When is a photograph not a photograph? When it's a teeming colony of bacteria.

In the beginning, there was black and white film, a tool of artists like Ansel Adams and Robert Doisneau. Then came color film, and, more recently, digital. And now there is this: bacteria prints.

Scientists in Texas and California recently created the first living photographs -- black and white pictures recorded on a ''film" made of bacteria genetically modified to sense light and produce pigment.

The new system is bulky and takes hours to develop an image, so it is unlikely that photographers will be that interested in using it: There will not be, in other words, an Adams of the petri dish.

But the scientists said that the new technology could be used to build microscopic structures to exact specifications. Instead of pigment, the bacteria could be modified to make plastic, for example. Such precision pieces -- accurate to a millionth of a meter, the size of a single bacterium -- might one day be useful for building futuristic machines smaller than a human hair.

Scientists said that the advance, reported in the journal Nature last month, shows the potential of an emerging field known as synthetic biology, which aims to make the construction and programming of genetically modified organisms like bacteria as easy as the construction of new computer circuits. The researchers behind the bio-camera are part of this field, and their work grew out of a new annual synthetic biology competition sponsored by the Massachusetts Institute of Technology. Advocates of synthetic biology said that the camera could be just the beginning of many potential applications.

''This sets the stage for more biologically-oriented devices going forward, ones with increasing complexity and functionality, as our ability to engineer and program them expands," said Jim Collins, a professor of biomedical engineering at Boston University.

Synthetic biology opens up vast possibilities for research, from cancer studies to cheaper drug production, said Collins and others. Several researchers are working on programming bacteria to more cheaply produce a chemical needed for a malaria drug; others are working on programming a cell to count the number of times it has divided, possibly providing new insights into the development of cancer.

The fundamental reason for doing the film experiment, said Christopher Voigt, the senior scientist on the team, was to provide a new way of exploring how bacteria and cells behave. A cell, or a bacterium, has many genes which, in a sense, are wired together -- with some genes able to turn on or off other genes. Voigt and others want to understand this wiring better, because this is what controls the behavior of the cell.

With the biocamera system, each bacterium has been genetically modified so that when not exposed to light, a gene switches off, turning the bacterium black. This same approach could be used to flip another gene, to study the biology of that gene and how it is wired to other genes. Their system also makes it possible to flip the genes of some bacteria in a single petri dish, but not others. This could yield new insights as well.

Biologists have been genetically modifying bacteria and other organisms for decades, but the process remains time-consuming and inefficient. The wiring of even lowly bacteria is so complex that man-made genetic changes often do not cause the intended effect, making what is known as genetic engineering more like trial and error. There is now a community of scientists, including those who worked on the living film, that is interested in making the process more like true engineering, by building a set of parts -- analogous to the electronic components of a radio -- that will work as expected when they are put together.

The biocamera team donated the genetic ''parts" -- each a sequence of DNA -- to the recently formed MIT Registry of Standard Biological Parts, in Cambridge. These parts are available for free. The team, which includes researchers from the University of California, San Francisco, and the University of Texas, Austin, wanted to give other scientists access to their work.

''Imagine how long it would take to build a bridge if you had to invent reinforced concrete every time," said Drew Endy, an assistant professor of biological engineering at MIT. ''They accomplished more in a matter of months than I was able to do in my PhD thesis."

At its most basic, synthetic biology is concerned with building biological systems, but scientists see very different possibilities in this approach. Some researchers, like Endy, are interested in creating synthetic versions of entire biological structures -- such as a virus or bacteria -- as a way to understand them better. Others are interested in using biological tools to perform chemical reactions that are difficult or impossible to perform today.

The biocamera team began the project with E. coli bacteria, according to Voigt, an assistant professor of pharmaceutical chemistry at UCSF and the senior scientist on the team. They then made a series of changes, which allowed the bacteria to sense light, and to spur a chemical reaction that creates a black dot when there is no light.

The team then exposed a petri dish full of the bacteria to a black and white image. At every point where the image was dark, the bacteria produced a black pigment. This left a pattern of black that exactly matched the original image, effectively recording it in the petri dish.

To test the system, the team created a variety of images, including the phrase ''Hello World," portraits of the scientists who were on the team, and the logo of the journal Nature where the work was published.

In theory, the living film could record high-resolution images because each bacterium is tiny: it would take about 100 bacteria to span the diameter of a human hair. But the resolution of the current setup is not that sharp because light bounces off the inside of the petri dish, illuminating some of the bacteria that should be dark.

Now the team is working on programming the bacteria to react to different colors of light. This will open up new research possibilities, Voigt said.

And, of course, it would make it possible to create another first: color bacteria prints.

Gareth Cook can be reached at cook@globe.com.