First evidence of microbial wood degradation in the coastal waters of the Antarctic

Charlotte G Björdal,Paul K Dayton

doi:10.1038/s41598-020-68613-y

Charlotte G Björdal, Paul K Dayton

Open Access

https://doi.org/10.1038/s41598-020-68613-y

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Abstract

Wood submerged in saline and oxygenated marine waters worldwide is efficiently degraded by crustaceans and molluscs. Nevertheless, in the cold coastal waters of the Antarctic, these degraders seem to be absent and no evidence of other wood-degrading organisms has been reported so far. Here we examine long-term exposed anthropogenic wood material (Douglas Fir) collected at the seafloor close to McMurdo station, Antarctica. We used light and scanning electron microscopy and demonstrate that two types of specialized lignocellulolytic microbes—soft rot fungi and tunnelling bacteria—are active and degrade wood in this extreme environment. Fungal decay dominates and hyphae penetrate the outer 2–4 mm of the wood surface. Decay rates observed are about two orders of magnitude lower than normal. The fungi and bacteria, as well as their respective cavities and tunnels, are slightly smaller than normal, which might represent an adaptation to the extreme cold environment. Our results establish that there is ongoing wood degradation also in the Antarctic, albeit at a vastly reduced rate compared to warmer environments. Historical shipwrecks resting on the seafloor are most likely still in good condition, although surface details such as wood carvings, tool marks, and paint slowly disintegrate due to microbial decay.

Highlights

Wood submerged in saline and oxygenated marine waters worldwide is efficiently degraded by crustaceans and molluscs
The wood retrieved outside McMurdo station showed active microbial degradation after 36 and 50 years of exposure in the cold waters of Antarctic
The two samples showed similar degradation profiles dominated by an extensive decay by soft rot fungi in the outermost 2–4 mm of the board accompanied by minor decay by tunneling bacteria

Summary

Introduction

Wood submerged in saline and oxygenated marine waters worldwide is efficiently degraded by crustaceans and molluscs. In marine waters wood degrading organisms can be divided into two groups. The first group consist of macro-organisms (mainly bivalves and crustaceans) that physically gnaw and feed on wood material. The second group are micro-organisms, fungi and bacteria, which by enzymatic processes dissolve and utilize the carbohydrates within the wood cell w all[2]. Shipworms (Teredinidae and Xylaphagainae) belong to the group of bivalves known as the most aggressive degraders of wood in oxygenated and saline waters world-wide. By forming large internal tunnels they are able to transform solid wooden boards to a perforated material within a few years This results in a rapid physical breakdown of the wood and a reduction in service life of man-made structures such as harbor pilings and boats[3]. A review on microbial degradation of wood in marine environments is given by Björdal (2012)[6]

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