Elucidating stream bacteria utilizing terrestrial dissolved organic matter.

Area of Science:

• Environmental Microbiology
• Aquatic Ecosystems
• Biogeochemistry

Background:

• Terrestrial dissolved organic matter (tDOM) is a crucial energy source in aquatic ecosystems.
• Microbial utilization of tDOM is significant, but specific bacterial groups involved remain largely undetermined.

Purpose of the Study:

• To identify microbial groups actively utilizing tDOM in stream sediments.
• To understand the role of tDOM in the aquatic ecosystem's energy flow.

Main Methods:

• Phospholipid fatty acid (PLFA) analysis to characterize microbial community structure.
• Stable-isotope probing (SIP) using 13C-labeled tDOM to identify metabolically active microbes.
• Mesocosm incubation experiments with labeled tDOM.

Main Results:

• Prokaryotes constituted 61% of the streambed microbial community.
• Specific bacterial PLFAs showed significant 13C incorporation, identifying aerobic, facultative anaerobic, and anaerobic bacteria as active tDOM utilizers.
• 13C incorporation into microeukaryotic fatty acids suggested bacterial consumption by microeukaryotes.

Conclusions:

• Stream bacteria actively utilize terrestrial dissolved organic matter.
• tDOM substantially contributes to the energy flow in aquatic ecosystems.
• Microbial food webs in streams involve the transfer of tDOM-derived carbon from bacteria to microeukaryotes.