Detection and quantification of rumen methanogens using F₄₂₀ autofluorescence profiling with spectral flow cytometry

Area of Science:

• Microbiology
• Environmental Science
• Biotechnology

Background:

• Methanogenic archaea in ruminant digestive systems produce significant greenhouse gas emissions.
• Rumen methanogens possess intracellular co-factor F420, causing autofluorescence.
• Existing methods for methanogen quantification are limited in complex environments.

Purpose of the Study:

• To develop a spectral flow cytometry method for direct quantification of autofluorescent methanogens in rumen.
• To overcome challenges posed by overlapping autofluorescence from feed particles.
• To provide a tool for assessing methane mitigation strategies targeting rumen methanogens.

Main Methods:

• Developed spectral flow cytometry utilizing autofluorescence of intracellular F420.
• Employed spectral unmixing to differentiate methanogens from autofluorescent feed particles.
• Validated quantification against known concentrations and correlated with methane yields.

Main Results:

• Successfully quantified methanogens in rumen content over a wide concentration range (4 × 10^4 to 4 × 10^7 cells/mL).
• Confirmed specificity by absence of signal in F420-lacking cultures and NaBH4-treated samples.
• Demonstrated a strong correlation between methanogen counts and methane yields in treated animals.

Conclusions:

• Spectral flow cytometry offers a rapid and precise method for enumerating autofluorescent methanogens in rumen.
• The method is robust, allowing for sample storage up to 3 days at 4°C.
• This technique is a valuable tool for evaluating the efficacy of methane reduction strategies in livestock.