Gordonia asplenii sp. nov., isolated from humic soil on bird’s nest fern (Asplenium nidus L.)

A novel member of the actinobacteria, designated strain A-T 0013T, was isolated from humic soil on a bird’s nest fern (Asplenium nidus L.) collected from Khao Yai National Park in Thailand. According the results of a polyphasic taxonomic study, A-T 0013T had characteristics typical of members of the genus Gordonia . The 16S rRNA gene sequence indicated that A-T 0013T shared ≤98 % sequence similarity with all members of the genus Gordonia . The most closely related species was Gordonia effusa IFM 10200T (97.92 % sequence similarity). The average nucleotide identity based on blast (ANIb) value with G. effusa IFM 10200T was 76.81 %. The cell-wall peptidoglycan contained meso-diaminopimelic acid. The whole-cell sugars contained ribose, arabinose and galactose. The predominant menaquinone was MK-9(H2). The predominant fatty acids were C16 : 0, C18 : 1ω9c, summed feature 3 (C16 : 1ω7c/C16 : 1ω6c), and C18 : 0 10-methyl. Mycolic acid was present. The polar lipid profile for this strain ncluded diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and phosphatidylinositol mannosides. The G+C content of the genomic DNA was 66.1 mol%. Differentiation of A-T 0013T from the most closely related species, Gordonia effusa IFM 10200T, was evident from digital DNA–DNA hybridization values of 21.8 %. On the basis of the results of comparative analysis of phenotypic, chemotaxonomic and genotypic data, strain A-T 0013T is concluded to represent a novel species of the genus Gordonia , for which the name Gordonia asplenii sp. nov. is proposed. The type strain is A-T 0013T (=TBRC 11910T=NBRC 114549T).

Glucose concentration controls priming effects and soil carbon storage under pasture and forest in volcanic ash soils of Hokkaido, Japan

<p><strong>Introduction & objectives:</strong> Over ten thousand years, soils have been formed through events of volcanic ash deposition in Hokkaido, Japan. The soil organic matter (SOM) in the past surface layer has been buried in the deeper soil. The buried humic horizons serve as a large carbon (C) reservoir. The SOM in the deeper soil horizons is preserved due to lower microbial activities and limited inputs of fresh organic matters. However, when the buried humic horizons are exposed to the surface by deep plowing and bottom plow tillage, decomposition of the exposed SOM may be accelerated through priming effects, due to the increased supply of low-molecular-weight (LMW) substances from fresh plant litter inputs. To test this, we examined glucose concentration dependency of priming effect and the change of SOC balance through priming effect using <sup>13</sup>C tracer incubation.</p><p><strong>Materials & methods:</strong> Soil samples were collected from the volcanic soil profiles in pasture site and adjacent forest sites in Hokkaido, Japan. The moist soils were sieved (< 4 mm) to eliminate plant debris and stones for the incubation study and the other analysis. A <sup>13</sup>C-glucose solution (99 atom%; 0 – 3.9 mg glucose g<sup>-1</sup>) was added to moist soil (equivalent to 10 g oven-dried weight) and incubated at 20ºC in the dark for 30 days. The head space gas sample was periodically taken into the vial, and <sup>13</sup>CO<sub>2</sub> and <sup>12</sup>CO<sub>2</sub> concentrations were determined by GC-MS. Priming effect (PE) was calculated by subtraction between the amounts of <sup>12</sup>CO<sub>2</sub> with and without glucose. The head space gas in the bottle was flush out and replaced to CO<sub>2</sub>-free-air every sampling time. We also measured soil microbial biomass C (MBC) by chloroform fumigation method, bacterial and fungal biomass by 16S and 18S rRNA genes targeted real-time PCR, SOC concentrations, inorganic N concentrations (ammonium and nitrate) and the other physicochemical properties of the soil profiles.</p><p><strong>Results & discussion: </strong>Glucose addition induced the positive PEs in the buried humic soil samples of both sites, and the magnitudes of PEs (cumulative primed-CO<sub>2</sub> amounts) in the buried humic soil samples were 0.4 to 1.5 times as those in the surface soils. However, the negative PEs were detected in the forest surface soil, probably because of low soil pH and relatively high inorganic N concentration. The magnitudes of PEs were dependent on added glucose concentrations for all the soils, and the threshold between negative and positive PEs corresponded to 3.5 % of glucose-C relative to MBC in the forest surface soil. The positive correlation between evolution rates of primed-CO<sub>2</sub> significantly and bacterial or fungal biomass suggests both bacteria and fungi contributes to PE in the soils studied. Even if glucose addition induced PE, total SOC after incubation increased when glucose-C was added more than 0.5 mg C g<sup>-1</sup> in the all soils. This implies that the optimized fresh litter input can control priming effects and C sequestration in volcanic soils.</p>