Acid-Tolerant Species of Medicago Produce Root Exudates at Low pH Which Induce the Expression of Nodulation Genes in Rhizobium meliloti

1992 ◽  
Vol 19 (3) ◽  
pp. 287 ◽  
Author(s):  
JG Howieson ◽  
AD Robson ◽  
LK Abbott
Keyword(s):  
Root Exudates ◽  
Rhizobium Meliloti ◽  
Acid Stress ◽  
Gene Induction ◽  
Lacz Gene ◽  
Annual Species ◽  
Nodulation Genes ◽  
Tolerant Species ◽  
Acid Tolerant ◽  
Nod Gene Induction

An acid rhizosphere may interfere with the transcription of nodulation genes in Rhizobium spp. by modifying the production of legume root exudates, or the rhizobial response to them. Certain annual species of Medicago (M. murex, M. polymorpha) can nodulate better in acid soils and solutions than other species (M. truncatula, M. littoralis). The mechanisms of this acid tolerance in nodulation are poorly understood. Root exudates collected at pH 5.8 and pH 6.0 from acid-tolerant species of annual medics induced the expression of nodulation genes in Rhizobium meliloti as indicated from a lacZ gene fusion, whereas exudates from acid-sensitive species grown at these pH values displayed decreased induction activity. For the acid-sensitive host, M. truncatula, increasing the Ca concentration from 0.5 to 5.0 mM at pH 5.8 increased the nod-gene induction activity of its exudates, but there was no effect at higher pH. There was no effect of Ca or pH on the nod-gene induction activity of exudates collected from M. murex. These results indicate a likely mechanism underlying differences in ability to nodulate under acid stress among annual species of Medicago.

scholarly journals Alfalfa Root Exudates and Compounds which Promote or Inhibit Induction of Rhizobium meliloti Nodulation Genes

1988 ◽  
Vol 88 (2) ◽  
pp. 396-400 ◽  
Author(s):  
N. Kent Peters ◽  
Sharon R. Long
Keyword(s):  
Root Exudates ◽  
Rhizobium Meliloti ◽  
Nodulation Genes ◽  
Alfalfa Root

Influence of soil pH on the development of symbiosis in field-grown acid-sensitive and acid-tolerant annual medics

1992 ◽  
Vol 32 (2) ◽  
pp. 167 ◽  
Author(s):  
RR Young ◽  
J Brockwell
Keyword(s):  
Soil Ph ◽  
Rhizobium Meliloti ◽  
New South ◽  
Annual Species ◽  
Resident Population ◽  
Growing Period ◽  
South Wales ◽  
Normal Expression ◽  
Acid Tolerant ◽  
Annual Medics

Relationships between soil pH, resident population of Rhizobium meliloti in the soil, rhizobial colonisation of the rhizosphere, and nodulation of annual species of Medicago were examined. Established swards of M. truncatula (acid-sensitive) and of M. murex and M. polymorpha (acid-tolerant) growing at 6 different locations in central and western New South Wales were sampled to measure soil pH, to enumerate the populations of R. meliloti resident in the soil and colonising plant rhizospheres, and to assess the extent of nodulation. Soil pH (0.01 mol CaCl2/L) varied from 4.70 to 7.25, soil populations from 3 to 100000 rhizobialg, and rhizosphere populations from 10 to >1 x 106 rhizobia/plant. Nodulation varied from poor to good, depending on growing period and location, but was consistently poorer on M. truncatula than on M. murex or M. polymorpha. Regression analysis showed a consistent and significant (P<0.01) relationship between rhizobial colonisation of the rhizosphere and extent of nodulation. There was also a significant (P<0.001) correlation over all 44 sampling sites between soil pH and the population of R. meliloti resident in the soil. The relationships between soil pH and rhizosphere colonisation, and between soil pH and nodulation, were significant for M. truncatula (P<0.01, P<0.02, respectively) but not for either M. murex or M. polymorpha. These data suggest that the range of soil pH at which M. truncatula was growing (4.80-7.25, but mainly 4.8-5.6) spanned the threshold at which unfavourable soil pH began to obstruct normal expression of its symbiosis, whereas, the critical soil pH levels for symbiotic development of M. murex and M. polymorpha were below this range.

Increased yield in annual species of Medicago grown in acidic soil in response to inoculation with acid tolerant Rhizobium meliloti

1991 ◽  
pp. 589-595 ◽  
Author(s):  
J. G. Howieson ◽  
M. A. Ewing ◽  
C. W. Thorn ◽  
C. K. Revell
Keyword(s):  
Rhizobium Meliloti ◽  
Acidic Soil ◽  
Annual Species ◽  
Acid Tolerant

scholarly journals Aldonic Acids: A Novel Family of nod Gene Inducers of Mesorhizobium loti, Rhizobium lupini, and Sinorhizobium meliloti

1998 ◽  
Vol 11 (10) ◽  
pp. 988-998 ◽  
Author(s):  
Hubert Gagnon ◽  
Ragai K. Ibrahim
Keyword(s):  
Root Exudates ◽  
Sinorhizobium Meliloti ◽  
Gene Induction ◽  
Signal Molecules ◽  
Mesorhizobium Loti ◽  
Tetronic Acid ◽  
Lacz Fusions ◽  
Rhizobium Lupini ◽  
Nod Gene Induction ◽  
The Impact

Molecular signals, such as flavonoids (or nonflavonoid type), nod gene-inducers, and bacterial lipochitin oligosac-charides (LCOs) act as modulators of species specificity during early stages of infection in Rhizobium spp.-legume interactions. The fact that signaling in Lupinus albus remains to be determined prompted us to investigate the flavonoid signal responsible for nod gene induction in Rhizobium lupini. A screening method was used based on the measurement of β-galactosidase activity of R. lupini strains harboring nodC::lacZ fusions in the presence of (i) authentic lupin isoflavones, (ii) carbohydrate-like inducers, and (iii) high-pressure liquid chromatography (HPLC)-fractionated lupin seed effusates and root exudates, as putative nod gene inducers. The results indicate that both erythronic and tetronic acids (4-C sugar acids) led to low but significant increases in β-galactosidase activities, compared with the controls. In addition, lupi-wighteone, a monoprenylated isoflavone, exerts a synergistic effect with the carbohydrate-like inducers, compared with other isoflavone treatments. The natural occurrence of aldonic acids in L. albus root exudates and seed effusates has been demonstrated by HPLC analysis. When tested with nodC::lacZ fusions, tetronic acid resulted in nod gene induction in Sinorhizobium meliloti. In addition, a combination of luteolin and tetronic acid promotes further increases in S. meliloti nod gene expression, as shown by β-galactosidase assays. Incorporation studies with [14C]LCO precursors confirmed the inductive role of both erythronic and tetronic acids in promoting LCO biosynthesis in R. lupini cultures, and of tetronic acid in Mesorhizobium loti and S. meliloti. Hydrolysis of the LCOs with various enzymes substantiated their putative identities. These results are discussed in relation to the impact of these unusual signal molecules on our knowledge of flavonoid signaling in Rhizobium-legume symbiosis.

scholarly journals Interference between Rhizobium meliloti and Rhizobium trifolii nodulation genes: genetic basis of R. meliloti dominance.

1988 ◽  
Vol 170 (12) ◽  
pp. 5718-5727 ◽  
Author(s):  
F Debellé ◽  
F Maillet ◽  
J Vasse ◽  
C Rosenberg ◽  
F de Billy ◽  
...  
Keyword(s):  
Genetic Basis ◽  
Rhizobium Meliloti ◽  
Rhizobium Trifolii ◽  
Nodulation Genes

A plant flavone, luteolin, induces expression of Rhizobium meliloti nodulation genes

Science ◽  
1986 ◽  
Vol 233 (4767) ◽  
pp. 977-980 ◽  
Author(s):  
N. Peters ◽  
J. Frost ◽  
S. Long
Keyword(s):  
Rhizobium Meliloti ◽  
Nodulation Genes

Six nodulation genes of nod box locus 4 in Rhizobium meliloti are involved in nodulation signal production: nodM codes for d-glucosamine synthetase

1991 ◽  
Vol 228 (1-2) ◽  
pp. 113-124 ◽  
Author(s):  
Nedelcho Baev ◽  
Gabriella Endre ◽  
György Petrovics ◽  
Zsofia Banfalvi ◽  
Adam Kondorosi
Keyword(s):  
Rhizobium Meliloti ◽  
Nodulation Genes ◽  
Signal Production

Impact of Cold and Cold-Acid Stress on Poststress Tolerance and Virulence Factor Expression ofEscherichia coli O157:H7†‡

2004 ◽  
Vol 67 (1) ◽  
pp. 19-26 ◽  
Author(s):  
D. ELHANAFI ◽  
B. LEENANON ◽  
W. BANG ◽  
M. A. DRAKE
Keyword(s):  
Cold Stress ◽  
Virulence Factor ◽  
Acid Stress ◽  
Acid Tolerance ◽  
Ofescherichia Coli ◽  
Simulated Gastric Fluid ◽  
Prolonged Storage ◽  
Lacz Gene ◽  
Virulence Gene Expression ◽  
Freeze Thaw

The effect of extended cold or cold-acid storage ofEscherichia coli O157:H7 on subsequent acid tolerance, freeze-thaw survival, heat tolerance, and virulence factor (Shiga toxin, intimin, and hemolysin) expression was determined. ThreeE. coli O157:H7 strains were stressed at 4°C in TSB or pH 5.5 TSB for 4 weeks. The acid (TSB [pH 2.0] or simulated gastric fluid [pH 1.5]) tolerance, freeze-thaw (−20°C to 21°C) survival, and heat (56°C) tolerance of stressed cells were compared with those of control cells. The β-galactosidase activities of stressed and control cells containing a lacZ gene fusion in the stx2, eaeA, or hlyA gene were determined following stress in TSB or pH 5.5 TSB at 37°C and in the exponential and stationary phases. Cold and cold-acid stresses decreased acid tolerance (P &lt; 0.05), with a larger decrease in acid tolerance being observed after cold stress than after cold-acid stress (P &lt; 0.05). Cold stress increased freeze-thaw survival for all three strains (P &lt; 0.05). Prior cold or cold-acid stress had no effect on virulence factor production (P &gt; 0.05), although growth in acidic media (pH 5.5) enhanced eaeA and hlyA expression (P &lt; 0.05). These results indicate that the prolonged storage ofE. coli O157: H7 at 4°C has substantial effects on freeze-thaw tolerance but does not affect subsequent virulence gene expression.

Anti-Escherichia coliO157:H7 activity of free fatty acids under varying pH

2010 ◽  
Vol 56 (3) ◽  
pp. 263-267 ◽  
Author(s):  
Jinli Yang ◽  
Xianzhi Hou ◽  
Priya S. Mir ◽  
Tim A. McAllister
Keyword(s):  
Fatty Acids ◽  
Bactericidal Activity ◽  
Acid Stress ◽  
Acid Tolerance ◽  
Capric Acid ◽  
Luria Bertani ◽  
E Coli ◽  
Luria Bertani Broth ◽  
Colony Forming Units ◽  
Acid Tolerant

Following screening of 4 strains of Escherichia coli O157:H7 (E32511, E318N, H4420N, and R508N) for acid tolerance, strain H4420N was selected for further study into the influence of pH on bactericidal activity of 6 fatty acids (capric, lauric, palmitic, oleic, linoleic, and linolenic). Strain H4420N was cultured for 6 h in Luria–Bertani broth amended with individual fatty acids at 20 mmol/L, with pH adjusted to 7.0, 4.3, or 2.5. None of the fatty acids exhibited bactericidal activity at pH 7.0 (p >0.05). At pH 4.3, only capric, lauric, and linoleic acids reduced viability of H4420N (p < 0.05). At pH 2.5, oleic (C18:1) and linolenic (C18:3) acids had modest effects on H4420N viability, whereas capric (C10:0), lauric (C12:0), and linoleic (C18:2) acids resulted in a reduction ≥5 log10colony-forming units (CFU)/mL (p < 0.05). Capric and lauric acids were examined further at pH 2.5 over a range of concentrations (0.15–20 mmol/L). After 10 min of exposure, 5 log10 CFU/mL reductions (p < 0.05) were achieved by lauric acid at 2.5 mmol/L and by capric acid at 0.31 mmol/L. Acid stress increased the sensitivity of acid-tolerant E. coli O157:H7 strain H4420N to fatty acids. Including sources of these fatty acids in diets for cattle might impair the ability of this zoonotic pathogen to survive passage through the stomach, possibly reducing the potential for its colonization in the lower gut.

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