Coral reefs are noisy places, with sounds emanating from water movement, ocean creatures, and other sources. A previous study by Lauren Freeman identified a component of the underwater soundscape that correlated with the abundance of macroalgae (those that form leaf-like structures and filaments) present over the reef, but the mechanism responsible for the sound was unknown. To determine whether the algae themselves were responsible, the authors studied sound emissions from a tank of the Hawaiian invasive algae Salicornia gracilaria. They found that release of gas bubbles — a combination of oxygen released from photosynthesis and nitrogen — produced a “ringing” from the oscillations of the bubbles as they assumed a spherical shape in the water. The sound ranged from 2 to 20 kiloHertz, matching that from oceanic coral reefs.

Bubble production and sound emission is not unique to this algal species, the authors note, and so the measurement of this type of sound in marine environments may be a proxy for algal and aquatic plant photosynthetic activity in general. If so, this may allow a rapid and inexpensive alternative to visual methods for estimating algal abundance, which are time-consuming and expensive.

Simon Freeman notes: “We discovered that algae make sound by first listening to coral reefs, and finding a link between what we heard and how much algae had smothered the coral. Intrigued, we performed experiments with algae in tanks to verify the source, and how the sounds made by algae contributed to coral reef soundscapes.”

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To process vast amounts of data, the brain uses a kind of digital code. Its cells produce discrete bursts of electric current, known as action potentials, that function as the zeros and ones of the nervous system. This code is assumed to be a vital aspect of computation in animals — that is, in most animals. The tiny roundworm C. elegans has long been considered a curious exception; until now, action potentials had never been observed in the organism.

But in a recent study, Rockefeller scientist Cori Bargmann and her colleagues, Qiang Liu, Phil Kidd, and May Dobosiewicz, discovered, among other things, a C. elegans olfactory neuron that produces action potentials. The finding, published in Cell, overturns decades of dogma and could help scientists understand fundamental principles of brain computation.

Trial by fire

Neurons communicate with one another by exchanging chemical messages. Each message alters the state of the receiving cell; and as a neuron collects more and more chemical input, it approaches a threshold of activation. An action potential occurs when the cell reaches this threshold, at which point the neuron is said to “fire” or “spike” as an electrical impulse ripples through its extremity. In producing this spike, the cell translates analog chemical messages into digital electric code.

Despite the apparent importance of action potentials, for years researchers believed that C. elegans and other nematodes simply didn’t use this information processing strategy.

“There’s this whole class of animals where the neurons didn’t seem to spike,” says Bargmann, the Torsten N. Wiesel Professor. “So our question was: Well, what do these neurons do?” Seeking an answer, her team set out to measure the electrical behavior of C. elegans neurons — every single one of them, if necessary.

“The C. elegans has just 302 neurons, so it’s one of the few animals where you can look at each individual neuron,” says Liu, a research assistant professor in Bargmann’s lab who set out to measure how all of these neurons respond to stimulation.

Almost immediately, Liu was met with a surprise. While stimulating AWA, a neuron that processes smell signals, he observed that the cell’s electrical voltage rose very rapidly before dramatically plummeting. Though unexpected, this dynamic was also very familiar: it looked like an action potential.

A neuron with potential

Additional experiments confirmed that AWA neurons indeed spike. The researchers suspect that other C. elegans cells also produce action potentials; yet they note that this is not the norm for this animal’s neurons. In fact, their experiments revealed that even AWA fires rather infrequently. Typically, the neuron responds to odors in a more subtle, graded manner. Liu observed action potentials only during experiments in which the stimulus grew stronger over time, suggesting that in nature, AWA fires when the animal is approaching the source of an important smell.

“Here we have a neuron that encodes information in two ways: one way that is slower and graded, and one way that’s very nonlinear and sharply tuned to particular circumstances,” says Bargmann. “And this lets us see what a spike might be uniquely important for.”

While this study initiates C. elegans into the ranks of spike-producing animals, the action potentials observed in this organism were not identical to those seen elsewhere. To define the characteristics of worm-specific spikes, postdoctoral associate Phil Kidd created a mathematical model of AWA’s electrical dynamics — a step that, the scientists hope, will allow their research to enter into conversation with other advances in computational neuroscience.

“There’s a huge field of people working on the coding and computational principles of nervous systems,” says Kidd. “And our work with C. elegans is likely to uncover principles that were unfamiliar to scientists who have been working in these areas for a long time.”

This line of research indeed has the potential to both expand scientific understanding of C. elegans, and of nervous systems at large.

“Computation in the brain is a deep and important problem,” says Bargmann. “With this study, we’ve shown that C. elegans can help solve this puzzle — and in fact, we’ve already exposed a whole new piece of it.”

The new process, assuming it can be scaled up to industrial production, is important because recent studies conducted by universities in the Netherlands and UCLA School of Medicine, among others, show essential health benefits associated with large doses of vitamin K — especially the Menaquinone-7 form, known as MK-7. These benefits include reducing risks of cardiovascular disease and strokes, osteoporosis, and even battling cancer.

Foods that are rich in vitamin K — such as kale, red meat and egg yolk — do not provide enough of the vitamin to achieve high-dose therapies, which will require supplements.

However, MK-7 production on an industrial level is expensive and limited because the bacterial fermentation needed to create the vitamin so far has relied on “static” fermentation strategies that are inadequate to ramp up output of the vitamin.

The present production system — incorporating shallow trays of solid, soy-based medium growing microorganisms only on the surface — will not support the expected increased demand for vitamin K, explained researcher Ehsan Mahdinia, a postdoctoral scholar in food science at Penn State.

“Using biofilm reactors, however, appears to be a practical alternative,” said Mahdinia. “Biofilm reactors provide a controlled environment for the microorganisms to form mature and robust biofilms that enable them to produce value-added products such as vitamin K with increased efficiency.”

Integral to the ability of biofilm reactors to produce vitamin K are specially designed internal plastic composite supports that microorganisms adhere to and on which they build intertwined colonies — called biofilms — that can withstand aeration and agitation needed to spur the microorganisms to secrete more vitamin K.

“The supports [comprise] half plastic and half soybean hulls, with other nutrients mixed in, that are extruded together at high temperatures,” said Mahdinia. “The composite material is porous enough to allow microbes to colonize and hold onto it. At the same time, it is hard enough that the supports do not fall apart when they are in the liquid.”

The study looked at producing MK-7 with an improved fermentation process, comparing the performance of strains of the microorganisms that create vitamin K. Researchers evaluated Bacillus species such as Bacillus subtilis natto, Bacillus licheniformis and Bacillus amyloliquifaciens.

Bacillus subtilis natto was determined to be the most efficient microorganism to be used in future Penn State studies in biofilm reactors, according to Mahdinia.

It is a type of bacteria that produces fermented soy food such as Japanese traditional sticky natto, he pointed out.

“Natto is a goo resulting from the microbes partially digesting soybeans, and like all fermented foods, it is very nutritious,” he said. “It’s basically rotten soybeans. I have been told it doesn’t taste good, but I must admit that I have never had the courage to taste it.”

Finally, researchers experimented with the liquid medium, suspending and feeding the microorganisms in 12-day fermentation runs. The medium started as a soy broth supplemented with 0.8 percent yeast extract. In the study, they tested the addition of glucose and glycerol to the base media in the biofilm reactors.

The carbon source addition seemed crucial in batch fermentations, Mahdinia noted.

“Our results indicated that ‘fed-batch’ strategies can be significantly effective in glucose-based medium, rendering the biofilm reactors a promising replacement for static fermentation strategies. Under the same operational and medium conditions, suspended-cell bioreactors (with no biofilm present) could not reach MK-7 concentrations higher than 8.7 milligrams per liter, while in biofilm reactors concentrations were higher than 28.7 milligrams per liter — a 2.3-fold enhancement.”

Ali Demirci, Penn State professor of agricultural and biological engineering, whose research group in the College of Agricultural Sciences conducted the study, has high hopes for this new technology. He is planning to scale up the 2-liter laboratory biofilm reactors and introduce pilot scale fermenters of perhaps 200 liters.

“We believe those pilot scale biofilm reactors can produce a significant amount of vitamin K to compete with what is done in industry right now,” he said. “Then we hope we can turn this into a patent and go to the industry and say, ‘you can easily scale up these liquid fermenters to thousands of liters, similar to what is in use now for bioethanol production.’ Each fermenter can reach up to 850,000 gallons of volume and produce much larger amounts of vitamin K.”

The research, recently published in Applied Microbiology and Biotechnology, was Mahdinia’s doctoral thesis. He recently graduated with a doctoral degree in agricultural and biological engineering.

Also collaborating in the research was Aydin Berenjian, University of Waikato, New Zealand.

The U.S. Department of Agriculture’s National Institute of Food and Agriculture supported this work.

The troposphere is the portion of the atmosphere from the ground to about 10 kilometers in the air. Nearly all of the atmosphere’s water vapor and aerosol exist in the troposphere, and this is also where weather occurs. The Pico Observatory rises above the first layer of clouds in the troposphere, known as the atmospheric marine boundary layer. At that boundary the temperature drops rapidly, and relatively high humidity decreases as cooling air forces water to condense into cloud droplets.

Pico is often ringed in clouds, with its summit climbing above them. This feature allows scientists to study the aerosols above the boundary layer, including a set of three samples a research team at Michigan Technological University recently observed that challenges the way atmospheric scientists think about aerosol aging.

In “Molecular and physical characteristics of aerosol at a remote free troposphere site: Implications for atmospheric aging” published Tuesday, October 2 in the journal Atmospheric Chemistry and Physics, Michigan Tech chemists demonstrate that some aerosol particles — those that originate from wildfire combustion — are existing for longer periods in the atmosphere undergoing less oxidization than previously thought.

“Previously, brown carbon was expected to become mostly depleted within approximately 24 hours, but our results suggested the presence of significant brown carbon roughly a week downwind of its initial wildfire source in northern Quebec,” says Simeon Schum, a chemistry doctoral candidate at Michigan Tech and the paper’s first author.

“If these aerosols have a longer lifetime than expected, then they may contribute more to light absorption and warming than expected, which could have implications for climate predictions.”

This work builds on a previous paper published in the same journal, “Molecular characterization of free tropospheric aerosol collected at the Pico Mountain Observatory: a case study with a long-range transported biomass burning plume.”

Honey or marbles? Aerosol consistency explained

In order to determine where the molecules in aerosols originate, the team, led by the article’s corresponding author and associate professor of chemistry, Lynn Mazzoleni, used a Fourier Transform-Ion Cyclotron Resonance mass spectrometer, located at Woods Hole Oceanographic Institution, to analyze the chemical species of molecules from within the samples.

Aerosols, depending on their chemical and molecular composition, can have both direct and indirect effects on the climate. This is because some aerosols only scatter light, while others also absorb light, and others uptake water vapor, changing cloud properties. Aerosols play a cooling role in the atmosphere, but there are great uncertainties about the extent of forcing and climate effects.

Understanding how specific aerosols oxidize — break down — in the atmosphere is one piece in the puzzle of understanding how Earth’s climate changes. Aerosols take on a variety of consistencies, called viscosities, depending on their composition and their surroundings. Some have a consistency similar to olive oil or honey, and these tend to oxidize more rapidly than more solidified aerosol particles, which can become like pitch, or even marble-like.

The three samples analyzed by the Michigan Tech team are named PMO-1, PMO-2 and PMO-3. PMO-1 and PMO-3 traveled to Pico in the free troposphere, while PMO-2 traveled to Pico in the boundary layer. Aerosols are less likely to occur in the free troposphere than in the boundary layer, but pyro-convection from wildfires can lift the particles higher up in the air. Though PMO-2 had been in the atmosphere for only two to three days, it had oxidized more than PMO-1 and PMO-3, which had been in the atmosphere roughly seven days and were estimated to be glassy in consistency.

“We were puzzled by the substantial difference between PMO-2 compared to PMO-1 and PMO-3. So, we asked ourselves why we would see aerosols at the station which were not very oxidized after they had been in the atmosphere for a week,” says Mazzoleni. “Typically, if you put something into the atmosphere, which is an oxidizing environment, for seven to 10 days, it should be very oxidized, but we weren’t seeing that.”

Cold and dry aerosols

Schum said the research team hypothesized that the first and third samples had oxidized more slowly because of the free tropospheric transport path of the aerosol after being injected to that level by wildfires in Quebec. Such a path toward Pico meant lower average temperature and humidity causing the particles to become more solid, and therefore less susceptible to oxidative destruction processes in the atmosphere.

That a particle would oxidize at a slower rate despite more time in the atmosphere because of its physical state provides new insight toward better understanding how particles affect the climate.

“Wildfires are such a huge source of aerosol in the atmosphere with a combination of cooling and warming properties, that understanding the delicate balance can have profound consequences on how accurately we can predict future changes,” says Claudio Mazzoleni, professor of physics, and one of the authors of the paper.

As wildfires increase in size and frequency in the world’s arid regions, more aerosol particles could be injected into the free troposphere where they are slower to oxidize, contributing another important consideration to the study of atmospheric science and climate change.