RESULTS:

Two novel strictly aerobic sulfur-dependent thermoacidophilic strains IC-006T and IC-007 were isolated from a solfataric field at Hakone Ohwaku-dani Kanagawa Japan. Cells of the two strains were irregular cocci with a diameter of 1.0–1.8 µm. They were strict aerobes and grew in a temperature range between 45 and 69 °C (optimally at 65 °C) and a pH range between 0.4 and 5.5 (optimally at pH 3.5). They required sulfur or a reduced sulfur compound and sulfur was oxidized to sulfate. They grew autotrophically or mixotrophically utilizing several sugars and complex organic substances as carbon sources. The DNA G+C content was 42.4 mol%. A comparison of the 16S rRNA gene sequences among members of the order Sulfolobales indicated that they were closely related to Sulfolobus metallicus forming an independent lineage within this order. The two isolates and Sulfolobus metallicus were also diffentiated based on their phenotypic properties from the other members of the order Sulfolobales . Detailed comparisons of the phenotypic properties and DNA–DNA hybridization study illustrated that the two isolates belong to a species different from Sulfolobus metallicus . On the basis of the phylogenetic and phenotypic comparisons we propose a new genus and species Sulfuracidifex tepidarius gen. nov. sp. nov. to accommodate strains IC-006T and IC-007. The type strain of Sulfuracidifex tepidarius is IC-006T (=JCM 16833T=DSM 104736T). In addition Sulfolobus metallicus should be transferred to the new genus as Sulfuracidifex metallicus comb. nov.: the type strain is Kra23T (=DSM 6482T=JCM 9184T=NBRC 15436T).

A novel marine bacterium designated strain CHFG3-1-5T was isolated from mangrove sediment sampled at Jiulong River estuary Fujian PR China. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain CHFG3-1-5T belonged to the genus Marinobacter with the highest sequence similarity to Marinobacter segnicrescens SS011B1-4T (97.6%) followed by Marinobacter nanhaiticus D15-8WT (97.5%) Marinobacter bohaiensis T17T (97.1%) and Marinobacter hydrocarbonoclasticus SP.17T (90.6%). The bacterium was Gram-stain-negative facultative anaerobic oxidase- and catalase-positive rod-shaped and motile with a polar flagellum. Strain CHFG3-1-5T grew optimally at 32–37 °C pH 6.0–8.0 and in the presence of 2.0–3.0% (w/v) NaCl. The G+C content of the chromosomal DNA was 61.1 mol%. The major respiratory quinone was determined to be Q-9. The principal fatty acids were C16 : 0 summed feature 3 (C16 : 1 ω7c/ω6c) C12 : 0 summed feature 9 (C17 : 1 iso ω9c and/or C16 : 0 10-methyl) C12 : 0 3-OH and summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c). The polar lipids were diphosphatidylglycerol phosphatidylethanolamine phosphatidylglycerol three phospholipids one glycolipid and two aminolipids. The average nucleotide identity and digital DNA–DNA hybridization values among the genomes of strain CHFG3-1-5T and the reference strains were 73.4–79.4 and 19.6–22.4% respectively. Like many other species reported in the genus Marinobacter strain CHFG3-1-5T was able to oxidise iron. The combined genotypic and phenotypic data showed that strain CHFG3-1-5T represents a novel species within the genus Marinobacter for which the name Marinobacter mangrovi sp. nov. is proposed with the type strain CHFG3-1-5T (=MCCC 1A18306T=KCTC 82398T).

A new species of ferrous-iron-oxidizing moderately thermophilic acidophilic bacteria Acidimicrobium ferrooxidans has been described. Two isolates of the species differed only in the tendency of one previously known as strain TH3 to grow in filaments. The chromosomal DNA base composition is between 67 and 69 mol% G + C. The capacity of this species to fix CO2 from air was greater than that of iron-oxidizing thermoacidophiles of the genus Sulfobacillus which required an enhanced CO2 concentration for optimum autotrophic growth. Under air ferrous iron oxidation in mixed cultures of A. ferrooxidans with either Sulfobacillus thermosulfidooxidans or Sulfobacillus acidophilus was more extensive than in pure cultures of these three strains. The greater part of ferrous iron oxidation in mixed cultures probably resulted from activity of the Sulfobacillus species which possess a greater tolerance of ferric iron and which presumably grew mixotrophically utilizing organic compounds from A. ferrooxidans.

A neutrophilic iron-oxidizing and -reducing bacterium strain MIZ03T was previously isolated from a wetland in Ibaraki Japan. Here we report the detailed characteristics of this strain. It was motile with a single polar flagellum and Gram-stain-negative. It could grow not only chemolithoautotrophically but also chemoorganotrophically by aerobic respiration and fermentation. Major cellular fatty acids were C16 : 1  ω7c/C16 : 1  ω6c and C16 : 0. Phylogenetic analyses indicated that strain MIZ03T belonged to the genus Rhodoferax. This strain was closely related to Rhodoferax ferrireducens with 98.5 % of 16S rRNA gene sequence similarity. Based on its phenotypic and genomic based characteristics we conclude that strain MIZ03T represents a new species in the genus Rhodoferax. We propose the name Rhodoferax lithotrophicus sp. nov. to accommodate this strain. The type strain is MIZ03T (=JCM 34246T=DSM 113266T). We also propose the name Rhodoferax koreensis sp. nov. of which the type strain is DCY110T (=KCTC 52288T=JCM 31441T) for the effectively but not yet validly published name ‘Rhodoferax koreense’.