The Research: Harnessing the Ways Algae Harness Metals from the Sea
Vanadium: Critical for Natural Product Production, and Possibly Cleaning Your Laundry One of the Butler group's key interests is enzymes called vanadium bromoperoxidases (V-BrPOs). The group has found these enzymes in every seaweed it has ever examined, which is perhaps not too surprising given that vanadium is one of the most abundant metals in seawater. One reason for interest in the V-BrPOs is that they are critical in the production of important natural products, specifically halogenated compounds, which are those that contain elements common in the marine environment such as chlorine, bromine and iodine. Because of the critical role played by V-BrPOs, a better understanding of these enzymes could be a key step in harnessing certain biosynthetic pathways to sustainably produce pharmaceutically important products. Among other advancements, the team has discovered how V-BrPOs catalyze key steps in the biosynthesis of terpenes critical to production of halogenated marine natural products. When Butler first began studying the vanadium bromoperoxidases, she looked to the work of Bill Fenical and John Faulkner, both of the Scripps Institution of Oceanography, and focused on seaweeds these researchers had identified as producing important halogenated natural products. Later her search for the enzymes and work to better understand them led to work on samples from as far away as Antarctica that were either provided by colleagues or collected by her team. Collected seaweed samples are tested for the presence of V-BrPOs by placing small portions in standard 96-well plates with diphenol red. This is a chemical that acts as a colorimetric test for the enzymes, which react with the diphenol red to form bromophenol blue, an easily recognized color change. Originally the group would work with ground up samples but later learned that snippets of the whole piece of algae would activate the assay, illustrating that the V-BrPO reactions take place on the surface of the seaweeds. Besides their importance in natural product biosynthesis, the V-BrPOs may also prove useful in a very different applicationÑcleaning laundry. Clorox funded the Butler team to assess whether the enzymes might be useful for clothing spot removal. The company sent to the lab standard stained bed sheets, which the researchers soaked in V-BrPOs. "It did remarkably well on ink stains, which are a really tough thing," says Butler, "but they dropped [the project] and I don't know why. I actually think we'll probably try to develop it ourselves a little bit." Because There's No Spinach In the Sea Another major focus of the Butler group is how bacteria acquire the iron essential to their survival and, with a variety of applications in mind, ways to block that iron uptake. Nearly every bacterium known to science requires iron to grow. For marine bacteria especially, this poses a challenge because the oceans have very low iron levels. To get around the problem, many bacteria produce compounds called siderophores, which solubilize and bind with iron to form a complex that bacteria can then take up. Butler's work is focused on understanding this fundamental biological process, in large part because interrupting the process can offer a strategy for controlling bacterial growth or infectious processes. The group is, for instance, looking at biosynthesis of the siderophores, which are small peptide compounds, to figure out a way to disrupt the actual production. Possible uses of such technology would be to control bacterial growth in aquaculture or to slow fish spoilage. Another goal is to identify siderophores that might themselves be used as drugs to treat iron overload conditions such as hemochromatosis [ext. link: http://www.hemochromatosis-info.com]. Left unchecked, such conditions can lead to clogged vital organs and ultimately, to cancer, heart disease, cirrhosis of the liver, and a range of other potential problems. One siderophore is already used in a drug for treating iron overload, but it requires a long, painful delivery via intravenous injection. So, a key goal would be to find a siderophore that works as a treatment but that can be administered orally. An additional promising and intriguing potential application for siderophores is as a novel delivery system for antibiotics, though the team's research on this topic has so far focused mainly on siderophores from non-marine bacteria. Some antibiotic resistance stems from certain bacteria's ability to pump antibiotics out of their cells. If an antibiotic were bound to a siderophore, it would either be successfully delivered into the cells, thus killing them, or, if the bacteria ejected the siderophores, they would still die because that is their means of obtaining essential iron. The Butler team's fieldwork to collect siderophore producers, like the V-BrPO work, depends on a colorimetric test. The researchers take ocean water samples and plate them on Petri dishses that conatin a blue iron dye. When iron is removed by siderophore activity, the dye turns orange, so that a bacterial colony that's growing and pulling iron out of the medium will have halos of orange or yellow around them. The researhcers also use a similar test for bacteria grown in flasks of liquid medium. Siderophores are removed for study using a variety of different materials that bind with them to pull them out of samples. Everyone Should Take a Cruise Butler and her group have worked with samples from their own Pacific backyard to as far away as Antarctica. The team has done sampling work locally, in the Bahamas, and the Black Sea, but colleagues working in other areas have provided many of the bacterial samples Butler studies. The group is especially interested in samples from areas with interesting chemical profiles. For instance, the Black Sea has very low levels of iron relative to other open ocean areas making it an ideal location to search for novel siderophores. Butler recalls her first research cruise, with Bill Fenical aboard the University of Miami's R/V Columbus Iselin in the late '80s, as her most exciting fieldwork experience. Each morning the team would go collect samples and then come back to the shipboard lab to screen the samples for enzymes of interest. In the afternoon they'd go get more. She says that because the bunks were so close to the lab you could get up in the middle of the night to check the progress of an experiment, making for intense, but exciting work. "To chemists who are used to working in a lab this was a big eye-opening experience and I recommend it to everybody," says Butler, "it's a wonderful way to do science." Looking Forward "I think that metallobiochemistry in the marine environment is a huge field with a lot of untapped potential," says Butler. She credits the current promise to oceanographers over the past couple of decades that have made huge advances in the study of metal concentrations in seawater. Prior to these advances, all measurements of iron and other metals in seawater had been unknowingly contaminated by metals from glassware used in sampling and experimentation and other sources. This made accurate understanding of the importance of metals in marine systems impossible. Today, says Butler, there are many more researchers interested in metallobiochemistry in the marine environment and she is confident that new enzymes related to metal uptake and processing will reveal new kinds of reactions with significant biotechnological benefits. Attracted by Discovery As an undergraduate at Reed College, in Portland, Oregon, Butler majored in chemistry. She completed graduate work at the University of Calif., San Diego, in inorganic chemistry, but says she always had an interest in biological processes. So, for postdoctoral research at UCLA and, later, Cal Tech, she switched to bioinorganic chemistry. When she took her current position at U.C. Santa Barbara, she was attracted to vanadium research because the first vanadium enzyme had just been discovered. She had no experience at that time in marine chemistry or marine biology, so she contacted researchers she knew at Scripps Institution of Oceanography and began speaking to them, then went on research cruises with them to screen for enzymes. "That really was the big start of our work in marine biotechnology," she says, and her work and interests have continued from there. |
