Salt tolerance of rhizobial populations from contrasting environmental conditions: understanding the implications of climate change

Biodegradable Microplastics from Agricultural Mulch Films: Implications for Plant Growth-Promoting Bacteria and Plant's Oxidative Stress

This study explores the interactions between biodegradable (BIO) microplastics and plant growth-promoting bacteria (PGPB), assessing their effects on soil health and crop productivity. Five bacterial strains, Bacillus, Enterobacter, Kosakonia, Rhizobium, and Pseudomonas, were exposed to BIO microplastics to examine strain-specific responses. This study revealed that while most bacteria experienced growth inhibition, Kosakonia sp. O21 was poorly affected by BIO microplastics, indicating a potential for microplastic degradation. This study further investigated the effect of these microplastics on plant growth and biochemistry. Results showed that exposure to BIO microplastics significatively reduced plant growth and caused oxidative stress, affecting membranes and proteins and inducing the activity of glutathione S-transferases (GSTs), catalase (CAT), and superoxide dismutase (SOD) as antioxidant responses. Bacterial inoculation alleviated plant oxidative stress, especially at lower concentrations of microplastics. These findings emphasize the critical role of oxidative stress in mediating the negative effects of BIO microplastics on plants and the relevance of bacterial strains that can tolerate BIO microplastics to protect plants from BIO microplastics' effects. Results also highlight the importance of extending research to assess the long-term implications of biodegradable microplastics for soil PGPBs and plant health and crop productivity. This study contributes to sustainable agricultural practices by offering insights into mitigating the risks of microplastic pollution through microbial-based interventions.

Application of Plant Growth-Promoting Bacteria from Cape Verde to Increase Maize Tolerance to Salinity

Salinity constitutes a major abiotic factor that negatively affects crop productivity. Inoculation with plant growth-promoting bacteria (PGPB) is proven to increase plant tolerance to abiotic stresses and enhance plant growth, development and productivity. The present study aims to increase the resilience of crops to salinity using bacteria from the microbiome of plants growing in saline environments. For that, the halotolerance of bacteria present in the roots of natural plants growing on Sal Island, which is characterized by its arid environment and maritime influence, was determined, with some strains having extreme halotolerance. Their ability to produce plant growth-promoting traits was evaluated, with most strains increasing indole acetic acid (26-418%), siderophore (>300%) and alginate (2-66%) production and phosphate solubilization (13-100%) under salt stress. The strains evidencing the best performance were inoculated in maize (Zea mays L.) plants and their influence on plant growth and biochemical status was evaluated. Results evidenced bacterial ability to especially increase proline (55-191%), whose osmotic, antioxidant and protein-protecting properties reduced protein damage in salt-stressed maize plants, evidencing the potential of PGPB to reduce the impact of salinity on crops. Enhanced nutrition, phytohormone production and osmolyte synthesis along with antioxidant response all contribute to increasing plant tolerance to salt stress.

At the Crossroads of Salinity and Rhizobium-Legume Symbiosis

Legume roots interact with soil bacteria rhizobia to develop nodules, de novo symbiotic root organs that host these rhizobia and are mini factories of atmospheric nitrogen fixation. Nodulation is a sophisticated developmental process and is sensitive to several abiotic factors, salinity being one of them. While salinity influences both the free-living partners, symbiosis is more vulnerable than other aspects of plant and microbe physiology, and the symbiotic interaction is strongly impaired even under moderate salinity. In this review, we tease apart the various known components of rhizobium-legume symbiosis and how they interact with salt stress. We focus primarily on the initial stages of symbiosis since we have a greater mechanistic understanding of the interaction at these stages.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

A Multifactorial Approach to Untangle Graphene Oxide (GO) Nanosheets Effects on Plants: Plant Growth-Promoting Bacteria Inoculation, Bacterial Survival, and Drought

Drought is a limiting factor for agricultural productivity. Climate change threatens to expand the areas of the globe subjected to drought, as well as to increase the severity and duration of water shortage. Plant growth-promoting bacteria (PGPB) are widely studied and applied as biostimulants to increase plant production and to enhance tolerance to abiotic and biotic constraints. Besides PGPB, studies on the potential of nanoparticles to be used as biostimulants are also thriving. However, many studies report toxicity of tested nanoparticles in bacteria and plants in laboratory conditions, but few studies have reported effects of nanoparticles towards bacterial cells and communities in the soil. The combined application of nanoparticles and PGPB as biostimulant formulations are poorly explored and it is important to unravel the potentialities of their combined application as a way to potentiate food production. In this study, Rhizobium sp. E20-8 and graphene oxide (GO) nanosheets were applied on container-grown maize seedlings in watered and drought conditions. Bacterial survival, seedling growth (dry weight), and biochemical endpoints (photosynthetic pigments, soluble and insoluble carbohydrates, proline, lipid peroxidation, protein, electron transport system, and superoxide dismutase) were evaluated. Results showed that the simultaneous exposure to GO and Rhizobium sp. E20-8 was able to alleviate the stress induced by drought on maize seedlings through osmotic and antioxidant protection by GO and mitigation of GO effects on the plant’s biochemistry by Rhizobium sp. E20-8. These results constitute a new lead on the development of biostimulant formulations to improve plant performance and increase food production in water-limited conditions.

Exopolysaccharide II Is Relevant for the Survival of Sinorhizobium meliloti under Water Deficiency and Salinity Stress

Sinorhizobium meliloti is a soil bacterium of great agricultural importance because of its ability to fix atmospheric nitrogen in symbiotic association with alfalfa (Medicago sativa) roots. We looked into the involvement of exopolysaccharides (EPS) in its survival when exposed to different environmental stressors, as well as in bacteria-bacteria and bacteria-substrate interactions. The strains used were wild-type Rm8530 and two strains that are defective in the biosynthesis of EPS II: wild-type Rm1021, which has a non-functional expR locus, and mutant Rm8530 expA. Under stress by water deficiency, Rm8530 remained viable and increased in number, whereas Rm1021 and Rm8530 expA did not. These differences could be due to Rm8530's ability to produce EPS II. Survival experiments under saline stress showed that viability was reduced for Rm1021 but not for Rm8530 or Rm8530 expA, which suggests the existence of some regulating mechanism dependent on a functional expR that is absent in Rm1021. The results of salinity-induced stress assays regarding biofilm-forming capacity (BFC) and autoaggregation indicated the protective role of EPS II. As a whole, our observations demonstrate that EPS play major roles in rhizobacterial survival.