What is essential for life? Not much, it seems. It was revealed this week that some bacteria - tiny though they be - carry around a lot of extra genetic baggage.
Only 12 per cent of the DNA of a common freshwater microbe was necessary for its survival, researchers discovered, after knocking out the other 88 per cent. Not unexpectedly, these vital bits of the genetic code included genes, and other segments of DNA that switch genes on and off.
''But there were many surprises,'' a Stanford University biologist, Dr Lucy Shapiro, says. ''For example, we found 91 essential DNA segments where we have no idea what they do.''
Whittling down the genetic blueprint of an organism to its most basic essentials is part of a new quest to understand life better, and then redesign it.
The big promise is the ability to construct new, artificial lifeforms that can solve many of the world's problems: to clean up oil spills and other pollutants, and to produce foods, fuel, plastics and drugs.
Formal engineering principles are the key to this controversial quest, known as synthetic biology, which is still in its infancy, Dr Jim Haseloff, an Australian plant expert at the University of Cambridge, says.
''The field is in a situation similar to mechanical engineering in the early 1800s and microelectronics in the early 1950s,'' he says.
Two centuries ago, mechanical engineers constructed each steam engine individually. But the development of standardised parts, such as screw threads in the 1830s, and modular construction, led to the mass production of engines from blueprints.
Electrical engineering followed a similar pathway, with the development of key components, such as transistors and integrated circuits, leading to today's international electronics industry. ''And now you have the same kind of trajectory occurring in biology,'' Dr Haseloff says.
Like the early engine builders, biologists have become very good at creating their own particular genetically modified organisms by adding one or two genes to a plant or microbe.
But a revolution in design of new organisms is needed if the world is to escape its reliance on non-renewable sources of energy and materials, Dr Haseloff, who recently gave a talk at the University of Sydney, says.
Lego blocks in a child's play box provided the first inspiration. In recent years, scientists have created a library of thousands of standardised, biological building blocks. These small DNA spare parts can be used by any researchers to assemble new microbes that can, for example, operate at higher temperatures, soak up carbon dioxide or latch onto heavy metals.
''It is a simple idea. But it is also a profound change in the way you do things - akin to moving from biology into engineering,'' Dr Haseloff says.
The latest, more sophisticated phase involves construction of complex genetic circuits, made of interacting genes and proteins, to control cell behaviour.
Natural circuits, for example, direct cells to grow, divide, produce a signal, or turn into a different type of cell. Synthetic circuits might be able to be integrated with natural circuits to ''rewire'' cells and get a plant or microbe to produce the fuel, medicine or material that is desired.
Dr Haseloff is particularly interested in how to modify the shape of plants, by altering the number of cells that proliferate or change type during development, to increase the amount of certain tissues, such as fruit.
He points to the remarkable differences between the ancient, small tomatoes of Peru and the large, red juicy ones we enjoy today, achieved by traditional breeding. ''The question is whether you can rationally engineer and produce those changes [with synthetic circuits].''
Medical researchers have already begun to use synthetic biology techniques in the laboratory, to try to tackle infectious disease and cancer, researchers report this week in the journal, Science.
For example, bacteria have been engineered to produce a protein that allows them to invade cancer cells, and to then produce a small piece of RNA that turns down the effect of a gene in the cell that stimulates colon cancer.
Concerns about synthetic biology focus on bioterror - the potential for development of new deadly microbes as weapons - and bioerror - their escape into the environment or unforseen harm to human health.
Some environmental groups have called for a moratorium on the science, but many researchers say the technology is an extension of genetic modification techniques widely used now. ''And we already have a very efficient framework of regulation and governance for these kinds of manipulations,'' Dr Haseloff says.