The authors show that Brevibacillus massiliensis, an obligately aerobic microbe isolated from human feces, takes up tungsten and incorporates it into an aldehyde-oxidizing enzyme (BmWOR). The purified enzyme carries one tungsten-pyranopterin cofactor and oxidizes aldehydes found in the gut and in cooked foods with high affinity, and it worked in air when its ferredoxin partner was present.
Key numbers
- Low-metal growth medium contained 2 nM molybdenum and less than 0.7 nM tungsten by ICP-MS; tungstate and molybdate were added at 100 nM (Results).
- Cytoplasmic tungsten rose roughly 16-fold when 100 nM tungstate was added; without additions both metals were below 0.1 micromol per g protein (Figure 3A; Results).
- Benzaldehyde oxidation in cytoplasmic extracts was about four-fold higher with 100 nM tungsten added (Figure 3B; Results).
- About 0.3 mM furoic acid formed from added furfural only when tungsten was supplied (Figure 3C; Results).
- Apparent Km below about 6 micromolar for gut-related aldehydes including furfural, propionaldehyde, benzaldehyde and tolualdehyde; apparent Km for ferredoxin below 5 micromolar (Abstract; Results).
Methods (brief)
Cells were grown with and without added tungstate and molybdate in a medium built from high-purity reagents. Metal content of cytoplasmic extracts was measured by ICP-MS (Agilent 7900), gene expression by qPCR, and the tungsten enzyme was purified from native biomass and characterized for substrate range, kinetics and oxygen tolerance. Genome analysis placed the enzyme in a clade of tungsten oxidoreductases.
Evidence fitness
Supports mechanistic statements that some human gut bacteria take up tungsten and use it in enzymes that oxidize dietary and microbial aldehydes. It does not measure tungsten in foods, stool or people, and does not show any effect of dietary tungsten on the gut community or human health.
Limitations
A single bacterial strain studied in culture. Tungsten levels were set by the experimenters, not drawn from gut conditions. The proposed detoxification and energy roles in the gut are inferences from enzyme properties and genome content.
Related evidence
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