Microbial Functional Responses to Cholesterol Catabolism in Denitrifying Sludge

Area of Science:

• Microbiology
• Environmental Science
• Biochemistry

Background:

• Cholesterol is a recalcitrant steroid abundant in wastewater sludge.
• Anaerobic cholesterol degradation pathways are poorly understood at the community level.
• Microbial responses to cholesterol in complex environments remain largely elusive.

Purpose of the Study:

• To investigate microbial community responses to cholesterol in denitrifying sludge.
• To identify key microorganisms and metabolic pathways involved in anaerobic cholesterol degradation.
• To understand the role of the rare biosphere in steroid bioremediation.

Main Methods:

• Mesocosm incubation and 16S rRNA gene sequencing to profile microbial communities.
• Metatranscriptomic analysis to identify expressed genes and metabolic pathways.
• Metabolite analysis to confirm degradation products and enzyme activity.

Main Results:

• Three low-abundance betaproteobacterial operational taxonomic units (OTUs) were identified as cholesterol degraders.
• These OTUs utilize the 2,3-seco pathway, involving steroid C25 dehydrogenase and 1-testosterone dehydrogenase/hydratase.
• Degraders exhibit chemotaxis towards cholesterol, potentially using FadL-like transporters for uptake.
• Cofactor synthesis and salvage pathways are active, suggesting inter-species cooperation for nutrient supply.

Conclusions:

• Cholesterol degradation in sludge is primarily carried out by specific members of the rare biosphere.
• Steroid C25 dehydrogenase is a potential biomarker for anaerobic sterol degradation.
• The rare biosphere plays a crucial role in the bioremediation of steroids in wastewater treatment plants.