The Study and Development of Endophytic Bacteria for Enhancing Organic Rice Growth

Biological functions of endophytic bacteria in Robinia pseudoacacia 'Hongsen'

Introduction

Endophytes and their host plants have co-evolved for a very long time. This relationship has led to the general recognition of endophytes as a particular class of microbial resources. R. pseudoacacia 'Hongsen' is drought- and barren-resistant species that can be grown in both the north and south of China, efficiently addresses the ecological issues caused by China's 'southern eucalyptus and northern poplar. Up to date, cultured-dependent studies are available for the R. pseudoacacia nitrogen-fixing and other endophytes. Therefore, the present research studied the R. pseudoacacia 'Hongsen,' microbiome in detail by high-throughput sequencing and culture dependant.

Methods

This study examined microbial species and functional diversity in Robinia pseudoacacia 'Hongsen' using culture-dependent (isolation) and culture-independent techniques.

Results

A total of 210 isolates were isolated from R. pseudoacacia 'Hongsen.' These isolates were clustered into 16 groups by the In Situ PCR (IS-PCR) fingerprinting patterns. 16S rRNA gene sequence analysis of the representative strain of each group revealed that these groups belonged to 16 species of 8 genera, demonstrating the diversity of endophytes in R. pseudoacacia 'Hongsen'. 'Bacillus is the most prevalent genus among all the endophytic bacteria. High-throughput sequencing of endophytic bacteria from R. pseudoacacia 'Hongsen' of the plant and the rhizosphere soil bacteria showed that the bacterial populations of soil near the root, leaf, and rhizosphere differed significantly. The microbial abundance decreased in the endophytes as compared to the rhizosphere. We observed a similar community structure of roots and leaves. With and without root nodules, Mesorhizobium sp. was significantly different in R. pseudoacacia 'Hongsen' plant.

Discussion

It was predicted that R. pseudoacacia 'Hongsen' plant endophytic bacteria would play a significant role in the metabolic process, such as carbohydrate metabolism, amino acid metabolism, membrane transport, and energy metabolism.

Plant-endophyte mediated improvement in physiological and bio-protective abilities of marigold (Tagetes patula)

Endophytic bacteria improve the growth, physiology, and metabolite profile of plants. They are known as potential biocontrol agents of soil-borne diseases. This study evaluated the effects of endophytic bacterial strains on growth, vase life, biochemical attributes, and antioxidant and nematicidal activities of French marigold (Tagetes patula). French marigold seeds were sole and consortium inoculated with three promising endophytic bacterial strains, Burkholderia phytofirmans (PsJN), Enterobacter sp. (MN17), and Bacillus sp. (MN54). The vase life of French marigold was promoted by 66.6% in the individual application of PsJN and 100% in plants treated with consortium compared to the uninoculated control. The shoot and root fresh weights were also increased by 65.9 and 68.7%, with the combined application of all three strains. The total phenolics, flavonoid, and protein contents were higher in consortium treatment with an increase of up to 38.0, 55.9, and 65.9%, respectively, compared to the uninoculated control. Furthermore, combined application of endophytic bacterial strains promoted DPPH radical scavenging, mortality of plant-parasitic nematodes, and ferric reducing antioxidant power activities with increase of up to 278.0, 103.8, and 178.0%, respectively, compared to uninoculated control. An increase in antioxidant activities of ascorbate peroxidase (APX), catalase (CAT), glutathione peroxidase (GPX), and superoxide dismutase (SOD) were observed up to 77.3, 86.0, 91.6, and 102.9%, respectively by combined application of endophytic bacterial strains. So, given the economic importance of floriculture crops, endophytic bacterial isolates studied here have shown a great potential for improving the productivity of cultivated ornamental French marigold.

Prospecting the significance of methane-utilizing bacteria in agriculture

Microorganisms act as both the source and sink of methane, a potent greenhouse gas, thus making a significant contribution to the environment as an important driver of climate change. The rhizosphere and phyllosphere of plants growing in natural (mangroves) and artificial wetlands (flooded agricultural ecosystems) harbor methane-utilizing bacteria that oxidize methane at the source and reduce its net flux. For several decades, microorganisms have been used as biofertilizers to promote plant growth. However, now their role in reducing net methane flux, especially from flooded agricultural ecosystems is gaining momentum globally. Research in this context has mainly focused on taxonomic aspects related to methanotrophy among diverse bacterial genera, and environmental factors that govern methane utilization in natural and artificial wetland ecosystems. In the last few decades, concerted efforts have been made to develop multifunctional microbial inoculants that can oxidize methane and alleviate greenhouse gas emissions, as well as promote plant growth. In this context, combinations of taxonomic groups commonly found in rice paddies and those used as biofertilizers are being explored. This review deals with methanotrophy among diverse bacterial domains, factors influencing methane-utilizing ability, and explores the potential of novel methane-utilizing microbial consortia with plant growth-promoting traits in flooded ecosystems.

Characterization of Endophytic-rhizobacteria from Areca Nut Rhizosphere to Dissolve Phosphates, Nitrogen Fixation of IAA Hormone Synthesis

BACKGROUND AND OBJECTIVE

The ability of rhizobacteria to dissolve phosphate, fix nitrogen and synthesize growth hormones has a direct or indirect effect on increasing the plant growth including seed growth. The rhizobacteria which are inoculated in seeds through biopriming are proven to increase seed growth. The study aims to obtain the potential indigenous rhizobacteria from areca nut plant rhizosphere on marginal soil of Southeast Sulawesi.

MATERIALS AND METHODS

Research was arranged in a completely randomized design (CRD) consisting of 10 isolates. The isolates were evaluated their ability to solubilize phosphate, fix nitrogen and synthesize IAA growth hormone. Also evaluated the effect of these isolates in increasing the root length of rice seedlings. Before tested, rice seeds were treated with rhizobacterium isolates of endo-rhizobacteria and germinated using standard germination procedures. Root length was observed on the 7th day after planting. At the same time all isolates were evaluated for their ability to solubilize phosphate, fix N and synthesize IAA.

RESULTS

The results showed that seed treatment using endo-rhizobacteria significantly increased the root length of treated rice seeds (percentage increase compared to untreated seeds at root length up to 140%). All rhizobacteria isolates tested were able to solubilize phosphate, fix N and synthesize IAA. Although all of the rhizobacteria synthesized IAA, growth promoting effects of the rhizobacteria may not only be due to the synthesized growth regulator. Other factors may have involved in the positive effects of the endo-rhizobacteria on rice seed germination.

CONCLUSION

The endophytic and rhizobacterial dominant from the areca nut rhizosphere are the Pseudomonas spp. and the Bacillus spp. and have ability to solubilize phosphate, fix nitrogen and synthesize IAA and also could increase rice seed growth.

Isolation and prospection of diazotrophic rhizobacteria associated with sugarcane under organic management

Microorganisms associated with organic management are essential in nutrient transformation and release for plant use. The present study aimed to isolate, identify and characterize plant growth promoting diazotrophic rhizobacteria associated with sugarcane under organic management. Rhizospheres of organic sugarcane varieties IAC 911099 and CTC4 were sampled and inoculated onto nitrogen free NFb and Burk media. The isolated microorganisms were screened in vitro concerning their ability to produce plant growth promoting factors. Eighty-one bacteria were isolated; 45.6% were positive for the nifH gene and produced at least one of the evaluated plant growth promotion factors. The production of indole-3-acetic acid was observed in 46% of the isolates, while phosphate solubilization was observed in 86.5%. No isolates were hydrogen cyanide producers, while 81% were ammonia producers, 19% produced cellulases and 2.7%, chitinases. Microorganisms belonging to the Burkholderia genus were able to inhibit Fusarium moniliforme growth in vitro. Plant growth promoting microorganisms associated with organic sugarcane, especially belonging to Burkholderia, Sphingobium, Rhizobium and Enterobacter genera, can be environmentally friendly alternatives to improve sugarcane production.

Molecular characterization and identification of plant growth promoting endophytic bacteria isolated from the root nodules of pea (Pisum sativum L.)

Root nodule accommodates various non-nodulating bacteria at varying densities. Present study was planned to identify and characterize the non-nodulating bacteria from the pea plant. Ten fast growing bacteria were isolated from the root nodules of cultivated pea plants. These bacterial isolates were unable to nodulate pea plants in nodulation assay, which indicate the non-rhizobial nature of these bacteria. Bacterial isolates were tested in vitro for plant growth promoting properties including indole acetic acid (IAA) production, nitrogen fixation, phosphate solubilization, root colonization and biofilm formation. Six isolates were able to produce IAA at varying level from 0.86 to 16.16 μg ml(-1), with the isolate MSP9 being most efficient. Only two isolates, MSP2 and MSP10, were able to fix nitrogen. All isolates were able to solubilize inorganic phosphorus ranging from 5.57 to 11.73 μg ml(-1), except MSP4. Bacterial isolates showed considerably better potential for colonization on pea roots. Isolates MSP9 and MSP10 were most efficient in biofilm formation on polyvinyl chloride, which indicated their potential to withstand various biotic and abiotic stresses, whereas the remaining isolates showed a very poor biofilm formation ability. The most efficient plant growth promoting agents, MSP9 and MSP10, were phylogenetically identified by 16S rRNA gene sequence analysis as Ochrobactrum and Enterobacter, respectively, with 99% similarity. It is suggested the potential endophytic bacterial strains, Ochrobactrum sp. MSP9 and Enterobacter sp. MSP10, can be used as biofertilizers for various legume and non-legume crops after studying their interaction with the host crop and field evaluation.