Methods for enrichment and pure culture isolation of filamentous gliding sulfate-reducing bacteria

Multicellular gliding filaments were observed among high numbers of other bacteria on the bottom of anaerobic marine enrichment culture flasks with sulfate and acetate or benzoate as substrates. An electronmicroscopical grid fixed in a glass tube was used as a sieve to wash the filaments free from the bulk of smaller bacteria with sterile sulfide-reduced medium. Subsequent dilution series in anaerobic soft agar tubes yielded a pure culture of a 3 μm wide filamentous bacterium, strain 5ac10, that grew by dissimilatory sulfate reduction with acetate as electron donor. A gliding sulfate-reducing bacterium of 6–8 μm diameter was enriched with benzoate; a pure culture, strain 4be13, was isolated by repeated transfer of single filaments through small portions of anoxic liquid medium. The description of these isolates as two new species of the new genus Desulfonema follows in a separate paper. Gliding filamentous bacteria similar to strain 5ac10 were also obtained in anaerobic freshwater raw cultures with added calcium sulfate and cellulose; all attempts failed to grow these bacteria in synthetic media.