Taxonomy, Physiology and Ecology of Heliobacteria

Madigan, Michael T.; Ormerod, John G.

doi:10.1007/0-306-47954-0_2

Cited by 48 publications

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“…In terms of carbon metabolism, heliobacteria are obligately heterotrophic. Growth occurs either photoheterotrophically (anoxic, with light) on a limited range of organic substrates or by fermentation of pyruvate in the dark (22,34). By contrast, autotrophic growth, the hallmark of photosynthetic organisms, has not been observed with cultures of any heliobacterium species (34).…”

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“…Growth occurs either photoheterotrophically (anoxic, with light) on a limited range of organic substrates or by fermentation of pyruvate in the dark (22,34). By contrast, autotrophic growth, the hallmark of photosynthetic organisms, has not been observed with cultures of any heliobacterium species (34). Heliobacteria are phylogenetically unique, as they are the only phototrophic organisms that group within the bacterial phylum Firmicutes using 16S rRNA gene sequence analyses (8,32).…”

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

et al. 2008

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Despite the fact that heliobacteria are the only phototrophic representatives of the bacterial phylum Firmicutes, genomic analyses of these organisms have yet to be reported. Here we describe the complete sequence and analysis of the genome of Heliobacterium modesticaldum, a thermophilic species belonging to this unique group of phototrophs. The genome is a single 3.1-Mb circular chromosome containing 3,138 open reading frames. As suspected from physiological studies of heliobacteria that have failed to show photoautotrophic growth, genes encoding enzymes for known autotrophic pathways in other phototrophic organisms, including ribulose bisphosphate carboxylase (Calvin cycle), citrate lyase (reverse citric acid cycle), and malyl coenzyme A lyase (3-hydroxypropionate pathway), are not present in the H. modesticaldum genome. Thus, heliobacteria appear to be the only known anaerobic anoxygenic phototrophs that are not capable of autotrophy. Although for some cellular activities, such as nitrogen fixation, there is a full complement of genes in H. modesticaldum, other processes, including carbon metabolism and endosporulation, are more genetically streamlined than they are in most other low-G؉C gram-positive bacteria. Moreover, several genes encoding photosynthetic functions in phototrophic purple bacteria are not present in the heliobacteria. In contrast to the nutritional flexibility of many anoxygenic phototrophs, the complete genome sequence of H. modesticaldum reveals an organism with a notable degree of metabolic specialization and genomic reduction.

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

et al. 2008

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“…The green nonsulfur bacteria (Chloroflexus group) contain bacteriochlorophyll c or d and chlorosomes, as do certain green sulfur bacteria, but produce a photosynthetic reaction center of the purple bacterial type (28). Heliobacteria are gram positive and produce a unique photosynthetic pigment, bacteriochlorophyll g (18,19). Phototrophic purple bacteria are the most phylogenetically diverse anoxyphototrophs, with members in the ␣, ␤, and ␥ subclasses of the Proteobacteria (36).…”

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Photosynthetic and Phylogenetic Primers for Detection of Anoxygenic Phototrophs in Natural Environments

Achenbach

Carey

Madigan

2001

Appl Environ Microbiol

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Primer sets were designed to target specific 16S ribosomal DNA (rDNA) sequences of photosynthetic bacteria, including the green sulfur bacteria, the green nonsulfur bacteria, and the members of the Heliobacteriaceae (a gram-positive phylum). Due to the phylogenetic diversity of purple sulfur and purple nonsulfur phototrophs, the 16S rDNA gene was not an appropriate target for phylogenetic rDNA primers. Thus, a primer set was designed that targets the pufM gene, encoding the M subunit of the photosynthetic reaction center, which is universally distributed among purple phototrophic bacteria. The pufM primer set amplified DNAs not only from purple sulfur and purple nonsulfur phototrophs but also from Chloroflexus species, which also produce a reaction center like that of the purple bacteria. Although the purple bacterial reaction center structurally resembles green plant photosystem II, the pufM primers did not amplify cyanobacterial DNA, further indicating their specificity for purple anoxyphototrophs. This combination of phylogenetic-and photosynthesis-specific primers covers all groups of known anoxygenic phototrophs and as such shows promise as a molecular tool for the rapid assessment of natural samples in ecological studies of these organisms.

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“…Microscopy of heat-shocked enrichments always shows spore-forming bacteria and free spores ( Figure 1b). From such enrichments, the isolation of heliobacteria is straightforward using routine microbiological techniques for the isolation of anoxygenic phototrophic bacteria (Madigan and Ormerod, 1995). As of 2010, 4 genera and 10 species of heliobacteria have been described and grouped together in their own taxonomic family, the Heliobacteriaceae (Beer-Romero and Gest, 1987;Madigan, 1992Madigan, , 2006Madigan and Ormerod, 1995;Madigan, 2009, 2010; Table 2).…”

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Heliobacteria

Asao

Madigan

2010

Encyclopedia of Life Sciences

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Heliobacteria are the most recently discovered of the anoxygenic phototrophic bacteria. Heliobacteria contain bacteriochlorophyll g , a pigment unique to species of this group, and synthesise the simplest photosynthetic complexes of all known phototrophs. Also, unlike all other phototrophs, heliobacteria produce endospores but cannot grow autotrophically. Four genera of heliobacteria are known. Species of Heliobacterium , Heliobacillus and Heliophilum grow best at neutral pH, whereas species of Heliorestis are alkaliphilic. Heliobacterium , Heliobacillus and Heliophilum species form one phylogenetic clade whereas Heliorestis species form a second within the phylum Firmicutes of the domain Bacteria. Heliobacteria have a unique ecology, being primarily terrestrial rather than aquatic, and some species may have evolved a mutualistic relationship with rice plants. The genome sequence of the thermophile Heliobacterium modesticaldum supports the hypothesis that heliobacteria are minimalist phototrophs, and because of this, heliobacteria may have played a pivotal role in the evolution of phototrophic bacteria. Key Concepts: Heliobacteria are unlike all known anoxygenic phototrophic bacteria because of their unique bacteriochlorophyll, Gram‐positive phylogeny, and primarily soil habitat. Heliobacteria employ the simplest of all photosynthetic energy‐generating systems and thus their study may yield important clues to when and how photosynthesis evolved. In addition to being phototrophic, heliobacteria are strong nitrogen‐fixing bacteria and possibly associate with plants such as rice in a type of symbiotic association.

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Taxonomy, Physiology and Ecology of Heliobacteria

Cited by 48 publications

References 26 publications

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

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

Photosynthetic and Phylogenetic Primers for Detection of Anoxygenic Phototrophs in Natural Environments

Heliobacteria

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