Co-metabolic degradation of benzo(e)pyrene by halophilic bacterial consortium at different saline conditions.

Polyaromatic hydrocarbons (PAHs) with high molecular weight (more than three benzene rings) were difficult to degrade in saline environment. The present study details about the bacterial consortium enriched from industrial sludge from salt manufacturing company, Tuticorin, Tamilnadu (India), which was capable of degrading 1, 4 dioxane (Emerging micropollutant) and also phenanthrene as sole carbon source under saline condition. The halophilic bacterial consortium was able to degrade low molecular weight (LMW) phenanthrene, but unable to degrade high molecular weight (HMW) benzo(e)pyrene. To overcome this problem, phenanthrene was added as co-substrate along with benzo(e)pyrene which enhanced the biodegradation process by co-metabolism under saline conditions. The consortium potentially degraded 80% and 99% of benzo(e)pyrene in 7 days and phenanthrene in 5 days at 30 g l⁻¹ of NaCl concentration. When the saline concentration increased to 60 g l⁻¹, degradation of phenanthrene (97% in 8 days) and benzo(e)pyrene (65% in 10 days) was observed. Further increase in saline concentration to 90 g I⁻¹ of NaCI showed reduction in the percent degradation of phenanthrene and benzo(e)pyrene leads to 30.3% and 9% respectively in 6 days. Potential bacterial strains, present in PAHs degrading bacterial consortium were identified as Achromobacter sp. AYS3 (JQ419751), Marinobacter sp. AYS4 (JQ419752) and Rhodanobacter sp. AYS5 (JQ419753). The present study details about the effect of salinity on PAHs degradation and vital role of co-metabolism on biodegradation of benzo(e)pyrene with phenanthrene under saline conditions.

Studies on in vitro culture supernatant of P. falciparum. Isolation of antigens for serology.

Twenty-four-hour-old in vitro culture supernatant of Plasmodium falciparum was collected and a comparative study was carried out using supernatant antigen and antigen prepared from in vitro culture of P. falciparum parasites in ELISA with sera from slide-positive malaria cases. The results were comparable, and in certain cases higher ELISA readings were observed with the supernatant antigen.

Evidence for repetitive structure of the large acyl-carrier protein subunit of Escherichia coli citrate lyase.

The amino acid composition of the unusually large acyl-carrier protein subunit of citrate lyase from Escherichia coli is characteristic of a protein with a highly repetitive structure. Peptide mapping studies provide further evidence of repetitive sequences within the subunit. Only a single Pauly-positive spot is detected in the tryptic peptide map although the subunit contains 8 histidine residues. The 4 prosthetic groups covalently bound to the subunit are recovered in a single tryptic fragment in almost quantitative yield. These structural features of the large acyl-carrier protein subunit probably reflect internal gene duplications.

Purification and properties of citrate lyase from Escherichia coli.

Citrate lyase (EC 4.1.3.6) has been purified from Escherichia coli and the homogeneity of the preparation established from the three-component subunits obtained on sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The purified enzyme has a specific activity of 120 mumol min-1 mg-1 and requires optimally 10 mM Mg2+ and a pH of 8.0 for the cleavage reaction. The native enzyme is polydispersed in the ultracentrifuge and in polyacrylamide gel electrophoresis. The enzyme complex is composed of three different polypeptide chains of 85 000, 54 000, 32 000 daltons. An estimate of subunit stoichiometry indicates that 1 mol of the largest polypeptide chain is associated with 6 mol each of the smaller ones. The polypeptide subunits have been isolated in pure state and their biological functions characterize. The 54 000-dalton subunit functions as the acyltransferase alpha subunit catalyzing the formation of citryl coenzyme A from citrate in the presence of acetyl coenzyme A and ethylenediaminetetraacetic acid. The 32 000-dalton subunit functions as the acyllyase beta subunit catalyzing the cleavage of (3S)-citryl coenzyme A to oxal-acetate and acetyl coenzyme A. The 85 000-dalton subunit, which carries exclusively the prosthetic group components, functions as the acyl-carrier protein gamma subunit in the cleavage of citrate in the presence of mg2+ and the alpha and beta subunits. The presence of a large ACP subunit and the unusual stoichiometry of the different subunits distinguish the complex from other citrate lyases. A ligase which acetylates the deacetyl[citrate lyase] in the presence of acetate and ATP has ben shown to be present in the organism.(ABSTRACT TRUNCATED AT 250 WORDS)

S-acylated residues of the acyl-carrier protein subunit of Klebsiella aerogenes citrate lyase.

Oxidation of the isolated deacetyl acyl-carrier protein subunit of citrate lyase from Klebsiella aerogenes with Cu2+-o-phenanthroline complex leads exclusively to intrapeptide disulfide bridge formation indicating that the cysteamine and the cysteine residues are located in close proximity. The S-acetylation of the cysteine residue in deacetyl acyl-carrier protein subunit is catalysed by a citrate lyase ligase preparation in presence of acetate and ATP. Reaction-inactivation of citrate lyase results in deacetylation of the S-acetyl cysteamine residue of the prosthetic group but not of the S-acylated cysteine residue in the acyl-carrier protein.

The presence of essential arginine residues at the active sites of citrate lyase complex from Klebsiella aerogenes.

The acyl-transferase and acyl-lyase activities of Klebsiella aerogenes citrate lyase complex are inactivated by the arginine specific reagents phenylglyoxal and 2,3-butanedione, the former reagent being the more potent inhibitor. Citrate and (3S)-citryl-CoA protect the transferase activity, while acetyl-CoA markedly enhances the rate of the inactivation. (3S)-Citryl-CoA protects the lyase subunit in the complex from inactivation. The kinetics of inactivation suggest the involvement of a single arginine residue at each of the active sites of the transferase and of the lyase subunits.

Photoaffinity labeling of Klebsiella aerogenes citrate lyase by p-azidobenzoyl coenzyme A.

p-Azidobenzoyl coenzyme A functions as a linear competitive inhibitor for (3S)-citryl-CoA in the citryl-CoA oxaloacetate-lyase reaction catalyzed by the Klebsiella aerogenes deacetylcitrate lyase complex (Ki = 80 microM; (3S)-citryl-CoA Km = 67 microM). Inactivation is irreversible on photolysis of p-azidobenzoyl-CoA in the presence of the deacetylcitrate lyase complex. Mg2+ is not required for the inactivation. Inactivation is blocked by (3S)-citryl-CoA in the presence of ethylenediaminetetraacetic acid. p-Azidobenzoyl-CoA has no effect on the acetyl-CoA:citrate CoA transferase activity of both the deacetylcitrate lyase complex and its isolated transferase subunit. The stoichiometry of the CoA ester binding has been investigated by the use of p-azido[14C]benzoyl-CoA as a photoaffinity reagent. The labeling is exclusively on the lyase beta subunit of the citrate lyase complex.