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CAMBRIDGE — It all began with the case of the crumbling Mayan temples. Then there was the enigma of the Apollo-era spacesuit with disintegrating gloves. That was followed by the mystery of the brown spots on the walls of King Tutankhamun’s tomb. Which brings us to the puzzle of the 7,000-year-old Chilean mummies liquefying into black jelly.

For years, Harvard University microbiologist Ralph Mitchell has found himself asking, “Whodunit?” — or, perhaps more accurately — what’s eating it?

When things begin to fall apart — and especially when those things are precious, irrecoverable cultural and historical artifacts — people call Mitchell to figure out whether fungi or bacteria are involved and what to do.

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“You take swabs and you bring ’em back to the lab, and you’ll ask who are the microbes doing this, and biochemically what are they doing and how can you protect this?” Mitchell said.

“The key word in all of these studies is opportunism. These are indigenous microorganisms,” he added. “Give them the opportunity, give them moisture, give them nutrients: They’ll grow. And they’ll produce acid and they’ll be very destructive. ”

Mitchell, a youthful 80-year-old with a lilting Irish accent, spent most of his career on a more conventional scientific track, studying environmental microbiology — questions about how waterborne pathogens survive, or how to use microbes to effectively break down hazardous chemicals.

Until recently, he presided over a freshman seminar called “Germs” in which he delighted in opening his students’ eyes to the many ways that microorganisms shape our world, for good and bad.

But about 20 years ago, Mitchell found his own eyes opened. He was approached by a foundation in Italy and asked to give a seminar on cultural heritage and microbiology. A seed was planted. Mitchell began to think about how microbes might threaten treasured cultural touchstones.

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Early on, he was called in to better understand how microbes might be contributing to the decay of Mayan temples in Mexico. From there, he expanded into spacesuits, mummies, and old documents.

He built an early-alert tool for mold — a test that could be swiped on artifacts that will light up before microbes have begun to do damage. He compares it to the screening tests used for early detection in cancer.

Mitchell has found interesting puzzles to be solved all over the world and from recent and ancient history, largely because scientists who cross the boundary between cultural heritage conservation and biology are few and far between.

“It’s a well kept secret in the United States,” said Robert Koestler, director of the Smithsonian’s Museum Conservation Institute, who said he and Mitchell are some of the few who do this kind of work. “Europe, with its huge amount of culture, has been concerned with this for many years.”

The solutions that Koestler and Mitchell suggest are often simple, such as controlling temperature and humidity so that microbes can’t grow. But they are scientists, not conservators. Often, they can merely offer their assessment of the situation and leave it to others to decide whether to take action.

Mitchell, for example, has found himself fascinated by the oil droplets leaking out of the wreckage aboard the sunken USS Arizona in Pearl Harbor. When samples of the corroding metal on the battleship were cut out and shipped on ice to Harvard in 2004, his laboratory found that three major types of bacteria had formed dense communities called “concretions” that were feeding off oil and secreting chemicals that could fuel further corrosion of the monument.

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He recommended further study to prevent damaging ecological or historical consequences, but said that so far — as in so much of science — the funding for the work hasn’t been forthcoming.

The tools of the trade are fairly standard, even if the scientific questions sound exotic.

When 7,000-year-old Chilean mummies began to turn to ooze, tiny samples of the skin were sent to his lab. In a shallow dish in the third-floor laboratory on Oxford Street equipped with a hood and microscopes, research fellow Alice DeAraujo shows the solution to that latest open case. The researchers took the microbes found on the mummy skin and put them on to a test patch of pig skin. When the skin was subjected to high humidity, it turned to black jelly, just like the mummies.

Climate change was destroying the mummies, Mitchell surmised. In Arica, Chile, where 120 mummies are kept by the University of Tarapacá, the humidity had increased in recent years. The mummies now need to be protected from moisture if they are to remain intact.

With that case closing, the professor has found himself interested in a bigger issue: climate change’s impact on antiquities. As the climate warms, he believes that unanticipated questions will become suddenly relevant. Warmer temperatures, changes in humidity, and flooding may all threaten our most treasured keepsakes.

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“Now the question is, at least for me, is something we’ve never thought about. Climate change is occurring all over the world. How much is climate change putting our cultural heritage at risk?” Mitchell said. “It’s time to start looking.”