Science Progress (2001), 84 (3)

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Science Progress (2001), 84 (3), 157–181

Fast trains, slow boats, and the

ancestry of the Polynesian

islanders

STEPHEN OPPENHEIMER AND MARTIN RICHARDS

The question of the origins of the Polynesians has, for over 200 years, been

the subject of adventure science. Since Captain Cook’s first speculations on

these isolated Pacific islanders, their language affiliations have been seen

as an essential clue to the solution. The geographic and numeric centre of

gravity of the Austronesian language family is in island Southeast Asia,

which was therefore originally seen as their dispersal homeland. However,

another view has held sway for 15 years, the ‘out of Taiwan’ model, popularly

known as the ‘express train to Polynesia’. This model, based on the

combined evidence of archaeology and linguistics, proposes a common

origin for all Austronesian-speaking populations, in an expansion of rice

agriculturalists from south China/Taiwan beginning around 6,000 years

ago. However, it is becoming clear that there is, in fact, little supporting

evidence in favour of this view. Alternative models suggest that the ancestors

of the Polynesians achieved their maritime skills and horticultural

Neolithic somewhere between island Southeast Asia and Melanesia, at an

earlier date. Recent advances in human genetics now allow for an independent

test of these models, lending support to the latter view rather than the

former. Although local gene flow occurring between the bio-geographic

regions may have been the means for the dramatic cultural spread out to

the Pacific, the immediate genetic substrate for the Polynesian expansion

came not from Taiwan, but from east of the Wallace line, probably in

Wallacea itself.

Science Progress (2001), 84 (3),183–204

Investigating urban geochemistry

using Geographical Information

Systems

CATHERINE THUMS AND MARGARET FARAGO

Geographical Information System (GIS) is an interactive digital extension

of the two-dimensional paper map. Customised maps are created by the

selection and aggregation of data from independent sources to assist studies

in urban geochemistry. The metropolitan area of Wolverhampton, in the

West Midlands, UK is used to illustrate the types of output that can be generated.

These include: geographic and geological feature; geochemical

data and land use. Multi-layered maps can be used to investigate spatial

relationships, for example, between elevated concentrations of metals in

soils and industrial land use. Such maps can also be used to assist the

assessment of potential exposure of groundwater, ecosystems and humans

using maps incorporating guideline values for metals in soils.

Science Progress (2001), 84 (3), 205–233

Extracellular sensing and

signalling pheromones switch-on

thermotolerance and other stress

responses in Escherichia coli

ROBIN J. ROWBURY AND MARGARET GOODSON

The findings reviewed here overturn a major tenet of bacterial physiology,

namely that stimuli which switch-on inducible responses are always

detected by intracellular sensors, with all other components and stages in

induction also being intracellular. Such an induction mechanism even

applies to quorum-sensed responses, and some others which involve functioning

of extracellular components, and had previously been believed to

occur in all cases. In contrast, for the stress responses reviewed here, triggering

is by a quite distinct process, pairs of extracellular components

being involved, with the stress sensing component (the extracellular sensing

component, ESC) and the signalling component, which derives from it

and induces the stress (the extracellular induction component, EIC), being

extracellular and the stimulus detection occurring in the growth medium.

The ESCs and EICs can also be referred to as extracellular sensing and

signalling pheromones, since they are not only needed for induction in the

stressed culture,but can act as pheromones in the same region activating

other organisms which fail to produce the extracellular component (EC)

pair. They can also diffuse to other regions and there act as pheromones

influencing unstressed organisms or those which fail to produce such ECs.

The cross-talk occurring due to such interactions, can then switch-on stress

responses in such unstressed organisms and in those which cannot form the

ESC/EIC pair. Accordingly, the ESC/EIC pairs can bring about a form of

intercellular communication between organisms.If the unstressed organisms,

which are induced to stress tolerance by such extracellular components,

are facing impending stress challenge, then the pheromonal activities

of the ECs provide an early warning system against stress. The specific

ESC/EIC pairs switch-on numerous responses; often these pairs are proteins,

but non-protein ECs also occur and for a few systems, full induction

needs two ESC/EIC pairs. Most of the above ECs needed for response

induction are highly resistant to irreversible inactivation by lethal agents

and conditions and, accordingly, many killed cultures still contain ESCs or

EICs. If these killed cultures come into contact with unstressed living

organisms, the ECs again act pheromonally, altering the tolerance to stress

of the living organisms. It has been claimed that bacteria sense increased

temperature using ribosomes or the DnaK gene product. The work

reviewed here shows that, for thermal triggering of thermotolerance and

acid tolerance in E. coli, it is ESCs which act as thermometers.

Science Progress (2001), 84 (3), 235–254

Bacterial biofilms and human

disease

MICHAEL WILSON

The term biofilm is used to denote a polymer-encased community of

microbes which accumulates at a surface. Biofilms are responsible for a

number of diseases of man and, because of the intrinsic resistance of these

structures to antibiotics and host defence systems, such diseases are very

difficult to treat effectively. The application of new microscopic and molecular

techniques to biofilms has revolutionised our understanding of their

structure, composition, organisation and activities. This review will

describe the role that biofilms play in human disease and will outline our

new millennial view of these complex and fascinating bacterial communities.