Temperature influences gene expression, life cycle in vibrio cholerae

May 20, 2016

Washington, DC - May 20, 2016 - Vibrio cholerae infects roughly four million people annually, worldwide, causing severe diarrheal disease, and killing an estimated 140,000 people. Its success as a pathogen belies the challenges this bacterium faces. The waters this bacterium inhabits when it's not infecting H. sapiens can be 40 degrees Fahrenheit cooler than our normal body temperature. Now a team of investigators from the University of California, Santa Cruz provides new insights into how different temperatures in the bacterium's environment control expression of genes required for life at those temperatures. The research is published ahead of print May 20, 2016 in Applied and Environmental Microbiology, a journal of the American Society for Microbiology.

In the study, the investigators grew V. cholera at human body temperatures, and then shifted them to the temperatures of the waters they normally inhabit when they are not infecting people, said corresponding author Fitnat Yildiz, PhD, professor of Microbiology and Environmental Toxicology, the University of California, Santa Cruz.

Loni Townsley, Yildiz' student who performed the experiments, used microarrays to determine which genes were expressed at the various temperatures. Low environmental temperatures of around 15oC (59oF), turn on genes that regulate biofilm formation, genes that code for a molecular weapon that secretes toxins, and genes that enable adaptation to cold.

Biofilms are tough microscopic mats of bacteria. These enable V. cholerae to abide hardily at the low environmental temperatures temperatures, growing on a species of zooplankton, Daphnia magna, which is a tiny crustacean. "V. Cholerae in biofilms are protected, sheltered," said Yildiz. (Growing on millions of zooplankton makes the V. cholerae independently mobile, raising the chances of encountering a human host to infect.)

As for the molecular weapon, a device called a "type VI secretion system," it was discovered only recently, said Yildiz. Although knowledge about the secretion system is increasing rapidly, much remains to be learned. "We do know that it is used to kill both bacterial and eukaryotic cells," said Yildiz. And V. cholerae is known to be able to take up DNA from these dead cells, in order to acquire new genes.

Beyond that, it's not certain what purposes killing other bacteria may serve. One speculation is that killing members of other bacterial species that inhabit the surface of Daphnia opens up more space for V. cholerae to grow, said Yildiz. Another speculation is that V. cholerae may procure nutrients -- carbon and nitrogen -- from the dead bacteria.

In any case, the investigators found that expression of a protein component of the type VI secretion system was highest at 25oC (77oF).

The investigators also found that expression of a major regulator of virulence is notably reduced at low temperature. That means that expression of virulence factors is curtailed at low temperatures, which makes sense since they are only needed during infection of a human host -- which happens at body temperature, said Yildiz.

Linking the genes that promote biofilm formation, cold adaptation, and production of the toxin-producing system to the Vibrio-zooplankton association, as was done in this study, was a breakthrough in understanding the environmental lifecycle of V. cholerae, said Yildiz.

"Our research focuses on environmental pathogenesis, with the goal of increasing our understanding of molecular detection, survival mechanisms, and dissemination dynamics of human pathogens into the environment," said Yildiz. "Our long-term goal is to develop strategies for disease prevention and treatment by identifying targets to reduce environmental survival and infectivity."
The American Society for Microbiology is the largest single life science society, composed of over 47,000 scientists and health professionals. ASM's mission is to promote and advance the microbial sciences.

ASM advances the microbial sciences through conferences, publications, certifications and educational opportunities. It enhances laboratory capacity around the globe through training and resources. It provides a network for scientists in academia, industry and clinical settings. Additionally, ASM promotes a deeper understanding of the microbial sciences to diverse audiences.

American Society for Microbiology

Related Bacterium Articles from Brightsurf:

Root bacterium to fight Alzheimer's
A bacterium found among the soil close to roots of ginseng plants could provide a new approach for the treatment of Alzheimer's.

Tuberculosis bacterium uses sluice to import vitamins
A transport protein that is used by the human pathogen Mycobacterium tuberculosis to import vitamin B12 turns out to be very different from other transport proteins.

Bacterium makes complex loops
A scientific team from the Biosciences and Biotechnology Institute of Aix-Marseille in Saint-Paul lez Durance, in collaboration with researchers from the Max Planck Institute of Colloids and Interfaces in Potsdam and the University of Göttingen, determined the trajectory and swimming speed of the magnetotactic bacterium Magnetococcus marinus, known to move rapidly.

Researchers show how opportunistic bacterium defeats competitors
The researchers discovered that Stenotrophomonas maltophilia uses a secretion system that produces a cocktail of toxins and injects them into other microorganisms with which it competes for space and food.

Genetic typing of a bacterium with biotechnological potential
Researchers at Kanazawa University describe in Scientific Reports the genetic typing of the bacterium Pseudomonas putida.

How the strep bacterium hides from the immune system
A bacterial pathogen that causes strep throat and other illnesses cloaks itself in fragments of red blood cells to evade detection by the host immune system, according to a study publishing December 3 in the journal Cell Reports.

The cholera bacterium can steal up to 150 genes in one go
EPFL scientists have discovered that predatory bacteria like the cholera pathogen can steal up to 150 genes in one go from their neighbors.

Exploiting green tides thanks to a marine bacterium
Ulvan is the principal component of Ulva or 'sea lettuce' which causes algal blooms (green tides).

The cholera bacterium's 3-in-1 toolkit for life in the ocean
The cholera bacterium uses a grappling hook-like appendage to take up DNA, bind to nutritious surfaces and recognize 'family' members, EPFL scientists have found.

Excellent catering: How a bacterium feeds an entire flatworm
In the sandy bottom of warm coastal waters lives Paracatenula -- a small worm that has neither mouth, nor gut.

Read More: Bacterium News and Bacterium Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.