Effect of dissimilatory iron and sulfate reduction on arsenic dynamics in the wetland rhizosphere and its bioaccumulation in wetland plants (Scirpus actus).

Microbial redox transformations of arsenic (As) are coupled to dissimilatory iron and sulfate reduction in the wetlands, however, the processes involved are complex and poorly defined. In this study, we investigated the effect of dissimilatory iron and sulfate reduction on As dynamics in the wetland rhizosphere and its bioaccumulation in plants using greenhouse mesocosms. Results show that high Fe (50µM ferrihydrite/g solid medium) and SO42- (5mM) treatments are most favorable for As sequestration in the presence of wetland plants (Scirpus actus), probably because root exudates facilitate the microbial reduction of Fe(III), SO42-, and As(V) to sequester As(III) by incorporation into iron sulfides and/or plant uptake. As retention in the solid medium and accumulation in plants were mainly controlled by SO42- rather than Fe levels. Compared to the low SO42- (0.1mM) treatment, high SO42- resulted in 2 times more As sequestered in the solid medium, 30 times more As in roots, and 49% less As in leaves. An As speciation analysis in pore water indicated that 19% more dissolved As was reduced under high SO42- than low SO42- levels, which is consistent with the fact that more dissimilatory arsenate-respiring bacteria were found under high SO42- levels.

Burkholderia novacaledonica sp. nov. and B. ultramafica sp. nov. isolated from roots of Costularia spp. pioneer plants of ultramafic soils in New Caledonia.

The taxonomic status of eleven rhizospheric bacterial strains belonging to the genus Burkholderia and isolated from roots of Costularia (Cyperaceae), tropical herbaceous pioneer plants growing on ultramafic soils in New Caledonia, was investigated using a polyphasic taxonomic approach. The genetic analyses (16S rRNA genes, gyrB, recA, nreB and cnr) confirmed that all strains are Burkholderia and cluster into two separated groups. The DNA hybridization results showed low relatedness values to the closest relatives Burkholderia species. The phenotypic analyses confirmed that the two groups of strains could be differentiated from each other and from other known Burkholderia species. This polyphasic study revealed that these two groups of strains represent each a novel species of Burkholderia, for which the names Burkholderia novacaledonica sp. nov. (type strain STM10272(T)=LMG28615(T)=CIP110887(T)) and B. ultramafica sp. nov. (type strain STM10279(T)=LMG28614(T)=CIP110886(T)) are proposed, respectively. These strains of Burkholderia presented specific ecological traits such as the tolerance to the extreme edaphic constraints of ultramafic soils: they grew at pH between 4 and 8 and tolerate the strong unbalanced Ca/Mg ratio (1/19) and the high concentrations of heavy metals i.e. Co, Cr, Mn and Ni. Noteworthy B. ultramafica tolerated nickel until 10mM and B. novacaledonica up to 5mM. The presence of the nickel (nreB) and cobalt/nickel (cnr) resistance determinants encoding for protein involved in metal tolerance was found in all strains of both groups. Moreover, most of the strains were able to produce plant growth promoting molecules (ACC, IAA, NH3 and siderophores). Such ecological traits suggest that these new species of Burkholderia might be environmentally adaptable plant-associated bacteria and beneficial to plants.

Enhanced inhibition of Aspergillus niger on sedge (Lepironia articulata) treated with heat-cured lime oil.

AIMS: This study aimed to examine heat curing effect (30-100°C) on antifungal activities of lime oil and its components (limonene, p-cymene, ß-pinene and α-pinene) at concentrations ranging from 100 to 300 µl ml(-1) against Aspergillus niger in microbiological medium and to optimize heat curing of lime oil for efficient mould control on sedge (Lepironia articulata). METHODS AND RESULTS: Broth dilution method was employed to determine lime oil minimum inhibitory concentration, which was at 90 µl ml(-1) with heat curing at 70°C. Limonene, a main component of lime oil, was an agent responsible for temperature dependencies of lime oil activities observed. Response surface methodology was used to construct the mathematical model describing a time period of zero mould growth on sedge as functions of heat curing temperature and lime oil concentration. Heat curing of 90 µl ml(-1) lime oil at 70°C extended a period of zero mould growth on sedge to 18 weeks under moist conditions. CONCLUSIONS: Heat curing at 70°C best enhanced antifungal activity of lime oil against A. niger both in medium and on sedge. SIGNIFICANCE AND IMPACT OF THE STUDY: Heat curing of lime oil has potential to be used to enhance the antifungal safety of sedge products.

Nocardioides caricicola sp. nov., an endophytic bacterium isolated from a halophyte, Carex scabrifolia Steud.

A Gram-staining-positive, coccoid to rod-shaped bacterium, designated strain YC6903(T), was isolated from a halophytic plant (Carex scabrifolia Steud.) collected from sand dunes at Namhae Island, Korea, and its taxonomic position was investigated by using a polyphasic approach. Strain YC6903(T) grew optimally at 30 °C and at pH 8.0. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain YC6903(T) belongs to the genus Nocardioides in the family Nocardioidaceae. Strain YC6903(T) was related most closely to Nocardioides pyridinolyticus OS4(T) (97.0 % 16S rRNA gene sequence similarity), Nocardioides dokdonensis FR1436(T) (96.6 %), Nocardioides aquiterrae GW-9(T) (96.6 %) and Nocardioides hankookensis DS-30(T) (96.6 %). The cell-wall peptidoglycan contained LL-diaminopimelic acid and MK-8(H(4)) was the major respiratory quinone. The mean (±SD) level of DNA-DNA relatedness between strain YC6903(T) and N. pyridinolyticus OS4(T) was 53.5±5.5 %. The predominant cellular fatty acid of strain YC6903(T) was iso-C(16 : 0) (28.9 %). The DNA G+C content was 71.7 mol%. Phenotypic, phylogenetic and chemotaxonomic data indicated that strain YC6903(T) represents a novel species of the genus Nocardioides, for which the name Nocardioides caricicola sp. nov. is proposed. The type strain is YC6903(T) (=KACC 13778(T) =DSM 22177(T)).

Polyphyly and two emerging lineages in the rust genera Puccinia and Uromyces.

The phylogenetic validity of Puccinia and Uromyces, Pucciniaceae, and closely related genera was evaluated using nucLSU rDNA sequences. Using a wide range of rust species with different life cycles and with different host specificities, Puccinia and Uromyces were shown to be highly polyphyletic and to also include representatives of the genera Aecidium, Cumminsiella, Dietelia, Endophyllum, Miyagia, and Uredo. Furthermore, the structure of the phylogenetic data did not reflect previous sub-generic delimitations based on teliospore pedicel structure, but rather suggests that at least two major lineages have evolved within Puccinia/Uromyces: Rusts with telial states on Poaceae were exclusively found in one of these groupings and those with telial states on Cyperaceae resided in the other lineage. This might suggest that the two lineages evolved in close association with these host groups in different biomes.