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

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. Wood is mainly composed of cellulose, lignin and hemicellulose. These organic components are arranged in complex macro-and micro-fibrils forming the cell wall matrix of each wood fibers. The high concentration of lignin (around 25%) makes wood a very difficult substrate to degrade and only a few specialized organisms in nature have this capacity 1. 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 microorganisms , fungi and bacteria, which by enzymatic processes dissolve and utilize the carbohydrates within the wood cell wall 2. Shipworms (Teredinidae and Xylaphagainae) belong to the group of bivalves known as the most aggressive degraders of wood in oxygenated and saline waters worldwide. 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. The growth, reproduction and distribution of different types of shipworms varies, and their ecology and physiology are well studied 4,5. Microbial degradation of wood in marine waters has received less attention than that of marine borers because the degradation processes are much slower. But in environments where bivalves are physiologically excluded, these specialized fungi and bacteria become the key degraders 6. Such environments include fresh waters, brackish waters, and anoxic waters 7-9. Here wood can survive on the seabed for centuries and unique historic shipwreck can be recovered by ma...

A Review on Bacterial Contribution to Lignocellulose Breakdown into Useful Bio-Products

“…The first report of wood degradation in the Antarctic reveals lignocellulolytic microorganism that degraded wood cells of subject materials, submerged for a long period. The study confirmed that lignocellulolytic bacteria are highly active even in such an extreme environment [ 46 ]. Bacteria can sometimes be versatile and exist in less than optimal temperatures.…”

Advances in Understanding Microbial Deterioration of Buried and Waterlogged Archaeological Woods: A Review

“…However, tunnelling type attack is most common in wood in contact with moist soils and exposed to wet environments, conditions unfavourable to the aggressive white and brown rot fungi. However, such conditions also support the activity of SR and EB, and thus mixed attacks on wood by SR, TB and EB have been reported [3,6,45,54,63,67,91], including waterlogged archaeological woods [16,20,62]. Moreover, when present in waterlogged archaeological woods, tunnelling type attack is generally confined to outer tissue layers of wooden objects.…”

“…Fungi causing type I soft rot are present in a wide range of terrestrial and aquatic environments [2,19,59]. Some species have even adapted to degrade wood under extreme conditions, such as those present in Arctic [60] and Antarctic [61,62] regions. Cavities in cell walls are produced by SR belonging to Ascomycetes, although some white-rot fungi have been reported to also produce cavities [59].…”

“…Cavities in cell walls are produced by SR belonging to Ascomycetes, although some white-rot fungi have been reported to also produce cavities [59]. SR are more common in moist/wet environments which discourage the growth and activity of the aggressive white and brown rot fungi, and where they often coexist with wood-degrading bacteria [3,5,6,45,62,63].…”

“…Following confirmation, using TEM, that certain bacteria can degrade lignified cell walls by way of tunnelling within the cell wall, it became possible to recognise this type of bacterial decay also using LM and SEM, which led to a flurry of activities leading to the reports of wide presence of tunnelling degradation of wood in terrestrial as well as aquatic environments [59,74,86], including waterlogged archaeological woods [15,16,20,52,62] from different parts of the world. However, tunnelling type attack is most common in wood in contact with moist soils and exposed to wet environments, conditions unfavourable to the aggressive white and brown rot fungi.…”