A lot of people—including biochemists––are downsizing these days. But these scientists have not downscaled begrudgingly out of economic necessity. Instead, they enthusiastically work to simplify things by eliminating unnecessary biochemical systems from bacteria. Their goal is to define life’s minimum complexity and they will spare no expense to accomplish this extraordinary task.
Researchers from Stanford University report on the latest work toward this end.1 The team determined the essential genome of the bacterium Caulobacter crescentus, a microbe that lives in freshwater lakes and streams. C. crescentus displays a complex life cycle. Its reproductive form has a stalk that extends from one pole of the cell, allowing C. crescentus to attach itself to surfaces. When this microbe reproduces it generates a daughter cell called a swarmer that swims freely. The swarmer cell eventually transforms into a stalked cell, attaching to a surface prior to its reproduction.
Understanding the genome—the entire genetic makeup—of this organism will increase researchers’ knowledge of this important microbe. A key aspect of this learning depends on identifying the essential DNA elements in the genome. That identification will also provide biochemists with a greater appreciation of life’s minimal complexity.
The Stanford investigators determined that the essential genome of C. crescentus consisted of just over 492,000 base pairs (genetic letters), which is close to 12 percent of the overall genome size. About 480 genes comprise the essential genome, along with nearly 800 sequence elements that play a role in gene regulation. The regulatory elements constitute about 10 percent of the essential genome.
The team also discovered that the elements of the fundamental genome clustered near the origin of replication In other words, they are not randomly distributed throughout the genome, but are localized, highlighting the genome’s organization.
When the researchers compared the C. crescentus essential genome to other essential genomes, they discovered a limited match. For example, 320 genes of this microbe’s basic genome are found in the bacterium E. coli. Yet, of these genes, over one-third are nonessential for E. coli. This finding means that a gene is not intrinsically essential. Instead, it’s the presence or absence of other genes in the genome that determine whether or not a gene is essential.
What does seem to be a constant from organism to organism are the biochemical operations specified by the essential genome. Typically, these processes involve protein production, cell division, energy harvesting, cell cycle control, and cell wall production. They appear to be the core processes needed for an entity to be recognized as “living” and, in effect, define life’s minimum complexity.
As I have discussed before, research continues to indicate that even in its most minimal form, life is intrinsically and irreducibly complex. Such complexity makes it difficult to imagine how undirected evolutionary processes could generate the first life-form. Conversely, as described in The Cell’s Design, the irreducible minimal complexity of life serves as a marker for intelligent design.
- Beat Christen et al., “The Essential Genome of a Bacterium,” Molecular Systems Biology 7 (2011): 528. doi: 10.1038/msb.2011.58.