Microbe Spotlight: Week 3

NDSU Microbiology
by NDSU Microbiology

The students in Infectious Disease Pathogenesis Lab will be blogging about the strange and wonderful this semester. This week's guest bloggers are: Diana Fontaine, Sara Bowman, Rhiannon Dockter, and Kendra Dowdle. Check back next week for a new selection of microbe spotlights.


In 2009, a bacterium called GFAJ-1 was discovered in Mono Lake, California by a team led by Felisa Wolfe-Simon, a NASA astrobiologist and
geomicrobiologist. Wolfe-Simon and her team collected sediment samples from the lake, isolated and cultured the organism, then discovered that when phosphorous starved, GFAJ-1 can substitute arsenic for a small percentage of the missing phosphorous.

This initial finding was published in Science in 2010 because of its evolutionary implications: if this microbe truly built the backbone of its DNA from something other than phosphorus, then it didn’t follow the rules of any other organism on this planet. This interpretation was met with sharp criticism, and it was later determined that the arsenic didn’t replace the phosphorous; instead, the microbe was considered arsenate-resistant, phosphate-dependent. This was discovered in 2012 at the University of British Colombia using liquid-chromatography-mass spectrometry.

GFAJ stands for “Give Felisa A Job.” Functionally, this microbe is an extremophile, Gram negative, rod-shaped, and is part of the family Halomonadaceae. Also, GFAJ-1 has a genome size of 3.5 million base pairs. Some interesting information about Mono Lake is that it is landlocked and hypersaline, which means it contains high amounts of NaCl – it surpasses ocean water in saline levels with 90 grams/liter salt. Also, this lake has one of the highest natural arsenic concentrations in the world at 200µM. Mono Lake has a pH of 9.8, which means it is highly alkaline.

By Diana Fontaine

Image Author: Jodi Switzer Blum

Image Permission: PD-USGOV-NASA

Caulobacter crescentus

Caulobacter crescentus is a Gram-negative bacillus that lives in aerobic, aquatic environments. It contains a single circular chromosome that contains approximately 3600 genes. Study of the genome of this organism has led to better understanding of the genomes of other, pathogenic microbes such as E. coli and Rickettsia prowazekii.

This microorganism is unique because it undergoes a process of cell division that is not symmetrical. It normally grows attached to organic debris via an organelle known as a holdfast. This form of the microbe is called a stalk cell. When the cell divides, the original stalk cell divides, but the daughter cell is a flagellated form called a swarmer cell. The swarmer cell swims for 30-45 minutes and then differentiates to a stalk cell and attaches to its own piece of organic debris.The regulation of gene expression to control these two cellular types is driven by several regulatory proteins: DnaA, GcrA, CtrA and CcrM.

There has been one known case of human infection with C. crescentus. The bacterium was isolated from the dialysis fluid of a 64-year-old male. The patient died (from other causes) before the source of the infection could be found. This microbe is generally not a human health concern because the human body does not provide the correct environment for the organism to thrive inside. Possible future research on this bacterium includes new underwater adhesives for use in boats and underwater structures, or for use in closing surgical wounds.

By Sara Bowman

Image Author: Joi Ito

Image Permission: CC Attribution-2.0 Generic License


Flavobacterium sp. K172 is a Gram-negative, aerobic rod about 2-5 micrometers long and 0.3-0.5 micrometers wide that can live in soil or water. The Flavobacterium genus claims a few pathogenic members, including F. psychrophilum, which causes rainbow trout fry syndrome and bacterial cold water disease in fish, and F. meningosepticum, which causes bacterial meningitis in infants. F. sp. K172 is not known to be pathogenic to humans or animals.

F. sp. K172 was discovered in 1975 by a team of Japanese scientists who were investigating a pond near a nylon factory. The microbe was found to survive on nylon 6 byproducts from a nearby plant as its only source of carbon and nitrogen. For this reason, it was given the nickname “nylon-eating bacteria.” This discovery was startling because no other bacterium is known to do this.

It was discovered that several enzymes, collectively known as “nylonase” were responsible for digesting the byproducts, such as the linear dimer of 6-aminohexanoate. The genes that produce the enzymes to break down nylon 6 byproducts are found on three plasmids: pOAD1, pOAD2, and pOAD3. A
plasmid transfer from F. sp. K172 to Escherichia coli yielded a recipient cell which produced nylonase enzymes and digested nylon 6 byproducts. Research found that Pseudomonas aeruginosa, when placed in an environment with only nylon 6 byproducts as a food source, was able to digest the byproducts, but not by the same enzymes as Flavobacterium sp. K172. Susumu Ohno, a geneticist, has suggested that the new gene was caused by a gene duplication and a frame shift mutation.

Flavobacterium sp. K172 has fueled the creationism/evolution debate. If an entirely new gene can come about due to a new food source, then all genes must be the product of evolution based on environmental selection. This raises a difficult question, which I am often troubled by: does evidence of evolution necessitate disbelief in creationism? Or is it possible for both concepts to coexist?

By Rhiannon Dockter

Image Author: Michael Strock

Image Permission: GNU Free Documentation License

Francisella tularensis

Francisella tularensis is a Gram-negative bacterium discovered in Tulare County, California, in 1911 by George Walter McCoy. It causes a disease called tularemia, which affects both humans and other animals. Tularemia is relatively rare, but it is a zoonotic disease of the northern hemisphere. F. tularensis is transmitted to humans who handle infected animals, ingest contaminated food or water, or inhale infected aerosols. Humans can also be infected through tick and deer fly bites.

Tularemia can range from mild (chills, headaches, fever) to life-threatening (fever and pneumonia). F. tularensis is highly infectious – as few as 10 bacterial cells can cause full-blown disease in humans; therefore, this bacterium is considered a potential biological weapon. Dispensing an aerosol of F. tularensis in a city could result in numerous cases of disease within just a few days.

A live vaccine is available to help with prevention, but is primarily used in high-risk groups. In addition, an F. tularensis infection can be treated with antibiotics, including streptomycin and ciprofloxacin, and patients usually recover completely within several weeks.

By Kendra Dowdle

Image Author: Jerry Kirkhart

Image Permission: CC Attribution-2.0 Generic License