Osmoregulation in Rhizobium meliloti: inhibition of growth by salts

Botsford, James L.

doi:10.1007/bf00414452

Cited by 68 publications

(48 citation statements)

References 14 publications

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“…Generally, the growth of B. japonicum is severely inhibited in media containing 100 to 200 mM NaCl, whereas Rhizobium species are often capable of growing in a 400-mM NaCl solution and sometimes grow in concentrations approaching that of seawater (68). Salt tolerance in microorganisms is closely related to the intra-cellular accumulation of organic solutes called osmolytes such as glutamate (6,42,141,175), trehalose (23,141), betaines (5), and dipeptide (140), although it also relates to extra-cellular polysaccharide production in certain rhizobia (98). The accumulation of osmolytes is thought to counteract the dehydrating effect of low water activity (11).…”

Section: Homospd and Environmental Stressmentioning

confidence: 99%

Biogenic Amines in Rhizobia and Legume Root Nodules

Fujihara

2009

Microb. Environ.

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Root-nodule bacteria (rhizobia) are of great importance for nitrogen acquisition through symbiotic nitrogen fixation in a wide variety of leguminous plants. These bacteria differ from most other soil microorganisms by taking dual forms, i.e. a free-living form in soils and a symbiotic form inside of host legumes. Therefore, they should have a versatile strategy for survival, whether inhabiting soils or root nodules formed through rhizobia-legume interactions. Rhizobia generally contain large amounts of the biogenic amine homospermidine, an analog of spermidine which is an essential cellular component in most living systems. The external pH, salinity and a rapid change in osmolarity are thought to be significant environmental factors affecting the persistence of rhizobia. The present review describes the regulation of homospermidine biosynthesis in response to environmental stress and its possible functional role in rhizobia. Legume root nodules, an alternative habitat of rhizobia, usually contain a variety of biogenic amines besides homospermidine and the occurrence of some of these amines is closely associated with rhizobial infections. In the second half of this review, novel biogenic amines found in certain legume root nodules and the mechanism of their synthesis involving cooperation between the rhizobia and host legume cells are also described.

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Section: Homospd and Environmental Stressmentioning

confidence: 99%

Biogenic Amines in Rhizobia and Legume Root Nodules

Fujihara

2009

Microb. Environ.

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“…Much attention has been focused during the last decade on the mechanisms of osmotic adaptation in several rhizobium species (18,41,42). Rhizobium meliloti, the microsymbiont in alfalfa root nodules, has been extensively investigated (5,6,22,36), and the mechanisms governing turgor restoration of bacterial cells growing under hyperosmotic conditions have been partially elucidated. Specifically, concomitant accumulations of potassium and glutamate ions were pointed out as the primary response in R meliloti (6), and the same mechanism has been found in most of the bacterial species investigated thus far (7,27).…”

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confidence: 99%

Osmoadaptation in rhizobia: ectoine-induced salt tolerance

et al. 1994

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), we have investigated the involvement of this molecule in the osmotic adaptation of Rhizobium meliloti. Ectoine appeared almost as effective as glycine betaine in improving the growth of R. meliboti under adverse osmotic conditions (0.5 M NaCI). Moreover, improvement of growth of rhizobial strains insensitive to glycine betaine was also observed. Ectoine transport proved inducible, periplasmic protein dependent, and, as shown by competition experiments, distinct from the transport of glycine betaine. Medium osmolarity had little effect on the uptake characteristics, since the rate of influx increased from 12 to only 20 nmol min-' mg of proteinwhen NaCI concentrations were raised from 0 to 0.3 or 0.5 M, with a constant of transport of 80 FM. Natural-abundance "C-nuclear magnetic resonance and radiolabelling assays showed that ectoine, unlike glycine betaine, is not intracellularly accumulated and, as a consequence, does not repress the synthesis of endogenous compatible solutes (glutamate, N-acetylglutaminylglutamine amide, and trehalose). Furthermore, the strong rise in glutamate content in cells osmotically stressed in the presence of ectoine suggests that, instead of being involved in osmotic balance restoration, ectoine should play a key role in triggering the synthesis of endogenous osmolytes. Hence, we believe that there are at least two distinct classes of osmoprotectants: those such as glycine betaine or glutamate, which act as genuine osmolytes, and those such as ectoine, which act as chemical mediators.Rhizobia are soil bacteria which display symbiotic interactions with specific legume hosts. Most of these bacteria are very sensitive to a soil water deficit, which adversely affects their dinitrogen fixation capacity and hence the productivity of the whole legume plant (1,8,19,38). Much attention has been focused during the last decade on the mechanisms of osmotic adaptation in several rhizobium species (18,41,42). Rhizobium meliloti, the microsymbiont in alfalfa root nodules, has been extensively investigated (5,6,22,36), and the mechanisms governing turgor restoration of bacterial cells growing under hyperosmotic conditions have been partially elucidated. Specifically, concomitant accumulations of potassium and glutamate ions were pointed out as the primary response in R meliloti (6), and the same mechanism has been found in most of the bacterial species investigated thus far (7, 27). Trehalose and the dipeptide N-acetylglutaminylglutamine amide (NAGGN) (37) are also accumulated, probably to help the bacterial cells in balancing the high osmotic pressure of the medium. Among a series of exogenously supplied osmoprotectants, glycine betaine and proline betaine proved the most effective (3, 14).Their effect is quite similar to that found in members of the family Enterobacteriaceae (23) except that lowering medium osmolality triggers catabolism of betaines in R meliloti (3, 14, 36). A transport system involving a periplasmic glycine betainebinding protein was identified previously (24, 40). Glycine beta...

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“…Sodium and potassium were inhibitory but at very high levels, greater than 10,000 ppm. Calcium and magnesium were found to be toxic at concentrations below that typically used in bacteriological medium [12]. It is uncertain why these minerals inhibit reduction of the dye.…”

Section: Toxic Mineralsmentioning

confidence: 99%