The biotransformation of mercury in pH-stat cultures of microfungi

The biotransformation of mercury was monitored in Hymenoscyphus ericae (Read) Korf & Kernan, Neocosmospora vasinfecta E. F. Sm., and Verticillium terrestre (Link) Lindau following the exposure of these fungi to environmentally relevant doses of HgII(HgCl2) in aerated pH-controlled cultures. Mercury applied at 120 and 300 μg·L–1quickly associated with cells of N. vasinfecta. Within 3 h, approximately 80% of the remaining Hg in both treatments had been converted to β-HgS, and at 8 h, 15% and 53% of the original doses had been converted into volatile Hg0. Hymenoscyphus ericae was less efficient at converting HgIIto β-HgS, but it volatilized larger amounts of Hg0. A mercury-tolerant isolate of V. terrestre withstood levels of Hg in the parts per million. When exposed to 270, 1000, or 2000 μg·L–1HgCl2, 93% ± 3% of the amounts remaining in cultures of V. terrestre after 2 h was β-HgS. At 2 mg·L–1, 72% of the Hg was reduced to Hg0in 2 h. Volatilization accounts for the tolerance of V. terrestre to high doses of Hg, whereas the conversion of Hg to β-HgS was the major detoxifying mechanism at lower doses. The formation of β-HgS occurs preferentially with volatilization operating as the default pathway, when the former biotransformation mechanism is saturated.

Graffenrieda emarginata (Melastomataceae) forms mycorrhizas with Glomeromycota and with a member of the Hymenoscyphus ericae aggregate in the organic soil of a neotropical mountain rain forest

Graffenrieda emarginata (Ruiz & Pav.) Triana (Melastomataceae) was found to be the most frequent tree on the nutrient-poor organic soil in a species-rich tropical mountain rain forest of southern Ecuador. Our studies revealed that the rootlets are symbiotically associated with arbuscular mycorrhizal fungi and simultaneously form ectomy corrhizas displaying a superficial Hartig net but no hyphal mantle. Molecular phylogeny revealed a multitude of previously unknown glomeromycete sequence types. Ultrastructure of the ectomycorrhiza-forming fungus indicated an ascomycete, and molecular phylogenetic studies identified the fungal symbiont as a new taxon within the Hymenoscy phus ericae (Read) Korf & Kernan aggregate (Ascomycota). The mycorrhizal state of G. emarginata is considered crucial for its competitiveness and abundance in these sites.Key words: arbuscular mycorrhiza, ectomycorrhiza, Glomeromycota, Hymenoscyphus ericae aggregate, neotropical mountain rain forest, Ecuador.

Host Range of a Select Isolate of the Ericoid Mycorrhizal Fungus Hymenoscyphus ericae

Studies were conducted to examine the host range of a select isolate of the ericoid mycorrhizal fungus Hymenoscyphus ericae (Read) Korf and Kernan [American Type Culture Collection (ATCC) #32985]. Host status was tested for 15 ericaceous species, including: Calluna vulgaris (L.) Hull, Enkianthus campanulatus (Miq.) Nichols, Gaultheria procumbens L., Kalmia latifolia L., Leucothoe fontanesiana Sleum., Oxydendrum arboreum (L.) DC.,Pierisfloribunda (Pursh) Benth. & Hook.,Rhododendron calendulaceum (Michx.) Torr.,Rhododendron carolinianum Rehd., Rhododendron catawbiense Michx., Rhododendron maximum L., Rhododendron mucronulatumTurcz., Vaccinium corymbosum L., and Vaccinium macrocarpon Ait. Arbutus unedo L., an ericaceous species that forms arbutoid, not ericoid, mycorrhizae, was used as a negative control. All of the species were colonized by the ericoid isolate with the exception of Enkianthus campanulatus and the negative control. Inoculation with this isolate of H. ericae resulted in a significant increase in shoot growth. However, intensity of root colonization was not correlated to amount of shoot growth. In fact, an increase in growth was observed in the two species that lacked fungal colonization.

In Vitro Colonization of Micropropagated Pieris floribunda by Ericoid Mycorrhizae. I. Establishment of Mycorrhizae on Microshoots

Selected isolates of Hymenoscyphus ericae (Read) Korf and Kernan, Oidiodendron griseum Robak, O. maius Barron, and a second O. Robak species were evaluated as inocula for in vitro establishment of micropropagated plantlets of Pieris floribunda (Pursh ex Sims) Benth. and Hook. Severity of shoot necrosis on microshoots differed for each isolate of Oidiodendron. Inoculation of micropropagated plantlets with isolates of H. ericae benefited initial shoot and root development on agar-solidified Woody Plant Medium (WPM) supplemented with sucrose and covered by a layer of autoclaved 1 peat: 1 vermiculite (v/v). Inoculation of microshoots with H. ericae or isolates of Oidiodendron did not stimulate production of adventitious roots.