Streptomycetes contributing to atmospheric molecular hydrogen soil uptake are widespread and encode a putative high‐affinity [NiFe]‐hydrogenase

Summary Uptake of molecular hydrogen (H 2 ) by soil is a biological reaction responsible for ∼80% of the global loss of atmospheric H 2 . Indirect evidence obtained over the last decades suggests that free soil hydrogenases with an unusually high affinity for H 2 are carrying out the reaction. This assumption has recently been challenged by the isolation of Streptomyces sp. PCB7, displaying the high‐affinity H 2 uptake activity previously attributed to free soil enzymes. While this finding suggests that actinobacteria could be responsible for atmospheric H 2 soil uptake, the ecological importance of H 2 ‐oxidizing streptomycetes remains to be investigated. Here, we show that high‐affinity H 2 uptake activity is widespread among the streptomycetes. Among 14 streptomycetes strains isolated from temperate forest and agricultural soils, six exhibited a high‐affinity H 2 uptake activity. The gene encoding the large subunit of a putative high‐affinity [NiFe]‐hydrogenase ( hydB ‐like gene sequence) was detected exclusively in the isolates exhibiting high‐affinity H 2 uptake. Catalysed reporter deposition‐fluorescence in situ hybridization (CARD‐FISH) experiments targeting hydB ‐like gene transcripts and H 2 uptake assays performed with strain PCB7 suggested that streptomycetes spores catalysed the H 2 uptake activity. Expression of the activity in term of biomass revealed that 10 6 –10 7 H 2 ‐oxidizing bacteria per gram of soil should be sufficient to explain in situ H 2 uptake by soil. We propose that specialized H 2 ‐oxidizing actinobacteria are responsible for the most important sink term in the atmospheric H 2 budget.