Effects of salt on rhizobia and bradyrhizobia: a review

Elsheikh, Elsiddig A.E.

doi:10.1111/j.1744-7348.1998.tb05226.x

Cited by 36 publications

(21 citation statements)

References 89 publications

(137 reference statements)

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“…This result contrasts with the frequent conclusion that rhizobial growth rate and salt‐tolerance are positively correlated (e.g. Elsheikh 1998; Marsudi et al . 1999; Barboza et al .…”

Section: Discussioncontrasting

confidence: 87%

Rhizobial mediation of Acacia adaptation to soil salinity: evidence of underlying trade‐offs and tests of expected patterns

2008

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Summary 1.The ecological importance of host-soil symbiont associations for plant community structure and dynamics has been recently highlighted, particularly with regard to ecological and evolutionary responses along environmental gradients. 2. We used a range of native Australian shrubby legumes ( Acacia spp.) and associated root-nodule forming bacteria (rhizobia) in laboratory and glasshouse studies to investigate the ecology of Acaciarhizobial interactions with respect to soil salinity, a major environmental stressor in many parts of the world. 3. Analysis of laboratory growth data provided clear evidence of a trade-off in that growth rate of individual rhizobial isolates was reduced with increasing salt tolerance in culture. 4. A large replicated glasshouse inoculation trial using 40 strains of rhizobia and nine species of Acacia that varied in their ability to grow in saline soils found strong evidence of host specificity, but neither the average growth promotion of host plants nor the specificity of growth promotion was related to salt tolerance of the isolates. 5. In a second glasshouse experiment, we used a subset of salt-sensitive and salt-tolerant rhizobia and six Acacia species to evaluate performance and symbiotic effectiveness across different levels of soil salinity. Overall, we found no evidence of a relationship between rhizobial salt-tolerance (as measured in the laboratory) and impact on host growth performance, either in saline or nonsaline soils, and there was no evidence that salt-tolerant rhizobia perform better in more saline environments. 6. Synthesis . More salt tolerant Acacia spp. were less responsive in growth to rhizobial inoculation than salt sensitive hosts, implying that evolution towards reduced dependence on the symbiosis may facilitate adaptation to salt, raising a general question regarding the extent to which shifts in dependence on microbial symbionts underlies plant adaptation to other environmental gradients.

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“…This result contrasts with the frequent conclusion that rhizobial growth rate and salt‐tolerance are positively correlated (e.g. Elsheikh 1998; Marsudi et al . 1999; Barboza et al .…”

Section: Discussioncontrasting

confidence: 87%

Rhizobial mediation of Acacia adaptation to soil salinity: evidence of underlying trade‐offs and tests of expected patterns

2008

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“…Higher concentrations inhibited growth. The results for this strain are thus similar to those presented by Boncompagni et al (1999) for B. japonicum USDA 110 and the strains surveyed by Elsheikh (1998).…”

Section: Growth In Liquid Medium With Different Concentrations Of Naclsupporting

confidence: 90%

“…Several strains of B. japonicum were reported as salt-sensitive compared to other rhizobia (Elsheikh 1998). The usual procedure to determine sensitivity is to grow the strain in media of increasing salinity and determine the cell count obtained at each salt concentration, NaCl is the most frequently tested salt.…”

Section: Growth In Liquid Medium With Different Concentrations Of Naclmentioning

confidence: 99%

Tolerance of Bradyrhizobium japonicum E109 to Osmotic Stress and the Stability of Liquid Inoculants Depend on Growth Phase

Soria

Pagliero

Correa

et al. 2006

World J Microbiol Biotechnol

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Salinity and drought induce osmotic stress in plants and nodulating bacteria. The introduction of soybean in areas with higher soil salt contents or periods of drought pose a challenge for the rhizobial inoculants used to improve nodulation and enhance nitrogen fixation. Bradyrhizobium japonicum is a slowgrowing rhizobium used for soybean inoculation that was previously regarded as salt-sensitive. We tested the survival ability of cultures of B. japonicum E109 at the exponential and stationary phases of growth in liquid culture medium against different concentrations of NaCl. We found that stationary-phase cells could tolerate higher levels of salt than exponential-phase cells. This result suggested that the physiological manipulation of the cultures could improve the salt tolerance of this strain. Nonetheless, we also found that exponential-phase cells adapted significantly better to two key situations that a commercial product must face, survival in liquid formulations and survival in soil microcosms resembling conditions of drought. These results suggest that the use of actively growing cells could be an improvement in the production of inoculants. However, it is not cost-effective, because bacteria should be harvested at a time when cell density is lower than that of early stationary-phase cultures, which are normally used in the industry. To overcome this drawback we proved that a fed-batch system can produce exponential-phase cultures with higher cell densities and able to produce liquid inoculants with acceptable survival rates.

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“…In a previous study, Fall et al (2008) showed that the three strains tolerated 20% of PEG 6000 and 1.5% of NaCl but a combination of high concentration of PEG 6000 (20%) and NaCl (1.5%) depressed strain growth. These two compounds have osmotic effects on rhizobial cells (El Sheikh EAE 1998;Räsänen et al 2004). One response of rhizobia to osmotic stress is morphological change which leads to a reduction in growth (Shoushtari and Pepper 1985;Busse and Bottomley 1989).…”

Section: Discussionmentioning

confidence: 97%

The efficiency and competitiveness of three Mesorhizobium sp. strains nodulating Acacia senegal (L.) Willd. under water deficiency conditions in the greenhouse

et al. 2011

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The combined effects of drought and salinity were investigated on the growth, efficiency and competitiveness of three Mesorhizobium sp. strains (ORS 3416, ORS 3428 and ORS 3437) isolated from Acacia senegal (L.) Willd. Sixteen combinations of polyethylene glycol (PEG) 6000 (0, 6, 12, 20%, w/v) and NaCl (0.005, 0.5, 1, 1.5%, w/v) were used to study rhizobial strains growth in screw-capped tubes containing yeast extract mannitol liquid medium. Whatever the combination, the strains grew. However, high concentrations of PEG 6000 and NaCl were depressed on rhizobial growth but strain ORS 3428 was the most tolerant. The effect of rhizobial inoculation on growth of A. senegal plants was also examined under non-limited (100% of water holding capacity, WHC) and water-limited conditions (50% WHC) in the greenhouse for 4 months on non-sterile sandy soil. A significant decrease in the nodulation rate, nodule dry weight, plant height and shoot dry weight was observed under water-limited conditions. Nevertheless, inoculation with the three selected Mesorhizobium strains significantly improved nodulation and A. senegal plant growth under water-limited conditions. Whatever the irrigation condition, strains ORS 3428 and ORS 3437 were more competitive than ORS 3416. These rhizobial strains may prove valuable for inoculation of Acacia senegal plants grown for transplantation to dry saline habitats.

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Effects of salt on rhizobia and bradyrhizobia: a review

Cited by 36 publications

References 89 publications

Rhizobial mediation of Acacia adaptation to soil salinity: evidence of underlying trade‐offs and tests of expected patterns

Rhizobial mediation of Acacia adaptation to soil salinity: evidence of underlying trade‐offs and tests of expected patterns

Tolerance of Bradyrhizobium japonicum E109 to Osmotic Stress and the Stability of Liquid Inoculants Depend on Growth Phase

The efficiency and competitiveness of three Mesorhizobium sp. strains nodulating Acacia senegal (L.) Willd. under water deficiency conditions in the greenhouse

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