For numerous industrial sectors, the isolation, characterisation
and engineering of proteins produced by bacteria living at temperatures
close to 0°C open up the prospect of the availability of enzymes that
are fully active at low temperatures. In this emerging area of research
on "psychrophile" micro-organisms, Europe has rapidly become a world
leader thanks to the coordinated research carried out under the Eurocold
concerted action and the Coldzyme project.
On the frozen expanses of the Antarctic,
researchers collect thousands of micro-organisms, characterised
by their extreme biodiversity and of particular interest to
the food and detergent industries.
Enzymes - proteins which catalyse the fundamental
biochemical reactions of all living cells - are used extensively by
industry in applications as diverse as preparing food, formulating
detergents and detecting pollutants using biosensors. Most of the
organisms that provide the enzymes currently in use live in environments
where the temperature ranges from 30°C to 40°C, and their effectiveness
is highly temperature-sensitive. Consequently, many enzymatic processes
require heating that is expensive - and, in certain cases, harmful
to the organoleptic qualities of a foodstuff - or simply not feasible.
Ensuring high-performance enzymatic activity at low temperatures therefore
represents an important industrial imperative. And where does the
solution lie? Out in the cold, of course.
The incredible biodiversity of the Antarctic
"The discovery of the extreme biodiversity of these psychrophile micro-organisms
is one of the unexpected spin-offs of our work," stresses Nick Russell
of the University of London and coordinator of the project. "I've
got more than a thousand different bacteria in my cold storage rooms,"
says Charles Gerday of the University of Liège (Belgium). "At present
we have identified 15 or so different types. We do not know much about
these organisms, and it is difficult to make comparisons. This complicates
the task of taxonomic research."
There are a wide variety of ecosystems on earth, all of which, in
differing degrees, have been colonised by living organisms. Researchers
have discovered numerous micro-organisms that are perfectly adapted
to diverse extreme conditions - be it temperatures in the region
of 100°C, acid or alkaline environments, or very high salinity levels.
The Antarctic, the second largest continent on earth where the temperature
rarely rises above zero, is no exception to this rule. It is here
on the Antarctic expanses, at the interface between the sea and
the icefields, and also on the icefields themselves, that Nicholas
Russell and Charles Gerday have collected thousands of micro-organisms
- bacteria, in particular, but also yeasts - which they are studying
as part of the Coldzyme project.
The primary objective of this vast project, which coordinates all
European research in this area, is to study the enzymes with a view
to understanding the rules governing their adaptation to the cold.
And we have not had to wait long for the results.
Computer-generated image of a protein isolated
in a bacterium from the Antarctic icefields, in the process
of digesting starch (alpha-amylase). The reptilian structure
of the protein enables it to remain flexible and to function
at very low temperatures. Such proteins are now being developed
to operate new biotechnology cold processes.
New biotechnological line
The researchers have focused their work on the type of enzymatic
activity where known equivalents exist in normal bacteria and which
are of genuine interest in the field of biotechnological applications
(see table). "Impressive progress has been
made," Charles Gerday points out enthusiastically. "In the space
of a year we have resolved the three-dimensional structure of two
major enzymes, alpha-amylase and a calcium-zinc protease, and two
patents have been applied for."
This research has enabled us to understand how enzymes are able
to adapt to the cold. The explanation lies not in any difference
in the three-dimensional structure of the enzymes of psychrophiles
but in the flexibility of the protein. The functioning of an enzyme
necessarily entails deformations in its structure to permit a preliminary
investigation of the substrate, the reaction proper, and then the
release of the modified substrate. These minor conformational changes
are very temperature-sensitive and, in order for them to occur in
cold conditions, the protein therefore needs to be extremely flexible.
This is the exact opposite of what happens in the case of organisms
living at high temperatures (close to 100°C), where the proteins
have to be extremely rigid to prevent their spatial conformation
from being totally destroyed by heat-induced agitation. "A further
aim of the project is to lay the foundations of a new biotechnological
line," Nick Russell goes on. Numerous proteins are in the process
of being cloned, and the researchers have succeeded in producing
mutants of certain enzymes, which have already been tested by the
partner manufacturers. Even if the enzymes provide the requisite
levels of activity, new adaptations will still be necessary before
detergent products and food additives incorporating Antarctic enzymes
can be placed on the market.
The research is being followed with interest by the manufacturers
who make up the Microbiology Industrial Platform. Negotiations on
bilateral agreements involving filing applications for patents and
their exploitation are currently under way. Thanks to psychrophile
bacteria, new ground is being broken in the area of cell factories,
whereby the emphasis is placed on cold shock proteins, special genetic
control systems, specific membrane compositions, different excretion
mechanisms, etc. The potential industrial applications are legion
and, if we take Nick Russell's word for it, "psychrophiles are hot
stuff". Given that all the skills required have been coordinated
under the aegis of the Community programmes, Europe now has a big
lead over its American and Japanese rivals.
|Some of the enzymes studied
under the Coldzyme project and their possible fields of application:
||breadmaking, textiles, brewing, detergents
||stonework cleaning, "bio-polishing"
||elimination of lactose from milk
||detergent additives, flavourings
||detergent additives, meat tenderising