Bacteria that line up to make a ‘live wire’

Necessity is the mother of natural selection. When conditions become threatening, maverick or mutant members of a group which can cope with the threat survive and multiply. The latest example is the discovery of a special type of bacteria in the ocean, which join together to form a long conducting nanowire cable to transport electrons and capture the oxygen at the surface for metabolic use. This wire is not made of metal, alloy or other usual material, but of living biological cells. The report by Dr. Christian Pfeiffer and others in the 8 November 2012 issue of Nature is a live example of the Panchatantra tale which teaches the value of cooperation between individuals to win over a problem.

All organisms gain energy for living through metabolism. The vital step in the process is the burning or oxidation of the food molecules. Chemists define oxidation as the loss of electrons and reduction as the gain of electrons. We burn our food by the breathing of oxygen in the air. When we oxidize our food and gain energy, the oxygen molecule is reduced by accepting or gaining electrons to make water, while the food molecule is oxidized by losing electrons; this is not much different from burning petrol for energy.

What if no oxygen?

What about organisms that live in places where there is no oxygen? They too metabolize their food through oxidation. But, rather than oxygen, they utilize whatever electron-acceptor molecules are available in the environment. One such group lives in marine sediments, below the surface, and it use the sulphates in the sediment as the electron-acceptors for ‘burning’ and gaining energy, an example of making do with available resources. In the process, however, the sulphate gains electrons and is reduced all the way to hydrogen sulphide (HS), a poisonous material. How then is this sulphide removed?

The problem

Look at the problem. If HS can be oxidized to sulphur, the situation turns safer. But in the process electrons are liberated and should be accepted by a partner. If only oxygen at the surface can be reached and the electrons transferred to it, we will have HS becoming S and the O reduced to H O. How does one transfer the electrons centimetres away? It is no longer a process within the cell where reactions happen within nanometres, and the oxidant and reductant molecules are in contact. What is needed is an efficient method — an electrical cable or wire for transporting the electrons from the sulphide to the oxygen above.

It is here that biology springs an unexpected surprise. In the sedimental layer beneath the marine surface lives a class of anaerobic bacteria called Desulfobulbaceae, which Pfeffer and colleagues find to densely populate the sediments. And these live not as individuals but in groups strung together as long, multicellular filaments or rods, some as long as 1.5 centimetres. And these filaments reach out from the sulphide-rich sedimental layer to the aerobic top layer a few centimetres above, which has dissolved oxygen (from the air). These filaments thus connect the anoxic layers to the oxic layer. And what do they do? They capture the electrons generated when the HS is oxidized to S at the bottom, and transport them all the way to the oxygen at the top, which accepts them and generates water or HO. In other words, the Desulfobulbaceae bacteria line up to make a live wire.

The researchers conducted a series of experiments to show how the filaments form and work. They layered the sedimental layer below in the lab and covered is with the overlying oxic sea water and studied the process. As the sulphide oxidation happened in the deeper anoxic layers, distinct change in the pH was noticed, confirming the process. And when they gently disturbed the layer, they found the 12-15 run long fibrous filaments entangled. Genetic analysis of the filaments showed their identity as Desulfobulbaceae. It appears that at least 40 million cells come together to assemble filaments of lengths as much as 1.5 cm, showing that the bacteria could span the length of the entire anoxic layer.

Liquid-filled layer

Electron microscopy showed that the cells were connected lengthwise, and each cell had a liquid-filled layer in the periplasmic space between the outer and inner cytoplasmic membranes. These liquid compartments formed ridges connecting the each cell to its neighbour, suggesting electron transport occurring through this fluid tubular structure covered with a continuous outer membrane along the filament acting as the insulator — the ancient precursor, if you will, of the electric cable of today. Hair-like appendages, called pili, of some bacteria are known to be electron transporters, but the whole cell acting so, and joining with others to make a conducting wire is novel, and reported for the first time.

Plenty of room

The physicist Richard Feynman famously remarked that there is plenty of room at the bottom. Bacterial filaments acting as electric nanowires is but one example. Some cyanobacteria called Anabena, which are able to ‘fix’ nitrogen, also form such continuous periplasmic filaments. And when a fluorescent protein was engineered into some its cells, the fluorescence was found to move along the filament from one cell to the other. Here is an example of material transfer, while with Desulfobulbaceae, it is electrons that are transported. Surely there is far more room at the bottom, and nanotechnologists can learn a lesson or two from such bacteria.

science of spirituality

In so many ways, our minds are involved in constructing the world we find ourselves in. Our perceptions and the concepts we hold determine the social reality we see and create. The very patterns of our thought – our suppositions, frameworks of understanding and the questions we are moved to ask or not ask – influence how we interact with and shape this reality. Thus, our conceptions of who we are, the interactions and discourses that inform our thinking, and our experiences in applying ideas and ideals, all serve to define the parameters of social existence.

In this respect, Bahá’u’lláh, the Prophet-founder of the Bahá’í Faith, provides clarity: “Do not busy yourselves in your own concerns; let your thoughts be fixed upon that which will rehabilitate the fortunes of mankind and sanctify the hearts and souls of men.” This challenging mandate of Bahá’í teachings indicates how spiritual understanding of human identity and purpose gives rise to social processes and policies essential for our collective progress.

As we now look at human society, its characteristics of complexity, interconnectedness and immediacy are unprecedented. As the sheer intensity and velocity of change challenges our assumptions about the nature and structure of social reality, a set of vital questions confront us: What is the source of our identity? Where should our attachments and loyalties lie? If our identity or identities so impel us, how – and with whom – should we come together? What is the nature of the bonds that bring us together? And how does such self-understanding give rise to the formation of individual and societal goals?

The organisation and direction of human affairs is inextricably connected to the future evolution of our identity. For it is from our identity that intention, action and social development flow. As we have many associational linkages, identity comes in a variety of forms. We identify ourselves by our family, ethnicity, nationality, religion, mother tongue, race, gender, class, culture or profession. There are multiple demands of loyalty placed upon us, and consequently, our identities, as Nobel laureate Amatrya Sen has noted, are “inescapably plural.”But which identity or identities are most important? Can divergent identities be reconciled? And do these identities enhance or limit our understanding of and engagement with the world?

Modernity has transformed identity in such a way that we must view ourselves as being not only dependent or independent but also interdependent. We need to determine conceptual and practical steps that will lead to an equitable and harmonious global order. This will require new models of social transformation that recognise the deep interrelationship between the material, ethical and transcendent dimensions of life. Such models can emerge only from a fundamental change in consciousness about who we are, how we regard others and how we collectively design the structures and processes of social life, whether local or global.

From a Bahá’í perspective, a universal identity is a vital precursor to action that is universal in its effects – to the “emergence of a world community, the consciousness of world citizenship, the founding of a world civilization and culture.” In emphasizing our global identity, Bahá’u’lláh presents a concept ;that insists upon a redefinition of all human relationships – between individuals, between human society and the natural world, between the individual and the community, and between individual citizens and their governing institutions.