Carotenoid pigments of facultatively anaerobic spirochetes

Bacterial symbionts of the precious coral Corallium rubrum are differentially distributed across colony-specific compartments and differ among colormorphs

Corals engage in symbioses with micro-organisms that provide nutrients and protect the host. Where the prokaryotic microbes perform their symbiotic functions within a coral is, however, poorly understood. Here, we studied the tissue-specific microbiota of the coral Corallium rubrum by dissecting its tissues from the skeleton and separating the white polyps from the red-coloured coenenchyme, followed by 16S rRNA gene metabarcoding of the three fractions. Dissection was facilitated by incubating coral fragments in RNAlater, which caused tissues to detach from the skeleton. Our results show compartmentalisation of the microbiota. Specifically, Endozoicomonas, Parcubacteria and a Gammaproteobacteria were primarily located in polyps, whereas Nitrincolaceae and one Spirochaeta phylotype were found mainly in the coenenchyme. The skeleton-associated microbiota was distinct from the microbiota in the tissues. Given the difference in tissue colour and microbiota of the polyps and coenenchyme, we analysed the microbiota of three colormorphs of C. rubrum (red, pink, white), finding that the main difference was a very low abundance of Spirochaeta in white colormorphs. While the functions of C. rubrum's symbionts are unknown, their localisation within the colony suggests that microhabitats exist, and the presence of Spirochaeta appears to be linked to the colour of C. rubrum.

1-Hydroxy monocyclic carotenoid 3,4-dehydrogenase from a marine bacterium that produces myxol

A crtD (1-HO carotenoid 3,4-dehydrogenase gene) homolog from marine bacterium strain P99-3 included in the gene cluster for the biosynthesis of myxol (3',4'-didehydro-1',2'-dihydro-beta, psi-carotene-3,1',2'-triol) was functionally identified. The P99-3 CrtD was phylogenetically distant from the other CrtDs. A catalytic feature was its high activity for the monocyclic carotenoid conversion: 1'-HO-torulene (3',4'-didehydro-1',2'-dihydro- beta, psi-caroten-1'-ol) was prominently formed from 1'-HO-gamma-carotene (1',2'-dihydro-beta, psi-caroten-1'-ol) in Escherichia coli with P99-3 CrtD, indicating that this enzyme has been highly adapted to myxol biosynthesis. This unique type of crtD is a valuable tool for obtaining 1'-HO-3',4'-didehydro monocyclic carotenoids in a heterologous carotenoid production system.

Spirochaeta bajacaliforniensis sp. n. from a microbial mat community at Laguna Figueroa, Baja California Norte, Mexico

A new anaerobic spirochete was isolated from anaerobic muds beneath the laminated sediment in the evaporite flat at Laguna Figueroa, Baja California Norte, Mexico. The organism is a member of the stratified microbial community involved in the deposition of the laminated sediments in the lagoon. The size of the spirochete is 0.3 by 30 micrometers, with a wave amplitude of 0.5 micrometer and a wavelength of 1.25 micrometers. The periplasmic flagella have a 1-2-1 arrangement. The outer membrane of the modified Gram-negative cell wall (the sheath) is irregularly crenulated and has a sillon. The growth medium contained yeast extract, trypticase, cellobiose, sodium thioglycolate and at least 20% natural seawater. Chemically defined artificial seawater media did not support growth. Optimal growth occurred with a seawater concentration of 80% at 36 degrees C and a pH of 7.5. Glucose was fermented to acetate, ethanol, carbon dioxide and hydrogen. The guanine + cytosine content of the DNA was 50 mol %. The spirochete body reacts positively to antibodies raised against eukaryotic brain tubulin protein. On the basis of its free-living anaerobic habitat, its unique morphological and physiological characteristics and G+C ratio, it is proposed that this isolated be considered a new species and names Spirochaeta bajacaliforniensis.

Isolation of the outer membrane and characterization of the major outer membrane protein from Spirochaeta aurantia

The outer membrane of Spirochaeta aurantia was isolated after cells were extracted with sodium lauryl sarcosinate and was subsequently purified by differential centrifugation and KBr isopycnic gradient centrifugation. The purified outer membrane was obtained in the form of carotenoid-containing vesicles. Four protein species with apparent molecular weights of 26,000 (26K), 36.5K, 41K, and 48.5K were readily observed as components of the vesicles. The 36.5K protein was the major polypeptide and constituted approximately 90% of the outer membrane protein observed on sodium dodecyl sulfate-polyacrylamide gels. Under mild denaturing conditions the 36.5K major protein exhibited an apparent molecular weight of approximately 90,000. This, together with the results of protein cross-linking studies, indicates that the 36.5K polypeptide has an oligomeric conformation in the native state. Reconstitution of solubilized S. aurantia outer membrane into lipid bilayer membranes revealed the presence of a porin, presumably the 36.5K protein, with an estimated channel diameter of 2.3 nm based on the measured single channel conductance of 7.7 nS in 1 M KCl.

Spirochaeta halophila sp. n., a facultative anaerobe from a high-salinity pond

A facultatively anaerobic spirochete isolated from a high-salinity pond grew optimally when 0.75 M NaCl, 0.2 M MgSO4, and 0.01 M CaCl2 were present in media containing yeast extract, peptone, and a carbohydrate. The organism failed to grow when any one of these three salts was omitted from the medium. Aerobically-grown colonies of the spirochete were red, whereas anaerobically-grown colonies showed no pigmentation. Non-pigmented mutants of the spirochete were isolated. The spirochete used carbohydrates, but not amino acids, as energy sources. Glucose was fermented to CO2, H2, ethanol, acetate, and a small amount of lactate. Determinations of radioactivity in products formed from glucose-1-14C and enzymatic assays indicated that glucose was dissimilated to pyruvate mainly via the Embden-Meyerhof pathway. Pyruvate was metabolized through a clostridial-type clastic reaction. Cells growing aerobically performed an incomplete oxidation of glucose mainly to CO2 and acetate. Comparison of aerobic and anaerobic growth yields indicated that oxidative phosphorylation occurred in cells growing aerobically. The guanine + cytosine content of the DNA of the spirochete was 62 moles %. It is proposed that the spirochete described herein be considered a new species and that it be named Spirochaeta halophila.