Survey of Genomes - Caulobacter crescentus

Tim Stucky takes us away from the human microbiome out into nature, specifically clean freshwater habitats with very few nutrients. He discusses the genome of Caulobacter crescentus, a stalked bacterium that can either swim or attached itself to a substrate.

Hello everyone, My name is Tim Stucky and today I’ll be taking you through the genetics of Caulobacter crescentus.  Caulobacter was first proposed in 1935 by Henrici and Johnson, two researchers who found the bacteria in microscope slides with samples from a freshwater lake.  It is considered a stalked organism, meaning it has a long tubelike extension in its mature form.  This organism fit into the Caulobacteriales which was a newly found order for bacteria at the time of its discovery.  It is a gram-negative bacteria that lives in nutrient poor areas of fresh water bodies.  There are two main strains of C. Crescentus, C15 which is the natural freshwater strain and NA1000 which is the experimental strain isolated in the 1970’s.  Caulobacter is a very important tool for studying the cell cycle because of its odd development.  There are two distinguishable developmental stages that it will go through which makes it easy to look at how its genome is used throughout its life.  It gives rise to daughter swarmer cells that are mobile and have flagella.  Soon they begin to secrete polysaccharide adhesins known as holdfast which makes it bound to the surface it is on.  Once it is bound to a surface, it sheds its flagellum and grows a stalk, or a long tubular extension.  In the stalk phase, it is mature and ready to replicate. 

Caulobacter is tightly regulated in how it can only replicate its DNA one time while in the stalk phase.  It will replicate its single chromosome and divide into two more swarmer cells.  In the C. crescentus 4,016,942 base pair genome, there are 3767 genes averaging 969 base pairs in size.  There are 3763 proteins thought to be produced by the genome with 1012 being hypothetical and 2751 having matches to known proteins.  This genome has the largest ratio of signal transduction proteins made to any other bacteria that has been fully sequenced.  This has allowed researchers to test and gain a much deeper understanding of these pathways and how they are used in regulating the cycles of development.  Researchers have also found that there were 13 undiscovered RNA Polymerase sigma factors made in C. crescentus.  Sigma factors help regulate changes in gene expression by coupling with outside stimuli.  This has significance in the organism’s development and has allowed deeper research into gene expression.  The last point of importance is that it initiates replication in different ways depending on the media it grows on.  This has allowed researchers to study in depth, how cells adapt and change their replication control based on the nutrients provided to them.

This bacteria has been vital in cell cycle research and has provided insight and discovery since its discovery in the 1930’s.  Thanks for joining me and I hope you enjoyed learning about Caulobacter crescentus and its contributions to genetics.


References

Gorbatyuk, B., & Marczynski, G. T. (2004, December 09). Regulated degradation of chromosome replication proteins DnaA and CtrA in Caulobacter crescentus. Retrieved from https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2958.2004.04459.x

Nierman, W. C., Feldblyum, T. V., Laub, M. T., Paulsen, I. T., Nelson, K. E., Eisen, J., . . . Fraser, C. M. (2001, March 27). Complete genome sequence of Caulobacter crescentus. Retrieved from https://www.pnas.org/content/98/7/4136.short

POINDEXTER, J. S. (1964, September). BIOLOGICAL PROPERTIES AND CLASSIFICATION OF THE CAULOBACTER GROUP. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC441226/?page=2

Toh, E., Kurtz, H. D., & Brun, Y. V. (2008, November 01). Characterization of the Caulobacter crescentus Holdfast Polysaccharide Biosynthesis Pathway Reveals Significant Redundancy in the Initiating Glycosyltransferase and Polymerase Steps. Retrieved from https://jb.asm.org/content/190/21/7219.short