Molecular evidence that the capacity for endosporulation is universal among phototrophic heliobacteria

Abstract

Although enrichment cultures for anoxygenic phototrophic heliobacteria commonly contain sporulating cells, once strains of heliobacteria are obtained in pure culture, they all but cease to sporulate. In fact, some species of heliobacteria have never been observed to sporulate. Thus, despite their phylogenetic connection to endospore-forming bacteria, the question of sporulation capacity in heliobacteria remains open. We have investigated this problem using PCR and Southern hybridization as tools and show here that all recognized species of heliobacteria tested, as well as several unclassified strains, contain homologs to the ssp genes of Clostridium and Bacillus species, genes that encode key sporulation-specific proteins. It can therefore be concluded that as a group, heliobacteria are likely all to be endosporeforming bacteria in agreement with their phylogenetic placement within the`low GC' Gram-positive bacteria. ß

The Genome of Heliobacterium modesticaldum , a Phototrophic Representative of the Firmicutes Containing the Simplest Photosynthetic Apparatus

“…Although genetic studies in which the B. subtilis spoIIB gene was altered resulted in only minor impairment of sporulation (35), the apparent absence of both spoIIB and spo0M in heliobacteria could adversely affect the ability of these organisms to sporulate. Consistent with this hypothesis is the fact that sporulation of pure cultures of heliobacteria is rarely observed (24).…”

“…Many genes linked to endosporulation in Bacillus subtilis were not found in H. modesticaldum, which may have relevance for the ambiguous sporulation patterns observed in heliobacterial cultures (24). These results describe H. modesticaldum strain Ice1, the type strain of this species isolated from Icelandic hot spring volcanic soils (23).…”

“…Endosporulation appears to be universal among heliobacteria (24), and the ability of endospores to survive pasteurization (heating to 80°C for 15 min) can be exploited for selective enrichment of these organisms (33,49). H. modesticaldum contains genes encoding all five sigma factors deemed essential for sporulation in B. subtilis ( H , E , F , G , and K ).…”

A Genomic Signature and the Identification of New Sporulation Genes

“…However, endospore formers are found in other classes within the Firmicutes and encompass aerobic or anaerobic organisms with a wide range of morphologies, lifestyles, and metabolic traits, including rods, cocci, branching species, plant or animal pathogens or symbionts, syntrophs, sulfate reducers, phototrophs (11)(12)(13)(14)(15)(16)(17), and remarkably, didermic species (18). Despite the extreme diversity of endospore-forming bacteria, the basic architecture of an endospore is conserved across species (19).…”

Molecular evolution of the nif gene cluster carrying nifI1 and nifI2 genes in the Gram-positive phototrophic bacterium Heliobacterium chlorum

“…This strictly anaerobic organism contained a novel photosynthetic pigment, bacteriochlorophyll g, which became a main characteristic of the family 'Heliobacteriaceae' (Brockmann & Lipinski, 1983;Madigan, 2001). Phylogenetically, heliobacteria belong to the group of low-G+C-content Grampositive bacteria that includes Clostridium and Bacillus (Madigan, 1992(Madigan, , 2001, and they all have the capacity for endosporulation (Kimble-Long & Madigan, 2001). Hbt.…”