Cholesterol degradation by Gordonia cholesterolivorans

Area of Science:

• Microbiology
• Biochemistry
• Genomics

Background:

• Gordonia cholesterolivorans is a bacterium capable of degrading steroid compounds.
• Steroid side chain length is critical for bacterial degradation, with longer chains being preferred.
• Cholesterol degradation is a common trait within the Gordonia genus.

Purpose of the Study:

• To investigate the physiological and genetic basis of steroid degradation in Gordonia cholesterolivorans.
• To identify and characterize the genes responsible for cholesterol oxidation in G. cholesterolivorans.
• To compare the cholesterol degradation capabilities and genetic makeup of G. cholesterolivorans with other Gordonia species.

Main Methods:

• Physiological growth experiments using various steroids.
• Genome pyrosequencing of G. cholesterolivorans.
• Identification and characterization of cholesterol oxidase genes (ChoOx-1 and ChoOx-2).
• Targeted gene disruption to create a mutant strain.

Main Results:

• G. cholesterolivorans degrades steroids with long aliphatic side chains (e.g., cholesterol, ergosterol) but not shorter or non-aliphatic side chains.
• Two unique cholesterol oxidase genes (ChoOx-1 and ChoOx-2) were identified on distinct genomic fragments.
• ChoOx-2, phylogenetically related to Rhodococcus cholesterol oxidases, is constitutively transcribed and essential for steroid growth.
• A G. cholesterolivorans mutant lacking functional ChoOx-2 could not grow on steroids.

Conclusions:

• The ability to degrade cholesterol is widespread in the Gordonia genus.
• G. cholesterolivorans utilizes specific cholesterol oxidase enzymes, with ChoOx-2 playing a vital role in steroid metabolism.
• The genetic organization of cholesterol oxidase genes in G. cholesterolivorans is distinct from other known cholesterol-degrading bacteria.