A Dermatophytic Divergence

Your skin is a vast and complex habitat. There are all kinds of bacteria and fungi competing for every inch of real estate. But like all homesteads, resources are limited. Bacteria lower surface area pH rendering it inhospitable for others, and secrete chemical compounds to kill invaders. Fungi have found ways to more efficiently mine the "land" for minerals such as iron, as well as producing antibiotics that are specifically active against skin bacteria.

One of the families of fungi capable of infecting skin (Dermatophytes) is Arthrodermataceae, A family that includes the genera Microsporum and Trichophyton. These two fungi groups colonize keratinized areas and together are the most common cause of superficial fungal skin infections.

Microsporum

Trichophyton

 A study in the July 30, 2012 edition of PLoS One takes a look at some of the closely related genes, gene clusters, that allow the species from Microsporum and Trichophyton to take such good advantage of the terrain that is your skin.

Two Different Secondary Metabolism Gene Clusters Occupied the Same Ancestral Locus in Fungal Dermatophytes of the Arthrodermataceae


In essence gene clusters are several genes that are physically linked or clustered together that share a common effect, such as production of antibiotics, or metabolically important compounds. Gene clusters can allow for quicker adaptation to new sources of sustenance as well as large scale genome remodeling. Due to the closely knit nature of gene clusters they also open the possibility of acquiring new functions by gain and loss of entire gene pathways through horizontal transfer.

Arthrodermataceae have a lot of gene clusters that many think are involved in host specificity and pathogenicity, especially when compared to other dermatophytes. Focusing on variable loci nestled inside a stable portion of the genome of Microsporum canis, Microsporum gypseum, and Trichophyton spp.; the researchers discovered three distinct conformation forms.

This variable locus(VL) has a difference of both length and functions across the three species. M. canis VL (VLA) consists of 539 base pairs that lack any protein sequencing sequences, M. gypseum (VLB) only has 35.89 bp but codes 12 different proteins, and Trichophyton spp.'s VL (VLC) is 26.78 bp long coding for 10 proteins.


When looking at the evolutionary past of the gene region it becomes apparent that the studied clusters have a very different history than the areas surrounding them. Those flanking regions have a largely vertical inheritance while the VL genes have been shaped by several different processes, including gene duplications and gene transfers.

The VL's of M. gypseum and Trichophyton spp. contain genes to produce compounds that appear to target glycine, which is the largest amino acid in human skin. This means the VL may be involved in skin colonization and thus infection. The effects of this area along with the evidence of gene duplications and losses led the team conclude that the common ancestor of these dermatophytes shared either a polymorphic version of VLB and VLC or both of them separately.

If the first scenario is correct, the common ancestor originally contained a version of the VL that alternated between the VLB and VLC form. During the evolution following that point the entire area was deleted from M. canis and the alleles were separated into the stable forms in M. gypseum and Trichophyton spp.

If the secondary version is true than at different times the main lineages came into their current genomic distributions by separate deletions in and of the VL.

It would take additional genome sequencing of closely related species in Arthrodermataceae, to determine the more likely of these two scenarios.

In the end, the mere existence of variable loci, like those in this study, could help explain how closely related species could show a dramatic difference in ability to establish an epidermal foothold.


Awesome Researchers:
Han Zhang, Antonis Rokas, & Jason C. Slot (2012). Two Different Secondary Metabolism Gene Clusters Occupied the Same Ancestral Locus in Fungal Dermatophytes of the Arthrodermataceae PLoS One DOI: 10.1371/journal.pone.0041903

Photo creds: 
Robert J. Galindo & the CDC via Wikimedia

Inkfish: Enjoy Wine? Thank a Wasp

A much cooler contributer to Research Blogging has totally beat me to this Study. And She has done a much better job bloggin about it than I could have.

Inkfish: Enjoy Wine? Thank a Wasp: Where would we be without yeast? Sober, for one thing. And stuck assembling our sandwiches between two crackers. Humans have relied on th...

Foreign Spore Germination : Teen Skepchick

First, Teen Skepchick is cool. Second, Cordyceps are cool. Third, combining them gets a link on this blog.

Teen Skepchick Science Sunday : Zombie (Ant) Apocalypse

This is a good post about one of the most popular fungal interactions. Cordyceps enslaving the minds of carpenter ants. Plus it includes an Attenborough video, so score.

Beetles Bring Yeast to Bamboo for Babies

Humans are not alone when it comes to farming. We are not even alone when it comes to growing fungi. There is a long history of fungal agriculture in social insects. Ant and termites often even go so far as to have what could basically be considered proper gardens of fungal blooms; getting them into the right growth medium, tending to their needs, even defending them from invaders. It is all quite industrial, but that is the kind of thing we come to expect from ants.

Now a Japanese study is demonstrating that at least one less industrialized, even non-social, beetle has tapped into the joys of harvesting fungi.

Fungal Farming in a Non-Social Beetle

This study focuses on a species of lizard beetle, Doubledaya bucculenta, that lives in Japan and lays eggs in dead bamboo. Collecting specimens of D. bucculenta at Kawaminami, Miyazaki Prefecture, Japan The team found that there was a white coating in internode cavities that were used to contain larvae, as well as on the larvae themselves.

D. bucculenta, its host bamboo, and W. anomalus

Analyzation of this growth consistently showed the saccharomycete yeast Wickerhamommyces anomalus present in the shoots used by D. bucculenta. Looking at bamboo not used for the incubation of young this same fungus was absent. When you find a fungus repeatedly, and only, growing in the presence of developing larvae, you might want to wonder if something is up.

By gathering and dissecting both adult males and females of D. bucculenta an interesting structure was catalogued. The females all displayed a yellowish exoskeletal pocket on the eight abdominal segment, right next to the ovipositor, and guess what they found there. Correct! They found small yeast particles that when isolated and sequenced turned up with the identical DNA of W. anomalus that had already been collected.

So, is this yeast a parasite, perhaps feeding off the larvae of the beetle or the insides of the bamboo? Or, could it be that the beetle was engaging in some low level farming, putting a crop into its young's room for later. W. anomalus is known to be saprophytic so it could potentially be using the beetle as a transport to get on the inside of freshly dead bamboo, but that would hardly be cause for the storage pocket on the female beetle. If however, the beetle were harvesting the fungus and seeding the bamboo chamber with it when she deposited her egg, how would that affect the larva?

To test this, the researchers grew some beetle larvae under a variety of scenarios. When inoculated with W. anomalus the larvae grew normally into adulthood, however when grown on sterile media or in autoclaved bamboo they stopped growing at the second instar. Furthermore after this if W. anomalus was added the larvae returned to its normal growth and development.

So, it appears that D. bucculenta does indeed harvest and transplant W. anomalus into the incubation chamber of its young. This interesting mutualistic relationship has led the beetle to becoming obligately dependent on the very fungus it developed a structure to harvest.

In the end finding this fungal farming tactic in a non-social insect could help shed light on how some of the higher levels of mutualistic cultivation developed. And in the end, the researchers think this could shed light even on how agriculture developed as a whole.

Awesome researchers:
Wataru Toki, Masahiko Tanashi, Katsumi Togashi, & Takema Fukatsu (2012). Fungal Farming in a Non-Social Beetle PLoS One DOI: 10.1371/journal.pone.0041893

Fungal Word Friday

Germ Tube

A germ tube is the initial hypha produced from a spore.

Germ tubes on C. albicans

Photo cred:
Wikimedia contributor Y tambre

Cryptococcus neoformans Stops Pumping Iron

Cryptococcus neoformans is a well know fungal pathogen that can cause severe infections of the pulmonary and nervous systems. Infections of people with well functioning immune systems are rare but in those with compromised systems such as those with HIV, this opportunistic yeast is responsible for encephalitis and fungal meningitis.

Cryptococcus neoformans

Of course it needs its daily recommended allowance of vitamins and minerals. A Study conducted by scientists from Konkuk University and Chung-Ang University in Republic of Korea seeks to specifically check out the effect iron regulation has on C. neoformans day to day life.

Influence of Iron Regulation on the Metabolome of Cryptoccocus neoformans.

You see, iron is important for a whole host of processes. It is used in the tricarboxylic acid cycle, amino acid creation, respiration, as well as making lipids and sterols. The thing is, too much iron is bad, if level get to high it leads to the creation of oxygen radicals. Oxegyn radicals are bad mamma jammas; they cause things like DNA breakage and protein denaturing. Yup, iron is important, but you need to keep it in check or all kinds of things are going wrong.

It has been established that Cir1 is an important regulatory protein for iron transport and homeostasis. The same study showed Cir1 to be important to melanin formation and synthesis of spore capsules, things very important to the virulence of C. neoformans. With all of the metabolic pathways influenced by deletion of this protein and its importance on the regulation of iron, the team of researchers chose see the metabolic effects the deletion of Cir1 would have in order to get a large picture on its function in C. neoformans.

To study this they utilized Gas chromatography mass spectrometry and chemometric multivariate statistics to analyze the metabolomic profiles of a wild type and a Cir1 mutant strain lacking the regulatory protein. They attempted to find the pathway(s) most affect by a lack of Cir1 and how it affects the metabolome of C. neoformans. The strains were grown on a range of media, with varying amounts of available iron.

Because of the similarity and complexity between the Cir1 mutant and the wild type, the researchers used principle component analysis on the 972 peaks shown in the data sets, comparing the variation in 18 discriminative metabolites that showed significant difference.

When compared between the high and low iron mediums the chosen metabolites of the Cir1 strain showed little changes despite a significantly increased level of iron present in the Cir1 mutant cells. That led the team to conclude that iron availability was only responsible for minor differences in C. neoformans.

However, when looking at the regulation of genes in the wild type things were a little different. 483 genes were down-regulated and 250 were up-regulated in low iron vs high iron growth medium. Most of those differently expressed genes had to do with iron transport and homeostasis, as well as DNA repair and metabolism.

The study also showed dramatic influence of Cir1 on metabolism and production of those molecules involved.

One of the most interesting differences in the mutant was a large increase in glucose production. An increase in glucose implies that deleting the Cir1 had affects on the major carbon assimilation processes because glucose is metabolized in glycolysis and important in the TCA cycle and respiration. The TCA cycle and respiration are also influenced by iron so there is potentially connection there.

Combining those observations allows for the suggestion that an increase in intracellular iron and glucose are evidence of lowered iron requiring processes like glycolysis and respiration.

Another increase was shown in ergostol and its derivatives. Ergostol is the major constituent in fungal cell walls and is the target of some antifungal drugs. This increase of production is evidence of why Cir1 mutants have been demonstrated to be more resistant to anti-fungal treatment. A change in the production of ergostol and its derivative molecule  means a remodeling of membrane biosynthesis.

The basis of many secondary messengers, inositol was also increased significantly in the Cir1 mutant. This suggested up-regulation of inositol metabolism in Cir1 deletion was further seen by an increase in virulence important genes that are derived from it.

All of this together revealed that deletion of one of the major iron regulating genes in C. neoformans also impacts several of the iron required pathways. Taking out the Cir1 protein led to a change in respiration, glycolysis, as well as synthesis of membranes and messenger pathways.

When studying the effects of a protein, gene, or any other molecule on a system, this study demonstrates that one must remember, life is complex as all get out. While not everything is truly intertwined, the impact one thing has another is often multifaceted and unpredictable.

Awesome Researchers:
Jung Nam Choi, Jeongmi Kim, Won Hee Jung, & Choong Hwan Lee (2012). Influence of Iron Regulation on the Metabolome of Cryptococcus neoformans PLoS One DOI: 10.1371/journal.pone.0041654

Photo cred:
Centers for Disease Control and Prevention's Public Health Image Library  identification number #3771

How's your immune system doing? Candida albicans knows.

Chances are it is inside you right now, waiting. The moment you let your guard down Candida albicans will be there to spring into action. This versatile fungus can grow both as a yeast and pseudohyphally and it knows how healthy you are.

White and Opaque versions of Candida albicans

Candida albicans normally colonizes our bodies without symptoms; but when your immune system becomes compromised it takes quick advantage and moves on the offensive, generally causing minor infections but capable of much deadlier ones.

But how does it know what is up? A study published in mBio looks to answer that very question.

Variation in Candida albicans EFG1 Expression Enables Host-Dependent Changes in Colonizing Fungal Populations

Growing C. albicans in mice with healthy and immunodeficient mice, the team hoped to compare growth patterns and phenotypic variants, concentrating largely on transcription factor Efg1p activity.
Efg1p is an important physiological regulator for C. albicans and earlier studies have demonstrated that it influences the harmful potential that the fungal cell has.

In this study the scientists show that it also regulates colonization dynamics, having different expression and activity in individual cells throughout. Their study also demonstrates how the host environment changes the C. albicans population composition, thus changing the colonizer's physiology.

To test the growth rates of C. albicans with different levels of Efg1p the researchers basically fed healthy and immunosensitive mice with strains of C. albicans that had both low and high expression of the transcription factor. Then they counted fecal pellets for colonization patterns.

As it turns out those mice with strong immune systems showed a higher growth of cells with a high expression of Efg1p and those with a compromised immune system showed larger growth of those with low activity. The scientists propose that in a general,  there is a heterogeneous population growth. With that expression as the C. albicans comes into contact with an immune system it can adjust its physiology to be most productive despite the varying levels of immune system health.

What this could mean is that as the host's immune system becomes less affective the larger population of low Efg1p active cells will show a spike in growth, thus setting up the colony for engaging in pathogenic actions.

So, in the end,  measuring the ratio of high and low active Efg1p cells in a system could help to us determine host immune status as well as develop new methods for detecting and fighting Candida caused infections before they become severe or deadly.

This study gives us a small insight to how we can keep an eye on one fungus that is just waiting for us to falter.


Citation:
Jessica V. Pierce, & Carol A. Kumamoto (2012). Variation in Candida albicans EFG1 Expression Enables Host-Dependent Changes in Colonizing Fungal Populations mBio DOI: 10.1128/​mBio.00117-12

Photo: Rebecca E. Zordan, Mathew G. Miller, David J. Galgoczy, Brian B. Tuch, Alexander D. Johnson via http://en.wikipedia.org/wiki/File:Whiteopaquecandida.jpg