Rhizosphere Isolates Research Articles

The Effect of Arbuscular Mycorrhizal Fungi and Azotobacter on the Growth of Toona sureni Merr (Suren) Seedlings on Post-Coal Mining Land

. This research aimed to investigate the growth of Toona sureni Merr (suren) seedlings inoculated with arbuscular mycorrhizal fungi (AMF) and azotobacter on land previously used for coal mining. We also investigated the source of AMF and azotobacter isolates, resulting in the best growth of suren seedlings on the post-coal mining land. We used a completely randomized design in a factorial manner with two treatment factors. The first factor was the inoculation of AMF isolates (C), which consisted of 5 levels, namely: without AMF (C0), AMF from the suren rhizosphere (C1), AMF from Gmelina arborea (gmelina) rhizosphere (C2), AMF from Durio zibethinus (durian) rhizosphere (C3), and AMF from Acacia mangium (acacia) rhizosphere (C4). The second factor was the inoculation of azotobacter isolates (A), which consisted of 4 levels, namely: without azotobacter (A0), azotobacter from the suren rhizosphere (A1), azotobacter from the gmelina rhizosphere (A3), and azotobacter from the durian rhizosphere (A4). Each treatment had six replications. Data analysis used ANOVA at a 5% test level. Then, we used the orthogonal contrast test to compare the growth of the inoculated seedlings with AMF and azotobacter with that of the un-inoculated seedlings. Meanwhile, to find out the source of isolates for AMF and azotobacter, which resulted in the best growth of the seedlings, we analyzed them with a two-way Duncan Multiple Range Test (DMRT). The results of the ANOVA showed that the AMF inoculation had a significant difference in height growth, diameter growth, and growth in the number of leaves. In contrast, azotobacter inoculation had no significant difference in the same growth variables. The interaction between AMF inoculation and Azotobacter was not significantly different in height growth but in diameter and leaf number growth. The DMRT analysis showed that AMF from suren rhizosphere isolates resulted in the best growth of the suren seedlings.

Identification of lead-resistant rhizobacteria of Carthamus tinctorius and their effects on lead absorption of Sunflower

Using rhizobacteria as plant growth-promoting agents for improving heavy-metal phytoremediation processes in contaminated soil has attracted a lot of attention mainly because of their eco-friendliness. The aim of this study was the evaluation of lead phytoremediation by Carthamus tinctorius improved with the isolated and molecularly identified lead-resistant rhizobacteria. Rhizobacteria were isolated from C. tinctorius root and was identified using macroscopic and microscopic characteristics, biochemical testing and PCR. Then, the indole acetic acid production and phosphate-solubilizing activity were determined. Finally, the amount of lead in the plant was measured by atomic absorption method. Five strains of Bacillus cereus, Bacillus muralis, Bacillus sp., Pseudomonas fluorescens and Brevibacterium frigoritolerans with the ability of mineral phosphate solubilizing, high levels of indole acetic acid production and resistance to lead were isolated from the rhizosphere of C.tinctorius. The amount of produced indole acetic acid and the level of phosphate solubilizing by the isolates were 7.1-69.54µgml-1 and 91-147.3µgml-1 respectively. Lead assimilation in aerial part of safflower ranged from 925 to 2175ppm. P. fluorescens and B. cereus strains had the highest effect on Lead assimilation with 2175 and 1862ppm respectively. The results showed that different bacterial treatments influenced the rate of lead absorption by C. tinctorius exposed to lead stress. Use of rhizosphere isolates of C. tinctorius can improve phytoremediation capability and lead absorption in lead-contaminated soil.

Genome Sequencing and Analysis of Trichoderma (Hypocreaceae) Isolates Exhibiting Antagonistic Activity against the Papaya Dieback Pathogen, Erwinia mallotivora.

Erwinia mallotivora, the causal agent of papaya dieback disease, is a devastating pathogen that has caused a tremendous decrease in Malaysian papaya export and affected papaya crops in neighbouring countries. A few studies on bacterial species capable of suppressing E. mallotivora have been reported, but the availability of antagonistic fungi remains unknown. In this study, mycelial suspensions from five rhizospheric Trichoderma isolates of Malaysian origin were found to exhibit notable antagonisms against E. mallotivora during co-cultivation. We further characterised three isolates, Trichoderma koningiopsis UKM-M-UW RA5, UKM-M-UW RA6, and UKM-M-UW RA3a, that showed significant growth inhibition zones on plate-based inhibition assays. A study of the genomes of the three strains through a combination of Oxford nanopore and Illumina sequencing technologies highlighted potential secondary metabolite pathways that might underpin their antimicrobial properties. Based on these findings, the fungal isolates are proven to be useful as potential biological control agents against E. mallotivora, and the genomic data opens possibilities to further explore the underlying molecular mechanisms behind their antimicrobial activity, with potential synthetic biology applications.

Organophosphorus insecticides mineralizing endophytic and rhizospheric soil bacterial consortium influence eggplant growth-promotion.

This study was aimed to evaluate eggplant's growth-enhancing activity of chlorpyrifos and diazinon-degrading endophytic and rhizospheric soil bacteria isolated from cauliflower and tomato roots and the rhizospheric soil of rice roots, respectively. The identified endophytes belong tothe Acinetobacter,Enterobacter andKlebsiellagenera, while rhizospheric soil isolates belong toPantoea,Acinetobacter,Kosakonia,Morganella,Enterobacter, andKlebsiellagenera with species variation and genetic distances. All the strain's consumed 100% (50mg/5mL) chlorpyrifos and diazinon after 14days of exposure, except forPantoeasp. HSTU-Sny4 (84%) andKosakoniasp. HSTU-ASn39 (42%). The strain's exhibited N-fixation, P-solubilization, indole-3-acetic acid (IAA), and ACC-deaminase production capabilities. The individual strain's and consortium treatment enhanced eggplant growth at germination, seedling, vegetative and reproductive stages. Plant growth-promoting genes, e.g., nif-cluster, chemotaxis, phosphates, sulfur, abiotic stress, chemotaxis, biofilm formation and organophosphorus insecticide-degrading genes were annotated inKlebsiellasp. HSTU-Sny5 andMorganellasp. HSTU-ASny43 genomes. Importantly, the mixed consortium supplemented with 40% urea-treated eggplants demonstrated similar growth parameters compared to the 100% urea eggplants. Plenty of insecticide-degrading proteins belonged to HSTU-Sny5 andHSTU-ASny43 strain's and had interacted with 100 different insecticides as confirmed in virtual screening. This research has a significant role in reducing the application of chemical fertilizer and bioremediation of pesticides in agriculture.

Plant growth promoting rhizobacterial diversity in potato grown soil in the Gwalior region of India

There seems to be meager studies with regards to rhizo and non-rhizo microbial association with potato plant from the central India. Present study was undertaken to evaluate the microbial diversity of rhizospheric and non-rhizospheric isolates from three varieties of potato viz Kufri sindhuri, Kufri lauvkar and Kufri chipsona-3 procured from the Central Potato Research Station, Maharajpura, Gwalior. A total of 130 bacterial forms were isolated, and amongst these forty isolates were further characterized on their morphological basis, and those showing some of PGPR characteristics were identified to species level using VITEK-2 method. Various bacterial populations were found in potato rhizosphere and dominant presence was those of Bacillus subtilis, Bacillus Megaterium and Lysinibacillus sphaericus. The non-rhizospheric soil was dominant in the forms like Aeromonas salmonicida, Morxella group and Bacillus coagulans. Highest bacterial diversity was found in the rhizosphere soil of different potato cultivars than in the non-rhizospheric soil of potato.

Acinetobacter calcoaceticus SJ19 and Bacillus safensis SJ4, two Algerian rhizobacteria protecting tomato plants against Botrytis cinerea and promoting their growth

BackgroundBotrytis cinerea, the causal agent of grey mould, is a polyphagous fungus that infects a wide range of plants, including tomato. In many countries, including Algeria, the management of grey mould is a challenging problem, even with chemical control. This necessitates the search for other strategies. The objective of this study was to evaluate the biocontrol potential of two rhizospheric bacterial isolates for the protection of tomato against B. cinerea.ResultsOn tomato plants, the two bacterial isolates consistently provided high levels of protection (on average 72.1% for SJ19 and 52.3% for SJ4). Their applications as a 1:1 mixture reinforced their effect (87.8% protection), indicating their compatibility and a potential use as a consortium. In vitro, the isolates significantly inhibited the mycelial growth of B. cinerea strains, both through direct confrontation in dual-culture assays (12–69% inhibition) and through the production of volatile compounds (36–46% inhibition). The two isolates, applied as seed treatment and as drench on seedlings, also showed strong growth-promoting effects on tomatoes. They substantially increased the length and fresh weight of shoots and roots, as well as stem diameter, leaf number and chlorophyll content, compared to untreated plants.ConclusionThe two bacteria tested in this study showed a high potential for use as biostimulants and as biofungicides against tomato grey mould.

Antifungal potential of Streptomyces rameus GgS 48 against mungbean root rot [Rhizoctonia bataticola (Taub.) Butler

Mungbean root rot caused by Rhizoctonia bataticola (Taub.) Butler is the most devastating disease inflicting yield loss up to 60%. The use of beneficial antagonist, viz., Streptomyces with diverse antifungal activity and prolific secondary metabolites production, is the ecofriendly and environmentally acceptable alternative to the existing chemical control methods. In this investigation we have identified the promising isolate of Streptomyces sp. which potentially reduced the mungbean root rot. A total of nine mungbean rhizospheric actinobacterial isolates were evaluated for their antagonistic potential against root rot pathogen and growth promoting trait of mungbean. The actinobacterial isolate GgS 48 was shown to be effective in reducing the mycelial growth of R. bataticola by 65.3% in dual culture technique and enhancing the growth of mugbean under in vitro condition. Morphological, biochemical and molecular characterization confirmed the isolate GgS 48 as Streptomyces rameus. The actinobacteria S. rameus GgS 48 exerted antifungal action against R. bataticola by hyphal coiling, which was confirmed under scanning electron microscopy (SEM), and promoted the growth through the production of IAA. It showed positive for the production of siderophore and hydrolytic enzymes, viz., chitinase and protease. The chitinase produced by the GgS 48 was purified and its molecular weight was determined as 40 kDa and it had great potential in reducing the mycelial growth of R. bataticola. The talc-based formulation of S. rameus GgS 48 was found to be promising in suppressing the root rot severity and enhancing the growth and yield attributes of mungbean both under glass house and field conditions.

Native Rhizospheric and Endophytic Fungi as Sustainable Sources of Plant Growth Promoting Traits to Improve Wheat Growth under Low Nitrogen Input.

Wheat crops require effective nitrogen fertilization to produce high yields. Only half of chemical N2 fertilizers are absorbed into plants while the rest remains in the soil, causing environmental problems. Fungi could maximize nitrogen absorption, and from an environmental and biodiversity point of view, there is an urgent necessity for bioprospecting native fungi associated with wild plants growing in harsh environments, e.g., St. Katherine Protectorate (SKP) in the arid Sinai. Recovered taxa, either endophytic and/or rhizospheric, were screened for their plant growth-promoting (PGP) traits. Eighteen fungal isolates (15 rhizospheric and 3 endophytic) belonging to anamorphic ascomycetes were recovered from 9 different wild plants, and their PGP traits (indole-3-acetic acid [IAA] production, phosphate solubilization, siderophore production, and hydrolytic enzyme production) were measured. Rhizospheric isolate NGB-WS14 (Chaetosphaeronema achilleae) produced high levels of IAA (119.1 μg mL−1) in the presence of tryptophan, while NGB-WS 8 (Acrophialophora levis) produced high IAA levels (42.4 μg mL−1) in the absence of tryptophan. The highest phosphate-solubilizing activity (181.9 μg mL−1) was recorded by NGB-WFS2 (Penicillium chrysogenum). Endophytic isolate NGB-WFE16 (Fusarium petersiae) exhibited a high percentage level of Siderophore Unit (96.5% SU). All isolates showed variability in the secretion of extracellular hydrolytic enzymes. Remarkably, all isolates had antagonistic activity (55.6% to 87.3% suppression of pathogen growth) against the pathogenic taxon Alternaria alternata (SCUF00001378) in the dual-assay results. Out of the 18 isolates, 4 rhizospheric and 1 endophytic isolate showed significant increases in shoot dry weight and shoot nitrogen and chlorophyll content of wheat plants subjected to low inputs of chemical nitrogen (N) fertilizers (50% reduction) compared with the non-inoculated control in a pot experiment. Potent taxa were subjected to sequencing for molecular confirmation of phenotypic identification. The retrieved ITS sequences in this study have been deposited in GenBank under accession numbers from LC642736 to LC642740. This study considered the first report of endophytic fungi of Cheilanthes vellea, a wild plant with PGPF which improves wheat growth. These results recommend using PGPF as inoculants to alleviate low nitrogen fertilization.

Antagonistic activity of resident biological agents against wilt and root rot pathogens of pea in different culture media

Antagonistic potential of rhizospheric fungal and bacterial isolates evaluated against wilt and root-rot pathogens of pea exhibited significant effect on radial growth inhibition of pathogens in comparison to control. Two isolates of Trichoderma spp., one isolate of Aspergillus niger, one isolate of Penecillium oxalicum and three isolates of Pseudomonas were isolated from rhizosphere of pea and were evaluated for their antagonistic potential against three soil borne plant pathogens viz., Fusarium oxysporum f. sp, pisi, Rhizoctonia solani and Pythium ultimum using dual culture technique in different culture media (potato carrot agar, czapek dox agar, rose bengal chloramphenicol and czapek malt agar). Antagonistic potential of fungal and bacterial isolates were found to be significantly influenced in different culture media. All fungal and bacterial isolates preferred potato carrot agar and czapek dox agar media and resulted in maximum reduction in growth of test pathogen on the culture media.

Evaluation of the anti-oomycete bioactivity of rhizosphere soil-borne isolates and the biocontrol of soybean root rot caused by Phytophthora sojae

Phytophthora sojae is an important pathogen that causes soybean root rot. In this study, 200 rhizosphere bacteria were isolated from soybean rhizosphere soil. Six rhizosphere strains that showed antagonistic activity against Phytophthora sojae, SN337-SN342, were screened with further confrontation experiments. The biocontrol activities of the 6 strains, especially SN337, were subsequently characterized and evaluated. In vitro experiments showed that SN337, as a newly developed biocontrol agent, had good antagonistic activity against Phytophthora sojae. In the evaluation of soybean growth promotion, a fermented broth of strain SN337 increased shoot height and root length by 13% and 37.5%, respectively, compared with a control. Importantly, the incidence caused by P. sojae decreased in soybean plants treated with SN337. The fermentation broth of strain SN337 also clearly disintegrated zoospores of P. sojae. The biocontrol effects were further investigated based on the changes in rhizosphere soil microorganisms before and after inoculation with pathogens. Compared to P. sojae infection without SN337 treatment, the abundance of bacteria, fungi, actinomycetes and total microbes were increased, whereas P. sojae was decreased in the rhizosphere of soybean infected by P. sojae inoculation with SN337 treatment. The results indicated that strain SN337 played a role in the maintenance of the soybean rhizosphere environment by increasing the proportion of beneficial microorganism in the soil. In this study, the biocontrol effects of strain SN337 were evaluated based on antagonistic activity and biocontrol assays and on soil microbial analysis. Our results provide new practical clues for developing fungicides for the sustainable management of soybean root rot caused by P. sojae.

Antagonistic activity of rice rhizosphere isolates against Xanthomonas oryzae pv. oryzae bacterial blight pathogen

Attempts were made to isolate beneficial bio agents from rice rhizosphere which resulted in isolation of 46 Bacillus spp and 15 fluorescent Pseudomonas spp which were further investigated for their potential aginst BB of rice diseaseAmong twenty six isolates of Bacillus, two isolates were most antagonistic and showed highest inhibition percentage (57.09) The potential isolates of Pseudomonas (P-4, P-5, P-6, P-7 and P-8), Bacillus (ARI 1-2, ARI 2-4, ARI 1-3, D1-1-2 and D2-1-1) were tested in vivo under glass house conditions for antagonism against Xoo which revealed that P-7 was effective in reduction of lesion length (18.5cm) when compared to control (20.37cm). The potential isolates of Pseudomonas (P-4, P-5, P-6, P-7 and P-8), Bacillus (ARI 1-2, ARI 2-4, ARI 1-3, D1-1-2 and D2-1-1) were tested in vivo under glass house conditions for antagonism against Xoo which revealed that P-7 was effective in reduction of lesion length (18.5cm) when compared to control (20.37cm). The present study indicated that PGPR isolates P-4, P-6, P-7 and P-8 can be used as biofertilizers, which will add up for enhanced growth of rice.

SYNERGISM BETWEEN RHIZOSPHERE BACTERIA ISOLATES FROM Scleria sp., Clidemia sp., AND Panicum sp. TO INCREASE THE EFFECTIVENESS OF MIXED CULTURES IN HYDROCARBON BIODEGRADATION

The purpose of this research is to obtain hydrocarbon degrading bacteria that work synergistically in a consortium. Consortium microorganisms is mixture of microbial populations in the form of communities that have mutualistic relationships and doesn’t inhibition the growth of other microbes. In this study, isolates were obtained from the rhizosphere of soil contaminated with petroleum. The isolates obtained were tested for synergism to determine the relationship between bacterial isolates. Synergism testing was carried out using the spread plate method on agar media. The results of this study showed that isolate number one showed antagonistic properties to other bacterial isolates by forming a clear zone around the disc paper. A total of eight bacterial isolates showed the greatest percentage of synergism, namely ≥ 80% so that the eight rhizosphere bacterial isolates could be used as materials for mixed culture.

Indirect reduction of Ralstonia solanacearum via pathogen helper inhibition

The rhizosphere microbiome forms a first line of defense against soilborne pathogens. To date, most microbiome enhancement strategies have relied on bioaugmentation with antagonistic microorganisms that directly inhibit pathogens. Previous studies have shown that some root-associated bacteria are able to facilitate pathogen growth. We therefore hypothesized that inhibiting such pathogen helpers may help reduce pathogen densities. We examined tripartite interactions between a model pathogen, Ralstonia solanacearum, two model helper strains and a collection of 46 bacterial isolates recovered from the tomato rhizosphere. This system allowed us to examine the importance of direct (effects of rhizobacteria on pathogen growth) and indirect (effects of rhizobacteria on helper growth) pathways affecting pathogen growth. We found that the interaction between rhizosphere isolates and the helper strains was the major determinant of pathogen suppression both in vitro and in vivo. We therefore propose that controlling microbiome composition to prevent the growth of pathogen helpers may become part of sustainable strategies for pathogen control.

Diversity of culturable bacteria endowed with antifungal metabolites biosynthetic characteristics associated with tea rhizosphere soil of Assam, India

BackgroundRhizosphere soil is a crucial niche for the diverse beneficial microbial communities in plant-microbe interactions. This study explores the antagonistic potential and diversity of the rhizosphere soil bacteria from commercial tea estates of Assam, India which comes under the Indo-Burma mega-biodiversity hotspot. Rhizosphere soil samples were collected from six different tea estates to isolate the bacteria. The bacterial isolates were subjected to evaluate for the antagonistic activity against fungal pathogens. The potential isolates were investigated for chitinase production and the presence of chitinase gene. The bacterial genetic diversity was studied by Amplified Ribosomal DNA Restriction Analysis (ARDRA) and BOX-PCR fingerprinting.ResultsA total of 217 rhizobacteria were isolated from tea rhizosphere soil, out of which 50 isolates exhibited the potential antagonistic activity against fungal pathogens. Among them, 12 isolates showed extracellular chitinase activity and the presence of chitinase genes. The chitinase genes were sequenced and the analysis of the sequences was performed by using PDB protein databank at the amino acid level. It showed the presence of ChiA and ChiA74 gene in the 6 most potent isolates which are involved in the hydrolysis of chitin. These isolates also exhibited antagonistic activity against all tested fungal pathogens. The diversity of 50 antagonistic bacterial isolates were analyzed through ARDRA and BOX-PCR fingerprinting. Diversity analysis and molecular identification of the rhizosphere isolates revealed that these antagonistic isolates predominantly belonged to the genus Bacillus followed by Enterobacter, Serratia, Lysinibacillus, Pseudomonas, and Burkholderia.ConclusionThe present study establishes that rhizobacteria isolated from the poorly explored tea rhizosphere soil could be a rich reservoir for the investigation of potential antagonistic bacterial candidates for sustainable agricultural and industrial applications.

Isolation and Biochemical Characterization of Indole-3-Acetic Acid (IAA) Produced in Pseudomonas Sp. Isolated from Rhizospheric Soil

A phytohormone is a molecule that controls the development of plants. Auxin and cytokines, which may be acquired as synthetic compounds or produced by microorganisms, which promote plant growth, are employed to enhance crop yield. Indole-3-Acetic Acid (IAA) is a key phytohormone that controls a number of physiological processes in plants. Indole-3-acetic acid (IAA), the most prevalent endogenous auxin, is involved in stem elongation and root formation. Auxin levels are usually higher in the rhizosphere. The possibility of rhizosphere bacteria to encourage direct plant development has been recognised as a crucial component of auxin (IAA) production. They promote the growth of lateral roots, which increases the surface area available for nutrition absorption and enhances nutrient and water absorption from the soil. The objective of this research is to isolate, characterise, and identify bacteria that produce indole acetic acid in rhizospheric soil. Bacterial colonies were isolated using the serial dillution technique on nutrient agar medium from rhizospheric soil samples of a rice crop. Five rhizospheric bacterial isolates (RIPB-1 to RIPB-30) were identified as effective Indole acetic acid makers after qualitative screening. The quantity of Indole acetic acid produced by five bacterial strains was tested for up to 120 hours. The amount of Indole acetic acid they could generate ranged from 1 to 11.2 g/ml. The bacterial strain RIPB-20 (11.2 g/ml) generated the highest Indole acetic acid after 72 hours of incubation, followed by RIPB-14. Based on morphological, physiological, and biochemical features, the bacterial isolate RIPB-20 was tentatively identified as Bacillus sp. Finally, the finding shows that the bacteria, which have capacity to produce Indole acetic acid, are good biofertilizer inoculants for growth of plant.

Periphytic biofilm and rice rhizosphere phosphate-solubilizing bacteria and fungi: A possible use for activating occluded P in periphytic biofilms in paddy fields

Periphytic biofilm is a complex mixture of algae, cyanobacteria, heterotrophic microbes, and detritus that is attached to submerged surfaces in most aquatic ecosystems. They have been shown to assimilate and store bio-available phosphorus (P) in paddy fields. However, it is necessary to make the occluded P available to the rice plant in the final stage of the plant growth. It has been reported that phosphate-solubilizing bacteria and fungi have a role in activating the occluded P in the periphytic biofilms. However, the ability of the bacteria and fungi isolated from the periphytic biofilms to solubilize sparingly soluble phosphates has not been reported. The aim of this study was to investigate the ability of bacterial and fungal isolates isolated from periphytic biofilms and rice rhizosphere soil, as an origin of bacteria and fungi present in periphytic biofilms, to dissolve different sparingly soluble phosphate sources as single and in combination. In addition, effective phosphate-solubilizing bacterial and fungal isolates and the organic acids produced by these microbes were also identified. The isolated bacterial and fungal isolates had different ability to solubilize various P sources. The order of P dissolution from different P sources by bacterial and fungal isolates was as follows: Ca3PO4 ˃ Ca5(PO4)3(OH) ˃ mixed medium (a combination of 7 different P sources) ˃ Ca5(PO4)3Cl ̴ C6H17NaO24P6 ˃ Ca5(PO4)3F ˃ AlPO4 ˃ FePO4. The type and amount of the organic acids produced by these isolates depended on the type of microbe (bacterial isolate or fungal isolate), used P source, microbial inoculation (single or consortium), and type of the microbe used in consortium (bacterium-bacterium, bacterium-fungus, and fungus-fungus). Based on this assay, it was found that the bacterial and fungal consortiums, due to diversity in the production of different organic acids, showed a better ability to dissolve different forms of P. Based on the sequence of 16S rRNA gene and ITS region, the effective rhizosphere isolates of 8BR15, 8BR17, 2FR3, and 2FR18 and the effective periphytic biofilm isolates of 6BP11, 13BP25, 8FP12, and 6FP9 showed the most similar to Burkholderia vietnamiensis, Arthrobacter luteolus, Talaromyces minioluteus and Talaromyces pinophilus, and Acinetobacter calcoaceticus, Bacillus cereus, Talaromyces stipitatus and Talaromyces minioluteus, respectively. According to these results, periphytic biofilms and rice rhizosphere soil can be as a potential repository for isolating bacteria and fungi effective in solubilizing various P source. In general, the results suggest that the effective phosphate-solubilizing microorganisms have the potential to be used as microbial inoculants to release the bio-available P assimilated and stored in periphytic biofilms for sustainable rice cultivation in paddy lands.

The carbon source-dependent pattern of antimicrobial activity and gene expression in Pseudomonas donghuensis P482

Pseudomonas donghuensis P482 is a tomato rhizosphere isolate with the ability to inhibit growth of bacterial and fungal plant pathogens. Herein, we analysed the impact of the carbon source on the antibacterial activity of P482 and expression of the selected genes of three genomic regions in the P482 genome. These regions are involved in the synthesis of pyoverdine, 7-hydroxytropolone (7-HT) and an unknown compound (“cluster 17”) and are responsible for the antimicrobial activity of P482. We showed that the P482 mutants, defective in these regions, show variations and contrasting patterns of growth inhibition of the target pathogen under given nutritional conditions (with glucose or glycerol as a carbon source). We also selected and validated the reference genes for gene expression studies in P. donghuensis P482. Amongst ten candidate genes, we found gyrB, rpoD and mrdA the most stably expressed. Using selected reference genes in RT-qPCR, we assessed the expression of the genes of interest under minimal medium conditions with glucose or glycerol as carbon sources. Glycerol was shown to negatively affect the expression of genes necessary for 7-HT synthesis. The significance of this finding in the light of the role of nutrient (carbon) availability in biological plant protection is discussed.

Potential of isolated bacteria biostimulant from soil roots on white turmeric plants (Curcuma zedoaria)

The abundance of microbes around the roots of plants is an interesting thing where there is an interaction between plants and surrounding microbes. The purpose of this study was to obtain rhizosphere isolates from the soil of white turmeric roots, to determine the potential activity of rhizosphere bacteria from white turmeric as a biostimulating agent and biofertilizer agent that can help plant growth. The research method used was screening for potential growth hormone-producing bacteria (biostimulants), nitrogen fixation ability, enzyme production (protease, amylase, catalase) and biocontrol and bacterial colony PCR. The results showed that twelve rhizosphere bacteria isolates from white turmeric were isolated. Rhizosphere bacteria have the potential as a biostimulant agent, multipotential agent (biofertilizer agent, biodegradation agent and biocontrol agent) which is useful for helping plant growth, especially white turmeric plants. The twelve bacteria that had PCR amplification of the 16 S rRNA gene were performed, the results showed that the DNA bands could be continued for further identification. The results of the study by utilizing the potential of rhizosphere bacteria which have commercial value to be promoted into a safe and multi-functional biostimulant product based on superior isolates to support plant growth, especially white turmeric plants.

The measurement of indole acetic acid from rhizosphere bacteria

In Indonesia, synthetic chemical fertilizers are generally used to spur plant growth. The use of synthetic chemical fertilizers is known to reduce soil quality, causing resistance to pests and plant diseases. One of the natural potencies that can be used as growth promoters is Indole Acetic Acid (IAA) producing bacteria. The objective of this study was to measure the levels of Indole Acetic Acid (IAA) from the rhizosphere bacterial isolate of green beans which is thought to be able to produce Indole Acetic Acid (IAA). The method used was a descriptive approach, including the isolation of green bean rhizosphere bacteria, measurement of Indole Acetic Acid (IAA) levels in bacterial isolate, and data analysis. Green bean rhizosphere bacterial isolate produced Indole Acetic Acid (IAA) with an indication of a color change after the addition of the Salkowski reagent, and quantitatively the results of calculations in the standard curve equation for Indole Acetic Acid (IAA) obtained a value of Indole Acetic Acid (IAA) levels was 50.91 ppm.Keywords: Indole acetic acid, rhizosphere, bacteria

Genomic and Metabolomic Investigation of a Rhizosphere Isolate Streptomyces netropsis WLXQSS-4 Associated with a Traditional Chinese Medicine.

Rhizosphere microorganisms play important ecological roles in promoting herb growth and producing abundant secondary metabolites. Studies on the rhizosphere microbes of traditional Chinese medicines (TCMs) are limited, especially on the genomic and metabolic levels. In this study, we reported the isolation and characterization of a Steptomyces netropsis WLXQSS-4 strain from the rhizospheric soil of Clematis manshurica Rupr. Genomic sequencing revealed an impressive total of 40 predicted biosynthetic gene clusters (BGCs), whereas metabolomic profiling revealed 13 secondary metabolites under current laboratory conditions. Particularly, medium screening activated the production of alloaureothin, whereas brominated and chlorinated pimprinine derivatives were identified through precursor-directed feeding. Moreover, antiproliferative activities against Hela and A549 cancer cell lines were observed for five compounds, of which two also elicited potent growth inhibition in Enterococcus faecalis and Staphylococcus aureus, respectively. Our results demonstrated the robust secondary metabolism of S. netropsis WLXQSS-4, which may serve as a biocontrol agent upon further investigation.