Phenol toxicity in the tropics

Phenol, a compound that is toxic to a wide range of organisms including humans and microbes, has become a more widespread pollutant in Malaysia with the concentration of phenolic compounds exceeding the limit set down by The National Guidelines for Raw Drinking Water Quality (0.002mg L^-1). The authors of this paper have outlined the need to isolate microbes that can be used for degrading the phenol within the water for bioremediation purposes. This paper has been able to isolate a clade of phenol degrading microbes known as Rhodococcus sp. from soil samples that, when tested, registered growth of the microbe on phenol of concentrations up to 2000mg L^-1. It was found that the supernatant of the culture contained 2-hydroxymuconate semialdehyde which is the meta-degradation of phenol. This seems to indicate that the Rhodococcus both excretes this compound extracellularly and then absorbs the resulting carbon based compounds, or that it absorbs the phenol across the cell envelope and then deals with the toxin intracellularly. The authors have also reasoned that due to Rhodococcus’ ability to withstand starvation conditions Rhodococcus is very well adapted to be used as a bioremediator commercially.  

The strain isolated in this investigation was shown to exhibit a broad range of optimal temperatures for the growth on phenol, which can be a large advantage in commercial applications in many geographical regions. It is also stated within the paper that the presence of phenol and/or other toxic xenobiotics resulted in changes in the fluidity of the cell envelope of Rhodococcus which probably plays an important role in the resistance mechanism of Rhodococcus to the toxic effects of phenol. Specific growth rate was shown to be severely inhibited when this strain wasexposed to high phenol concentrations, despite this degradation was found to continue suggesting that the cellular processes were being directed more towards phenol degradation than growth.  There is the possibility that this could be used to grow Rhodococcus in lower phenol concentrations until the culture reaches a kind of critical mass which can then theoretically be used to more quickly degrade higher concentrations of phenol more efficiently. Overall this paper has shown that the Rhodococcus which was isolated has possible commercial applications for biodegradation of phenol concentrations within the ground water well of Malaysia, though this will need to be further researched before this can be implemented as a measure against phenol poisoning.

Arif NM., Ahmad SA., Syed MA., Shukor MY., 2013, Isolation and characterisation of a phenol-degrading Rhodococcus sp. strain AQ5NOL 2 KCTC 11961BP, Journal of Basic Microbiology, 53, 9-19