Biomedical subjects

S G Hales

Publications and source records attributed to S G Hales.

4 recordsLinked to original sources

PubMed1996

A respirometer with improved sensitivity for ready biodegradation testing.

In this paper we describe a respirometry system with improved sensitivity, that was used to test materials at concentrations down to 3 mg C/l. Data obtained with this system, operating under the conditions of the OECD ready biodegradability tests 301B, C, D and F, is presented and compared with CO2-production data obtained under 301B conditions in the Sealed Vessel Test. For simple materials, the shape of the curves, not easily seen with CO2 production or DOC removal data, is clearly biphasic with a sigmoidal first part-suggesting growth of the inoculum on the test materials. For a selection of rapidly and readily biodegradable materials, the removal of soluble carbon was complete at the end of the first, sigmoidal part of the biodegradation curve; It is speculated that the remainder of the curve probably represents the mineralisation of part of the biomass. The respirometer generated many hundred data points per degradation curve and Monod or exponential growth models were fitted and growth parameters were derived. Growth rates under ready test conditions were derived for six materials as follows: aniline mu = 0.31 h-1, ethanolamine mu = 0.13 h-1, 1,6-hexanediol mu = 0.05 h-1, pentaerythritol mu = 0.04 h-1, C12.8EO mu = 0.13 h-1 and commercial LAS mu = 0.05 h-1.

Biodegradation, Environmental↗

PubMed1994

Biodegradation of sulphosuccinate: direct desulphonation of a secondary sulphonate.

The bacterial biodegradation of a secondary sulphonate, sulphosuccinate, has been shown to occur by direct desulphonation. A bacterium, designated Pseudomonas sp. BS1, was isolated from activated sewage sludge, for its capacity to grow on sulphosuccinate as the sole source of carbon and energy. Cultures grown on sulphosuccinate were able to convert this substrate to sulphite which was subsequently oxidized rapidly to sulphate. The sequence of desulphonation and carbon-chain catabolism of sulphosuccinate was determined from measurements of the kinetics of sulphite and 14CO2 release from specifically radiolabelled sulpho[1,4-14C]succinate and sulpho[2,3-14C]succinate, which were synthesized from the corresponding maleic anhydrides. When each radiolabelled compound was incubated separately with washed-cell suspensions of Pseudomonas BS1, sulphite was released before 14CO2, as shown by chemical assay and radiorespirometry, respectively. Differences in the kinetics and extent of 14CO2 release from the 1,4- and 2,3-labelled substrates were consistent with entry of the intact C4 chain into the citric acid cycle. When carrier oxaloacetate was added to incubation mixtures containing resting-cell suspensions and radiolabelled sulphosuccinate, a radiolabelled metabolite with the same HPLC retention time as oxaloacetate accumulated. No radioactive metabolites accumulated when carrier oxaloacetate was replaced with succinate, fumarate or malate. Collectively, the data indicated co-production of sulphite and oxaloacetate from sulphosuccinate, which is interpreted in terms of an oxidative desulphonation mechanism.

Biodegradation, Environmental↗

PubMed1986

A comparative study of the biodegradation of the surfactant sodium dodecyltriethoxy sulphate by four detergent-degrading bacteria.

The 35S-labelled metabolites produced during biodegradation of sodium dodecyltriethoxy [35S]sulphate (SDTES) by four bacterial isolates were identified and quantified. All four isolates used ether-cleavage as the predominant primary degradation pathway. In two of the organisms, the etherase system (responsible for approx. 60-70% of primary biodegradation) liberated mono-, di- and triethylene glycol monosulphates in substantial proportions, the last two esters undergoing some further oxidation to acetic acid 2-(ethoxy sulphate) and acetic acid 2-(diethoxy sulphate), respectively. For these isolates, liberation of SO4(2-) directly from SDTES was also significant (30-40%) and the organisms were shown to contain alkyl sulphatases active towards SDTES. For the remaining two isolates, etherase action was even more important (responsible for greater than 80% of primary biodegradation) and was restricted almost totally to the alkyl-ether bond to generate mainly triethylene glycol sulphate, some of which was further oxidized. Very small amounts of diethylene glycol monosulphate were also produced, but its mono-homologue, and the oxidation products of both these esters, were absent. Small amounts of inorganic sulphate (approx. 10%) were liberated by these isolates and one of them also produced compounds tentatively identified as intermediates of omega-/beta-oxidation.

Biodegradation, Environmental↗

PubMed1986

Metabolite production during the biodegradation of the surfactant sodium dodecyltriethoxy sulphate under mixed-culture die-away conditions.

Sodium dodecyltriethoxy sulphate (SDTES), either pure or as a component of commercial surfactant mixtures, underwent rapid primary biodegradation by mixed bacterial cultures in OECD screen and river-water die-away tests. Inoculation of [35S]SDTES-containing solutions with OECD screen test media acclimatized to surfactants or their degradation products led to production of various 35S-labelled glycol sulphates and their oxidation products, all known to occur during degradation of [35S]SDTES by pure bacterial isolates. Triethylene glycol monosulphate was the major catabolite together with smaller amounts of di- and monoethylene glycol monosulphates implying, by analogy with pure cultures, that ether-cleavage was the major primary biodegradation step. The oxidation product (carboxylate derivative) of each glycol sulphate was also detected together with metabolites tentatively identified as omega-/beta-oxidation products of the dodecyl chain. Relatively little SO2-4 was liberated directly from SDTES but mixed cultures derived from sewage could metabolize the sulphated glycols to SO2-4. The environmental relevance of these degradation routes was established by following metabolite production from [35S]SDTES in full-scale river-water die-away tests. Triethylene glycol sulphate was formed first, then rapidly oxidized to acetic acid 2-(diethoxy sulphate) which persisted as the major metabolite for 2-3 weeks. Small amounts of sulphated derivatives of di- and monoethylene glycols were also detected during the same period. Very little SO2-4 was formed directly from SDTES but large amounts accompanied the eventual disappearance of glycol sulphate derivatives. None of the 35S-labelled organic metabolites was persistent and, whenever [35S]SDTES was a component of a commercial mixture, all ester sulphate was completely mineralized to 35SO4(2-) within 28 d.

Biodegradation, Environmental↗