The Employment of Endophytic Bacteria for Phytodegradation of Pyridine

Pyridine is considered a heterocyclic aromatic chemical that is poisonous and carcinogenic to a variety of living species. The use of plant and endophytic- bacteria to improve the efficiency of pollutants extraction is considered a viable technique since the endophytic bacteria help in the adaptation of the plant itself in various ecosystems and have significant ecological importance because they improve the soil fertility and quality. This research aims to stimulate the pyridine phytodegradation by Phragmites australis plants using the endophytic bacterial strain, Acinetobacter by inoculation these bacterial cells to the plants to see if it might increase plant growth and pyridine phytodegradation. In the present study, the system of pyridine phytodegradation basins with the vertical subsurface flow (VSSF) was adopted, since this system has better ventilation. In addition, the retention time is several hours due to the penetration of water molecules to the layers of packing materials of the basin, which have a relatively high hydraulic conductivity. After conducting the experiments, samples were collected and tests were done to find out the optimum conditions. The results were recorded as 40 plants of P. australis/m2 of VSSF systems; bacterial cells concentration, 250 mg/L; pyridine concentration, 400 mg/L; temperature, 35 °C and pH, 8±2 for 10 hrs incubation duration. As a result, endophytic bacteria can break down toxic organic substances in combination with certain plants. When the endophytic bacterium, Acinetobacter was not used to enhance the role of Phragmites australis plants in the pyridine-phytodegradation process, the rate of phytodegradation was reduced to less than 30% at a pyridine concentration of 700 mg/L, indicating the importance of this endophytic bacterium in the pyridine phytodegradation process.

Microbial Degradation of Pyridine by Co-culture of Two Newly Isolated Strains, Arthrobacter sp. Strain PDC-1 and Rhodococcus sp. Strain HPD-2

Pyridine is one of the most widespread heterocyclic contaminants. Microbial degradation of pyridine seems quite promising for its safety and efficiency. A bacterial consortium, which could use pyridine as the sole source of carbon, nitrogen, was obtained from the petroleum-contaminated soil from Liao River estuarine wetland. Two pyridine degrading strains, designated as PCD-1 and HPD-2, were isolated from the bacterial consortium. PCD-1 was identified as an Arthrobacter , and HPD-2 was identified as the Rhodococcus genus. The effects of pH, temperature, and pyridine concentration were investigated, and the optimum growth conditions for two strains were similar at pH 7.0 and 30°C. The co-culture of the two strains, CoPD, has better degradation efficiency compared with the individual strain. Haldane's inhibitory growth kinetics equation could be fitted to the growth of co-culture CoPD well for the entire concentration range. The kinetic constants obtained were μ max = 0.141 h -1 , K s = 37.9 mg/L, and K i = 3830 mg/L. Co-culture CoPD was able to remove more than 98% pyridine with an initial pyridine concentration of 5,000 mg/L within 120 h. Strain PCD-1 and HPD-2 have a novel pyridine degradation pathway different from the reported pathways. Major intermediates of pyridine degradation by two strains, including 2,5-pyrroldione, maleic semialdehyde, furanone, and butyrolactone, were identified using LC-MS analysis. CoPD is a promising tool for the treatment of wastewater containing pyridine, and this study contributes to the knowledge of the pyridine biodegradation by bacterial consortium.

The trans–cis isomerisation of bis(dioxolene)bis(pyridine) ruthenium complexes

The isomerisation of trans to cis bis(3,5-di-t-butylbenzosemiquinonato)bis(R-pyridine)ruthenium, Ru(R-Py)2(DTBDiox)2, is induced by warming with an excess of R-pyridine, where R = 3-chloro, 4-methyl, 4-phenyl, or 4-butyl. The rates of these reactions, for the species with R-Py = 3-chloropyridine, were monitored in o-dichlorobenzene by UV–visible spectroscopy against varying 3-chloropyridine and varying trans-[Ru(3-ClPy)2(DTBDiox)2] concentration. The data were found to obey first-order kinetics, −d[Ru(3-ClPy)2(DTBDiox)2/dt = kobsd[Ru(3-ClPy)2(DTBDiox)2], over a considerable range of pyridine concentration. A plot of 1/kobsd vs. [3-chloropyridine] is linear with a positive intercept. A dissociative mechanism is proposed for the isomerisation reaction. The activation parameters were determined for the specific case of R-Py = 3-chloropyridine. Electronic and electrochemical features of these species are briefly discussed.

Ionic dissociation in pyridine–iodine solutions

An electrochemical technique has been employed to study the ionization of the pyridine–iodine complex in pure pyridine and in 1,2-dichloroethane. A mechanism for the ionization in accord with the experimental data is proposed. The results indicate that, for wide ranges of iodine and pyridine concentration, one quarter of the I2 is dissociated into ionic species.

The structure of haem in pyridine/water mixtures and its implication in studies of haem catabolism

1. A study of haem spectra in pyridine/water mixtures at low pyridine concentrations revealed changes in haemochrome structure consistent with an aggregation process. No corresponding change in the structure of the haemichrome species was observed. 2. This aggregation has been correlated with a previously observed sharp decrease in the rate of coupled oxidation (degradation) of haem as pyridine concentration is decreased. The decrease appears to be due primarily to haem aggregation and not to changes in the hydrophobic nature of the solvent. The effect of ethanol and butanone addition was examined and supports this conclusion. 3. Evidence is presented that coupled oxidation occurs via the iron (II) species (haemochrome).

Efficiency of Photosubstitution of Arenetricarbonylchromium(0) Complexes

The quantum efficiency of the formation of (arene)Cr(CO)2(pyridine) (arene=benzene, mesitylene) is reported as a function of the irradiation wavelength of (arene)Cr(CO)3 and as a function of pyridine concentration. The quantum efficiency is independent of pyridine concentration in the range 0.008-0.17 M. The quantum efficiency is 0.72 ± 0.07 upon 313, 366, or 436 nm irradiation. The (arene)Cr(CO)3 complexes are found to quench triplet excited benzil at a diffusion controlled rate and the quenching is accompanied by reaction of the (arene)Cr(CO)3. The reaction product which presumably arises from CO release is the same as that obtained from direct irradiation of (arene)Cr(CO)3 in the presence of benzil. However, the triplet sensitized reaction occurs with a quantum efficiency of only 0.15 ± 0.05 in contrast to the high substitution efficiency (0.72 ± 0.07) of (arene)Cr(CO)3 upon direct irradiation.