An Enterobacter cloacae strain NG-33 that can solubilize phosphate and promote maize growth

Seed Endophytic Bacteria from Manilkara zapota L. and Their Influence as Rice Seed Priming Agents

In recent years, seed endophytes have gained significant attention due to their impact on the ecology, health, and productivity of host plants. Extensive research is being conducted to explore novel endophytic bacteria for sustainable crop improvement. Manilkara zapota L. P. Royen (Sapotaceae) is a highly stress-tolerant tree widely cultivated in tropical countries, yet its associated endophytes remain unexplored. In this study, nine bacterial isolates were obtained from M. zapota seeds, of which three (LA2, LA4, and NS1) were selected based on their IAA production capability which ranged from 2.3, 6.34, and 16.1 µg mL-1, respectively. Identification through 16S rRNA sequencing confirmed LA2 as Pseudomonas rhodesiae, LA4 as Bacillus cereus, and NS1 as Enterobacter cloacae. All isolates exhibited nitrogen-fixing ability, while NS1 uniquely solubilized potassium and phosphorus with KSI and PSI value as 2.9 and 2.3, respectively. Further, the efficacy of the bacterial isolates in promoting rice seedling growth was evaluated, and novel bioformulation was prepared from the consortia of LA2 + LA4, LA2 + NS1, LA4 + NS1, and LA2 + LA4 + NS1. All the isolates and bioformulations were tested as biopriming agents. Rice seedling growth experiments revealed a significant increase in germination percentage, root length, and shoot length following biopriming with individual isolates and consortia. Among treatments, the LA2 + LA4 combination exhibited the highest growth promotion, with a root length increase of 2.1-fold and shoot length increase of 2.3-fold as compared to control. Thus, our results highlighted that bioprospecting microbes from M. zapota seeds can help in nutrient management and seedling establishment.

Isolation of the inorganic phosphorus-solubilizing bacteria Lysinibacillus sphaericus and assessing its role in promoting rice growth

Soluble phosphorus scarcity severely limits plant growth and crop yield. In this study, a strain of inorganic phosphorus-solubilizing bacteria, Lysinibacillus sphaericus, was isolated from rice rhizosphere soil. The available phosphorus content in liquid inorganic phosphorus identification medium and in L. sphaericus-inoculated soil increased from 204.28 mg/L to 1124.68 mg/L and from 4.75 mg/kg to 7.04 mg/kg, respectively. The pH decreased significantly from 6.87 to 6.14. Incubation with L. sphaericus significantly increased malic and succinic acid content in the liquid inorganic phosphorus identification medium and increased acid phosphatase and alkaline phosphatase activity in the soil. Inoculation with L. sphaericus significantly increased rice growth, chlorophyll a/b content, and photosynthesis by increasing the soluble phosphorus content in the rice rhizosphere soil under phosphorus-deficient conditions. Further analysis revealed that L. sphaericus improved soil phosphorus release by decreasing soil pH and promoting acid phosphatase and alkaline phosphatase activity. This study supports the production of microbial fertilizers to improve rice yield in phosphorus-deficient conditions.

Tea seedlings growth promotion by widely distributed and stress-tolerant PGPR from the acidic soils of the Kangra valley

This is the first report of widespread and stress-tolerant PGPR from the tea rhizosphere of the Kangra valley. A total of 493 rhizobacteria were isolated from the major tea-growing regions of the Kangra valley. Molecular fingerprinting of 160 distinct morphotypes using ARDRA and ERIC techniques revealed intergenic and intragenic variability, resulting in the identification of 52 rRNA and 56 ERIC types belonging to 21 distantly related genera, identified by 16S rRNA gene sequencing. Bacillus constituted more than half of the genotypes, followed by Pseudomonas, Burkholderia, Lysinibacillus, Citrobacter, Enterobacter, and Paenibacillus. Bacillus altitudinis, B. cereus, B. megaterium, B. subtilis subsp. inaquosorum, B. methylotropicus, Pseudomonas frederiksbergensis, P. mohnii, and P. moreiii were found to be the most common in the tea rhizosphere across various locations. Quantitative assaying of 42 selected strains revealed significant variations in PGP activities ranging from 55-624 µg/ml for tri-calcium phosphate (TCP) solubilization, 4-3145 nM α-ketobutyrate h/mg/protein ACC-deaminase activity, 2-85 µg/ml IAA-like auxins production, and 2-83% siderophore production. Nine out of 42 PGPR also solubilized aluminium phosphate (Al-P) and iron phosphate (Fe-P). These efficient PGPR are suitable for application in tea soils, which are generally low in available phosphorus, a growth-limiting factor for tea cultivation. Five highly efficient PGPR also showed robust growth under different abiotic stresses under controlled conditions. Inoculum application of 5 efficient and abiotic stress tolerant PGPR showed a significant increment of 1.8-9.4%, 12-16.2%,18.1-30.3% and 21.4-39.2% in plant height, leaf number, fresh and dry weight of tea seedlings under the nursery conditions with 50% reduced NPK concentrations after one year of inoculations, respectively. These selected PGPR genotypes with multifarious PGP activities and natural ability to occur widely can be useful in developing plant microbial inoculants for improving tea productivity.

Plant growth-promoting effects of a novel Lelliottia sp. JS-SCA-14 and comparative genome analysis

Bacteria associated with plants play crucial roles in promoting plant growth and health by aiding in nutrient acquisition, including phosphorus. This study presents the isolation and genomic characterization of a potentially new bacterial strain, Lelliottia sp. JS-SCA-14, which exhibits significant plant growth-promoting effects through phosphorus solubilization. A comparative phylogenomic analysis of the complete genome of strain JS-SCA-14 and its closely related strains revealed a unique genomic profile, suggesting it could be a novel species. Genomic identity calculations indicated that JS-SCA-14 significantly deviates from strains belonging to closely related genera, such as Buttiauxella, Citrobacter, Enterobacter, Leclercia, and Lelliottia. A biochemical assay comparing JS-SCA-14 and a closely related strain, Lelliottia jeotgali PFL01T, showed differing patterns in carbon source utilization and enzyme activities. To assess the plant growth-promoting capabilities of strain JS-SCA-14, tests were conducted to evaluate its siderophore-producing and phosphate-solubilizing abilities. Seed germination assays demonstrated an improvement in germination, seedling length, and vigor compared to untreated controls. Notably, the phosphate-dissolving strain JS-SCA-14 led to a significant increase of 34.4% in fresh weight and 35.4% in dry weight of tomato plants compared to the negative control. These findings underscore the significant potential of strain JS-SCA-14 in solubilizing phosphate, thereby enhancing phosphorus availability in the rhizosphere and promoting plant growth and development. This study contributes to our understanding of plant-microbe interactions and suggests the potential application of strain JS-SCA-14 as a bioinoculant for sustainable agriculture and plant nutrient management strategies.

Shift in the soil rhizobacterial community for enhanced solubilization and bioavailability of phosphorus in the rhizosphere of Allium hookeri Thwaites, through bioaugmentation of phosphate-solubilizing bacteria

Allium hookeri is an indigenous perennial herb known for its therapeutic properties. It's grown in the eastern Himalayas and East Asia, where it is used as a flavoring agent in local cuisines. This research aims to enhance soil phosphorus mobilization and promote A. hookeri growth using a consortium of phosphate-solubilizing bacteria (PSB). The synergistic effect of a bacterial consortium containing multiple PSBs (Arthrobacter luteolus and several Klebsiella spp.) combined with tricalcium phosphate (TCP), was investigated to enhance the growth of A. hookeri plants, and its influence on modulating the rhizosphere microbiome was also assessed. The greenhouse experiment revealed that the bacterial consortium with tricalcium phosphate (BTCP) treatment enhanced the dry shoot weight by 70%. Proteobacteria dominated the rhizosphere's microbiome in all treatments. BTCP treatment enhanced the relative abundance of several beneficial genera such Bacillus, Mesorhizobium, Pseudomonas, Ensifer, Hyphomicrobium, Planctomyces, and Bradyrhizobium. The augmentation of bacterial consortium increased P in shoots (4.36 ± 0.63 mg/g) and in roots (2.34 ± 0.27 mg/g), which was more than 500% higher as compared to the uninoculated control. Canonical correspondence analysis (CCA) indicated significant correlations (p ≤ 0.05) between phosphorus content in the shoot, fresh weight, and dry weight, with higher relative abundances of Bacteroidetes, Cyanobacteria, and Fibrobacteres. Functional genes related to siderophore biosynthesis, ABC transporters, phosphatenate, and phosphinate metabolism exhibited positive modulation, indicating higher relative abundances associated with the BTCP treatment. The findings demonstrate the crucial contribution of the bacterial consortium in promoting plant development, improving soil nutrient levels, and influencing the rhizospheric microbiota, implying its significance in sustainable agriculture.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-04026-2.

Inhibitory effects of Bacillus vallismortis T27 against apple Valsa canker caused by Valsa mali

Apple Valsa canker caused by the pathogenic fungus Valsa mali, are one of the most destructive diseases of woody plants worldwide. One rhizosphere microbe strain, designated as T27 and subsequently identified as Bacillus vallismortis based on morphological and phylogenetic analyses, was studied as a potential biocontrol agent. Inoculation assay showed the B. vallismortis T27 suppressed the mycelial growth of V. mali with 81.33% antifungal effect on dual culture plates and caused hyphal deformities, wrinkles. The T27 fermentation broth significantly suppress the fungi's ability to acidify the surrounding environment. The addition of T27 cell-free supernatant (CFS) caused the pH of the fungal culture medium to increase from 3.60 to 5.10. B. vallismortis T27 showed the presence of Surfactin, IturinA and Bacilysin antimicrobial biosynthetic genes by the PCR assay. In addition, the B. vallismortis T27 was able to promote plant growth by producing siderophores and solubilizing phosphorus. The application of 2% fermentation broth of T27 resulted in a significant increase of 55.99% in the height of tomato plants and a 33.03% increase in the fresh weight of tomatoes. Under laboratory and field conditions, the B. vallismortis T27 exhibited strong antifungal activities on detached twigs and intact plants. The treatment of T27 resulted in a 35.9% reduction in lesion area on detached twigs. Furthermore, when applied to intact plants, T27 demonstrated a scar healing rate of 85.7%, surpassing the 77.8% observed in the treatment with tebuconazole. Comparative transcriptome analysis showed down-regulation of the genes associated with the fungal cell wall and cell membrane's synthesis and composition during V. mali treated with the B. vallismortis T27. In addition, gene transcription level analysis under treatment with B. vallismortis T27 revealed a significant increase in the expression levels of genes associated with diterpene biosynthesis, alanine, aspartic acid and glutamate metabolism, and plant hormone signaling in the apple, consistent with qRT-PCR and RNA-seq results. In this study, B. vallismortis T27 isolated from rhizosphere soil and identified as a novel biological control agent against apple Valsa canker. It exhibited effectively control over Valsa canker through multiple mechanisms, including disrupting the fungal cell membrane structure, altering the fungal growth environment, activating the plant MAPK pathway, and inducing upregulation of plant terpene biosynthetic genes. These findings highlight the potential of B. vallismortis T27 as a promising and multifaceted approach for managing apple Valsa canker.