Re: How and why did Serratia marcescens produce prodigiosin?

Hi Jared -

You have noted an interesting temperature-regulated phenotype (or characteristic) in your strain of Serratia marcescens.

The prodigiosin pigment produced by the bacteria has a number of proposed activites, including ability to bind iron and to suppress certain cells of the immune system, though work is ongoing to ascertain its function.

The majority of S. marcescens strains that we isolate from humans do not produce pigment when grown at 37°C. However, a small subset of these produce it when grown a lower temperatures such as 25°C or 30°C. In contrast, environmental isolates of S. marcescencs commonly produce the pigment. Some people have hypothesized that strains acclimated to growing in mammals have mechanisms to turn off, or downregulate, the genes synthesizing proteins needed to make prodigiosin. In spite of its ability to inhibit some immune cells, the compound is potentially antigenic, meaning it could also stimulate the production of antibody and T cell responses against S. marcescens. Over time, strains living in humans as commensals (living on or in you without causing problems) or as pathogens (disease causing bacteria), may have evolved temperature-regulated controls over prodigiosin synthesis to limit production when in a warm-blooded host. Alternatively, many strains appear to have lost the ability to produce it at all.

How something comes to be regulated by temperature is a fascinating subject that covers topics in chemistry, biochemistry and physical chemistry - thermodynamics in particular. I don't know the specific reason for temperature-dependent expression of prodigiosin in S. marcescens, but can give you some possible guesses.

Proteins can change shape depending on a variety of factors, including the temperature of the system, concentration of salts and ions in the near surroundings, and presence of compounds that could chemically modify parts of the protein.

All proteins will denature, or lose their optimal shape for carrying out a specific purpuse, when heated. Some proteins denature at low temperature (say 42°C), while other denature at temperatures above the boiling point of water.

In some cases proteins that regulate the expression of other genes may not fully denature but lose their ability to bind DNA when a certain temperature is exceeded. If the loss is reversible, these regulators regain the ability to bind DNA and activate or inhibit gene expression at lower temperatures. This mechanism represents one way in which bacteria can temperature-regulate gene expression.

Another possibility is that temperature affects the activity of one or more enzymes involved in the synthesis of prodigiosin. At temperatures over 30°C a particular enzyme the pathway to synthesize prodigiosin may lose activity.

A number of factors can also affect temperature regulation of synthetic reactions - temperature may affect how well the cell absorbs material needed to synthesize the pigment, or how quickly it is degraded.

You can learn more about prodigiosin by querying search engines such as Google's Scholar database or PubMed. You may want to print out some of the pages and go over the material with your teacher at school if they talk about things you have not yet had in school.

Good luck with your project!.

-L. Bry, MadSci Admin