Gene cluster encoding cholate catabolism in Rhodococcus spp

Area of Science:

• Microbiology
• Biochemistry
• Environmental Science

Background:

• Bile acids are crucial steroids in vertebrate digestion.
• Bacterial bile acid catabolism impacts the carbon cycle and gut ecology.
• Potential commercial applications exist for bile acid degradation pathways.

Purpose of the Study:

• To identify and characterize the genetic basis for cholate catabolism in Rhodococcus jostii RHA1.
• To investigate the enzymes and genes involved in bile acid degradation.
• To differentiate cholate catabolism from cholesterol catabolism pathways.

Main Methods:

• Transcriptomic analysis of RHA1 grown on cholate.
• Gene deletion studies to assess essentiality for growth.
• Heterologous expression and biochemical characterization of key enzymes (CoA synthetases).
• Comparative genomics to identify orthologous gene clusters.

Main Results:

• A distinct gene cluster upregulated on cholate was identified in R. jostii RHA1.
• kshA3, encoding a 3-ketosteroid-9α-hydroxylase, is essential for cholate growth.
• CasG initiates cholate degradation by forming cholyl-CoA, and CasI processes intermediates.
• Orthologous gene clusters are present in other Rhodococcus species and Thermomonospora curvata.
• Bacteria lacking the cluster cannot grow on cholate, confirming its role.

Conclusions:

• The identified gene cluster specifically encodes cholate catabolism in Rhodococcus.
• This pathway is evolutionarily conserved within Rhodococcus and related bacteria.
• The findings distinguish cholate catabolism from the well-known cholesterol catabolism pathway.