Exogenous ACC Deaminase Is Key to Improving the Performance of Pasture Legume-Rhizobial Symbioses in the Presence of a High Manganese Concentration

Abstract

Manganese (Mn) toxicity is a very common soil stress around the world, which is responsible for low soil fertility. This manuscript evaluates the effect of the endophytic bacterium Pseudomonas sp. Q1 on different rhizobial-legume symbioses in the absence and presence of Mn toxicity. Three legume species, Cicer arietinum (chickpea), Trifolium subterraneum (subterranean clover), and Medicago polymorpha (burr medic) were used. To evaluate the role of 1-aminocyclopropane-1-carboxylate (ACC) deaminase produced by strain Q1 in these interactions, an ACC deaminase knockout mutant of this strain was constructed and used in those trials. The Q1 strain only promoted the symbiotic performance of Rhizobium leguminosarum bv. trifolii ATCC 14480T and Ensifer meliloti ATCC 9930T, leading to an increase of the growth of their hosts in both conditions. Notably, the acdS gene disruption of strain Q1 abolished the beneficial effect of this bacterium as well as causing this mutant strain to act deleteriously in those specific symbioses. This study suggests that the addition of non-rhizobia with functional ACC deaminase may be a strategy to improve the pasture legume–rhizobial symbioses, particularly when the use of rhizobial strains alone does not yield the expected results due to their difficulty in competing with native strains or in adapting to inhibitory soil conditions.

Recent Developments in the Study of Plant Microbiomes

“…More recently, several commercial strains have been applied simultaneously [ 125 , 126 ]. According to Santoyo et al [ 88 ], three different types of microbial consortia may be envisioned: those that include (i) several bacterial strains [ 112 , 127 , 128 , 129 ], (ii) consortia including bacteria and mycorrhizae [ 104 ], and (iii) consortia containing both bacteria and plant growth-promoting fungi (such as Trichoderma spp.) [ 130 , 131 ].…”

Pseudomonas 1-Aminocyclopropane-1-carboxylate (ACC) Deaminase and Its Role in Beneficial Plant-Microbe Interactions

“…Lost the ability to decrease flower senescence Decreased ability to promote tomato growth and protect it from salt stress Decreased ability to protect periwinkle from phytoplasma infection [17,62] P. ogarae F113 Lost the ability to promote maize root growth and seed germination [75,83] P. palleroniana Q1 Decreased ability to promote the nodulation process of rhizobia [84] P. azotoformans CHB 1107 Decreased ability to promote tomato plant growth and resistance to salt stress [85] Effects of Exogenous acdS Expression…”

“…Q1 (P. palleroniana), but not its acdS − mutant, promoted the symbiotic performance of R. leguminosarum bv. trifolii ATCC 14480 T and Ensifer meliloti ATCC 9930 T under both normal and excess Mn stress conditions [84].…”

Dual Microbial Inoculation, a Game Changer? – Bacterial Biostimulants With Multifunctional Growth Promoting Traits to Mitigate Salinity Stress in Spring Mungbean

“…Therefore, salt tolerant microbial types with ACC deaminase are known to curb salt stress caused due to higher ethylene levels. Research literature suggests that salt tolerant bacterial strains with ACC deaminase activity mitigate various biotic and abiotic stresses such as attack by phyto-pathogens, salinity, drought and flood conditions in plants ( Pourbabaee et al, 2016 ; Ravanbakhsh et al, 2017 ; Ghosh et al, 2018 ; Albdaiwi et al, 2019 ; Gupta and Pandey, 2019b ; Paco et al, 2020 ). Implementation of biofertilizer able to tolerate salt stress can function as a promising technology in terms of economic, environmental and agronomic benefits and can largely be applied to partially replace agro-chemicals known to enhance economic yield under stress conditions.…”