SPIROSYMPLOKOS-DELTAEIBERI NOV GEN, NOV-SP - VARIABLE-DIAMETER COMPOSITE SPIROCHETE FROM MICROBIAL MATS

Large (up to 100 mum long), loosely coiled, free-living spirochetes wi th variable diameters (from 0.4 to 3 mum in the same cell) were seen a t least 40 times between August 1990 and January 1993. These spirochet es were observed in mud water and enrichment media from highly specifi c habitats in intertidal evaporite flats at three disjunct localities, one in Spain and two in Mexico. All three are sites of commercial sal tworks. Associated with Microcoleus chthonoplastes, the large spiroche tes from Spain display phototaxis and a composite organization. Shorte r and smaller-diameter spirochetes are seen inside both healthy and sp ent periplasm of larger ones. Small spirochetes attached to large ones have been observed live. From two to twelve spirochete protoplasmic c ylinders were seen inside a single common outer membrane. A distinctiv e granulated cytoplasm in which the granules are of similar diameter ( 20-32 nm) to that of the flagella (26 nm) was present. Granule diamete rs were measured in thin section and in negatively-stained whole-mount preparations. Based on their ultrastructure, large size, variable dia meter, number of flagella (3 to 6), and phototactic behavior these uni que spirochetes are formally named Spirosymplokos deltaeiberi. Under a noxic (or low oxygen) conditions they formed blooms in mixed culture i n media selective for spirochetes. Cellobiose was the major carbon sou rce in 80% seawater, the antibiotic rifampicin was added, mat from the original field site was present and tubes were incubated in the light at from 18-31-degrees-C. Within 1-2 weeks populations of the large sp irochete developed at 25-degrees-C but they could not be transferred t o fresh medium.