Johannes F. Imhoff

Variation of environmental features and microbial populations with salt concentrations in a multi-pond saltern

A multi-pond saltern that creates a gradient of salt concentrations has been studied with respect to some characteristics of the resulting environments and their microbial populations. The increase in salt concentration was correlated with increase in diurnal temperature and biomass present and with decrease in oxygen concentrations. Many types of organisms below 15% (w/v) total salts, were found, many of them normal inhabitants of seawater and even freshwater. Most organisms over 15% salts were halophilic. The salt concentrations comprised two ranges, each characterized by different microbial populations. First, between 15 and 30% salts, the populations ofDunaliella increased, reaching large numbers; moderately halophilic eubacteria and some fast-growing halobacteria predominated as heterotrophic microorganisms and, among the first, thePseudomonas-Alteromonas-Alcaligenes group andVibrio were the more abundant taxonomic groups; and gram-positive cocci appeared mainly over 25% salts. Phototrophic bacteria, both oxygenic and anoxygenic, were also found in this range, and among the anoxygenic type,Chromatium species andRodospirillum salexigens were probably predominant. Second, over 30% salts the diversity decreased greatly, all organisms found at the lower salt concentrations disappeared, and instead large populations of halobacteria developed. Over 50% salts, only three species of halobacteria were found.

Ectothiorhodospira halochloris sp. nov., a new extremely halophilic phototrophic bacterium containing bacteriochlorophyll b

A new bacteriochlorophyll b containing phototrophic bacterium was isolated from extremely saline and alkaline soda lakes in Egypt. Enrichment and isolation were performed using a synthetic medium with high contents of sodium carbonate, sodium sulfate and sodium chloride. Photoautotrophic growth occurred with hydrogen sulfide as photosynthetic electron donor. During oxidation of sulfide to sulfate extracellular elemental sulfur globules appeared in the medium. Cells were also capable to grow under photoheterotrophic conditions with acetate, propionate, pyruvate, succinate, fumarate or malate as carbon sources and electron donors. Under these conditions sulfate was assimilated. Optimal growth under the applied experimental conditions occurred at a total salinity of 14–27%, a pH-range between 8.1 and 9.1 and a temperature between 47°C and 50°C. The cells were 0.5–0.6 μm wide and, depending on cultural conditions, 2.5–8.0 μm long; they were spiral shaped, multiplied by binary fission and were motile by means of bipolar flagella. Intercytoplasmic photosynthetic membranes were present as stacks. Bacteriochlorophyll b was the main photosynthetic pigment; small amounts of carotenoids were mainly present as glucosides of rhodopin and its methoxy derivative. The new organism is described as Ectothiorhodospira halochloris.

Marine Sponges as Habitats of Anaerobic Phototrophic Bacteria

Enrichment cultures were prepared with different media for phototrophic bacteria from four species of marine sponges, collected from oxic coastal waters near Split (Yugoslavia). We obtained pure cultures of six strains ofChromatiaceae and two strains ofRhodospirillaceae by agar shake dilution. TheRhodospirillaceae were identified asRhodopseudomonas sulfidophila and a marine form ofRhodopseudomonas palustris. TheChromatiaceae were identified asChromatium vinosum, Chromatium gracile, Chromatium minutissimum. Ectothiorhodospira mobilis, and a Chromatium species, which in some respects resemblesChromatium minus. The occurrence of strictly anaerobic phototrophic bacteria in aerobic sponges is discussed with respect to nutrition and possible syntrophism.

Ectothiorhodospira vacuolata sp. nov., a new phototrophic bacterium from soda lakes

A new phototrophic bacterium was isolated from Jordanian and Kenyan alkaline salt lakes. Cells are rod shaped, 1.5 μm wide and 2–4 μm long, and motile by polar flagella. They divide by binary fission, and possess photosynthetic membranes as lamellar stacks similar to those in the other species of the genus Ectothiorhodospira and the brown colored Rhodospirillum species. The presence of bacteriochlorophyll a and carotenoids of the normal spirilloxanthin series is indicated by the absorption spectra of living cells. Under certain growth conditions the cells form gas vacuoles, may become immotile and float to the top of the culture medium. Sulfide and thiosulfate are used as photosynthetic electron donors. During the oxidation of sulfide to sulfate, elemental sulfur is formed, which is accumulated outside the cells. The organisms are strictly anaerobic, do not require vitamins, are moderately halophilic and need alkaline pH-values for growth. The new species Ectothiorhodospira vacuolata is proposed.

Rhodopseudomonas adriatica sp. nov., a new species of the Rhodospirillaceae, dependent on reduced sulfur compounds

A new purple nonsulfur bacterium was isolated from enrichment cultures of a sulfide-containing marine lagoon. The bacterium is similar to Rhodopseudomonas capsulata and is described as a new species of the genus Rhodopseudomonas: Rhodopseudomonas adriatica. Cells are non-motile, 0.5–0.8 μm by 1.3–1.8 μm, and multiply by binary fission. Intracytoplasmic membranes are of the vesicular type. The photosynthetic pigments are bacteriochlorophyll a and carotenoids of the spheroidene group. Growth is possible anaerobically in the light and at low pO2 in the dark. Biotin and thiamine are required as growth factors. A wide variety of organic compounds, as well as sulfide and thiosulfate, are used as photosynthetic electron donors. Sulfide is oxidized to elemental sulfur, which is subsequently converted to sulfate, whereas thiosulfate oxidation occurs without measurable intermediate. Rhodopseudomonas adriatica is unable to assimilate sulfate, growth is only possible in the presence of a reduced sulfur compound.

Influence of salt concentration and temperature on the fatty acid compositions of Ectothiorhodospira and other halophilic phototrophic purple bacteria

Influences of the salt concentration on the fatty acid composition of Ectothiorhodospira species and other phototrophic purple bacteria have been analysed. Major fatty acids in bacteria of the genera Rhodobacter, Rhodopseudomonas, Chromatium, and Ectothiorhodospira were straight chain saturated and monounsaturated C-16 and C-18 fatty acids. Salt-dependent responses of all investigated bacteria revealed relations to their salt optima. Minimum values of C-16 and saturated fatty acids and maximum values of C-18 and unsaturated fatty acids were found at or close to the salt optima. Responses of Ectothiorhodospira mobilis upon changes in salinity were nearly identical, whether cells were grown in batch culture or in continuous culture with identical dilution rates at all salt concentrations. With increasing temperature, the fatty acid composition of Ectothiorhodospira mobilis and Ectothiorhodospira halophila strains showed decreasing portions of C-18 and of unsaturated fatty acids, while the contents of C-16 and saturated fatty acids increased. The results are discussed with respect to bilayer stabilisation and membrane fluidity.

Towards a phylogeny of phototrophic purple sulfur bacteria — the genus Ectothiorhodospira

Seven strains of five species of the genus Ectothiorhodospira were characterized by oligonucleotide cataloguing of their 16S rRNA in order to determine the phylogenetic relationship to one another and to other phototrophic purple bacteria. All representatives of Ectothiorhodospira are members of that line of descent defined by phototrophic purple sulfur bacteria and relatives, showing a moderate relationship to those phototrophic organisms forming globules of elemental sulfur inside the cell (Chromatium and relatives). The 5 Ectothiorhodospira species fall into two subgroups. E.halophila, E. halochloris and E. abdelmalekii form one, E. mobilis, E. shaposhnikovii and the unnamed strain BN 9906 form the second subgroup. Within the two subgroups the strains are closely related, while the degree of relatedness found between members of the two subgroups is more distant.

Ectothiorhodospira abdelmalekii sp. nov., a New Halophilic and Alkaliphilic Phototrophic Bacterium

A new species of the genus Ectothiorhodospira is described isolated from alkaline soda lakes of the Wadi Natrun in Egypt. In most of its properties it resembles the recently described Ectothiorhodospira halochloris, which had been isolated from similar lakes of the same area. The new species, Ectothiorhodospira abdelmalekii, has spiral-shaped cells with 0.9-1.2 μm diameter, it is polarly flagellated with sheated flagella, has lamellar photosynthetic membrane stacks, possesses bacteriochlorophyll b as the main photosynthetic pigment, and has a DNA base composition of 63.3–63.8 mol% G + C. Photolithotrophic growth with sulfide or elemental sulfur as electron donors is the predominant mode of life. During sulfide oxidation to sulfate, elemental sulfur is accumulated outside the cells. Acetate, pyruvate, fumarate and succinate are photoassimilated. The properties of E. halochloris and E. abdelmalekii are compared.

The effect of salt on the lipid composition of Ectothiorhodospira

Major components of polar lipids of halophilic phototrophic Ectothiorhodospira species were PG, CL, PC and PE. PA was only present in minor amounts. According to 14C-incorporation, polar lipids approximated to 75%–93% of the total lipid carbon. With increasing salinity, a strong increase in the portion of PG and a decrease in that of PE (especially in Ectothiorhodospira mobilis BN 9903) and CL (especially in E. halophila strains) were observed. Moreover, there was a significant increase in the excess negative charges of phospholipids upon increasing medium salinity. This increase was most dramatic in the slightly halophilic E. mobilis BN 9903, but quantitatively less important in both strains of E. halophila which had, however, a higher percentage of negative charges of their lipids. During salt-shift experiments, E. halophila BN 9630 responded to suddenly increased salinity by promoting the biosynthesis of PG and decreasing that of PC, CL and PE. Upon dilution stress, responses were reversed and resulted in a strong increase in PE biosynthesis. The effects of lipid charges and bilayer forming forces in stabilizing the membranes of Ectothiorhodospira species during salt stress are discussed.

Chromatium purpuratum, sp. nov., a new species of the Chromatiaceae

Enrichment cultures inoculated with fragments of the sponge Ircinia spec, under autotrophic culture conditions and with thiosulfate as sole electron donor yielded the predominant development of a small cell Chromatium strain, which is described herein as the new species Chromatium purpuratum. Autotrophically grown cells are 1.2–1.7 μm wide and 3–4 μm long. The cells are motile by means of one single polar flagellum. Intracytoplasmic membranes are present as vesicles as in the other Chromatium species. Multiplication occurs by binary fission. The photopigments are bacteriochlorophyll a and carotenoids of the okenone series. The G + C content of the type strain BN 5500 is 68.9 mole%. n nChromatium purpuratum grows well photoautotrophically with sulfide or thiosulfate as electron donor. Photoheterotrophic growth is possible with various fatty acids serving as electron donor and carbon source. The new species is a marine isolate with an optimal salinity of 5% NaCl. It is compared with other known species of the genus Chromatium