It’s time again for the weekly My Tiny Highlight (MyTH). This week we will explore one of my favorites, Caulobacter crescentus. C. crescentus is a unique bacterium that has made it the focus of a lot of research due to its lifestyle and easy observable changes in cell shape. Part of the C. crescentus life cycle is spent freely swimming in its aquatic habitat using a single flagellum. These are called swimmer cells. At some point in development, the swimmer cell ejects the flagellum from itself and begins growing a stalk on the opposite cell pole as the flagellum. As the stalk continues growing, the cell produces a VERY stickly glue called holdfast at the tip of the stalk which is used to attach to a surface and is called a stalked cell. The cell undergoes division assymetrically; meaning, the two daughter cells produced are not identical (as is the case for most bacteria). One daughter becomes a swimmer cell due to new flagellum synthesis on one pole while the other remains stalked.
Thinking about split personality, how can one cell contain both a flagellum and a stalk simultaneously; both being functional? This is the focus of years of research. One answer refers to my favorite molecule discussed in earlier MyTH posts, the bacterial second messengercyclic-di-GMP. Cyclic-di-GMP is constantly being made and degraded in C. crescentus. However, the production and degradation are sequestered to opposite poles of the cell via precise protein localization. The enzyme needed to produce c-di-GMP is at the stalked pole while the enzyme to degrade c-di-GMP is at the swimmer pole. Although there are no physical compartments within this bacterial cell, the concentration of c-di-GMP is not uniform throughout. The proteins that interact with c-di-GMP are predominantly at the stalked pole and allow for the stalk to elongate and leave the flagellated pole alone. Brilliant!
C. crescentus is also of importance for its ability to clean up contaminated surface and subsurface groundwater because it is resistant to the effects of heavy metal exposure. Also, examination of the genome was used to determine the ancestry of C. crescentus. It contains gene clusters similar to Pseudomonas species and others that are predominantly found in the soil. This fact along with the presence of genes necessary to breakdown plant-derived carbon molecules suggests C. crescentus originated on land (or under it) before winding up in its present day niche.
English: Graphical representation of Caulobacter crescentus (Photo credit: Wikipedia)