Search

Rhizobacteria and endophytic bacteria are popular for its abilities in influencing plant growth and development. The strategy employed these bacteria as biofertilizer for planting is believed to bring several benefits such as low cost, eco-friendly, and feasible. One of the remarkable products for plant growth promoting provided by rhizobacteria and endophytic bacteria were the advantageous enzymes such as 1-aminocyclopropane-1-carboxylate deaminase, phosphatase, and cellulase. These biocatalysts then involve in several direct or indirect pathways of nutrient, growth factor, and/or defense factor synthesizes. From five different essential leafy vegetables in Thailand, this study aimed to investigate the plant growth promoting potentials of endophytic bacteria and rhizobacteria isolated from root tissue and rhizosphere, respectively, via IAA quantitative and enzyme activity assays. The selected bacterial strains were further identified using 16S rRNA gene sequencing and observed their interaction with plant root using scanning electron microscope method. Our study, thus far, has isolated two bacterial strains of Bacillus subtilis MSE5 and Bacillus cereus AVR1, respectively, with multifunctional traits of potential on the plant growth. Importantly, these two strains of MSE5 and AVR1 had shown the capacity to advance root colonization. Therefore, MSE5 and AVR1 are recommended for further studies in developing eco-friendly biofertilizer. In addition, some novel cellulose-degrading bacterial strains with significant potential on hydrolysis capacity were also isolated that might be valuable for industrial applications. [ABSTRACT FROM AUTHOR]

Indole‐3‐acetic acid (IAA) synthesis is a major property of rhizosphere bacteria. The IAA‐producing ability of rhizobacteria may be influenced by agricultural management. We therefore evaluated the IAA‐producing potential of rhizobacteria isolated during organic rice farming (ORF) and conventional rice farming (CRF) in Thung Kula Rong Hai areas of Thailand. The results indicated that ORF gave a significantly higher percentage of IAA producers (95·8%) than CRF (69·9%). The average IAA values of the ORF isolates were around two times higher than those of the CRF isolates both in the absence (12·8 and 5·8 μg IAA ml−1, respectively) and presence of L‐tryptophan (L‐Trp) (35·2 and 17·2 μg IAA ml−1, respectively). The 16S rRNA gene sequence analysis indicated that the 23 selected isolates belonged to 8 different genera—Sinomonas sp., Micrococcus sp., Microbacterium sp., Fictibacillus sp., Bacillus sp., Burkholderia sp., Leclercia sp. and Enterobacter sp. Interestingly, only three ORF isolates, i.e. ORF15‐20 (Micrococcus sp.), ORF15‐21 (Sinomonas sp.) and ORF15‐23 (Sinomonas sp.), exhibited high IAA production ability without L‐Trp (128·5, 160·8 and 174·7 μg IAA ml−1, respectively). Meanwhile, a slight decrease in IAA production with L‐Trp was noticed, suggesting that the L‐Trp was not used for the IAA synthesis of these isolates. Biopriming with rhizobacterial isolates significantly enhanced the rate of germination of KDML 105 rice seeds compared to the control. [ABSTRACT FROM AUTHOR]

This research aimed to study lead accumulation and the type of rhizobacteria associated with maize grown in the lead-contaminated area of Klity village, Kanchanaburi Province, Thailand. The results showed that lead concentrations in different tissues were roots > shoots > grains. The highest lead concentration was recorded on day 120 (54.31, 110.67 and 4.79 mg⋅kg-1 in shoots, roots, and grains, respectively). The lowest lead concentration was recorded on day 40 (27.80 and 71.90 mg⋅kg-1 in shoots and roots, respectively) with no detectable lead in the grain. Results indicate that lead concentration in grains on day 120 of the experiment exceeded the European Union Standard (0.2 mg⋅kg-1), which might not be safe for human consumption but did not exceed the standard as animal feed (30 mg⋅kg-1). This research found four species of bacteria that could grow in soil at a lead concentration exceeding 3,600 mg⋅kg-1, namely Bacillus sp. B26, Pseudomonas sp. S169, Pseudomonas putida strain RW10S2, and Bacillus subtilis strain SM10. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the potential of rhizospheric bacteria in promoting the growth and Pb accumulation by the woody plant Eucalyptus camaldulensis under hydroponic conditions was investigated for the first time. Three Pb-tolerant bacteria were isolated from the rhizosphere of E. camaldulensis grown in Pb-contaminated soils in the Bo Ngam Pb mine, Thailand. Based on analysis of partial 16S rRNA gene sequence, the three isolates were identified as Microbacterium paraoxydans BN-2, Ochrobactrum intermedium BN-3, and Bacillus fusiformis BN-4. Among these strains, O. intermedium BN-3 showed the highest tolerance to not only Pb but also Cd and Zn. After growth in the presence of Pb, the membranes of O. intermedium BN-3 cells exhibited an increase in unsaturated fatty acid levels but a decrease in fluidity. In hydroponic studies, inoculation of O. intermedium BN-3 significantly increased the biomass and Pb accumulation by E. camaldulensis compared to the uninoculated control. The results suggested the role of the natural rhizospheric bacteria localized to the root surface of E. camaldulensis in promoting Pb accumulation and plant growth. Our results indicate that O. intermedium BN-3 and other indigenous rhizospheric bacteria have the potential to improve the efficiency of phytoremediation of Pb-contaminated sites. [Copyright &y& Elsevier]

Abstract: Plant Growth Promoting Rhizobacteria (PGPR) play an important role in agricultural systems, especially as biofertilizer. The objectives of this study were to select effective PGPR for forage corn (Zea mays L.) cultivation and to investigate the effect of their inoculation on indigenous microbial community structure. The putative genera Pseudomonas sp. SUT 19 and Brevibacillus sp. SUT 47 were selected for determining their efficiency in forage corn growth promotion in both pot and field experiments. In field experiment, PGPR amended with compost gave the highest results in comparison to all treatments. Denaturing Gradient Gel Electrophoresis (DGGE) fingerprints of 16S rDNA amplified from total community DNA from rhizosphere confirmed that our isolates existed in rhizosphere throughout this study. The microbial community structures were slightly different among all treatments whereas major changes depended on stages of plant growth. In order to evaluate whether PGPR have effect on species diversity in rhizosphere, DNA sequencing of excised DGGE bands was done. The results demonstrated that dominant species in microbial community structure were not interfered by PGPR, but strongly influenced by plant development. [ABSTRACT FROM AUTHOR]

Simple Summary: The major aroma compound (2-acetyl-1-pyrroline) of the world-famous Thai jasmine rice, variety KDML105, has declined due to high soil salinity and agrochemical input. In this work, the rhizobacteria from rice were investigated for the aroma compound's production, as well as their potential for increasing the compound content in Thai jasmine rice seedlings under saline conditions. Our results provide evidence that the addition of aroma compound-producing rhizobacteria increases the aroma content in the rice seedlings under salt stress. Sinomonas sp. strain ORF15-23 which colonize the rice roots, is a promising rhizobacteria in promoting the aroma level of the Thai jasmine rice grown under salt stress and could be developed as a bioinoculant for Thai jasmine rice cultivation in a salt-affected area. Thai jasmine rice (Oryza sativa L. KDML105), particularly from inland salt-affected areas in Thailand, is both domestically and globally valued for its unique aroma and high grain quality. The key aroma compound, 2-acetyl-1-pyrroline (2AP), has undergone a gradual degradation due to anthropogenic soil salinization driven by excessive chemical input and climate change. Here, we propose a cheaper and an ecofriendly solution to improve the 2AP levels, based on the application of plant growth-promoting rhizobacteria (PGPR). In the present study, nine PGPR isolates from rice rhizosphere were investigated for the 2AP production in liquid culture and the promotion potential for 2AP content in KDML105 rice seedlings under four NaCl concentrations (0, 50, 100, and 150 mM NaCl). The inoculation of 2AP-producing rhizobacteria resulted in an increase in 2AP content in rice seedling leaves with the maximum enhancement from Sinomonas sp. ORF15-23 at 50 mM NaCl (19.6 µg·kg−1), corresponding to a 90.2% increase as compared to the control. Scanning electron microscopy confirmed the colonization of Sinomonas sp. ORF15-23 in the roots of salinity-stressed KDML105 seedlings. Our results provide evidence that Sinomonas sp. ORF15-23 could be a promising PGPR isolate in promoting aroma level of Thai jasmine rice KDML105 under salt stress. [ABSTRACT FROM AUTHOR]

Nowadays, oil crops are very attractive both for human consumption and biodiesel production; however, little is known about their commensal rhizosphere microbes. In this study, rhizosphere samples were collected from physic nut and sacha inchi plants grown in several areas of Thailand. Rhizobacteria, cultivable in nitrogen-free media, and arbuscular mycorrhizal (AM) fungi were isolated and examined for abundance, diversity, and plant growth-promoting activities (indole-3-acetic acid (IAA) and siderophore production, nitrogen fixation, and phosphate solubilization). Results showed that only the AM spore amount was affected by plant species and soil features. Considering rhizobacterial diversity, two classes—Alphaproteobacteria (Ensifer sp. and Agrobacterium sp.) and Gammaproteobacteria (Raoultella sp. and Pseudomonas spp.)—were identified in physic nut rhizosphere, and three classes; Actinobacteria (Microbacterium sp.), Betaproteobacteria (Burkholderia sp.) and Gammaproteobacteria (Pantoea sp.) were identified in the sacha inchi rhizosphere. Considering AM fungal diversity, four genera were identified (Acaulospora, Claroideoglomus, Glomus, and Funneliformis) in sacha inchi rhizospheres and two genera (Acaulospora and Glomus) in physic nut rhizospheres. The rhizobacteria with the highest IAA production and AM spores with the highest root-colonizing ability were identified, and the best ones (Ensifer sp. CM1-RB003 and Acaulospora sp. CM2-AMA3 for physic nut, and Pantoea sp. CR1-RB056 and Funneliformis sp. CR2-AMF1 for sacha inchi) were evaluated in pot experiments alone and in a consortium in comparison with a non-inoculated control. The microbial treatments increased the length and the diameter of stems and the chlorophyll content in both the crops. CM1-RB003 and CR1-RB056 also increased the number of leaves in sacha inchi. Interestingly, in physic nut, the consortium increased AM fungal root colonization and the numbers of offspring AM spores in comparison with those observed in sacha inchi. Our findings proved that AM fungal abundance and diversity likely rely on plant species and soil features. In addition, pot experiments showed that rhizosphere microorganisms were the key players in the development and growth of physic nut and sacha inchi. [ABSTRACT FROM AUTHOR]

Maize fields near Mae Tao Creek in Pha Te Village, Tak Province, Thailand are contaminated with Zn, Cd, and Pb. This research studied the interaction between levels of the metals contaminating the soil and maize development, heavy metal accumulation in the seeds, and the soil bacterial community structure. Our field experiment was carried out in five plots with metal contents that gradually decreased from a high level near the creek to a lower level further into the land: Zn 380-4883 mg kg -1 , Cd 6-85 mg kg -1 , and Pb 34-154 mg kg -1 . Cultivation and isolation on nutrient agar (NA) was utilized to study the culturable bacterial community, and polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) was utilized for the unculturable bacterial communities. All statistical analyses clearly indicated that rainfall and irrigation were the main factors affecting total Zn concentration and bioavailable Zn, Cd, and Pb in the field. The variation in the contents of the heavy metals was weakly correlated with the culturable bacterial community indices (Shannon-Wiener, evenness and richness), but the contents resulted in a difference in the overall diversity of the bacteria in the soil. The richness, numbers of culturable rhizobacteria, and maize growth stage significantly affected the amount of Zn and Cd that accumulated in the roots. In addition, maize accumulated a high level of Zn in the seeds, while the low contents of Cd and Pb in the seeds were below our limit of detection. The results obtained could be informative for the management of maize cultivation in the area.