{"id":91,"date":"2012-07-02T17:26:07","date_gmt":"2012-07-02T17:26:07","guid":{"rendered":"http:\/\/www.certainly-strange.com\/?p=91"},"modified":"2012-07-03T00:37:29","modified_gmt":"2012-07-03T00:37:29","slug":"long-filaments-of-bacteria-acting-as-living-electrical-cables","status":"publish","type":"post","link":"http:\/\/www.certainly-strange.com\/?p=91","title":{"rendered":"Long Filaments of Bacteria Acting as Living Electrical Cables!"},"content":{"rendered":"

Imagine this: bacteria that need a metal to put electrons onto in order to respire.\u00a0 It\u2019s not too strange, really; we need oxygen to put electrons onto when we respire so in that sense it\u2019s a similar mechanism.\u00a0 These bacteria just use iron or molybdenum et cetera whereas we would use oxygen when we breathe.\u00a0 But now here\u2019s where things get weird: if the bacteria just need something to dump electrons onto, why not just give them an electrode, and let them dump their electrons onto the anode?\u00a0 Indeed, that\u2019s how many microbiologists have grown metal-respiring bacteria, and bacteria that can grow in these conditions are called \u201canode-respiring bacteria.\u201d<\/p>\n

Years ago when I first heard about bacterial nanowires<\/a> in anode-respiring bacteria, I thought that my mind had been very thoroughly blown.\u00a0 Basically, microbiologists found that the mats of bacteria which grow on the anode are very thick, and indeed are so thick that you would think that the bacteria on top of the mat would not have sufficient access to the anode in order to respire.\u00a0 Further analysis suggested that the bacteria in these mats or \u201cbiofilms\u201d actually had little \u201chairs\u201d (since termed \u201cbacterial nanowires”) which they used to pass electrons to their neighbours, and then they would pass the electrons on to their neighbours, and so on until it got to the bacteria living directly on top of the anode, who would then transfer the electrons onto it.\u00a0 It is an amazing network of electrical interactions between bacteria!\u00a0 This is also cool, because you can quantitatively measure the respiration rates by measuring how much of an electrical current your bacteria are putting into the anode:<\/p>\n

\"\"
A diagram of bacterial nanowires, and how they manage to pass electrons from the top of the biofilm to the anode at the bottom<\/figcaption><\/figure>\n

Now, my mind has been totally blown all over again, with Lars Nielsen<\/a>\u2019s ASM 2012 talk on Bacterial \u201cMicrocables\u201d and electrical currents in filamentous bacteria.<\/p>\n

Lars noticed that his bacteria needed oxygen and iron sulfide in order to live and consume.\u00a0 First, both of these things were distributed evenly throughout the growth area.\u00a0 But as the bacteria grew, they consumed the nutrients where the environment would not replenish them.\u00a0 His bacteria produced large zones of depletion, wherein there was no oxygen and no sulfide.\u00a0 The top had lots of oxygen, but none of the iron sulfide it needed.\u00a0 All the iron sulfide was at the bottom, many centimetres away.\u00a0 The bacteria need both at the same time in order to survive.\u00a0 How were the bacteria getting access to both at the same time?\u00a0 Was it more nanowires?\u00a0 Were they using minerals in the anoxic zone to pass electrons down to the bottom?\u00a0 Were they using exofactors as shuttles to shuttle the electrons down?<\/p>\n

Lars investigated this question, and found that they were actually filamentous bacteria acting as living cables themselves!\u00a0 A bacterium would divide incompletely, forming two cells attached by a shared outer membrane.\u00a0 Then those cells would divide incompletely, forming four cells attached the same way, et cetera.\u00a0 Soon there is a centimetres-long chain of the bacteria, all with one common outer membrane.\u00a0 Electron microscopy revealed fibres, which are presumably the conductive cables, running down the length of these chains.\u00a0 The cells were bridged together by these fibres and an outer membrane.\u00a0 A cross section gave a better look at the cables inside the periplasmic space of the membrane.<\/p>\n

\"\"
A diagram showing the chain of bacterial cells bridged by filaments in the periplasmic space of their shared membrane<\/p>\n
\n
\n
\"\"<\/dt>\n
A cross-section of a cell in the chain, showing the filaments in the periplasmic space of the shared membrane<\/figcaption><\/figure>\n<\/dd>\n<\/dl>\n<\/div>\n

To test whether the bacterial chains were using these \u201cmicrocables\u201d to conduct electrons downwards through the anoxic zone, Lars\u2019s lab did several tests.\u00a0 Here are two of my favourites:<\/p>\n

They passed a thin wire through the anoxic zone, effectively \u201ccutting\u201d the bacterial chains in half.\u00a0 They found that growth stopped, and no more current was being produced in the electrode.\u00a0 After 24 hours, neither growth nor current had returned.\u00a0 So, cutting the chain of microcables correlated with the cessation of respiration.\u00a0 Respiration stopped instantly and the results were lasting.<\/p>\n

They put a small film barrier in the middle of an anoxic zone, with holes large enough to let molecules and proteins through, but too small to let bacteria through.\u00a0 This was to test whether they could still use secreted shuttles and exofactors.\u00a0 The bacteria could not grow with this film blocking them in the middle.<\/p>\n

I think the Nielsen lab has some very compelling evidence that they\u2019ve found something totally new and awesome!\u00a0 Consider my mind blown.<\/p>\n","protected":false},"excerpt":{"rendered":"

Imagine this: bacteria that need a metal to put electrons onto in order to respire.\u00a0 It\u2019s not too strange, really; we need oxygen to put electrons onto when we respire so in that sense it\u2019s a similar mechanism.\u00a0 These bacteria just use iron or molybdenum et cetera whereas we would use oxygen when we breathe.<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_crdt_document":"","footnotes":""},"categories":[59,62,58,61],"tags":[340,69,68],"class_list":["post-91","post","type-post","status-publish","format-standard","hentry","category-biology","category-microbiology","category-science","category-science-reporting","tag-biology","tag-microbiology-2","tag-science-2"],"_links":{"self":[{"href":"http:\/\/www.certainly-strange.com\/index.php?rest_route=\/wp\/v2\/posts\/91","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.certainly-strange.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.certainly-strange.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.certainly-strange.com\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"http:\/\/www.certainly-strange.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=91"}],"version-history":[{"count":10,"href":"http:\/\/www.certainly-strange.com\/index.php?rest_route=\/wp\/v2\/posts\/91\/revisions"}],"predecessor-version":[{"id":101,"href":"http:\/\/www.certainly-strange.com\/index.php?rest_route=\/wp\/v2\/posts\/91\/revisions\/101"}],"wp:attachment":[{"href":"http:\/\/www.certainly-strange.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=91"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.certainly-strange.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=91"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.certainly-strange.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=91"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}