Gudni A. Alfredsson

Rhodothermus marinus, gen. nov., sp. nov., a Thermophilic, Halophilic Bacterium from Submarine Hot Springs in Iceland

SUMMARY: Thermophilic, reddish-coloured heterotrophic bacteria different from Thermus were isolated from submarine alkaline hot springs in Iceland. The bacteria were obligately aerobic, moderately halophilic, Gram-negative rods, about 0.5 μm in diameter and 2-2.5 μm long. Neither spores, flagella nor lipid granules were observed, but a slime capsule was formed on carbohydrate-rich medium. Optimum growth was at 65°C, pH 7.0, and at about 2% (w/v) NaCl. The bacteria were oxidase negative, catalase positive and contained a carotenoid pigment with the main absorbance peak at 476 nm and shoulders at 456 and 502 nm. The GC content of the DNA was about 64 mol%. Electron micrographs clearly showed an outer membrane, about 9 nm thick, and the cytoplasmic membrane together with the peptidoglycan layer was about 14 nm in thickness. The isolates were nutritionally different from Thermus. They utilized several common sugars but glutamate and aspartate were the only amino acids that most strains used. These bacteria are considered to represent a new genus which we name Rhodothermus, with the type species Rhodothermus marinus.

Thermus scotoductus, sp.nov., a pigment-producing thermophilic bacterium from hot tap water in Iceland and including Thermus sp. X-1

Summary Thermophilic, aerobic heterotrophic bacteria, producing a water soluble dark brown melanin-like pigment, were isolated from a hot water pipeline in a small town in southern Iceland. The bacteria stained Gram-negative, are short rods, 1.5 urn long and 0.5 um in diameter. The cells vare usually single or in pairs. A very dense peptidoglycan layer was seen as well as cytoplasmic membrane and an outer membrane. The bacteria are nonmotile and do not form spores. They could grow at 42-73 °C with optimum growth temperature of 65 °C and optimum pH at 7.5. The bacteria were oxidase and catalase positive, sensitive to the antibiotics penicillin, erythromycin, tetracyclin, chloramphenicol and streptomycin but resistant to polymyxin B and rifampicin. The GC was about 64.5%. The isolates were compared to other known aerobic, heterotrophic bacteria and turned out to resemble to colourless Thermus strain X-1, which was also found to produce the brown pigment. The DNA : DNA similarity between the new isolates and Thermus X-1 was about 83%, whereas the similarity with Thermus aquaticus was about 46%. The new isolates together with strain X-1 are therefore considered to represent a new species, Thermus scotoductus .

Isolation of thermophilic obligately autotrophic hydrogen-oxidizing bacteria, similar to Hydrogenobacter thermophilus, from Icelandic hot springs

Thermophilic obligately autotrophic hydrogen-oxidizing bacteria were isolated from several alkaline hot springs in Iceland. The bacteria were Gram negative rods, 0.4–0.5 μm in diameter and 3–4 μm long but 6–7 μm long cells without septa were often seen. Long and short laments are formed. Spores, flagella or lipid granules were not observed. Strains H1 and H12 grew optimally at 70° C and pH 6.5 under mixture of air plus 0.6 atm H2 and 0.1 atm CO2. The cells contained cytochromes and carotenoid-like pigments. They would not grow on agar or silicia gel plates. The cells would not grow heterotrophically on organic substrates and were inhibited by most of these same organic compounds and agar in low concentrations. They were very sensitive to common antibiotics. The role of these bacteria in the hot spring ecosystem is discussed.

A Polyphasic Study on the Taxonomic Position of Industrial Sour Dough Yeasts

The sour dough bread making process is extensively used to produce wholesome palatable rye bread. The process is traditionally done using a back-slopping procedure. Traditional sour doughs in Finland comprise of lactic acid bacteria and yeasts. The yeasts present in these doughs have been enriched in the doughs due to their metabolic activities, e.g. acid tolerance. We characterized the yeasts in five major sour bread bakeries in Finland. We found that most of the commercial sour doughs contained yeasts which were similar to Candida milleri on the basis of 18S rDNA and EF-3 PCR-RFLP patterns and metabolic activities. Some of the bakery yeasts exhibited extensive karyotype polymorphism. The minimum growth temperature was 8 degrees C for C. milleri and also for most of sour dough yeasts.

Nutritional Diversity Among Thermus spp. Isolated from Icelandic Hot Springs

Summary Thermophilic bacteria of the genus Thermus were isolated from hot springs in Iceland. Growth factor requirement was tested for 24 strains. More than half of the strains would only grow in a minimal medium with single carbon sources if vitamins were also added. From a collection of about a hundred strains, 28 were used to test growth on 44 different single-carbon-source compounds. Nineteen compounds were not utilized by any of the strains. More than 70 % of the strains grew on galactose, maltose, acetate, pyruvate, α-keto-glutarate, asparagine, glutamate, glutamine and proline. The utilization of other compounds was variable and indicated a high degree of nutritional diversity among strains of Thermus .

Growth of thermophilic obligately autotrophic hydrogen‐oxidizing bacteria on thiosulfate

Thermophilic obligately autotrophic H2‐oxidizing bacteria from Icelandic hot springs were tested for growth on thiosulfate. Ten strains were tested and all grew on thiosulfate but not on sulfite or sulfur. The product of thiosulfate oxidation was sulfate. The growth rate on thiosulfate was slower (μ=0.12 h‐1) than on H2 (μ=0.34 h‐1). Washed cells which had been grown on thiosulfate could oxidize thiosulfate rapidly but H2‐grown cells oxidized thiosulfate much more slowly and with about a 3 h lag time. The bacteria would not grow on agar medium under H2 but grew on agar medium containing thiosulfate.

Ecology, Distribution, and Isolation of Thermus

Temperature is one of the most important environmental factors determining the physiological activities of organisms and their evolution. High temperatures can be tolerated to varying degrees by different organisms. Many complex multicellular organisms are unable to withstand a temperature of 50 °C, even for very short periods, whereas many microorganisms survive, and even thrive, in much higher temperatures for extended periods.

Characterization of alanine and malate dehydrogenases from a marine psychrophile strain PA-43

Abstract. Alanine dehydrogenase (AlaDH: EC 1.4.1.1), malate dehydrogenase (MDH: EC 1.1.1.37), and glutamate dehydrogenase (EC 1.4.1.2), all NAD+ dependent, were detected in extracts from a psychrophilic bacterium, strain PA-43, isolated from a sea urchin off the Icelandic coast. Characterization tests suggested that the strain had a close relationship to Vibrio, but sequencing of part of the 16S rDNA gene placed the bacterium among Shewanella species in a constructed phylogenetic tree. The bacterium had an optimum growth temperature of 16.5°C, and maximum dehydrogenase expression was obtained in a rich medium supplemented with NaCl. Both AlaDH and MDH were purified to homogeneity. AlaDH is a hexamer, with an approximate relative molecular mass of 260,000, whereas MDH is dimeric, with an apparent relative molecular mass of approximately 70,000. Both enzymes were thermolabile, and the optimum temperatures for activity were shifted toward lower temperatures than those found in the same enzymes from mesophiles, 37°C for MDH and approximately 47°C for AlaDH. The pH optima for AlaDH in the forward and reverse reactions were 10.5 and 9, respectively, whereas those for MDH were 10–10.2 and 8.8, respectively. Partial amino acid sequences, comprising approximately 30% of the total sequences from each enzyme, were determined for N-terminal, tryptic, and chymotryptic fragments of the enzymes. The AlaDH showed the highest similarity to AlaDHs from the psychrotroph Shewanella Ac10 and the mesophile Vibrio proteolyticus, whereas MDH was most similar to the MDHs from the mesophiles Escherichia coli and Haemophilus influenzae, with lower identity to the psychrophilic malate dehydrogenases from Vibrio 5710 and Photobacterium SS9.