mBiosphere

Men are more likely than women to commit misconduct? Not so fast, say Commentary authors

A Commentary in mBio today takes issue with a recent study of research misconduct among life scientists. Molly Carnes and her coauthors say the data may not be as straightforward as they appear at first blush, and that we shouldn't be too quick to condemn men for activities that hew close to gender stereotypes.

In their analysis published in January, Fang et al. say data from the Office of Research Integrity indicates male researchers funded by the Department of Health and Human Services commit research misconduct more often than their female peers, a gender disparity that is most pronounced among senior scientists.

In their Commentary, Kaatz et al. point out that a few key facts are missing that, if taken into account, could confound these results. For one thing, they say, men may have more opportunities to commit misconduct. Although men outnumber women among researchers in the life sciences, men are even more overrepresented in the pool of "potential perpetrators": men are more likely to hold more than one large R01 award, lead large center grants, and compete successfully in the renewal process. What's more, men's research awards are about $100,000 more than women's. So, women make up about 30% of faculty in the life sciences, but since they have less money to work with, and, presumably, fewer projects, they have fewer opportunities to commit misconduct and get caught by the ORI.

Kaatz et al. also point out that male representation among grad students and postdocs may not be as reliable as we think, and even a few percentage points difference can skew the data, making it appear that women commit misconduct more often than men.

We need to be careful not to jump to conclusions when faced with ambiguities like these, say Kaatz et al., since our deductions about men and women will probably adhere to long-held and pernicious stereotypes about how men and women behave. A quick acceptance of the idea that men are more easily corrupted could prevent a hard look at the data - data that indicate that although women have an increasing share of faculty spots, their piece of the funding pie isn't keeping pace.

Chitinase: A multi-use tool for environmental pathogens

Humans don't make chitin. So why do many bacterial pathogens require chitinases to maintain an infection? A study in mBio this week reveals that in Listeria monocytogenes, at least, chitinase helps the environmental pathogen live a double life, digesting chitin while the bacterium lives in the soil and attacking the innate immune system when it makes its way into the human host. This is the first study to demonstrate chitinase activity against a specific host immune response, say the authors.

The fact that chitinase is involved in the pathogenicity of certain environmental pathogens has been known for a while. Chitin binding proteins are now linked to pathogenicity of Serratia marcescens, Legionella pneumophila, and L. monocytogenes, and in L. monocytogenes, two chitinase-encoding genes and one chitin binding protein are known to contribute to virulence of L. monocytogenes in vivo. Freitag and her co-authors followed up on the ability of one chitinase, ChiA, to enhance virulence in Listeria.

"We found that while the Listeria chitinase mutant has no discernible defects in establishing infections in mice, it was cleared much more rapidly by the host immune response," says the study's lead author, Nancy Freitag of the University of Illinois at Chicago. Freitag says they pitted ΔchiA, a Listeria mutant that lacks a functioning ChiA chitinase, against mice. Although the mutant could establish an infection and replicate, by 72 to 96 hours postinfection, about the time when an immune response should kick in, the numbers of bacteria fell off. Without chitinase, the mice won out against Listeria.

But how does chitinase attack the innate immune system? Freitag says they don't have a firm answer, but their experiments suggest inducible nitric oxide synthase is involved. To find out whether the enzyme alters the host immune response by changing the expression of certain proinflammatory cytokines, they looked at the expression of tumor necrosis factor alpha, interleukin 1β, and of the inducible nitric oxide synthase (iNOS) in the mice livers 48 hours after infection. The levels of iNOS was four-fold higher in mice infected with the ΔchiA strain than in mice infected with the wild type strain, indicating that a functioning chitinase knocks down iNOS.

" We don't yet know the direct target of Listeria ChiA, but we speculate that the enzyme might target a carbohydrate-modified host factor linked to transcriptional induction of NOS2, thereby inhibiting iNOS expression," says Freitag.

The dual-use aspect of chitinase would make for a nice fitness advantage for environmental pathogens. In the environment, it enables the bacterium to exploit chitin as an energy source. In the host, the enzyme helps the pathogen sidle past the innate immune system and on to a progressively worse infection. And having one tool for both cuts down on the genetic luggage the bacterium has to carry around.

Geobacter's nanowires carry electricity along aromatic amino acids

Geobacter's pili conduct electrons along their length using the rings on aromatic amino acids, according to a study in mBio this week. Contrary to all other known forms of biological electron transport, in which electrons are carried by discrete entities and passed from one to another, Geobacter's pili have a core of aromatic amino acids that turn these hair-like appendages into functioning electron-carrying biological wires, adding credence to a controversial idea in biology.

"It's the aromatic amino acids that make it a wire," says lead author Derek Lovley. Lovley and his colleagues developed a strain of Geobacter, Aro-5, that lacked aromatic amino acids in parts of the pili implicated in electron conduction, replacing them with smaller, non-aromatic amino acids. Without the aromatic amino acids, Lovley says, the pili are nothing more than protein strings. Importantly, Aro-5's pili were complete with OmcS, a multi-heme c-type cytochrome essential for iron oxide reduction that was long suspected of carrying the electrons along the length of the pili. But the presence of working OmcS wasn't enough.

"We showed it's not good enough to just make the string - you've got to make a wire," says Lovley.

Geobacter pili have metallic-like conductivity

G. sulfurreducens respires by removing electrons from organic materials and funneling them to iron oxides or to other microorganisms, much the way humans pull electrons out of organic molecules in food and dump them on oxygen. The bacteria use their pili to reach out to iron oxides or other microbes, transferring the "waste" electrons along the structure to the destination. Geobacter's pili are only 3-5 nanometers wide, but they can be 20 micrometers long, many times longer than the cell itself.

Trafficking in electrons is how all living things breathe, but it is normally carried out by discrete proteins or other molecules that act like containers for shuttling electrons from one place to another. Lovley says earlier results showed the pili in G. sulfurreducens possess metallic-like conductivity, the ability to carry electrons along a continuous structure, a controversial finding.

To investigate how pili accomplish this singular feat, Lovley says they looked to non-biological organic materials that can conduct electricity. "In those synthetic materials, it's aromatic compounds that are responsible for the conductivity. We hypothesized that maybe it's similar in the Geobacter pili. In this case, it would be aromatic amino acids." Aromatic compounds have a highly stable ring-shaped structure made of carbon atoms.

Turning to the pili, Lovley says his group compared the Geobacter pilus protein, PilA with those of other pili-makers, including Pseudomonas, Neisseria and Vibrio species, that aren't capable of long-range electron transport. By comparison, Geobacter lacks a highly conserved N-terminal domain these other sequences retain. Lovley's group guessed that the aromatic amino acids in this area where Geobacter is atypical could be carrying electrons via overlapping pi-pi orbitals.

Using genetic techniques, they developed a strain of Geobacter, Aro-5, that makes pili that lack aromatic amino acids in this key region, then they tested whether these pili could still conduct electricity. They could not. Removing the aromatic amino acids was a bit like taking the copper out of a plastic-covered electrical wire: no copper means no current, and all you're left with is a string.

Removing aromatic amino acids from the pili prevents the bacteria from reducing iron, too, says Lovley, an important point because it adds further proof that Geobacter uses its pili as nanowires for carrying electrons to support respiration.

Where to go from here?

Metal reducers like Geobacter show a lot of promise for use in fuel cells, says Lovley, and by feeding electrons to methanogens, they're an important component of anaerobic digesters that produce methane gas from waste products. Understanding how they shuttle their electrons around and how to optimize the way the pili function could lead to better technologies.

Moving forward, Lovley says his own lab plans to explore the possibilities of biological nanowires, exploring how to make them more or less conductive. "The fact that we were able to make the physical filament, but it's no longer a wire gives us a lot of power for looking at those phenotypes," says Lovley.