Michael Pelczar leaves the kitchen table and heads for his home office in the next room. His desk is piled high with papers and, like Colwell's office, the walls are covered with photographs and diplomas. Pictures of each of his six children, grandchildren, and great-grandchildren hold places of honor. He returns to the table carrying a copy of the textbook Microbiology. Pelczar first authored and published the book in 1958. He's updated it over the years as the field has changed, publishing the most recent edition in 1986. The book has become a classic in undergraduate courses. Now colleagues in India want to carry the torch. Pelczar's book sold over 29,000 copies there in 2006 and publishers have recently contacted him for advice on updating it again. "Let me take this opportunity to convey my heartfelt appreciation for the wonder that your text on microbiology is," begins the note from publisher McGraw-Hill, Inc.

One of the major breakthroughs in the field of marine microbiology that Pelczar had not been able to capture in the first edition of his book was the discovery of the so-called microbial loop in marine food webs, a paradigm-shifting change that began to gather momentum in the mid-1970s. Selected by NSF as one of the landmark discoveries in ocean sciences in the past half century, the emerging concept of the role of microbes in the open water (pelagic) food web upset the commonly held belief that phytoplankton, zooplankton, and fish were the major players.

Questions about whether the marine food web is actually microbe-centric began in the early 1970s with work by Tom Malone, now at the University of Maryland Center for Environmental Science, who introduced the notion that very small plankton (picoplankton) and micrograzers might be playing an important role in the food web (see "Thinking Deeply about the Shallows"). A prescient paper published in 1974 by ecologist Lawrence Pomeroy at the University of Georgia receives credit for propelling the microbial loop into the limelight. In his paper, "The ocean's food web: A changing paradigm," Pomeroy posed a series of questions about the marine food web. He asked whether single-celled grazers (protozoa) played an important role as consumers of other microorganisms in the food web and as recyclers of dead matter. He questioned whether microbes, more than any other group of organisms, might carry out the bulk of the cellular respiration in the food web, using oxygen to make energy to live.

But the answers to Pomeroy's questions would not be possible until two technological breakthroughs took place. The first came in 1977, with the invention of a fluorescent staining technique that permitted rapid counting and discrimination of bacteria, protozoa, and phytoplankton. The second, flow cytometry, a technique which uses laser light to count, examine, and sort microscopic particles suspended in a stream of fluid, came in the mid-1980s. Flow cytometry enabled the discovery of a novel microbe (a picoplankter, so-called for its size range of 0.2 to 2 microns) that would prove to be the most abundant photosynthesizer (autotroph) in the world.

The discovery of the microbial loop revealed the key role that bacteria, picoplankton, micrograzers, and viruses play in directing nutrients through marine systems. This paradigm shift was selected by the National Science Foundation as one of the major breakthroughs in 50 years of ocean sciences. Diagram by Matt First.

Understanding the complex role that microbes play in marine food webs like the Chesapeake's was a major advance in basic science. This discovery would help map the flow of energy through the Chesapeake Bay's food web and show how microbes could shunt energy away from larger organisms like fish, crabs, and birds to feed their own metabolism. By inserting the concept of the microbial loop into the Bay's food web, scientists would learn how to connect the dots between excess nutrients like nitrogen, algal blooms, and low oxygen conditions (hypoxia) — filling out a picture for how microbial demands for oxygen would pull it away from fish and the tiny animals that they eat (zooplankton).

The current hypothesis: Excess nitrogen fuels more algal growth than can be eaten by zooplankton, fish, oysters, and others. When the algae dies and sinks to the bottom, it becomes food for microbes — populations of single-celled protozoans and bacteria that comprise the microbial loop. The microbial population grows in response. Since small organisms have faster metabolisms than large organisms — a pound of bacteria consumes more oxygen than a pound of fish — microbes can suck oxygen away from larger organisms.

Today, the identity of most of the microbes in the microbial loop remains a mystery. In fact, some 90 percent of the microbial world is still believed to be unknown to science. And approaches that can go the next step to connect specific microbes to their function in the food web are still in their infancy (see "Biocomplexity and the Bay"). But not for long. The Sorcerer II's journey of microbial exploration, led by the J. Craig Venter Institute, recently started publishing the findings of a trans-oceanic voyage of discovery meant to recreate the expedition of Charles Darwin's HMS Beagle. Researchers sampled the ocean in 41 locations, isolating and subsequently freezing bacterium-sized cells. They also recorded the temperature, salinity, pH, oxygen concentration, and depth. So far their efforts have turned up over 400 novel species of microbes able to make millions of proteins that were previously unknown to science.

As in the 1970s, microbiology once again may be poised on the cusp of revolution. In March 2007, a new report from the National Research Council stated that the emerging field of environmental genomics (metagenomics), where the DNA of entire communities of microbes can be studied simultaneously, presents the greatest opportunity — "perhaps since the invention of the microscope" — to revolutionize understanding of the microbial world.

As 1977 was dubbed the dawn of biotechnology, will 2007 begin an era of microbial rule?

Outspoken in his beliefs, Michael Pelczar has spent a lifetime devoted to the discipline of microbiology and to his home waters of the Chesapeake Bay. Author of the widely used textbook Microbiology, he has watched microbes like the parasite MSX destroy oysters. But he also knows that other microbes can fix nitrogen, degrade organic matter, and help maintain the health of the Bay. Photograph by Erica Goldman.

50 Years of Ocean Discovery: National Science Foundation 1950-2000

Bay Journal article on the microbial loop

National Research Council report on metagenomics

Sorcerer II Expedition

Marine Biotechnology in Maryland (video interviews)

Back at the kitchen table, Pelczar opens Microbiology and prepares to autograph it. He adjusts his thick glasses and flips past the Table of Contents, pointing to the beginning of the book's Preface. It opens with his favorite quote by Louis Pasteur, one of the founding fathers of microbiology. "Messieurs, c'est les microbes qui auront le dernier mot." Or "The microbes will have the last word."

Most still don't look at the problems of the Chesapeake and think about microbes orders of magnitude smaller than the eye can see. But what if Pasteur proves right? What if microbes do have the last word to say about the Chesapeake Bay? Will we be ready to hear what they are saying?

This page was last modified September 15, 2018