Isolation and characterization of a glyphosate-degrading rhizosphere strain, Enterobacter cloacae K7.

Plant-growth-promoting rhizobacteria exert beneficial effects on plants through their capacity for nitrogen fixation, phytohormone production, phosphate solubilization, and improvement of the water and mineral status of plants. We suggested that these bacteria may also have the potential to express degradative activity toward glyphosate, a commonly used organophosphorus herbicide. In this study, 10 strains resistant to a 10 mM concentration of glyphosate were isolated from the rhizoplane of various plants. Five of these strains--Alcaligenes sp. K1, Comamonas sp. K4, Azomonas sp. K5, Pseudomonas sp. K3, and Enterobacter cloacae K7--possessed a number of associative traits, including fixation of atmospheric nitrogen, solubilization of phosphates, and synthesis of the phytohormone indole-3-acetic acid. One strain, E. cloacae K7, could utilize glyphosate as a source of P. Gas-liquid chromatography showed that E. cloacae growth correlated with a decline in herbicide content in the culture medium (40% of the initial 5mM content), with no glyphosate accumulating inside the cells. Thin-layer chromatography analysis of the intermediate metabolites of glyphosate degradation found that E. cloacae K7 had a C-P lyase activity and degraded glyphosate to give sarcosine, which was then oxidized to glycine. In addition, strain K7 colonized the roots of common sunflower (Helianthus annuus L.) and sugar sorghum (Sorghum saccharatum Pers.), promoting the growth and development of sunflower seedlings. Our findings extend current knowledge of glyphosate-degrading rhizosphere bacteria and may be useful for developing a biotechnology for the cleanup and restoration of glyphosate-polluted soils.

Gas-liquid chromatography-obtained differences in the dissolution enthalpy between two positional isomers in a polar stationary phase: a measure of the inter- or intramolecular hydrogen bond energy?

Previous GLC work with several 2- and 4-substituted phenols and anilines, as well as with a pyrrolizidine alcohol, had determined the difference between the heats of dissolution of two positional isomers in a strong polar stationary liquid phase; one of these isomers forms an intramolecular hydrogen bond (intra-HB) and the other has no such bond for steric reasons. The energies of the intermolecular hydrogen bonds (inter-HBs), ΔH(inter-HB), formed by the 1,2- and 1,4-isomers with the molecules of a polar phase had been assumed approximately equal, so the difference between them could be ignored. The same assumption had been made for the energies of nonspecific interactions (NSIs), ΔH(NSI). It had been concluded that the found difference can be considered as an intra-HB energy (enthalpy), ΔH(intra-HB), when the energies (enthalpies) of inter-HBs formed by the 1,2- and 1,4-isomers under study with the molecules of a polar phase are much greater in absolute value than ΔH(intra-HB). And, conversely, when |ΔH(intra-HB)|>|ΔH(inter-HB)|, an inter-HB enthalpy will result. With the same assumptions, we here obtained an extended thermodynamic equation and corrected this above conclusion on the basis of a general consideration of the dissolution thermodynamics for two isomers of a molecule in a polar phase. Account was taken of the coefficients of isomer partitioning between the liquid and the gaseous phase at the experimental temperature. The conclusion made previously was adjusted for ΔH(NSI) and formulated as follows: The GLC method determines the intra-HB energy at |ΔH(intra-HB)|≤|ΔH(inter-HB)+ΔH(NSI)|. If |ΔH(intra-HB)|>|ΔH(inter-HB)+ΔH(NSI)|, the method yields the values of ΔH(inter-HB)+ΔH(NSI). This new conclusion was illustrated with virtual (numerical) experiments in which various ΔH(intra-HB), ΔH(inter-HB), and ΔH(NSI) values were postulated and results were obtained that would have been achieved by GLC if it had been done. Using a capillary column with the PEG 20M stationary phase, we measured the differences between the heats of dissolution for six pairs of isomers of phenolic compounds and for seven pairs of disubstituted benzene derivatives, which have similar structures but cannot form an intra-HB. The benzene derivatives served to make an approximate experimental estimate of the difference between the energies of NSIs of the isomers under study with a polar phase, ΔH(NSI).

Further consideration of the gas-liquid chromatographic method for determining the intramolecular hydrogen bond energies with the example of 2-substituted phenols.

The GLC method for determining the intramolecular hydrogen bond (intra-HB) energy as the difference between the heats of dissolution of two isomers, one of which forms an intra-HB and the other has no such bond for steric reasons, in a polar stationary liquid phase was further considered by taking account of a correction for the difference between the energies of nonspecific interactions of the isomers with a polar phase. With 4- and 2-substituted phenols as an example, the differences between their heats of dissolution in polyethylene glycol and in poly-1,4-butanediol succinate were measured. As a first approximation, corrections for the contribution of the energy of nonspecific interactions with a liquid phase to the total magnitude of the difference between the heats of isomer dissolution were found. These corrections were determined as the difference between the heats of dissolution for 1,4- and 1,2-disubstituted benzene derivatives--analogs of the compounds under study that either do not have hydroxyl groups altogether or, in the case of 1,2-isomers with a hydroxyl group, cannot form an intra-HB. On the basis of the obtained results, the average intra-HB energies of 2-fluoro- (1), 2-chloro- (2), 2-bromo- (3), 2-iodo- (4), 2-methoxyphenol (5), salicylaldehyde (6), methyl ether of salicylic acid (7) and 2-nitrophenol (8) were estimated to be 7.4+/-0.3, 13.3+/-0.8, 14.4+/-0.4, 12.8+/-0.3, 17.6+/-0.1, 24.6+/-1.2, 29.8+/-0.3 and 32.5+/-4.7 kJ/mol, respectively. The values were compared with those found in the literature.