A chemostat culture of A2 was grown under alternate limitation of acetate and thiosulphate at a dilution rate of 0·05 h. With a substrate alternation of 4 h acetate/4 h thiosulphate or 8 h acetate/16 h thiosulphate, uninterrupted growth of the culture was obtained. However, with 16 h acetate/8 h thiosulphate, required several hours before it attained autotrophic growth at a rate of 0·05 h following the transition from acetate to thiosulphate supply. In a two-membered mixed culture with the heterotrophic spirillum , A2 outcompeted the heterotroph when grown under alternating limitation of acetate (4 h) and thiosulphate (4 h). Under the same growth conditions A2 coexisted in equal numbers with , from which it was concluded that A2 grew only heterotrophically on acetate in this case. Analogous competition experiments with three-membered cultures, grown under the same conditions, resulted in complete elimination of A2 and coexistence of and spirillum in equal numbers. In an enrichment culture, again grown under the same regime, a facultatively chemolithotrophic spirillum-shaped or became dominant; this organism was subsequently isolated in pure culture.


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