophytic and rhizospheric bacterial isolates obtained from Citrullus colocynthis in suppressing Fusarium solani and Pythium aphanidermatum and promoting the growth of cucumber. Molecular identification of bacterial strains associated with C. colocynthis confirmed that these strains belong to the Achromobacter, Pantoea, Pseudomonas, Rhizobium, Sphingobacterium, Bacillus, Sinorhizobium, Staphylococcus, Cupriavidus, and Exiguobacterium genera. A dual culture assay showed that nine of the bacterial strains exhibited antifungal activity, four of which were effective against both pathogens. Strains B27 (Pantoea dispersa) and B28 (Exiguobacterium indicum) caused the highest percentage of inhibition towards F. solani (48.5% and 48.1%, respectively). P. aphanidermatum growth was impeded by the B21 (Bacillus cereus, 44.7%) and B28 (Exiguobacterium indicum, 51.1%) strains. Scanning electron microscopy showed that the strains caused abnormality in phytopathogens' mycelia. All of the selected bacterial strains showed good IAA production (>500 ppm). A paper towel experiment demonstrated that these strains improved the seed germination, root/shoot growth, and vigor index of cucumber seedlings. Our findings suggest that the bacterial strains from C. colocynthis are suppressive to F. solani and P. aphanidermatum and can promote cucumber growth. This appears to be the first study to report the efficacy of these bacterial strains from C. colocynthis against F. solani and P. aphanidermatum.

Pseudomonas aeruginosa strains belonging to phylogroup 3 frequently exhibit an atypical quorum sensing response: the case of MAZ105, a tomato rhizosphere isolate.

Pseudomonas aeruginosa is a widespread γ-proteobacterium and an important opportunistic pathogen. The genetically diverse P. aeruginosa phylogroup 3 strains are characterized by producing the pore-forming ExlA toxin and by their lack of a type III secretion system. However, like all strains of this species, they produce several virulence-associated traits, such as elastase, rhamnolipids and pyocyanin, which are regulated by quorum sensing (QS). The P. aeruginosa QS response comprises three systems (Las, Rhl and Pqs, respectively) that hierarchically regulate these virulence factors. The Pqs QS system is composed of the PqsR transcriptional factor, which, coupled with the alkyl-quinolones HHQ or PQS, activates the transcription of the pqsABCDE operon. The products of the first four genes of this operon produce HHQ, which is then converted to PQS by PqsH, while PqsE forms a complex with RhlR and stabilizes it. In this study we report that mutations affecting the Pqs system are particularly common in phylogroup 3 strains. To better understand QS in phylogroup 3 strains we studied strain MAZ105 isolated from tomato rhizosphere and showed that it contains mutations in the central QS transcriptional regulator, LasR, and in the gene encoding the PqsA enzyme involved in the synthesis of PQS. However, it can still produce QS-regulated virulence factors and is virulent in Galleria mellonella and mildly pathogenic in the mouse abscess/necrosis model; our results show that this may be due to the expression of pqsE from a different PqsR-independent promoter than the pqsA promoter. Our results indicate that using anti-virulence therapy based on targeting the PQS system will not be effective against infections by P. aeruginosa phylogroup 3 strains.

Potential of local Bacillus spp. isolates as wilt disease biocontrol agents for Fusarium oxysporum f. sp. cepae on Allium x wakegi

Abstract. Asrul. 2023. Potential of local Bacillus spp. isolates as wilt disease biocontrol agents for Fusarium oxysporum f. sp. cepae on Allium x wakegi. Biodiversitas 24: 4989-4997. Implementation of biological agents for eradication and inhibition of plant pathogens is often ineffective due to its protracted consequences. The objective of this research was to examine the potential of local isolates of Bacillus spp. as a biocontrol agent in suppressing Fusarium wilt disease (Fusarium oxysporum f. sp. cepae) on wakegi onions (Allium × wakegi Araki). The research was conducted in a completely randomized design (CRD) with the treatment of rhizospheric bacterial isolates. The treatments included control (without isolate application) and seven bacterial isolates, namely KP17, KP5, DB9, DB12, DB18, DG4 and DG11. Each treatment was repeated five times and each replication consisted of 10 wakegi onion plants. The results showed that a total of 46 isolates were isolated from the rhizosphere of wakegi onion and seven isolates among them were selected as biocontrol agents. These isolates had similarities with Bacillus spp. in accordance with the colony morphology, physiology and biochemical characteristics. Among the isolates found, DB12 emerged as the isolate that had the potential to be developed as a biocontrol agent.

Exploring the potential of halotolerant bacteria from coastal regions to mitigate salinity stress in wheat: physiological, molecular, and biochemical insights.

Salinity stress, a significant global abiotic stress, is caused by various factors such as irrigation with saline water, fertilizer overuse, and drought conditions, resulting in reduced agricultural production and sustainability. In this study, we investigated the use of halotolerant bacteria from coastal regions characterized by high salinity as a solution to address the major environmental challenge of salinity stress. To identify effective microbial strains, we isolated and characterized 81 halophilic bacteria from various sources, such as plants, rhizosphere, algae, lichen, sea sediments, and sea water. We screened these bacterial strains for their plant growth-promoting activities, such as indole acetic acid (IAA), phosphate solubilization, and siderophore production. Similarly, the evaluation of bacterial isolates through bioassay revealed that approximately 22% of the endophytic isolates and 14% of rhizospheric isolates exhibited a favorable influence on seed germination and seedling growth. Among the tested isolates, GREB3, GRRB3, and SPSB2 displayed a significant improvement in all growth parameters compared to the control. As a result, these three isolates were utilized to evaluate their efficacy in alleviating the negative impacts of salt stress (150 mM, 300 mM, and seawater (SW)) on the growth of wheat plants. The result showed that shoot length significantly increased in plants inoculated with bacterial isolates up to 15% (GREB3), 16% (GRRB3), and 24% (SPSB2), respectively, compared to the control. The SPSB2 strain was particularly effective in promoting plant growth and alleviating salt stress. All the isolates exhibited a more promotory effect on root length than shoot length. Under salt stress conditions, the GRRB3 strain significantly impacted root length, leading to a boost of up to 6%, 5%, and 3.8% at 150 mM, 300 mM, and seawater stress levels, respectively. The bacterial isolates also positively impacted the plant's secondary metabolites and antioxidant enzymes. The study also identified the WDREB2 gene as highly upregulated under salt stress, whereas DREB6 was downregulated. These findings demonstrate the potential of beneficial microbes as a sustainable approach to mitigate salinity stress in agriculture.

Siderophore-producing Bacillus amyloliquefaciens BM3 mitigate arsenic contamination and suppress Fusarium wilt in brinjal plants.

Arsenic contamination in agricultural soils poses a serious health risk for humans. Bacteria that produce siderophores, primarily for iron acquisition, can be relevant in combating arsenic toxicity in agricultural soils and simultaneously act as biocontrol agents against plant diseases. We evaluated the arsenic bioremediation and biocontrol potential of the rhizosphere isolate Bacillus amyloliquefaciens BM3 and studied the interaction between the purified siderophore bacillibactin and arsenic. BM3 showed high arsenic resistance [MIC value 475 and 24mM against As(V) and As(III), respectively] and broad spectrum in-vitro antagonism against several phytopathogenic fungi. BM3 was identified by biochemical characterization and 16S rRNA gene sequencing. Scanning electron microscopy (SEM) analysis revealed increased cell size of BM3 when grown in presence of sub-lethal arsenic concentrations. Bioremediation assays showed a 74% and 88.1% reduction in As(V) and As(III) concentrations, respectively. Genetic determinants for arsenic resistance (arsC and aoxB) and antifungal traits (bacAB and chiA) were detected by PCR. Arsenic chelating ability of bacillibactin, the siderophore purified from culture filtrate of BM3 and identified through spectroscopic data analysis, was observed in CAS assay and fluorescence spectrometry. In-vivo application of talc-based formulation of BM3 in brinjal seedlings showed significant reduction in Fusarium wilt disease. Strain B. amyloliquefaciens BM3 may be useful in arsenic bioremediation and may be considered for large field trials as an alternative to chemical fungicides by inhibiting soil borne pathogens.

Heavy metal, salinity and azo dye tolerant, Cr (VI) reducing, plant growth-promoting Pseudomonas aeruginosa R32 reverses Cr (VI) biotoxic effects in Vigna mungo

Hexavalent chromium [Cr (VI)], derived from various industries, including fly ash from coal-based Thermal Power Plants, can be a source of toxic pollution of land and water bodies. This study aimed to bioremediation of such pollutant dump sites using bacteria capable of both Cr(VI) reduction and plant growth-enhancing substance production. The bacteria were isolated from the rhizospheric fly ash of a Thermal Power Plant, Kanpur. One of the rhizospheric isolate, Pseudomonas aeruginosa R32 showed high minimum inhibitory concentration (MIC) for Cr(VI) (1250 µg/ml), heavy metal tolerance (ZnCl2, CdCl2, Pb(NO3)2) up to 100 µg/ml, Acid Red 249 (AR) tolerance and halotolerance (6% NaCl). The isolate R32 also produces plant growth-promoting (PGP) hormones in the absence or presence of Cr (VI). R32 could completely reduce Cr(VI) at a tested dose of 100 and 500 μg/ml after 24h and 72h, respectively. However, decolorization of AR was observed after 48 hours at an initial concentration of 100 µg/ml and confirmed by Fourier transform infrared spectroscopy analysis. Vigna mungo seed inoculation with isolate R32 showed increased rootling growth compared to shoot after 7 d treatment with 0, 100, 500, and 1000 μg/ml of Cr(VI) concentrations, respectively. Root length tolerance index in Cr(VI) treated V. mungo seedlings was reduced to 56%, 35%, and 29%, respectively, when treated with 100, 500, and 1000 μg/ml Cr(VI) in comparison to control. Cr(VI) sub-MIC concentrations can affect the plant growth-promoting properties of rhizospheric bacteria. Herein, we report the isolation of rhizospheric bacteria P. aeruginosa R32 showing concurrent PGP substance production and Cr(VI) bioreduction capabilities in the presence of PGP inhibitory Cr(VI) concentrations.