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Sep 25

Far from the light of day, and somewhere near Hampstead

Paddock is the codename of a bunker that was built in the late 1930s as a back-up for the better known Cabinet War Rooms located in Whitehall.

Cabinet war room junction box at Paddock [CC-BY-SA-3.0 Steve Cook]

Junction box in the upper basement floor of the Paddock bunker; CWR-AWR almost certainly stands for ‘Cabinet War Room – Air Raid Warning’

The bunker was abandoned at the end of the war, and was only used intermittently after that by the Post Office, whose Research Station sat atop it. In 1998, the surface site and the bunker were sold off, and a housing development was built on top. Unfortunately, during the development, the concrete slab that kept the bunker watertight was damaged, and since then, Paddock has been slowly decaying.

Twice a year – once in May for local residents, and again to the general public during Open House Weekend – the Housing Association kindly allow members of Subterranea Britannica to take members of the public into the bunker to see the place that Churchill allegedly described as:

far from the light of day […and…] somewhere near Hampstead

Churchill’s grasp of North London geography was apparently even worse than mine: the bunker is considerably nearer Neasden (or Neeeeeeeeasden, as the Jubilee Line announcements would have it)  than Hampstead. I’ve served as wrong-door-blocker and trip-hazard-pointer for open days twice now, and if you missed out on a trip to Paddock during Open House Weekend this year, I’d heartily recommend it for next.

We shall not explore the underlying reasons for my darling husband’s interest in dungeon-like holes in the ground:

Alex at Drakelow [CC-BY-SA-3.0 Steve Cook]

Alex calls in a tactical nuclear strike on Croydon from the Drakelow nuclear bunker

but like abandoned bunkers for their dankness, and for their decay, and for their reminder to us all of the essential futility of existence in the face of the Second Law.

I also like the fungi.

Paddock door with fungus [CC-BY-SA-3.0 Steve Cook]

Ph’nglui mglw’nafh Cthulhu R’lyeh wgah’nagl fhtagn

If you keep the wood in a building above about 25% moisture, it will slowly but surely be destroyed by fungi whose ecological niche is turning the presumptuous handiwork of humans into carbon dioxide. The most well-known of these is the dry rot fungus, Serpula lacrymans. Dry rot and other wood-destroying fungi make their living by breaking down wood to release sugars that they can use as food. Wood is a very complex material; a fibre-composite of many hollow tubes cemented together:

Scanning electron micrograph of hardwood [© Ian Morris, used with permission]

Scanning electron micrograph of a small block of hardwood. The wood is made of assorted hollow tubes, each of which is the remains of a dead cell’s multilayered cell wall.

Wood is made principally of cellulose, which is the same stuff from which cotton clothes and paper are constructed. Cellulose is difficult to break down, as the individual molecular strands are tightly packed together by hydrogen bonding, making a near-crystalline material that is very impermeable to water, and even more impermeable to digestive enzymes. Most herbivorous animals subcontract out the work of breaking-down cellulose to the bacteria and fungi that live in their guts.

Cellulose [CC-BY-SA-3.0 Steve Cook]

Cellulose consists of thousands of glucose molecules chained together.

Although cellulose is difficult to break down, the other main component of wood, lignin, makes cellulose look positively fragile. Plants make lignin by secreting phenolic alcohols into their cell walls, and then semi-randomly polymerising these alcohols together using free-radicals. The mechanisms of lignin synthesis and its global structure are still areas of active research (or furious argument, depending on your point of view). From the plant’s perspective, lignin is a marvellous glue: it creates a substance that cannot be broken down by conventional enzymes, as you’d need hundreds of them, one for each of the many kinds of linkage found in the lignin. It also provides the concrete to the cellulose’s reinforcing bars. For would-be wood-eaters though, it poses a significant problem.

Lignin structure [CC-BY-SA-3.0 Steve Cook, based on User:Chino's structure on Wikipedia]

Small part of possible lignin structure.

Brown rot fungi like the dry rot, wet rot (a.k.a. cellar fungus, Coniophora puteana), mine fungus (Fibroporia vaillantii) and many of the others that infest the Paddock bunker (and who knows, maybe your basement too?) break down wood by more-or-less the reverse of the process by which lignin is made. Brown rot fungi release free-radicals into the wood. These tiny free-radicals can penetrate where no bulky enzyme every could, and they oxidise and smash the cellulose into fragments.

This is not the most elegant way of breaking down wood, and it leaves a lot of brown lignin muck behind (hence the name ‘brown rot’), much of which I trudged over my kitchen floor when I got home on Saturday.

White rot fungi, such as the honey fungus (Armillaria mellea), have a more delicate way of dealing with wood. They also generate free-radicals, but they are able to fully break down the lignin to carbon dioxide. As they break down the lignin, the remaining wood becomes a bleached and friable cellulose fluff. White rots use an enzyme called lignin peroxidase to make these free-radicals. Because free-radicals are not very fussy about quite what they oxidise, white-rot fungi can break down a lot more than just lignin. Some, like Phanerochaete chrysosporium, have been used in the bioremediation of soil that has become contaminated with explosive or creosote residues.

Lignin peroxidase [CC-BY-SA-3.0 Steve Cook; based on Blodig, Smith, Doyle & Piontek; PDB 1B82]

Lignin peroxidase. The flat thing in the middle is a haem group, similar to the one you find in haemoglobin in human blood. However, rather than binding oxygen, it binds hydrogen peroxide. The smaller highlighted bit below the haem is a tryptophan residue. The hydrogen peroxide oxidises the enzyme’s haem group, which in turn oxidises the tryptophan residue, which in turn oxidises lignin.

Contrary to what you may have guessed, the delicate white-rot approach actually seems to be the more evolutionary ancient mechanism, with the heavy-handed brown rot approach being a later innovation.

Wood destroying fungus phylogeny [CC-BY-SA-3.0 Steve Cook, with images from James Lindsey at Ecology of Commanster, Wikipedia's User:jensbn, User:ecornerdropshop, USer:Audriusa, and Flickr's Doug Bowman]

Highly abbreviated phylogeny of wood destroying fungi. White rots shown in grey; brown rots in brown. Note the way that the brown rot lifestyle has evolved at least twice (actually more!) from within separate groups of white rots. Schizophyllum is the closest relative of the cultivated mushroom (Agaricus bisporus) shown in the diagram above. Dry rot (Serpula) is not too distantly related to the penny bun bolete (cep, porcini, Boletus edulis). Based on Floudas, D. et al. (2012) The Paleozoic origin of enzymatic lignin decomposition reconstructed from 31 fungal genomes. Science 336 1715-1719.

If it weren’t for lignin, we might have had a harder time bringing on the climatic Armageddon that we’re all working so hard towards. Coal is the buried and compressed remains of lignin-rich trees that died around 360 to 300 million years ago, during the Carboniferous period. In modern ecosystems, dead trees are generally recycled by brown and white rot fungi, but for 60 million years, trees apparently had enough of an upper hand over their undertakers that huge deposits of coal were laid down. The oxygen concentration of the air was boosted to 35% by the imbalance between oxygen-producing photosynthesis by plants and oxygen-consuming respiration by wood decaying organisms, allowing enormous insects with half-metre wingspans to fly. It is possible that it was the evolution of lignin that brought on the Carboniferous, and the evolution of lignin peroxidase that ended it, but attributing cause and effect in Deep Time usually results in data-egg on speculator-face, so perhaps you should forget I even mentioned it.

Wood destroying fungi are not only biochemical marvels, they are also splendid architects. Unlike plants and animals, fungi are not composed of cells containing a single nucleus, but rather of hyphae, which are fibrous tubes containing many nuclei. Like cells, hyphae can be packed together in various ways to make specialised tissues and organs, the most familiar of which is probably the mushroom, which are the tasty genitals of the fungus Agaricus bisporus. Wood destroying fungi produce genitals of highly variable tastiness, including jelly ears:

Auricularia auricula-judae on wood at Silwood Park [CC-BY-SA-3.0 Steve Cook]

Ear fungus (Auricularia auricula-judae); tasty despite the look of the thing

Brackets:

Hoof fungus (Fomes fomentarius) on tree at Silwood Park [CC-BY-SA-3.0 Steve Cook]

Hoof fungus (Fomes fomentarius); not tasty

And wobbly yellow things:

Fungal fruiting bodies from Paddock [CC-BY-SA-3.0 Steve Cook]

Something eating the remains of a desk in Paddock’s BBC radio broadcast suite; indeterminate tastiness.

One of the more wonderful structures created by wood-destroying fungi, and one that is much evident at Paddock and at Drakelow (another bunker I have known and loved) is the rhizomorph:

Rhizomorphs growing out of a door-frame at Drakelow [CC-BY-SA-3.0 Alex Lomas]

Rhizomorphs growing out of a door-frame at Drakelow

Rhizomorphs are thick, cord-like structures resembling plant roots. They allow some wood destroying fungi to grow over inedible surfaces and locate new planks and door-frames and skirting-boards to colonise and destroy. Some fungi, like the honey mushroom mentioned above, use them to hop from living tree to living tree, destroying whole orchards of wood in their wake. The rhizomorphs of dry rot are particularly hardy and capable of penetrating masonry in their search for food.

Since my last visit to Paddock two years ago, the brown rots have released just a little more of the organic fixtures and fittings back into the carbon cycle. All flesh is grass; and all wood is ash. Quietly the fungi triumph.

Fungus at Paddock [CC-BY-SA-3.0 Steve Cook]

My name is Ozymandias, king of kings: Look on my works, ye mighty, and despair!

1 comment

  1. Spungletrumpet

    Thanks for the interesting article.

    Here’s yet another bunker with plenty of fungi:

    http://www.28dayslater.co.uk/forums/showthread.php/54343-Burlington-Corsham-2010?

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