Bioprospecting beneficial endophytic bacterial communities associated with Rosmarinus officinalis for sustaining plant health and productivity

Novel Bacillus and Prestia isolates from Dwarf century plant enhance crop yield and salinity tolerance

Soil salinity is a major environmental stressor impacting global food production. Staple crops like wheat experience significant yield losses in saline environments. Bioprospecting for beneficial microbes associated with stress-resistant plants offers a promising strategy for sustainable agriculture. We isolated two novel endophytic bacteria, Bacillus cereus (ADJ1) and Priestia aryabhattai (ADJ6), from Agave desmettiana Jacobi. Both strains displayed potent plant growth-promoting (PGP) traits, such as producing high amounts of indole-3-acetic acid (9.46, 10.00 µgml-1), ammonia (64.67, 108.97 µmol ml-1), zinc solubilization (Index of 3.33, 4.22, respectively), ACC deaminase production and biofilm formation. ADJ6 additionally showed inorganic phosphate solubilization (PSI of 2.77), atmospheric nitrogen fixation, and hydrogen cyanide production. Wheat seeds primed with these endophytes exhibited enhanced germination, improved growth profiles, and significantly increased yields in field trials. Notably, both ADJ1 and ADJ6 tolerated high salinity (up to 1.03 M) and significantly improved wheat germination and seedling growth under saline stress, acting both independently and synergistically. This study reveals promising stress-tolerance traits within endophytic bacteria from A. desmettiana. Exploiting such under-explored plant microbiomes offers a sustainable approach to developing salt-tolerant crops, mitigating the impact of climate change-induced salinization on global food security.

Assessment of Plant Growth Promotion Potential of Endophytic Bacterium B. subtilis KU21 Isolated from Rosmarinus officinalis

The current study aimed to evaluate the plant growth-promoting (PGP) potential of endophytic strain Bacillus subtilis KU21 isolated from the roots of Rosmarinus officinalis. The strain exhibited multiple traits of plant growth promotion viz., phosphate (P) solubilization, nitrogen fixation, indole-3-acetic acid (IAA), siderophore, hydrogen cyanide (HCN), lytic enzymes production, and 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. The isolate also exhibited antagonistic activity against phytopathogenic fungi, i.e., Fusarium oxysporum, Fusarium graminiarum, and Rhizoctonia solani. The P-solubilization activity of B. subtilis KU21 was further elucidated via detection of glucose dehydrogenase (gdh) gene involved in the production of gluconic acid which is responsible for P-solubilization. Further, B. subtilis KU21 was evaluated for in vivo growth promotion studies of tomato (test crop) under net house conditions. A remarkable increase in seed germination, plant growth parameters, nutrient acquisition, and soil quality parameters (NPK) was observed in B. subtilis KU21-treated plants over untreated control. Hence, the proposed module could be recommended for sustainable tomato production in the Northwest Himalayan region without compromising soil health and fertility.

Agronomic strategies to enhance the early vigor and yield of maize. Part I: the role of seed applied biostimulant, hybrid and starter fertilization on rhizosphere bacteria profile and diversity

The sustainable intensification of maize-based systems may reduce greenhouse-gas emissions and the excessive use of non-renewable inputs. Considering the key role that the microbiological fertility has on crop growth and resilience, it is worth of interest studying the role of cropping system on the rhizosphere bacterial communities, that affect soil health and biological soil fertility. In this work we monitored and characterized the diversity and composition of native rhizosphere bacterial communities during the early growth phases of two maize genotypes of different early vigor, using a nitrogen (N)-phosphorus (P) starter fertilization and a biostimulant seed treatment, in a growth chamber experiment, by polymerase chain reaction-denaturing gradient gel electrophoresis of partial 16S rRNA gene and amplicon sequencing. Cluster analyses showed that the biostimulant treatment affected the rhizosphere bacterial microbiota of the ordinary hybrid more than that of the early vigor, both at plant emergence and at the 5-leaf stage. Moreover, the diversity indices calculated from the community profiles, revealed significant effects of NP fertilization on richness and the estimated effective number of species (H2) in both maize genotypes, while the biostimulant had a positive effect on plant growth promoting community of the ordinary hybrid, both at the plant emergence and at the fifth leaf stage. Our data showed that maize genotype was the major factor shaping rhizosphere bacterial community composition suggesting that the root system of the two maize hybrids recruited a different microbiota. Moreover, for the first time, we identified at the species and genus level the predominant native bacteria associated with two maize hybrids differing for vigor. These results pave the way for further studies to be performed on the effects of cropping system and specific crop practices, considering also the application of biostimulants, on beneficial rhizosphere microorganisms.

Characteristics of endophytic bacteria and active ingredients in the Eucommiae cortex from different origins

Objective

This study aimed to explore the differences between Eucommiae cortex (EC) endophytic bacteria from different origins and their effects on the active ingredients of EC.

Methods

A total of 10 samples of Eucommia ulmoides Oliv. (E. ulmoides) bark were collected from each of the following four regions, namely, Zunyi in Guizhou (GZ), Baokang in Hubei (HUB), Cili in Hunan (HUN), and Loyang in Shaanxi (SX). Subsequently, the contents of the main active ingredients of EC were determined by ultra-performance liquid chromatography (UPLC), and the endophytic bacteria of EC were detected by 16S rRNA sequencing. The relationship between the dominant endophytic bacteria and the active ingredients was investigated by correlation analysis.

Results

A total of 4,551 different operational taxonomic units (OTUs) were delineated in the four groups of samples, of which 585, 439, 957, and 684 genera were annotated from GZ, HUB, HUN, and SX, respectively. The richness and diversity of endophytic bacteria from different origins were ranked as HUN > SX > GZ or HUB. The analysis demonstrated that there was no significant correlation between the diversity and richness of endophytic bacteria in EC and its active ingredients. Nevertheless, notable variations in the community structures of endophytic bacteria were observed across different origins, and they had a considerable impact on certain active ingredients in EC. Comamonas and Cedecea were the dominant genera. Characteristic bacteria of different origins could be clearly distinguished. Simultaneous, significant correlations had been identified between some characteristic endophytic bacteria derived from different origins and active ingredients of EC. For example, Delftia, a characteristic bacterium from GZ, showed a significant positive correlation with pinoresinol diglucoside. Paenibacillus and Klebsiella, two characteristic bacteria from HUB, exhibited significant positive correlations with geniposidic acid. Thauera, a characteristic bacterium from HUN, demonstrated a significant positive correlation with geniposide. Brevundimonas, a characteristic bacterium from SX, displayed a significant positive correlation with pinoresinol diglucoside.

Conclusion

There was a complex correlation between EC endophytic bacteria and active ingredient content, while EC endophytic bacteria from different origins had significant differences at the genus level.

Bioprospecting Plant Growth Promoting Rhizobacteria for Enhancing the Biological Properties and Phytochemical Composition of Medicinally Important Crops

Traditionally, medicinal plants have long been used as a natural therapy. Plant-derived extracts or phytochemicals have been exploited as food additives and for curing many health-related ailments. The secondary metabolites produced by many plants have become an integral part of human health and have strengthened the value of plant extracts as herbal medicines. To fulfil the demand of health care systems, food and pharmaceutical industries, interest in the cultivation of precious medicinal plants to harvest bio-active compounds has increased considerably worldwide. To achieve maximum biomass and yield, growers generally apply chemical fertilizers which have detrimental impacts on the growth, development and phytoconstituents of such therapeutically important plants. Application of beneficial rhizosphere microbiota is an alternative strategy to enhance the production of valuable medicinal plants under both conventional and stressed conditions due to its low cost, environmentally friendly behaviour and non-destructive impact on fertility of soil, plants and human health. The microbiological approach improves plant growth by various direct and indirect mechanisms involving the abatement of various abiotic stresses. Given the negative impacts of fertilizers and multiple benefits of microbiological resources, the role of plant growth promoting rhizobacteria (PGPR) in the production of biomass and their impact on the quality of bio-active compounds (phytochemicals) and mitigation of abiotic stress to herbal plants have been described in this review. The PGPR based enhancement in the herbal products has potential for use as a low cost phytomedicine which can be used to improve health care systems.