The Role of Plant Growth-Promoting Rhizobacteria (PGPR) in Mitigating Plant’s Environmental Stresses

Abstract

Phytoremediation is a cost-effective and sustainable technology used to clean up pollutants from soils and waters through the use of plant species. Indeed, plants are naturally capable of absorbing metals and degrading organic molecules. However, in several cases, the presence of contaminants causes plant suffering and limited growth. In such situations, thanks to the production of specific root exudates, plants can engage the most suitable bacteria able to support their growth according to the particular environmental stress. These plant growth-promoting rhizobacteria (PGPR) may facilitate plant growth and development with several beneficial effects, even more evident when plants are grown in critical environmental conditions, such as the presence of toxic contaminants. For instance, PGPR may alleviate metal phytotoxicity by altering metal bioavailability in soil and increasing metal translocation within the plant. Since many of the PGPR are also hydrocarbon oxidizers, they are also able to support and enhance plant biodegradation activity. Besides, PGPR in agriculture can be an excellent support to counter the devastating effects of abiotic stress, such as excessive salinity and drought, replacing expensive inorganic fertilizers that hurt the environment. A better and in-depth understanding of the function and interactions of plants and associated microorganisms directly in the matrix of interest, especially in the presence of persistent contamination, could provide new opportunities for phytoremediation.

Root Exudates: Mechanistic Insight of Plant Growth Promoting Rhizobacteria for Sustainable Crop Production

“…Plant-growth promoting rhizobacteria significantly reduce the dependence on chemical fertilizers and pesticides (Liu et al, 2017 ). Plant growth-promoting rhizobacteria promote plant growth through root-hair proliferation, enhancing root hair branching; increase in seedling emergence; early nodulation; nodule functioning; enhanced leaf surface area; improvement in vigor and biomass; increased indigenous plant hormones levels; and most importantly, by improving nutrient use efficiency (Vocciante et al, 2022 ). The plant growth-promoting rhizobacteria induce the accumulation of carbohydrates in plants and consequently the yield of various plant species (Bhattacharyya and Jha, 2012 ; Table 1 ).…”

Bacterioplankton Associated with Toxic Cyanobacteria Promote Pisum sativum (Pea) Growth and Nutritional Value through Positive Interactions

“…Bacterial plant growth promotion by bacteria is a hot research topic that interests many researchers searching for the most economical way to increase yields naturally. Thus, PGPB are used as an alternative to conventional artificial fertilizers to maximize crop yields [ 68 , 69 , 70 , 71 ] and protect the environment [ 39 ]. Typically, these bacteria are isolated in the plant’s rhizosphere [ 36 , 68 , 72 ], but they can also emanate from water [ 73 ].…”

“…As a result, PGPB increase plant growth vigor and nutritional value [ 33 , 35 ]. Furthermore, other vital aspects of PGPB include the production of plant growth hormones, such as indole acetic acid (IAA) [ 34 ], gibberellins [ 36 , 37 ], exopolysaccharides, and siderophores, and atmospheric nitrogen fixation [ 38 , 39 ].…”

Screening of Plants and Indigenous Bacteria to Improve Arsenic Phytoextraction

“…The selection of bacterial strains capable of improving the efficiency of the phytoremediation is a fundamental step, made non-trivial by the specificity of the action of PGPR and by their effectiveness, which depends on numerous factors related to the complex interactions with the soil and plants [38]. In this study, the addition of a selected microbial consortium with indigenous endophytic bacteria made it possible to obtain detectable levels of phytoextraction even without the addition of chemical mobilizing agents.…”

“…Another possibility to help phytoextraction by maximizing its effectiveness is the use of plant growth-promoting rhizobacteria (PGPR) [37]. This strategy involves rhizobacteria that can stimulate plant growth both by facilitating the bioavailability of soil nutrients and by modulating the production and level of phytohormones in plants [38]. In addition, thanks to the microbial processes active in the rhizosphere, PGPR can also promote the mobility and bioavailability of metals in the soil, increasing their uptake by plants [39,40].…”