Thiomicrospira kuenenii sp. nov., and Thiomicrospira frisia sp. nov., two mesophilic obligately chemolithoautotrophic sulfur-oxidizing bacteria isolated from an intertidal mud flat

Two new members of the genus Thiomicrospira were isolated from an intertidal mud flat sample with thiosulfate as the electron donor and CO2 as carbon source. On the basis of differences in genotypic and phenotypic characteristics, it is proposed that strain JB-A1(T) (= DSM 12350(T)) and strain JB-A2(T) (= DSM 12351(T)) are members of two new species, Thiomicrospira kuenenii and Thiomicrospira frisia, respectively. The cells were Gram-negative vibrios or slightly bent rods. Strain JB-A1(T) was highly motile, whereas strain JB-A2(T) showed a much lower degree of motility combined with a strong tendency to form aggregates. Both organisms were obligately autotrophic and strictly aerobic. Nitrate was not used as electron acceptor. Chemolithoautotrophic growth was observed with thiosulfate, tetrathionate, sulfur and sulfide. Neither isolate was able to grow heterotrophically. For strain JB-A1(T), growth was observed between pH values of 4.0 and 7.5 with an optimum at pH 6.0, whereas for strain JB-A2(T), growth was observed between pH 4.2 and 8.5 with an optimum at pH 6.5. The temperature limits for growth were between 3.5 and 42 degrees C and 3.5 and 39 degrees C, respectively. The optimum growth temperature for strain JB-A1(T) was between 29 and 33.5 degrees C, whereas strain JB-A2(T) showed optimal growth between 32 and 35 degrees C. The mean maximum growth rate on thiosulfate was 0.35 h(-1) for strain JB-A1(T) and 0.45 h(-1) for strain JB-A2(T).