Interviw with Susan Greenfield

By David Bradley

Elemental Discoveries  

July 2000, Issue 31 - Biological Feedback from Susan Greenfield, Interview by David Bradley

Bacterial builders

British chemists have enlisted bacteria to help them build porous fibres from zeolites. The research could lead to the development of filamentous materials for catalytic and separation applications as well as in creating novel biocompatible materials.
       Stephen Mann, Sean Davis and Bao Zhang at the University of Bristol have worked with molecular biologist Neil Mendelson of the University of Arizona at Tucson to extend the technology of chemical templating to the bacterial world.
      Until recently, chemists have relied on small molecules and supramolecular aggregates to assist them in creating inorganic frameworks with well- defined networks of pores. There have been many success in synthesising artificial versions of natural minerals such as the zeolites with wide pores and channels and with unusual cross-sectional shapes, such as clover leaves.
       According to Mann, these molecular templates influence the size and nature of the pore size and architecture. He reasoned that rather than relying on molecular scale templates, mineral pores might be opened wider using cell-sized species, such as bacteria. His team has previously shown that cellular templates can help extend the length scale of ordering in new porous materials such as the silica-based MCM-41. Now, the team has used a similar strategy to create zeolite fibres with ordered pores.
The researchers used a stable aqueous dispersion of zeolite nanoparticles as building blocks and a supercellular thread of bacteria Bacillus subtilis as the template. The thread consists of a hexagonally packed array of long multicellular filaments which swells when placed in a colloidal sol of zeolite nanoparticles. This causes the silicalite nanoparticles to diffuse into the spaces between the filaments to give an ordered composite. The team then blast the composite at 600 Celsius to destroy the bacterial template leaving behind an intact white zeolite fibre with ordered macroporous channels lined by 100 nm-wide walls of the coalesced silicalite nanoparticles.
        Various techniques, such as X-ray and electron diffraction and electron microscopy were used to demonstrate that the resulting porous fibres are composed of crystalline silicalite. The materials have a hierarchical structure based on channel-like pores on both the micrometre and nanometre length scales. They could therefore be useful in flow systems where the larger channels reduce back-pressure and allow easy access of reactants or waste-products to the zeolitic molecular channels contained within the silicalite walls.

The researchers report their work in more detail in Chem. Commun., 2000, 781.

Scuttling sulphur bugbearers

Ancient olenid trilobites survived the toxic undersea world of 500 million years ago by inbuilding their own chemical detoxification plant in the form of colonies of sulphur-digesting bacteria. The sulphur products from the bugs then provided a food supply for the trilobites.
        Richard Fortey of the UK's National History Museum believes the olenid trilobites lived at the bottom of the ocean that is now the Scandinavian land mass.
        While trilobites are now extinct, and have been for some 250 million years, we still find sulphur bacteria living in the sulphurous environment near undersea thermal vents where oxygen is rare and little light reaches them.
        The latest examination of olenid fossils has revealed to Fortey that these scuttling creatures had certain features in common with modern species that exploit the sulphur bugs, such as shrimp. For example, an olenid's mouth seems redundant while a wide thorax, thin shell and multiple segmentation hint at a large surface area that could be used to cultivate a bacterial crop.
  Gardening sulphur bugs meant the olenids were not poisoned by the toxic spew and could harness the sulphur's chemical energy in much the same way as animals that eat green plants on land harness the energy of the sun.
        Such a symbiotic relationship is very important in modern marine life, corals are the archetypal example. They allow animals to colonise the sea floor in places they otherwise would be unable. An understanding of such ecosystems could help in conservation of those that survive to this day.