Lk. Kimble et al., HELIOBACTERIUM MODESTICALDUM, SP-NOV, A THERMOPHILIC HELIOBACTERIUM OF HOT-SPRINGS AND VOLCANIC SOILS, Archives of microbiology, 163(4), 1995, pp. 259-267
Enrichment cultures for heliobacteria at 50 degrees C yielded several
strains of a thermophilic heliobacterium species from Yellowstone hot
spring microbial mats and volcanic soils from Iceland. The novel organ
isms grew optimally above 50 degrees C, contained bacteriochlorophyll
g, and lacked intracytoplasmic membranes. All isolates were strict ana
erobes and grew best as photoheterotrophs, although chemotrophic dark
growth on pyruvate was also possible. These thermophilic heliobacteria
were diazotrophic and fixed N-2 up to their growth temperature limit
of 56 degrees C. Phylogenetic studies showed the new isolates to be sp
ecific relatives of Heliobacterium gestii and, as has been found in H.
gestii, they produce heat-resistant endospores. The unique assemblage
of properties found in these thermophilic heliobacteria implicate the
m as a new species of this group, and we describe them herein as a new
species of the genus Heliobacterium, Heliobacterium modesticaldum.