Biodegradation of plasticizers by Rhodococcus rhodochrous

Area of Science:

• Microbiology
• Environmental Science
• Biochemistry

Background:

• Plasticizers are widely used industrial chemicals.
• Biodegradation of plasticizers by microorganisms is an area of environmental interest.
• Rhodococcus rhodochrous is a bacterium known for its metabolic versatility.

Purpose of the Study:

• To investigate the microbial degradation of three common plasticizers: bis 2-ethylhexyl adipate (BEHA), dioctyl phthalate (DOP), and dioctyl terephthalate (DOTP) by Rhodococcus rhodochrous.
• To identify any toxic intermediates formed during plasticizer degradation.
• To assess the impact of plasticizer degradation on the toxicity of the growth medium.

Main Methods:

• Culturing Rhodococcus rhodochrous in the presence of individual plasticizers and a co-substrate (hexadecane).
• Monitoring plasticizer degradation and intermediate formation using analytical techniques.
• Assessing the toxicity of the growth medium using the Microtox assay.

Main Results:

• Plasticizer degradation by R. rhodochrous required a co-substrate like hexadecane.
• BEHA was completely degraded, DOP slightly, and DOTP partially when hexadecane was present.
• Degradation led to increased media toxicity, with accumulation of 2-ethylhexanoic acid (for all three) and 2-ethylhexanol (for BEHA).
• Both intermediates were identified as toxic, explaining the observed increase in toxicity.

Conclusions:

• Rhodococcus rhodochrous can biodegrade certain plasticizers, but requires a co-substrate.
• The degradation process generates toxic intermediates, 2-ethylhexanoic acid and 2-ethylhexanol, which increase environmental toxicity.
• A common degradation pathway involving ester hydrolysis and alcohol oxidation is proposed for these plasticizers.