The simple answer for the question: “What does a simple form of life look like?” is “Not so simple.” Seems like this is the natural answer, pardon the reference. Almost always, when scientists dig into the molecular and biochemical nature of life, the results are “…more complex than we expected.” Ain’t life grand! Case in point, a new suite of studies that attempt to put more detail into a description of what the most elementary form of a cell looks like. The papers themselves are technical and very interesting – so maybe the road to the ‘results’ is more important than getting there – but the bottom line (if that’s an appropriate expression) for non-specialists is: Simple life is not so simple…

The simple answer for the question: “What does a simple form of life look like?” is “Not so simple.” Seems like this is the natural answer, pardon the reference. Almost always, when scientists dig into the molecular and biochemical nature of life, the results are “…more complex than we expected.” Ain’t life grand! Case in point, a new suite of studies that attempt to put more detail into a description of what the most elementary form of a cell looks like. The papers themselves are technical and very interesting – so maybe the road to the ‘results’ is more important than getting there – but the bottom line (if that’s an appropriate expression) for non-specialists is: Simple life is not so simple…

What are the bare essentials of life, the indispensable ingredients required to produce a cell that can survive on its own? Can we describe the molecular anatomy of a cell, and understand how an entire organism functions as a system? These are just some of the questions that scientists in a partnership between the European Molecular Biology Laboratory (EMBL) in Heidelberg, Germany, and the Centre de Regulacio Genòmica (CRG) in Barcelona, Spain, set out to address. In three papers published back-to-back today in Science, they provide the first comprehensive picture of a minimal cell, based on an extensive quantitative study of the biology of the bacterium that causes atypical pneumonia, Mycoplasma pneumoniae. The study uncovers fascinating novelties relevant to bacterial biology and shows that even the simplest of cells is more complex than expected.

[Source: EurekAlert]

One of the interesting aspects of this very collaborative set of papers is the divvying-up of cell biology study into three main areas (this may be unfamiliar terminology):

1. Transcriptome, the RNA components (or transcripts) produced by a cell’s DNA
2. Proteome, the myriad proteins and their associated complexes produced by a cell
3. Metabolome, the cell biochemistry of metabolism (energy production and use)

When studying both its proteome and its metabolome, the scientists found many molecules were multifunctional, with metabolic enzymes catalyzing multiple reactions, and other proteins each taking part in more than one protein complex. They also found that M. pneumoniae couples biological processes in space and time, with the pieces of cellular machinery involved in two consecutive steps in a biological process often being assembled together.

Remarkably, the regulation of this bacterium’s transcriptome is much more similar to that of eukaryotes – organisms whose cells have a nucleus – than previously thought. As in eukaryotes, a large proportion of the transcripts produced from M. pneumoniae’s DNA are not translated into proteins. And although its genes are arranged in groups as is typical of bacteria, M. pneumoniae doesn’t always transcribe all the genes in a group together, but can selectively express or repress individual genes within each group.

Unlike that of other, larger, bacteria, M. pneumoniae’s metabolism doesn’t appear to be geared towards multiplying as quickly as possible, perhaps because of its pathogenic lifestyle. Another surprise was the fact that, although it has a very small genome, this bacterium is incredibly flexible and readily adjusts its metabolism to drastic changes in environmental conditions. This adaptability and its underlying regulatory mechanisms mean M. pneumoniae has the potential to evolve quickly, and all the above are features it also shares with other, more evolved organisms.

In one sense the confirmation that life, even reduced to bare essentials, is sophisticated and complex is hardly a discovery. In another way though, research that tries to pin down what (exactly) are those essential elements of life and then find a substitute (or surrogate) to embody those essentials for study – now there’s a pathway to eventually isolating the biochemistry necessary for the key processes of life. As this study shows, despite the hype from other quarters, we have a way to go. Just as we’re learning that human DNA and RNA have much more complex expression than we thought, some of the same complexity applies to even the simplest of bacteria. Thus widens our horizon of what needs to be learned to explain the origin of life.