Design and validation of cyanobacteria-rhizobacteria consortia for tomato seedlings growth promotion

Altitudinal variation in rhizosphere microbial communities of the endangered plant Lilium tsingtauense and the environmental factors driving this variation

The rhizosphere soil properties and microbial communities of Lilium tsingtauense, an endangered wild plant, have not been examined in previous studies. Here, we characterized spatial variation in soil properties and microbial communities in the rhizosphere of L. tsingtauense. We measured the abundance of L. tsingtauense at different altitudes and collected rhizosphere and bulk soils at three representative altitudes. The results showed that L. tsingtauense was more abundant, and the rhizosphere soil was richer in nitrogen, phosphorus, potassium, water content, and organic matter and more acidic at high altitudes than at lower altitudes. The diversity and richness of rhizosphere bacteria and fungi increased with altitude and were higher in rhizosphere soil than in bulk soil. In addition, ectomycorrhizal fungi, endophytic fungi, and nitrogen-fixing bacteria were more abundant, and plant-pathogenic fungi were less abundant at high altitudes. Co-occurrence network analysis identified four key phyla (Bacteroidota, Proteobacteria, Ascomycota, and Basidiomycota) in the microbial communities. We identified a series of microbial taxa (Acidobacteriales, Xanthobacteraceae, and Chaetomiaceae) and rhizosphere soil metabolites (phosphatidylcholine and phosphatidylserine) that are crucial for the survival of L. tsingtauense. Correlation analysis and random forest analysis showed that some environmental factors were closely related to the rhizosphere soil microbial community and played an important role in predicting the distribution and growth status of L. tsingtauense. In sum, the results of this study revealed altitudinal variation in the rhizosphere microbial communities of L. tsingtauense and the factors driving this variation. Our findings also have implications for habitat restoration and the conservation of this species.

IMPORTANCE

Our study highlighted the importance of the rhizosphere microbial community of the endangered plant L. tsingtauense. We found that soil pH plays an important role in the survival of L. tsingtauense. Our results demonstrated that a series of microbial taxa (Acidobacteriales, Xanthobacteraceae, Aspergillaceae, and Chaetomiaceae) and soil metabolites (phosphatidylcholine and phosphatidylserine) could be essential indicators for L. tsingtauense habitat. We also found that some environmental factors play an important role in shaping rhizosphere microbial community structure. Collectively, these results provided new insights into the altitudinal distribution of L. tsingtauense and highlight the importance of microbial communities in their growth.

The underground world of plant disease: Rhizosphere dysbiosis reduces above-ground plant resistance to bacterial leaf spot and alters plant transcriptome

Just as the human gut microbiome is colonized by a variety of microbes, so too is the rhizosphere of plants. An imbalance in this microbial community, known as dysbiosis, can have a negative impact on plant health. This study sought to explore the effect of rhizosphere dysbiosis on the health of tomato plants (Solanum lycopersicum L.), using them and the foliar bacterial spot pathogen Xanthomonas perforans as model organisms. The rhizospheres of 3-week-old tomato plants were treated with either streptomycin or water as a control, and then spray-inoculated with X. perforans after 24 h. Half of the plants that were treated with both streptomycin and X. perforans received soil microbiome transplants from uninfected plant donors 48 h after the streptomycin was applied. The plants treated with streptomycin showed a 26% increase in disease severity compared to those that did not receive the antibiotic. However, the plants that received the soil microbiome transplant exhibited an intermediate level of disease severity. The antibiotic-treated plants demonstrated a reduced abundance of rhizobacterial taxa such as Cyanobacteria from the genus Cylindrospermum. They also showed a down-regulation of genes related to plant primary and secondary metabolism, and an up-regulation of plant defence genes associated with induced systemic resistance. This study highlights the vital role that beneficial rhizosphere microbes play in disease resistance, even against foliar pathogens.

A Comprehensive Review of Microalgae and Cyanobacteria-Based Biostimulants for Agriculture Uses

Significant progress has been achieved in the use of biostimulants in sustainable agricultural practices. These new products can improve plant growth, nutrient uptake, crop yield and quality, stress adaptation and soil fertility, while reducing agriculture's environmental footprint. Although it is an emerging market, the biostimulant sector is very promising, hence the increasing attention of the scientific community and agro-industry stakeholders in finding new sources of plant biostimulants. Recently, pro- and eucaryotic microalgae have gained prominence and can be exploited as biostimulants due to their ability to produce high-value-added metabolites. Several works revealed the potential of microalgae- and cyanobacteria-based biostimulants (MCBs) as plant growth promoters and stress alleviators, as well as encouraging results pointing out that their use can address current and future agricultural challenges. In contrast to macroalgae biostimulants, the targeted applications of MBs in agriculture are still in their earlier stages and their commercial implementation is constrained by the lack of research and cost of production. The purpose of this paper is to provide a comprehensive overview on the use of this promising new category of plant biostimulants in agriculture and to highlight the current knowledge on their application prospects. Based on the prevailing state of the art, we aimed to roadmap MCB formulations from microalgae and cyanobacteria strain selection, algal biomass production, extraction techniques and application type to product commercialization and farmer and consumer acceptance. Moreover, we provide examples of successful trials demonstrating the beneficial applications of microalgal biostimulants as well as point out bottlenecks and constraints regarding their successful commercialization and input in sustainable agricultural practices.

Symbiosis between cyanobacteria and plants: from molecular studies to agronomic applications

Nitrogen-fixing cyanobacteria from the order Nostocales are able to establish symbiotic relationships with diverse plant species. They are promiscuous symbionts, as the same strain of cyanobacterium is able to form symbiotic biological nitrogen-fixing relationships with different plants species. This review will focus on the different types of cyanobacterial-plant associations, both endophytic and epiphytic, and provide insights from a structural viewpoint, as well as our current understanding of the mechanisms involved in the symbiotic crosstalk. In all these symbioses, the benefit for the plant is clear; it obtains from the cyanobacterium fixed nitrogen and other bioactive compounds, such as phytohormones, polysaccharides, siderophores, or vitamins, leading to enhanced plant growth and productivity. Additionally, there is increasing use of different cyanobacterial species as bio-inoculants for biological nitrogen fixation to improve soil fertility and crop production, thus providing an eco-friendly, alternative, and sustainable approach to reduce the over-reliance on synthetic chemical fertilizers.

Synthetic Light-Driven Consortia for Carbon-Negative Biosynthesis

Synthetic light-driven consortia composed of phototrophs and heterotrophs have attracted increasing attention owing to their potential to be used in sustainable biotechnology. In recent years, synthetic phototrophic consortia have been used to produce bulk chemicals, biofuels, and other valuable bioproducts. In addition, autotrophic-heterotrophic symbiosis systems have potential applications in wastewater treatment, bioremediation, and as a method for phytoplankton bloom control. Here, we discuss progress made on the biosynthesis of phototrophic microbial consortia. In addition, strategies for optimizing the synthetic light-driven consortia are summarized. Moreover, we highlight current challenges and future research directions for the development of robust and controllable synthetic light-driven consortia.