Search Results (13)

Heliobacteraceae are unique endospore-forming photosynthetic bacteria that are known for possessing the simplest photosynthetic apparatus of any known organism. More genomic and physiological analysis is needed to further understand the evolution of photosynthesis and the unique metabolic pathways of nitrogen and sulfur metabolism in this family. Here, we present the genome and phylogenetic analysis of “Heliomicrobium sulfidophilum” strain BR4^T, which was isolated previously from an alkaline sulfide-containing hot spring. In addition to the presence of a Type I reaction center, genes for bacteriochlorophyll g synthesis and nitrogenase system, the genomic analysis also explains the need for biotin as a supplied growth factor in Heliomicrobium species. The Heliobacteriaceae genome comparison also revealed a previously unidentified gene cluster of heterodisulfide reductase-like proteins (Hdr genes) and molybdopterin-based enzymes for polysulfide reductase. The whole-genome comparison, including ANI, dDDH, and single-gene phylogenetic analyses, confirms the correct placement of strain BR4 in the Heliomicrobium genus and strengthens the overall phylogenetic distribution of the Heliobacteriaceae. Full article

A novel photoheterotrophic, beige-pigmented, bacteriochlorophyll a-containing strain KR11^T was isolated from Kaprový pond in Třeboň, Czechia. KR11^T cells were Gram-negative, rod-shaped, and motile. The isolated strain grew under photoheterotrophic conditions between 20 and 40 °C (optimum 22–25 °C), at pH ranges from 6.0 to 9.0 (optimum 7.0). It did not require NaCl for growth but tolerated NaCl concentrations up to 1.5% (w/v). No growth was observed under photoautotrophic conditions. Strain KR11^T showed the highest 16S rRNA gene sequence similarity to the type strains of Stagnihabitans tardus CYK-10^T (98.84%), Tabrizicola fusiformis SY72^T (95.95%), and Rhodobacter sediminis N1^T (95.37%). Phylogenetic analyses based on 16S rRNA gene sequences indicated that strain KR11^T clusters within the genus Stagnihabitans in the family Paracoccaceae of class Alphaproteobacteria. The whole-genome sequence of strain KR11^T comprises 4,085,976 bp with a 65 mol% G+C content. Phylogenomic analysis, including core-genome phylogeny, and the low genomic similarity (<95% ANI and <70% dDDH) to phylogenetically related taxa confirmed the taxonomic separation of strain KR11^T at the species level. The distinctive phenotypic traits, chemotaxonomic studies, phylogenetic, and genomic analysis establish strain KR11^T as a novel species within the genus Stagnihabitans. Accordingly, we propose the name Stagnihabitans lacustris sp. nov. KR11^T (=CCUG 74777^T, LMG 31924^T), isolated from fresh water. Full article

A pink colored, rod-shaped, prosthecate, Gram-negative bacterial strain MS644^T was discovered in saline spring water near Lake Winnipegosis, Manitoba, Canada. It produces bacteriochlorophyll a, which is incorporated into its reaction center and light harvesting I complex. Alongside no anaerobic or photoautotrophic growth, these features support its designation as an aerobic anoxygenic phototroph (AAP). Unlike most AAP, the photosynthetic apparatus is produced in significantly greater amounts compared to carotenoids. Sequence of the 16S rRNA gene identified relatedness to Glycocaulis albus (96.19%), Glycocaulis alkaliphilus (96.12%) and Glycocaulis abyssi (96.07%). The DNA G + C content was 66.01 mol %. Differences in salt tolerance and photosynthesis capability, alongside low average nucleotide identity, average amino acid identity and digital DNA-DNA hybridization compared to other Maricauaceae, support the designation of the strain as a representative of a new genus. Therefore, we propose that strain MS644^T (=NCIMB 15625^T = DSM 121292^T) be classified as the type species of a new genus Apolloniradiicaulis in Maricaulaceae with the name A. salifontis gen. nov., sp. nov. Full article

Utilization of various biomasses as raw materials in biorefineries represents a promising alternative for the production of valuable chemicals and biofuels. This study investigates the potential of the fungus Mucor indicus DSM 2158, cultivated on media containing the liquid phase of grass hydrolysates (LGH) and various nitrogen sources (yeast extract and corn steep liquor), for the production of valuable metabolites, such as ethanol, chitin, chitosan, and fatty acids. The ethanol yield varied depending on the cultivation media and conditions. The highest substrate-into-ethanol conversion coefficients (0.14–0.2 g g⁻¹) were achieved during M. indicus cultivation on the LGH medium containing 5 g L⁻¹ CSL in Erlenmeyer flasks and a bubble column bioreactor. In these cultivations, the highest fungal biomass concentrations (5.61–5.91 g L⁻¹) were also observed. In flask cultivations, the highest content of total lipids in fungal dry biomass (15.76%) was observed. The obtained fungal biomass contained up to 22 fatty acids, with oleic acid (≈50%) being the most predominant. Chitin and chitosan yields were from 0.1 g g⁻¹ to 0.3 g g⁻¹ of dry biomass depending on the cultivation media and conditions. The residual media from the cultivation of M. indicus were used for the growth of the non-sulfur purple bacterium Rhodovulum adriaticum DSM 2781. Cultivations of R. adriaticum DSM 2781 on the residual media, in Erlenmeyer flasks and a stirred-tank bioreactor, resulted in a biomass yield of 0.50 to 2.26 g L⁻¹. After extraction of bacterial biomass, total pigments (expressed as bacteriochlorophyll-a) were obtained in the range from 1.8 to 48.1 mg g⁻¹ dry biomass depending on the media and cultivation conditions. The highest titer of bacteriochlorophyll-a was achieved during cultivation on the exhausted LGH medium with 5 g L⁻¹ yeast extract. The established biorefinery system has to be optimized in order to reach capacity for transfer to a larger scale. Full article

A pink-pigmented, ovoid-rod-shaped, Gram-negative bacterial strain ML10^T was previously isolated in a study of a meromictic lake in British Columbia, Canada. It produces bacteriochlorophyll a, which is incorporated into the reaction center and light harvesting I complexes. This alongside no anaerobic or photoautotrophic growth supports the designation of the strain as an aerobic anoxygenic phototroph. The cells produce wavy polar flagellum and accumulate clear, refractive granules, presumed to be polyhydroxyalkanoate. Sequence of the 16S rRNA gene identified close relatedness to Salinarimonas rosea (97.85%), Salinarimonas ramus (97.92%) and Saliniramus fredricksonii (94.61%). The DNA G + C content was 72.06 mol %. Differences in cellular fatty acids and some physiological tests compared to Salinarimonadaceae members, as well as average nucleotide identity and digital DNA-DNA hybridization, define the strain as a new species in Salinarimonas. Therefore, we propose that ML10^T (=NCIMB 15586^T = DSM 118510^T) be classified as the type strain of a new species in the genus with the name Salinarimonas chemoclinalis sp. nov. Full article

A polyphasic taxonomic study was carried out on the rod-shaped, orange-pigmented strain C11^T, isolated from gold mine tailings. Sequencing of the 16S rRNA gene showed a relatedness to Brevundimonas, with a 98.4% and 98.2% similarity to Brevundimonas bacteroides and Brevundimonas variabilis, respectively. The average nucleotide identity and a digital DNA–DNA hybridization with the closest phylogenetic neighbor of strain C11^T indicate distinction at the species level, further confirmed by the differences in physiology. C_18:1 ω7c is the dominant cellular fatty acid. Its DNA G + C content is 68.3 mol %. Its predominant ubiquinone is Q-10; 1,2-Di-O-acyl-3-O-α-D-glucopyranuronosyl glycerol, phosphatidylglycerol, 1,2-di-O-acyl-3-O-α-D-glucopyranosyl glycerol, and 1,2-di-O-acyl-3-O-[D-glucopyranosyl-(1→4)-α-D-glucopyranuronosyl] glycerol are its major polar lipid constituents. This bacterium produces bacteriochlorophyll a and tolerates high concentrations of (μg/mL) the following: tellurium (>1500), selenium (1000 to >5000), and vanadium (>5000) oxyanions. The data support the inclusion of the strain C11^T into the genus Brevundimonas as a new species with the proposed name Brevundimonas aurifodinae sp. nov. (C11^T = NRRL B-65718^T; =DSM 118059^T). Full article

Several strains of a Gram-negative, anaerobic photoautotrophic, motile, rod-shaped bacterium, designated as B14B, A-7R, and A-7Y were isolated from biofilms of low-mineralized soda lakes in central Mongolia and Russia (southeast Siberia). They had lamellar stacks as photosynthetic structures and bacteriochlorophyll a as the major photosynthetic pigment. The strains were found to grow at 25–35 °C, pH 7.5–10.2 (optimum, pH 9.0), and with 0–8% (w/v) NaCl (optimum, 0%). In the presence of sulfide and bicarbonate, acetate, butyrate, yeast extract, lactate, malate, pyruvate, succinate, and fumarate promoted growth. The DNA G + C content was 62.9–63.0 mol%. While the 16S rRNA gene sequences confirmed that the new strains belonged to the genus Ectothiorhodospira of the Ectothiorhodospiraceae, comparison of the genome nucleotide sequences of strains B14B, A-7R, and A-7Y revealed that the new isolates were remote from all described Ectothiorhodospira species both in dDDH (19.7–38.8%) and in ANI (75.0–89.4%). The new strains are also genetically differentiated by the presence of a nitric oxide reduction pathway that is lacking from all other Ectiothiorhodospiraceae. We propose to assign the isolates to the new species, Ectothiorhodospira lacustris sp. nov., with the type strain B14B^T (=DSM 116064^T = KCTC 25542^T = UQM 41491^T). Full article

The production of phytylated chlorophyll a (Chl a_P) in Rhodobacter sphaeroides, which uses phytylated bacteriochlorophyll a (BChl a_P), is the first step in expanding the light absorption spectra. Unlike the chlorophyll synthase (ChlG) of the Synechocystis sp. PCC6803, ChlGs of angiosperms, including Arabidopsis thaliana, Nicotiana tabacum, Avena sativa, and Oryza sativa, showed bacteriochlorophyll synthase activity and resistance to inhibition by bacteriochlorophyllide a (BChlide a), geranylgeranylated BChl a (BChl a_GG), and BChl a_P, collectively called bacteriochlorins. Among the angiosperm ChlGs, N. tabacum ChlG had the highest bacteriochlorophyll synthase activity and resistance to inhibition by bacteriochlorins. Expression of N. tabacum chlG in R. sphaeroides resulted in the formation of free Chl a_P in the presence of BChl a_P during photoheterotrophic growth, even though reactive oxygen species were generated. Full article

Eight species of heliobacteria have had their genomes sequenced. However, only two of these genomes have been analyzed in detail, those from the thermophilic Heliomicrobium (Hmi.) modesticaldum and the alkaliphilic Heliorestis (Hrs.) convoluta. Here we present analyses of the draft genome sequence of a species of heliobacterium that grows optimally at a moderate temperature and neutral pH. The organism, Heliophilum (Hph.) fasciatum, is phylogenetically unique among cultured heliobacteria and was isolated from rice soil, a common habitat for heliobacteria. The Hph. fasciatum genome contains 3.14 Mbp—similar to that of other reported heliobacteria—but has a G+C base ratio that lies between that of Hmi. modesticaldum and Hrs. convoluta. Many of the genomic features of Hmi. modesticaldum and Hrs. convoluta, such as the absence of genes encoding autotrophic pathways, the presence of a superoperonal cluster of photosynthesis-related genes, and genes encoding endospore-specific proteins, are also characteristic of the Hph. fasciatum genome. However, despite the fact that Hph. fasciatum is diazotrophic, classical nif genes encoding the alpha and beta subunits of dinitrogenase (nifDK) present in other heliobacteria could not be identified. Instead, genes encoding several highly divergent NifDK homologs were present, at least one of which likely encodes a functional dinitrogenase and another a methylthio-alkane reductase (MarDK) for sulfur assimilation. A classical NifH (dinitrogenase reductase) homolog was also absent in Hph. fasciatum, but a related protein was identified that likely carries out this function as well as electron delivery to MarDK. The N₂-fixing system of Hph. fasciatum is therefore distinct from that of other heliobacteria and may have unusual properties. Full article

The effect of singlet oxygen on light-harvesting (LH) complexes has been studied for a number of sulfur (S⁺) and nonsulfur (S⁻) photosynthetic bacteria. The visible/near-IR absorption spectra of the standard LH2 complexes (B800-850) of Allochromatium (Alc.) vinosum (S⁺), Rhodobacter (Rba.) sphaeroides (S⁻), Rhodoblastus (Rbl.) acidophilus (S⁻), and Rhodopseudomonas (Rps.) palustris (S⁻), two types LH2/LH3 (B800-850 and B800-830) of Thiorhodospira (T.) sibirica (S⁺), and an unusual LH2 complex (B800-827) of Marichromatium (Mch.) purpuratum (S⁺) or the LH1 complex from Rhodospirillum (Rsp.) rubrum (S⁻) were measured in aqueous buffer suspensions in the presence of singlet oxygen generated by the illumination of the dye Rose Bengal (RB). The content of carotenoids in the samples was determined using HPLC analysis. The LH2 complex of Alc. vinosum and T. sibirica with a reduced content of carotenoids was obtained from cells grown in the presence of diphenylamine (DPA), and LH complexes were obtained from the carotenoidless mutant of Rba. sphaeroides R26.1 and Rps. rubrum G9. We found that LH2 complexes containing a complete set of carotenoids were quite resistant to the destructive action of singlet oxygen in the case of Rba. sphaeroides and Mch. purpuratum. Complexes of other bacteria were much less stable, which can be judged by a strong irreversible decrease in the bacteriochlorophyll (BChl) absorption bands (at 850 or 830 nm, respectively) for sulfur bacteria and absorption bands (at 850 and 800 nm) for nonsulfur bacteria. Simultaneously, we observe the appearance of the oxidized product 3-acetyl-chlorophyll (AcChl) absorbing near 700 nm. Moreover, a decrease in the amount of carotenoids enhanced the spectral stability to the action of singlet oxygen of the LH2 and LH3 complexes from sulfur bacteria and kept it at the same level as in the control samples for carotenoidless mutants of nonsulfur bacteria. These results are discussed in terms of the current hypothesis on the protective functions of carotenoids in bacterial photosynthesis. We suggest that the ability of carotenoids to quench singlet oxygen (well-established in vitro) is not well realized in photosynthetic bacteria. We compared the oxidation of BChl850 in LH2 complexes of sulfur bacteria under the action of singlet oxygen (in the presence of 50 μM RB) or blue light absorbed by carotenoids. These processes are very similar: {[BChl + (RB or carotenoid) + light] + O₂} → AcChl. We speculate that carotenoids are capable of generating singlet oxygen when illuminated. The mechanism of this process is not yet clear. Full article

An aerobic, yellow-pigmented, bacteriochlorophyll a-producing strain, designated AAP5 (=DSM 111157=CCUG 74776), was isolated from the alpine lake Gossenköllesee located in the Tyrolean Alps, Austria. Here, we report its description and polyphasic characterization. Phylogenetic analysis of the 16S rRNA gene showed that strain AAP5 belongs to the bacterial genus Sphingomonas and has the highest pairwise 16S rRNA gene sequence similarity with Sphingomonas glacialis (98.3%), Sphingomonas psychrolutea (96.8%), and Sphingomonas melonis (96.5%). Its genomic DNA G + C content is 65.9%. Further, in silico DNA-DNA hybridization and calculation of the average nucleotide identity speaks for the close phylogenetic relationship of AAP5 and Sphingomonas glacialis. The high percentage (76.2%) of shared orthologous gene clusters between strain AAP5 and Sphingomonas paucimobilis NCTC 11030^T, the type species of the genus, supports the classification of the two strains into the same genus. Strain AAP5 was found to contain C_18:1ω7c (64.6%) as a predominant fatty acid (>10%) and the polar lipid profile contained phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, sphingoglycolipid, six unidentified glycolipids, one unidentified phospholipid, and two unidentified lipids. The main respiratory quinone was ubiquinone-10. Strain AAP5 is a facultative photoheterotroph containing type-2 photosynthetic reaction centers and, in addition, contains a xathorhodopsin gene. No CO₂-fixation pathways were found. Full article

Generally, bacteriochlorophyllides were responsible for the photosynthesis in bacteria. Seven types of bacteriochlorophyllides have been disclosed. Bacteriochlorophyllides a/b/g could be synthesized from divinyl chlorophyllide a. The other bacteriochlorophyllides c/d/e/f could be synthesized from chlorophyllide a. The chemical structure and synthetic route of bacteriochlorophyllides were summarized in this review. Furthermore, the potential applications of bacteriochlorophyllides in photosensitizers, immunosensors, influence on bacteriochlorophyll aggregation, dye-sensitized solar cell, heme synthesis and for light energy harvesting simulation were discussed. Full article

Despite significant interest and past work to elucidate the phylogeny and photochemistry of species of the Heliobacteriaceae, genomic analyses of heliobacteria to date have been limited to just one published genome, that of the thermophilic species Heliobacterium (Hbt.) modesticaldum str. Ice1^T. Here we present an analysis of the complete genome of a second heliobacterium, Heliorestis (Hrs.) convoluta str. HH^T, an alkaliphilic, mesophilic, and morphologically distinct heliobacterium isolated from an Egyptian soda lake. The genome of Hrs. convoluta is a single circular chromosome of 3.22 Mb with a GC content of 43.1% and 3263 protein-encoding genes. In addition to culture-based observations and insights gleaned from the Hbt. modesticaldum genome, an analysis of enzyme-encoding genes from key metabolic pathways supports an obligately photoheterotrophic lifestyle for Hrs. convoluta. A complete set of genes encoding enzymes for propionate and butyrate catabolism and the absence of a gene encoding lactate dehydrogenase distinguishes the carbon metabolism of Hrs. convoluta from its close relatives. Comparative analyses of key proteins in Hrs. convoluta, including cytochrome c₅₅₃ and the F_o alpha subunit of ATP synthase, with those of related species reveal variations in specific amino acid residues that likely contribute to the success of Hrs. convoluta in its highly alkaline environment. Full article