Microbes play a major role in the ecological health of the Chesapeake Bay environment, yet little is known about the biology, population dynamics, and interactions of these critical players. Some of these microbes----the microalgae--have special importance. Not only are they major producers that support the food chain, but they also represent some of the richest potential sources of environmentally-friendly, high-energy biofuels. In both basic biology and in advanced applications such as algal biofuels, Dr. Feng Chen and his colleagues are making a real difference. Dr. Chen, a Marine Microbial Ecologist, is Associate Professor at UMBI's Center of Marine Biotechnology (COMB).

Dr. Chen got started in algal research by studying the ecology of a major group of microbes----the cyanobacteria, also known as blue-green algae----in the Chesapeake Bay. Before Chen, no one had described the population composition of cyanobacteria in this environment.

(Dr. Feng Chen checking an algal culture in his laboratory)

In research published in Applied Environmental Microbiology in 2006, Chen applied the powerful tools of molecular biology to cataloging the Chesapeake cyanobacteria. More than 20 strains of cyanobacteria have been isolated and characterized in the Chen lab. He found that the cyanobacteria of the Chesapeake are different than those found in other environments.

They are unique because they can tolerate a wide range of salinity conditions, ranging from freshwater to salt water from the ocean, Chen said. In the Bay, salinity can range from almost zero up to 30 parts per thousand.

More recently, Chen has studied the population dynamics of these microbes. He found that in summer months, cyanobacteria contribute over 50% of phytoplankton productivity that supports the food chain of the Chesapeake. Phytoplankton capture the energy of sunlight and represent the primary source of food for animals higher in the food chain. They grow like weeds----in the summer, they have population densities of over one million cells per milliliter [1/1000 of a liter], said Dr. Chen. But in the winter, the populations drop from over a million cells to only a thousand per milliliter, he said. These population dynamics are bound to have an important effect on animals such as crabs that are higher in the food chain.

Recently, Dr. Chen's lab also isolated many eukaryotic microalgae (microalgae with nuclei) from Chesapeake Bay, with assistance of Jidong Zhang, a graduate student in Dr. Russell Hill's lab. Among the algal strains isolated, several strains of Nannochloropsis have shown a great promise for use in development of biofuels, as this type of microalgae is well known to be a fast grower and contain high amount of fatty acids. They are rich in lipids, notes Chen-- fatty oils that can be converted to high-energy fuels.

Over the years, Dr. Chen has, by scientific trial and error, found the special conditions required to grow a broad variety of Chesapeake microbes in the laboratory. Consequently, he has developed large collections of microalgae that are unique to this environment. Chen has engaged in numerous collaborations, both within UMBI and throughout the world, to study these valuable collections.

(Microalgae infected by viruses are yummy foods for bacteria. Note: The larger red cells are microalgae, and the smaller green cells are bacteria. Viruses are not visible)

In addition to studying Chesapeake cyanobacteria, Dr. Chen's laboratory also studies the viruses----known as bacteriophage, or phage for short-- that prey upon them. This work resulted in a cover story in Environmental Microbiology in 2008. Working with Kui Wang, a former PhD student in his lab, Chen found that phage that prey on cyanobacteria could have an important effect on the population density of these primary producers, since variation in the populations of the phage is correlated with variations in the population density of their hosts.

Chen's laboratory has found that like their hosts, the phage that prey upon Chesapeake cyanobacteria are unique. Unlike phage found in the open ocean, which can infect many different cyanobacterial strains, the Chesapeake phage are much more host-specific----that is, they can only infect particular strains of Chesapeake cyanobacteria. Since cyanobacteria represent a major producer in the food chain of the Chesapeake Bay, these studies provide important data for environmental programs designed to improve the health of the Chesapeake Bay environment as a whole.

In addition to cyanobacteria, Dr. Chen's laboratory also studies a variety of other Chesapeake microbes. Jinjun Kan, a PhD student who graduated in 2006, surveyed microbial communities in the Chesapeake every two months for five years, and found that the populations have reproducible patterns of annual variation. In work published in Limnology and Oceanography in 2006, they showed that depending on the time of year, it is possible to predict the occurrence of specific types of Chesapeake microbes at a given time. Jinjun Kan also has two publications in 2008, describing population differences in summer and winter: one in Applied and Environmental Microbiology, and the other in Aquatic Microbial Ecology.

More recently, the Chen lab has worked on the genetic interaction between phage and marine bacteria of the genus Roseobacter, via collaboration with Dr. Robert Belas at COMB, Dr. Mary Ann Moran at the University of Georgia, Dr. Alison Buchan at the University of Tennessee, and Dr. Andrew Lang at the Memorial University, Canada. Roseobacters are abundant in the marine environment, and could make up 20-30% of the bacterial communities in the Chesapeake.

Working with Dr. Chen, a visiting student, Yanlin Zhao from Xiamen University, isolated two unique phages that prey on two different marine Roseobacter species. In terms of their morphology and genomic sequence, these viruses are unlike any other previously described species of marine phage. This is one example of many collaborations of the Chen lab with Xiamen University in China (Dr. N.Z. Jiao) and other institutions throughout the world. Dr. Chen currently has another visiting PhD student from Xiamen University, Sijun Huang in the laboratory, as well as a visiting professor, Lijian Long, from the South China Sea Institute of Oceanography, Chinese Academy of Science. A undergraduate student from Goucher College, Kate Hammond, is currently doing her internship in Dr. Chen's lab.

(Kui Wang and Jinjun Kan collecting water samples from the Chesapeake Bay on board the R/V Cape Helopen)

Chen's lab is also studying Gene Transfer Agents (GTA), which are highly unusual virus-like particles associated with Roseobacter. Unlike phage, GTA do not contain their own genetic material. Instead, they package bits of the DNA from their Roseobacter hosts. A recent study from the Chen lab showed that roseobacterial GTA are important to the host horizontal gene transfer ----a non-sexual way that the microbes can rapidly exchange genetic material. His work on roseobacterial GTA has been published in 2008 in Applied and Environmental Microbiology, and ISME Journal.

Dr. Chen also helped several middle and high school students with science fair projects related to algal biofuels. A high school intern, Shawn Mathew, from Mount Hebron High School in Howard County, has been working on how environmental factors affect the growth and oil content of eukaryotic microalgae. They are looking at ways to increase the lipid content of the microalgae to make them richer sources of oils that can be converted into biofuels.

Going forward, Dr. Chen continues to step up the pace of activities in his lab. In 2008, for example, he published 8 scientific papers, with 5 other manuscripts still under review. Through numerous collaborations and mentoring relationships, he continues to make a real impact on our knowledge of the microbial communities of the Chesapeake, along with research into production of environmentally-friendly biofuels from microalgae.