Wood-destroying soft rot fungi in the historic expedition huts of Antarctica

Abstract

Three expedition huts in the Ross Sea region of Antarctica, built between 1901 and 1911 by Robert F. Scott and Ernest Shackleton, sheltered and stored the supplies for up to 48 men for 3 years during their explorations and scientific investigation in the South Pole region. The huts, built with wood taken to Antarctica by the early explorers, have deteriorated over the past decades. Although Antarctica has one of the coldest and driest environments on earth, microbes have colonized the wood and limited decay has occurred. Some wood in contact with the ground contained distinct microscopic cavities within secondary cell walls caused by soft rot fungi. Cadophora spp. could be cultured from decayed wood and other woods sampled from the huts and artifacts and were commonly associated with the soft rot attack. By using internal transcribed spacer sequences of ribosomal DNA and morphological characteristics, several species of Cadophora were identified, including C. malorum, C. luteo-olivacea, and C. fastigiata. Several previously undescribed Cadophora spp. also were found. At the Cape Evans and Cape Royds huts, Cadophora spp. commonly were isolated from wood in contact with the ground but were not always associated with soft rot decay. Pure cultures of Cadophora used in laboratory decay studies caused dark staining of all woods tested and extensive soft rot in Betula and Populus wood. The presence of Cadophora species, but only limited decay, suggests there is no immediate threat to the structural integrity of the huts. These fungi, however, are widely found in wood from the historic huts and have the capacity to cause extensive soft rot if conditions that are more conducive to decay become common.

FIG. 1.

Historic huts and artifacts left in Antarctica after expeditions by Robert F. Scott and Ernest Shackleton. (A) Cape Royds hut built in 1908, showing the hut structure and area used for the stables and storage adjacent to the hut. (B) Cape Evans hut built in 1911. The hut structure contains an annex and stable area enclosed within the walls of the hut. A row of historic latrines is in front of the hut. (C) Wooden storage box and Adele penguins nesting at Cape Royds. Many wooden storage boxes and other artifacts are located in the area around the huts. (D) Exterior wall boards from Cape Evans hut. Melt water from the ground is absorbed by the lower boards during the austral summer.

FIG. 2.

Scanning electron micrographs of transverse sections of historic wood decayed by soft rot fungi. (A and B) Soft rot cavities in pine wood that was in contact with the ground from the exterior of Cape Evans hut. The secondary walls of tracheids contain numerous cavities of varying size. (C and D) Soft rot cavities in birch wood from a wooden storage box outside of the Cape Evans hut that was in contact with the ground. Advanced decay is present and large holes, formed by many secondary wall cavities that have coalesced together, are seen in fiber cell walls. Bar, 50 μm (A and C) or 25 μm (B and D).

FIG. 3.

One of 12 most parsimonious trees of Cadophora species and related discomycetes based on the ITS1, 5.8S, and ITS2 regions of rDNA. The tree is rooted to T. cinerella. Bootstrap values from 1,000 replications that were greater than 50% are indicated above or below the branches. Isolate numbers or accession numbers from Antarctic isolates are in bold and have asterisks. Consistency index = 0.7335; retention index = 0.8121; rescaled consistency index = 0.5957.

FIG. 4.

Schematic drawing of Cape Evans hut showing locations (•) where Cadophora species were isolated. Six isolates were obtained from wooden artifacts around the hut, and the direction where these woods were located is indicated by an arrow. Although cultures of Cadophora were obtained from all of these locations, not all of the samples had soft rot.

FIG. 5.

Scanning electron micrographs of transverse sections from wood decayed in the laboratory with isolates of Cadophora from Antarctica. (A) Soft rot cavities in wood from Betula inoculated with Cadophora sp. strain E. Fibers between vessel elements are riddled with holes caused by the soft rot fungus. (B) Soft rot in birch wood inoculated with C. malorum. Cavities within the secondary walls of fibers are evident, with hyphae present in cell lumina and within the cavities created by the soft rot fungus. (C and D) Extensive soft rot in Populus wood inoculated with C. luteo-olivacea. Large cavities have formed in the fiber cell walls, and large numbers of hyphae are present. In many cells, the entire S₂ region of the secondary wall has been degraded. A residual S₃ layer adjacent to cell lumina and the middle lamella between cells are left. Wood cells with advanced soft rot have lost most of their original cell wall strength. Bar, 50 μm (A and C) or 25 μm (B and D).