Current Topics

RESEARCH ADVANCES

Metalloproteases HelpPathogens To Cross fromBlood into Brain

Shannon Weiman

Some microbial pathogens depend onmetalloproteases to cross the bloodbrain barrier (BBB), and this mecha-nism may someday be harnessed to de-liver drugs to the brain, according toseveral researchers who spoke at thesymposium “This is Your Brain on Mi-crobes,” during the 2014 ASM GeneralMeeting in Boston last May. Whilesome metalloproteases are encoded bythe pathogens themselves, others areinduced in host tissues, the researcherspoint out.

At least 11 different families of DNAand RNA viruses cause encephalitis,according to Katherine Spindler of theUniversity of Michigan in Ann Arbor.The way that mouse adenovirus-1(MAV-1) disrupts the BBB differs fromseveral bacterial mechanisms, whichinstead depend on inflammation,T-cell responses, or endothelial cell ap-optosis, she says. The adenovirus actson tight junction proteins that ordinar-ily hold endothelial cells together,thereby compromising their functionas a barrier and thus allowing viral par-ticles to pass from the bloodstream intobrain tissue.

Specifıcally, the virus up-regulateshost matrix metalloproteinases(MMPs) that, in turn, digest the tightjunction proteins during such infec-tions, according to Spindler. “We haveseen increased MMP activity in wholemouse brain homogenates in multipleMAV-1-infected susceptible mousestrains and not in resistant mousestrains,” she says. Although the virus

infects endothelial cells, cell culturedata suggest that astrocytes produceMMPs, she points out.

The fungus Cryptococcus neofor-mans secretes its own metalloprotease,designated Mpr1, which enables thispathogen to traverse the BBB, accord-ing to Mantana Jamklang, who workswith Angie Gelli at the University ofCalifornia, Davis. Mutants of this fun-gus that are defıcient in Mpr1 are lessvirulent for mice, and such mutantfungi are found less frequently in thebrains of animals that they infect.However, when injected directly intothe brains of mice, the mutants survivejust as well as do wild-type fungi. Mpr1appears to enable the fungi to attach tohost endothelial cells of the BBB beforethe fungus can cross into the brain, ac-cording to Jamklang.

“We anticipate that our fındings willlead the way to the development of anovel class of antifungal drugs that mayprove to be more effıcacious and lesstoxic than the current limited reper-toire of drugs available to patients,”Gelli says. “The BBB is a major obstaclepreventing therapeutic drugs from get-ting into the brain, thus one of our re-search goals is to create a platformtechnology that will improve the safetyand effıcacy of treatments for brain dis-orders.”

Another collaborator of hers, JohnUhrig, is linking Mpr1 to silicon nano-particles, which cannot cross the BBBon their own but may do so when chap-eroned by Mpr1. If so, such particlescan be loaded with therapeutic com-pounds for delivery into the brain.Crosslinking retains the enzymatic

Cryptococcus neoformans cells in lung tissue. These opportunistic pathogens are able to cross theblood-brain barrier using a metalloprotease that disrupts the tight junctions that are normallyimpassable barrier to cells and large molecules. (Image © Cecil H. Fox/Science Source.)

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activity of Mpr1, and Uhrig next plansto test whether it also maintains thecapacity to cross the BBB while linkedto nanoparticles.Shannon Weiman is a freelance writer in SanFrancisco, Calif.

RESEARCH ADVANCES

Soil Bacteria Use RacemasesTo Detoxify, Grow onD-Amino Acids

Barry E. DiGregorioContrary to common lore, bacteria canand do grow on D-amino acids as nu-trients, depending on racemase en-zymes to convert the D to the morewidely used L isomers that are thebuilding blocks of proteins, accordingto Gaosen Zhang and Henry J. Sun atthe Desert Research Institute in LasVegas, Nev. Racemases thus perhapsshould be viewed as agents that act on aglobal scale, helping to recycle other-wise toxic D-amino acids. Detailsappear in the March 2014 PLOS ONE(doi:10.1371/journal.pone.0092101).

Soils from widely varied environ-ments, including South and NorthAmerican semiarid deserts, alpine for-ests, wetlands, and landscape lawns,contain about 106 CFU of bacteria pergram, according to Zhang and Sun.When they bathed such soils with D-and L-amino acids, the soil bacteria re-sponded in one of two distinct ways.Wetland and lawn soils used both typesof amino acids simultaneously. How-ever, bacteria from the other types ofsoils fırst consumed L-amino acids be-fore consuming the D forms.

All the bacteria from different soiltypes that were being tested “are capa-ble of reverse racemization,” Sun says.Moreover, the racemases that the bac-teria use when metabolizing severaldifferent types of D-amino acids, in-cluding D-aspartic acid, D-glutamicacid, and D-leucine, are inducible, headds. With D-alanine, for example,provided to soil bacteria in excess, “al-anine racemases are temporarily freed

. . . to serve a detoxifıcation and cata-bolic function.”

This mechanism for detoxifying D-amino acids is “potentially important,”says Robert A. Lodder of the Universityof Kentucky in Lexington. Althoughnot all D-amino acids are toxic to hu-mans, some of them cause “tinglingand burning sensations” when con-sumed, symptoms that suggest but byno means prove nerve damage.

In broader terms, these fındings donot fıt neatly with what textbooks sayabout amino acid racemases and D-amino acids, according to Sun. “Be-cause we always grow bacteria in L-amino acids, you only see the L to Dconversion,” he says. “Our work sug-gests that this is only half the picture.”Outside laboratories, however, soilbacteria are likely exposed to D-aminoacids. Instead of this proving harmful,he adds, the exposed bacteria “gain”nutrients that other organisms fındtoxic.

“Even though life on Earth is basedon L-amino acids, there is no reason tobelieve that life based on D-amino ac-ids could not exist on another planet,”Sun says. Based on our assessment, na-tive bacteria should always emerge vic-torious, and any alien organisms elim-inated. This is very different fromcurrent thinking where people worryabout alien organisms attacking us todecimate life on Earth. To me that isunlikely to happen.”

“Since they do not compete, L- andD- life forms could exist together, and Iwonder why they don’t on Earth,” saysGilbert Levin of Arizona State Univer-sity, who was a member of the NASA1976 Viking Lander biology experi-ment team. “Their statement that L-and D- life would consume each otheris interesting, but I do not get theirconclusion that indigenous life formswould win if Martian microbes werebrought to Earth.”

Barry E. DiGregorio is a freelance writer inMiddleport, N.Y.

RESEARCH ADVANCES

In Cell-Culture Model,Vaginal MicrobiomeHelps To Fend off HIV

Carol PoteraWhen in balance, the microorganismsof the vaginal tract help to protectagainst HIV infections and also sup-port the activity of the antiviral drugtenofovir, according to Richard Pylesat the University of Texas MedicalBranch UTMB), Galveston, and hiscollaborators. Once the balance is dis-rupted, however, that drug loses its po-tency, they fınd while using a cell cul-ture system that models the humanvaginal tract. “It’s the fırst time, to ourknowledge, that someone has recreatedan intact vaginal microbiome in adish,” he says. Details appear March

MINITOPIC

Pulsed Electric FieldsEffective in Mice againstInfected Burn Wounds

Microsecond-pulsed, high-voltage,nonthermal electric fields are effec-tive in killing antibiotic-resistantstrains of the bacterial pathogenAcinetobacter baumannii, whichwere applied to burns and causedlocalized infections in mice, accord-ing to Alexander Golberg of theMassachusetts General HospitalCenter for Engineering in Medicinein Boston, Mass., and his collabora-tors. Treating the mice with two40-pulse treatments five minutesapart, one group receiving 250V/mm pulses and another receiving500 V/mm pulses, reduced bacteriallevels up to 10,000-fold, they report.Pulsed electric fields (PEFs) are usedin the food industry to preserve foodproducts and, more recently, PEFsare being used to treat solid tu-mors—acting by forming pores inmembranes. Details appeared June2014 in Technology (doi:10.1142/S2339547814500101)

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27, 2014 in PLOS One [doi:10.1371/journal.pone.0093419].

Genomic sequencing data from theVaginal Microbiome Project helped re-searchers to identify six general typesof bacterial communities, largely dom-inated by Lactobacillus species, includ-ing L. iners, L. gasseri, and L. crispatus,within the vaginal tracts of healthywomen. Representatives of these sixcommunities were chosen to colonizethe vaginal culture model that Pylesand his collaborators are developing,he says.

Within the vaginal tract, Lactobacil-lus species produce hydrogen peroxideand lactic acid, both of which help toinhibit viral pathogens such as HIV,Pyles continues. However, whenwomen develop bacterial vaginosis, aninfection typically caused by Gardner-ella vaginalis or other similar anaer-obes, they will temporarily dominateand substantially reduce the numbersof Lactobacilli. This bacterial shift in-creases susceptibility to HIV and othersexually transmitted infections, hepoints out.

Some of these same conditions nowcan be studied in the cell culture sys-tem, which contains a mix of Lactoba-cillus species as well as vaginal epithe-lial cells that were collected fromhealthy women during routine exami-nations, according to Pyles. For exam-ple, the activity of a single dose of theanti-HIV drug tenofovir is substan-tially reduced when bacterial commu-nities associated with bacterial vagino-sis are also present within this system,they fınd. In contrast, tenofovir po-tently prevents HIV-1 replicationwhen similar vaginal cultures are pop-ulated by lactobacillus-dominatedhealthy microbiomes. These fındingsback up clinical observations that bac-terial vaginosis raises the risk forHIV-1 transmission during inter-course.

“The incorporation of cells compe-tent for HIV replication into the modelis novel and adds signifıcantly to itsutility to better understand how the

vaginal microbiome influences suscep-tibility to HIV infection in women andHIV shedding in chronically infectedwomen,” says David H. Martin, chief ofinfectious diseases at Louisiana StateUniversity Health Sciences Center inNew Orleans. The model also might beused to evaluate how variations in thevaginal microbiome affect conditionssuch as preterm delivery, and whetherprobiotics prevent such outcomes, headds.

The human multilayer vaginal cellmodel provides a new means for study-ing how mixed bacterial communitiesmight change how prescription medi-cines such as contraceptives or locallyapplied treatments affect the vaginaltract, according to Pyles. “A woman’sparticular microbiome may limit theactivity,” he says. “In the future, micro-biomes could be enhanced by probiot-ics to enhance the effıcacy of drugs.”Carol Potera is a freelance writer in Great Falls,Mont.

RESEARCH ADVANCES

Solar Electricity Eyed ToDrive Biofilms To ProduceButanol as Fuel

David HolzmanEngineering microbes to capture car-bon dioxide to produce organic chem-icals, especially butanol for use as a fuelfor cars and trucks, would be betterthan raising and then fermenting cornor other crops for that same end use,according to Derek Lovley of the Uni-versity of Massachusetts, Amherst. Heand his collaborators described proj-ects aimed to produce such materials atseveral poster sessions during the 2014ASM General Meeting in Boston lastMay.

Their general approach, called elec-trosynthesis, depends on electrical en-ergy to drive microorganisms to formbiofılms and to produce butanol orother organic chemicals. One suchproject focuses on Clostridium ljung-dahlii, which grows to form a biofılm atthe cathode of a redox cell. Electrici-

MINITOPIC

Bacteria Found inSurprising Places; LiverFilters Gut MicrobiotaResearchers report finding bacteria inanatomical sites that were formerlyconsidered sterile, including placentasand the bladder; meanwhile, biofilmsin arterial plaque respond to stresssignals, and the liver mops up bacteriathat leak from the gut.

The human placenta provides aniche for a small but diverse mix ofbacteria, resembling the microbiotaof the mouth, according to KjerstiAagaard of Baylor College of Medi-cine and Texas Children’s Hospital,both in Houston, and collaborators.Details appeared 21 May 2014 inScience Translational Medicine (doi/10.1126/scitranslmed.3008599).

Particular bacteria in the bladder—although the specific types remain tobe determined—may be responsiblefor causing overactive bladder syn-drome, according to Evann Hilt ofLoyola University in Chicago, Ill., andher collaborators at Loyola’s StritchSchool of Medicine. She presentedthese findings during the 2014 ASMGeneral Meeting in Boston last May.

Bacterial biofilms within humancarotid arterial plaques appear to re-spond to stress signals mediated viathe hormone norepinephrine, releas-ing bacteria and perhaps accountingfor how stress triggers heart attacks,according to David Davies of Bing-hamton University in Binghamton,N.Y., and his collaborators. Details ap-peared 10 June 2014 in mBio (doi:10.1128/mBio.01206–14).

In mice, Kupffer cell macro-phages of the liver filter gut micro-biota that seep from there into theblood, according to Maria Balmer ofthe University of Bern in Bern, Swit-zerland, and her collaborators thereand at several institutions in Europe.Details appeared 21 May 2014 inScience Translational Medicine (doi:10.1126/scitranslmed.3008618).

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ty—preferably captured from thesun— drives electrolysis at the anode,and electrons flow from there to thecathode, where the bacteria within thebiofılm add these electrons to carbondioxide, reducing it to acetyl coenzymeA (acetyl CoA).

Acetyl CoA is the “hub of metabo-lism” within many kinds of living cells,a critical building block for organicmolecules that microorganisms mightmake, according to Lovley. He and hiscollaborators engineered C. ljungdahliito produce high levels of butyrate fromacetyl-CoA, and also deleted genes en-coding enzymes that otherwise convertacetyl-CoA to acetate or that convertbutyrate to other products. Productioneffıciency is roughly 70%, leavingenough energy to support cell growthand maintenance, he says. Next stepscall for engineering a butanol- insteadof a butyrate-producing strain and alsoone that is lactose inducible to controlthe timing of the production phase ofthe process.

Such microbial systems mightsomeday offer advantages over agricul-tural biomass as a feedstock for fuelssuch as ethanol or butanol as well asother organic commodity chemicals,according to Lovley. In terms of landuse, solar electricity is 100 times moreeffıcient than is plant-based photosyn-thesis, and thus would avoid removingfarmland from food production, hesays. For another, while about 70 gal-lons of water go into producing a gal-lon of fuel from biomass, not countingthe water used earlier for irrigatingcrops, biofılm-based electrosynthesisspares such profligate water use. Non-agricultural fuel and organics produc-tion also avoids pollution problemssuch as nitrogen contamination ofdrinking water and the creation of oce-anic “dead zones.”

Although the C. ljungdahlii systemis strictly laboratory stage, Lovley iscollaborating with a group at Lanza-Tech, a biotechnology company inChicago, Ill., to scale up this and closelyrelated processes. The company, whose

main business is to use fermentationprocesses to convert carbon dioxide orother gases being produced on an in-dustrial scale into fuels, anticipatesproducing commercial fuel from Lov-ley-style, biofılm-based electrosynthe-sis as being at least a decade away, ac-cording to Robert Conrado, who is asenior development engineer at Lanza-Tech.David Holzman is the Microbe Journal HighlightsEditor.

RESEARCH ADVANCES

Archaella Resemble Pili ButPropel Archaea like Flagella

Jeffrey L. FoxArchaea differ from bacteria in howthey swim, marking yet another “newpoint into how different bacteria andarchaea are,” says Sonja Albers of theMax Planck Institute for TerrestrialMicrobiology in Marburg, Germany.She spoke during the plenary session,“A World of Archaea: a Tribute to CarlWoese,” convened as part of the 2014ASM General Meeting in Boston lastMay.

At fırst glance, the archaeal speciesSulfolobus acidocaldarius, which pre-fers to grow at 76°C and at a pH be-tween 2 and 4, appears to swim aboutin liquid media much like motile bac-teria such as Escherichia coli. However,the proteins responsible for motility inS. acidocaldarius more closely resem-ble those that are part of type IV piliassembly systems rather than flagella inbacteria, according to Albers. Indeed,those differences are so pronouncedthat she and her collaborators now re-fer to the archaeal flagella as the “ar-chaella.”

The genes encoding archaella pro-teins are well conserved and widely dis-seminated among motile archaea, ac-cording to Albers. In addition to itsarchaella, S. acidocaldarius has “severalstructures along the cell surface,” in-cluding pili that are important for en-abling such cells to adhere to one an-other and to other surfaces, she points

out. Those pili also play a role duringthe exchange of DNA between cells of

MINITOPIC

Plant Pathogens: Originsof Potato Blight, aPossible Remedy to RiceBlast, and a Mechanismbehind Viral TakeoversRecent developments involvingplant pathogens include:

• The pathogen Phytophthora in-festans, a fungus-like oomycetethat is responsible for potatoblight, likely originated in Mex-ico instead of South America aswas previously believed, accord-ing to Niklaus J. Grúnwald of theHorticultural Crops Research LabAgricultural Research Service fa-cility in Corvallis, Ore., and hiscollaborators. Details appeared 2June 2014 in the Proceedings ofthe National Academy of Sciences(doi:10.1073/pnas.1401884111).

• The soil bacterium Pseudomonaschlororaphis EA105 not only in-hibits the rice blast fungus Mag-naporthe oryzae directly but alsoinduces a system-wide defenseresponse in rice plants, accord-ing to Harsh Bais of the Univer-sity of Delaware in Newark andhis collaborators. Details ap-peared 13 May 2014 in BMCPlant Biology (doi: 10.1186/1471–2229-14 –130).

• After infecting host plants, theplantago asiatica mosaic virustriple gene block protein1 inter-acts with two cytoplasmic hostproteins, leading them to aggre-gate and thereby disarming RNAsilencing, a key host-defensemechanism, according toShigetou Namba and YukariOkano of the University of Tokyoin Tokyo, Japan, and their collab-orators. Details appeared May2014 in Plant Cell (doi: 10.1105/tpc.113.120535).

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the same species, helping them to formaggregates.

Meanwhile, the archaella formmuch longer fılaments that extend out-ward from the cell surface. Like flagellaof motile bacteria, the archaella of S.acidocaldarius can be tethered to solid

surfaces, preventing the cells fromswimming freely but showing that theycontinue to rotate when tied down inthis fashion. Although such experi-ments entail doing light microscopy at75°C, she refers to them as “reinventingthe wheel,” alluding to lower-tempera-

ture tethering experimentswith motile bacteria fromfour decades ago by How-ard Berg, now at HarvardUniversity, and his collabo-rators.

The rotary motor for thearchaella of S. acidocal-darius is “very simple” andconsists of seven differentproteins, several of them inmultiple copies, which is incontrast to the motor driv-ing bacterial flagella, con-sisting of about 50 differentproteins, Albers notes. Ofthe seven archaella pro-teins, Fla H appears to be aclock protein that is regu-lated by being phosphory-lated and then dephospho-

rylated. However, it appears not tohave a circadian function but to inter-act with the Fla X protein to determinethe overall length of the fılament aseach archaellum is being assembledand before it can begin to rotate, shesays. Meanwhile, Fla F appears to serveas the anchor protein in the envelope ofthe cell and to act as the stator part ofthe motor. “We are still mostly specu-lating about the mechanism,” she says.

Jeffrey L. Fox is the Microbe Current Topics andFeatures Editor.

NEW IN ASM JOURNALS

By Targeting Host ImmuneResponse Instead of Virus,Investigators IdentifyPotential Anti-H7N9Therapeutics

The seriousness ofdisease often resultsfrom the strength ofimmune response,rather than with thevirus itself. Turningdown that response,rather than attack-ing the virus, might

be a better way to reduce that severity,says Juliet Morrison of the Universityof Washington (UW), Seattle. She andher collaborators have now taken thefırst step in doing just that for theH7N9 influenza. “We found that vi-ruses that cause severe illness, likeH7N9, and the infamous 1918 virus,trigger gene expression signatures thatare different from those seen in milderinfections,” says coauthor and UW lab-oratory head Michael Katze. The inves-tigators searched databases containinggene expression profıles of culturedhuman cells that had been treated withdifferent drugs in order to fınd thosecells with gene expression profıles thatwere the reverse of those induced bythe H7N9 flu virus. Drugs that gener-ated such could potentially dampen theharmful host response, Morrison says.

MINITOPIC

Recent Findings Linking Gut Microbiota Diversity toDisease and Diet

Keeping current with research involving the microbiota of the gut proves a majorchallenge. Additional recent developments include:

• Malnutrition during childhood upsets the gut microbiota, leaving it so“immature” that food-based interventions prove only partly corrective, accord-ing to Jeffrey Gordon of Washington University Medical School in St. Louis, Mo.,and his collaborators. Details appeared 5 June 2014 in Nature (doi.org/10.1038/nature13421).

• The diversity of bacteria within the gastrointestinal tracts of mice that becomeinfected with Mycobacterium tuberculosis decreases quickly after infection,according to Kathryn Winglee and William Bishai at the Johns Hopkins Centerfor Tuberculosis Research in Baltimore, Md., and their collaborators. Detailsappeared 12 May 2014 in PLOS One (doi:10.1371/journal.pone.0097048).

• For two species of freshwater fish, stickleback and perch, the greater thediversity of fish in their respective diets, the lower is the diversity ofmicroorganisms in their gastrointestinal tracts, according to Daniel Bolnick ofthe University of Texas, Austin, and his collaborators. Details appeared 22 May2014 in Ecology Letters (doi:10.1111/ele.12301).

Electron micrograph of Sulfolobus acidocaldarius MW001showing archaella (black arrows) and pili (white arrows).

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Six of them are FDA approved andmight be repurposed as H7N9 influ-enza therapeutics. The data suggeststhat such severe influenzas are associ-ated with increased transcription of in-flammatory cytokine genes and reducedtranscription of lipid metabolism and co-agulation genes, according to the paper.

(J. Morrison, L. Josset, N. Tchitchek, J. Chang,Jessica A. Belser, D. E. Swayne, M. J. Pantin-Jackwood, T. M. Tumpey and M. G. Katze. 2014.H7N9 and other pathogenic avian influenzaviruses elicit a three-pronged transcriptomicsignature that is reminiscent of 1918 influenza andassociated with lethal outcome in mice. J. Virol.Online ahead of print 2 July 2014; doi:10.1128/JVI.00570-14.)

NEW IN ASM JOURNALS

Novel IntravaginalRing Shows Promisefor HIV Prevention

A novel intravagi-nal ring for preven-tion of HIV trans-mission, implantedwith antiretroviraldrug tablets, dem-onstrated sustained,controlled drug re-

lease and safety over 28 days. The ring,tested in pig-tailed macaque monkeys,is engineered to be inexpensive for usein developing countries, says corre-sponding author Marc Baum of theOak Crest Institute of Science, Pasa-dena, Calif. One of the two drug com-binations tested in the ring is the onlyproduct approved by the U.S. Food andDrug Administration (FDA) for HIVprophylaxis. The ring’s topical drugdelivery has critical advantages overoral therapy: “Issues such as adherenceto a regular dosing schedule are signif-icantly reduced,” says Baum. Addition-ally, concentrations in vaginal tissues,the key compartment for preventingsexual HIV transmission, lack thetroughs encountered with oral medica-tions. Further, “systemic levels are so

low as to usually be undetectable intopical delivery,” says Baum. “Thatmeans that side effects are dramaticallyreduced, or eliminated entirely.” Im-mune defenses and associated inflam-mation were not triggered. Baum notesthat the pig-tailed macaque model is anideal surrogate for humans. “Themodel has similarities with the humanmenstrual cycle, vaginal architecture,and vaginal microbiome, and the abil-ity to conduct effıcacy studies with sim-ian-human immunodefıciency virus,”he says.

(J. A. Moss, P. Srinivasan, T. J. Smith, I.Butkyavichene, G. Lopez, A. A. Brooks, A. Martin,C. T. Dinh, J. M. Smith, and M. M. Baum. 2014.Pod-intravaginal rings delivering antiretroviralcombinations for HIV prophylaxis:pharmacokinetics and preliminary safety in amacaque model. Antimicrob. Agents Chemother.Online ahead of print 16 June 2014; doi:10.1128/AAC.02871-14.)

NEW IN ASM JOURNALS

The Microbes Makethe Sake Brewery

“Understanding thebig picture of themicrobial interfacebetween food facili-ties and food prod-ucts will be impor-tant for controllingthe safety and qual-

ity of many foods and beverages,” saysDavid A. Mills of the University of Cal-ifornia, Davis. Now Mills et al. havetaken the fırst step towards that under-standing for rice wine, or sake. Theyshow that the microbial populationsinhabiting the environmental surfacesof the brewery change dramatically ateach step of the fermentation, althoughat the brewery they studied, only onemicrobe, Aspergillus oryzae, is inocu-lated— during the fırst stage. The re-sults echo those of studies Mills hasdone on an artisanal cheese maker, andsome wine facilities. “In terms of its

microbiome,” says Mills, “the facilitylooks like the product.” This is the fırstsuch study of a sake brewery.

(N. A. Bokulich, M. Ohta, M. Lee, and D. A. Mills.2014. Indigenous bacteria and fungi drivetraditional kimoto sake fermentations. Appl.Environ. Microbiol. Online ahead of print 27 June2014; doi:10.1128/AEM.00663-14.)

NEW IN ASM JOURNALS

Bacterial Colonies EvolveAmazing Diversity

Bacterial coloniesgenerate immensediversity amongtheir inhabitants,often even absentspecifıc selectionpressures, accord-ing to Ivan Matic ofINSERM, Paris,France, and his col-

laborators. Now, for the fırst time,Matic et al. have tracked this phenom-enon at the level of single cells. Startingeach colony with a small number ofidentical cells, Matic et al. observedthem as they grew and the colony aged.“Ultimately, most cells in the colonystop dividing and dead cells accumu-late,” says Matic. “We observed mas-sive phenotypic diversifıcation in agingE. coli colonies. Some variants showedimproved capacity to produce biofılms,whereas others were able to use differ-ent nutrients, or to tolerate antibiotics,or oxidative stress, compared to the an-cestral strain.” Among the most nota-ble changes: some cells evolve antibi-otic resistance, despite the absence ofboth resistance genes and antibiotics inthe initial colony. Says Matic: “This isfrightening.”

(C. Saint-Ruf, M. Garfa-Traore, V. Collin, C. Cordier,C. Franceschi, and I. Matic. 2014. Massivediversification in aging colonies of Escherichiacoli. Online ahead of print 30 June 2014, doi:10.1128/JB.01421-13.)

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NEW IN ASM JOURNALS

Study Reveals Fungus inYogurt Outbreak Poses aThreat to Consumers

The fungus respon-sible for an out-break of contami-nated Greek yogurt

last year is not harmless after all, but astrain with the ability to cause disease.In September 2013, customers of Cho-bani brand Greek yogurt complainedof gastrointestinal (GI) problems afterconsuming products manufactured inthe company’s Idaho plant. The com-pany issued a recall, and it was believedat the time that the fungal contaminant

Murcor circinelloides was only a poten-tial danger to immunocompromisedindividuals. However, complaints con-tinued from otherwise healthy custom-ers, prompting researchers to questionwhether the fungus could harm healthyhumans. In the study, the researchersisolated a strain of the fungus from ayogurt container that was subject to re-call, and identifıed it as Mucor circinel-loides f. circinelloides (Mcc). Unlikeother strains of the fungus, that partic-ular subspecies is commonly associ-ated with human infections. Whole-genome sequence analysis of theyogurt isolate revealed the possibilitythat this fungus could produce harmfulmetabolites that were previously un-known in this species. The researchers

then tested the strain on mice, wherethe fungus showed an ability to causelethal infections when the fungalspores were injected into the blood-stream as well as to survive passagethrough the GI tract when the sporeswere ingested orally.

“Fungal pathogens are not consideredas foodborne pathogens,” says study co-author Soo Chan Lee, of Duke Univer-sity. But the study shows otherwise.

(S. C. Lee, R. B. Billmyre, A. Li, S. Carson, S. M. Sykes,E. Y. Huh, P. Mieczkowski, D. C. Ko, C. A. Cuomo,and J. Heitman. 2014. Analysis of a food-bornefungal pathogen outbreak: virulence and genomeof a Mucor circinelloides isolate from yogurt. 8July 2014 mBio vol. 5 no. 4; doi: 10.1128/mBio.01390-14)

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