Sphingomonas parvus sp. nov. isolated from a ginseng-cultivated soil.

Strain GP20-2(T) was isolated from a soil cultivated with ginseng in Korea. The 16S rRNA gene sequence of this strain showed the highest sequence similarity with Sphingomonas daechungensis CH15-11(T) (96.7%) and Sphingomonas sediminicola Dae 20(T) (96.2%) among the type strains. The strain GP20-2(T) was a strictly aerobic, Gram-negative, non-motile, rod-shaped bacterium that formed very tiny colonies, less than 0.3 mm in diameter after 10 days on R2A agar. The strain grew at 10-35-C (optimum, 35-C), at a pH of 5.0-8.0 (optimum, pH 6.0), and in the absence of NaCl. The DNA G+C content of strain GP20-2(T) was 67.2 mol%. It contained ubiquinone Q-10 as the major isoprenoid quinone, and summed feature 8 (C18:1ω6c and/or C18:1ω7c, 49.8%) and C16:0 (17.0%) as the major fatty acids. On the basis of evidence from our polyphasic taxonomic study, we concluded that strain GP20-2(T) should be classified as a novel species of the genus Sphingomonas, for which the name Sphingomonas parvus sp. nov. is proposed. The type strain is GP20-2(T) (=KACC 12865(T) =DSM 100456(T)).

Mucilaginibacter ginsengisoli sp. nov., isolated from a ginseng-cultivated soil.

A dark-pink-coloured bacterial strain, B4Y-8T, was isolated from a soil cultivated with ginseng. The 16S rRNA gene sequence of this strain showed highest similarity with Mucilaginibacter litoreus BR-18T (96.8 %), Mucilaginibacter lutimaris BR-3T (96.6 %) and Mucilaginibacter defluvii A5T (96.2 %) among the type strains of species of the genus Mucilaginibacter. Strain B4Y-8T was a strictly aerobic, Gram-stain-negative, non-motile, short-rod-shaped bacterium producing a large amount of extracellular polymeric substance. The strain grew at 10-35 °C (optimum, 25 °C), at pH 3.0-11.0 (optimum, pH 7.0) and in the presence of 0-1 % (w/v) NaCl (optimum, 0 %). The DNA G+C content of strain B4Y-8T was 49.0 mol%. It contained menaquinone 7 (MK-7) as the major isoprenoid quinone, and summed feature 3 (C16 : 1ω6c and/or C16 : 1ω7c) and iso-C15 : 0 as the major fatty acids. On the basis of evidence from the present polyphasic taxonomic study, strain B4Y-8T should be classified as representing a novel species of the genus Mucilaginibacter, for which the name Mucilaginibacter ginsengisoli sp. nov. is proposed. The type strain is B4Y-8T ( = KACC 18152T = JCM 30759T).

Importance of c-Type cytochromes for U(VI) reduction by Geobacter sulfurreducens.

BACKGROUND: In order to study the mechanism of U(VI) reduction, the effect of deleting c-type cytochrome genes on the capacity of Geobacter sulfurreducens to reduce U(VI) with acetate serving as the electron donor was investigated. RESULTS: The ability of several c-type cytochrome deficient mutants to reduce U(VI) was lower than that of the wild type strain. Elimination of two confirmed outer membrane cytochromes and two putative outer membrane cytochromes significantly decreased (ca. 50-60%) the ability of G. sulfurreducens to reduce U(VI). Involvement in U(VI) reduction did not appear to be a general property of outer membrane cytochromes, as elimination of two other confirmed outer membrane cytochromes, OmcB and OmcC, had very little impact on U(VI) reduction. Among the periplasmic cytochromes, only MacA, proposed to transfer electrons from the inner membrane to the periplasm, appeared to play a significant role in U(VI) reduction. A subpopulation of both wild type and U(VI) reduction-impaired cells, 24-30%, accumulated amorphous uranium in the periplasm. Comparison of uranium-accumulating cells demonstrated a similar amount of periplasmic uranium accumulation in U(VI) reduction-impaired and wild type G. sulfurreducens. Assessment of the ability of the various suspensions to reduce Fe(III) revealed no correlation between the impact of cytochrome deletion on U(VI) reduction and reduction of Fe(III) hydroxide and chelated Fe(III). CONCLUSION: This study indicates that c-type cytochromes are involved in U(VI) reduction by Geobacter sulfurreducens. The data provide new evidence for extracellular uranium reduction by G. sulfurreducens but do not rule out the possibility of periplasmic uranium reduction. Occurrence of U(VI) reduction at the cell surface is supported by the significant impact of elimination of outer membrane cytochromes on U(VI) reduction and the lack of correlation between periplasmic uranium accumulation and the capacity for uranium reduction. Periplasmic uranium accumulation may reflect the ability of uranium to penetrate the outer membrane rather than the occurrence of enzymatic U(VI) reduction. Elimination of cytochromes rarely had a similar impact on both Fe(III) and U(VI) reduction, suggesting that there are differences in the routes of electron transfer to U(VI) and Fe(III). Further studies are required to clarify the pathways leading to U(VI) reduction in G. sulfurreducens.