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J C Philp

Publications and source records attributed to J C Philp.

6 recordsLinked to original sources
PubMed2002

Alkanotrophic Rhodococcus ruber as a biosurfactant producer.

In this report we examined the structure and properties of surface-active lipids of Rhodococcus ruber. Most historical interest has been in the glycolipids of Rhodococcus erythropolis, which have been extensively characterised. R. erythropolis has been of interest due to its great metabolic diversity. Only recently has the metabolic potential of R. ruber begun to be explored. One major difference in the two species is that most R. ruber strains are able to oxidise the gaseous alkanes propane and butane. In preparation for investigation of the effects of gas metabolism on biosurfactant production, we set out to characterise the biosurfactants produced during growth on liquid n-alkanes and to compare these with R. erythropolis glycolipids.

Alkanes↗
PubMed2001

Recovery of Rhodococcus biosurfactants using methyl tertiary-butyl ether extraction.

In the present study, we proposed methyl tertiary-butyl ether (MTBE) as a solvent for extraction of biosurfactants from Rhodococcus bacterial cultures. After comparison with other well known solvent systems used for biosurfactant extraction, it was found that MTBE was able to extract crude surfactant material with high product recovery (10 g/l), efficiency (critical micelle concentration (CMC), 130-170 mg/l) and good functional surfactant characteristics (surface and interfacial tensions, 29 and 0.9 mN/m, respectively). The isolated surfactant complex contained 10% polar lipids, mostly glycolipids possessing maximal surface activity. Ultrasonic treatment of the extraction mixture increased the proportion of polar lipids in crude extract, resulting in increasing surfactant efficiency. Due to certain characteristics of MTBE, such as relatively low toxicity, biodegradability, ease of downstream recovery, low flammability and explosion safety, the use of this solvent as an extraction agent in industrial scale biosurfactant production is feasible.

Glycolipids↗
PubMed1999

Identification and environmental detection of Rhodococcus species by 16S rDNA-targeted PCR.

Bacteria of the genus Rhodococcus can degrade a wide range of organic pollutants and catalyse many useful biotransformations. There is a need for improved tests to identify Rhodococcus species. PCR-based methods for species identification offer advantages in terms of speed and accuracy over traditional methods and can allow direct detection of microbes in environmental samples., PCR tests, using primers targeted at species-specific sequences in the 16S rRNA gene, were successfully developed for R. globerulus, R. erythropolis, R. opacus and R. ruber. These tests gave positive results with all or most strains of target species but did not generally cross-react with other species. Cases of apparent cross-reaction were shown to be due to prior misclassification of strains of R. opacus as R. erythropolis and of strains of R. ruber as R. rhodochrous. A simple and rapid method for the extraction and purification of DNA from soil was developed and successfully applied to the PCR detection of indigenous R. erythropolis in an environmental sample. Cell lysis in the samples was achieved by lysozyme and sarkosyl treatment, aided by freeze-thaw cycles. Removal of humic compounds inhibitory to PCR was accomplished by CTAB treatment with solvent extraction and, if necessary, passage of extracts through Sepharose CL-6B in a spun-column format. Extracts prepared using a tris-EDTA buffer were much clearer than those prepared using a sodium phosphate buffer, indicating lower levels of humic compounds. A detection limit of 104 cfu g-1 of soil was achieved and the use of a secondary PCR allowed detection of 1 cfu g-1.

Bacterial Typing Techniques↗
PubMed1996

Identification of Rhodococcus equi using the polymerase chain reaction.

Two regions in the gene coding for 16S rRNA in Rhodococcus equi were selected as species-specific primer sequences for the polymerase chain reaction (PCR). PCR using these primers was tested against 10 strains of R. equi (including the type strain) and gave positive results for all but was negative for all other tested species of Rhodococcus; representatives of the most closely related genera and a number of other bacterial species. This method could therefore be used to identify this species which can infect the lungs or other organs of horses, pigs, humans and other animals.

Actinomycetales Infections↗
PubMedDate not supplied

Surface-active lipids in rhodococci.

Like other hydrocarbon-oxidising bacteria, rhodococci respond to the presence of alkanes by producing biosurfactant molecules to improve their ability to utilise these hydrophobic compounds as growth substrates. In the rhodococci these surfactants are predominantly glycolipids, the majority of which remain cell-bound during unrestricted growth. Most work has been done on the trehalose mycolates formed by Rhodococcus erythropolis, but nitrogen-limited conditions lead to the production of anionic trehalose tetraesters also. As surfactants, these compounds, whether purified or in crude form, are able to reduce the surface tension of water from 72 mN m-1 to a low of 26, thus making them among the most potent biosurfactants known. They are also able to reduce the interfacial tension between water and a hydrophobic phase (e.g. n-hexadecane) from 43 mN m-1 to values less than one (Table 1). Biosurfactants have about a ten- to 40-fold lower critical micelle concentration than synthetic surfactants. Such properties suggest a range of industrial applications, where a variety of surface-active characteristics are appropriate. Interest in biosurfactants as industrial chemicals results from the toxicity of many petrochemical-derived surfactants. Currently world-wide surfactant production is on a very large scale, and the demand for them is increasing. However, the drive towards less environmentally damaging chemicals makes biosurfactants attractive as they have lower toxicity. The reason they have not achieved a significant market share is the cost of production, which is considerably higher than for synthetic surfactants. This problem is being addressed using several strategies. An approach where there is great scope for improvement with the rhodococci is an understanding of the genetic basis of glycolipid production, which is largely unknown. They may find applications in the near future in the environmental remediation industries, where the requirement for purified molecules is of less importance. This review summarises knowledge of the chemistry, biochemistry and production of Rhodococcus surface-active lipids. Where they have been used, or there is potential for use, in industrial applications is discussed.

Biodegradation, Environmental↗