Knowing Your E. coli

Escherichia coli on Tryptic Soy Agar

The recent outbreak of Escherichia coli poisoning in Germany is a stark reminder of the pathogenicity of certain strains of this bacterium. Most commonly found as a faculative organism in the human gastrointestinal tract, pathogenic strains of E. coli can cause a variety of diarrheal diseases in humans as well as being a major source of urinary tract infections. The strains that cause diarrheal diseases are generally divided into 6 pathotypes (1), the relationships between which are neatly illustrated below, after Donnenberg (2002) (2).

Pathotypes of Escherichia coli, after Donnenberg, 2002

The most closely associated of the six are Enteropathogenic E. coli (EPEC), Enterohaemorrhagic E. coli (EHEC) and the Verocytoxigenic E. coli (VTEC). EPEC attaches to the gut lining, altering it in the process which leads to bloody diarrhea. VTEC produces verocytotoxins (also called Shiga toxins) which disrupt protein synthesis in host cells and cause diarrhea. EHEC possess the attachment ability of EPEC and the toxin producing capacities of VTEC, and as such can be seen as a subset of the two (1). The most infamous EPEC strain (and possible the most infamous E. coli strain) is E. coli O157:H7. Most commonly associated with raw beef, this strain causes haemolytic uraemic syndrome (which results in renal failure) as well as other illnesses which can often lead to death. The “O157:H7” moniker refers to the specific O- and H- antigen proteins expressed by the bacterium.

Of the other pathotypes, Enterotoxigenic E. coli (ETEC) is a major cause of traveler's diarrhea worldwide, producing toxins upon colonisation of the gut. Enteroinvasive E. coli (EIEC) invades host cells in the epithelial layer of the gut, spreading from cell to cell and causing a mild form of dysentery. Enteroaggregative E. coli (EAggEC, or EAEC) causes persistent diarrhea, and acts by aggregating on the gut wall and producing a toxin. Diffusely Adherent E. coli is most commonly associated with urinary tract infections, however it has been suggested to have a role as a causative agent of diarrhea.

All of the above pathotypes enter the body by the faecal-oral route, most often through water contaminated with faeces. Some pathotypes, most notably the VTEC, are associated with ruminant animals, with cattle being historically their main reservoir (1).

According to the Center for Disease Control in the US, the outbreak in Germany was caused by the strain E. coli O104:H4, a VTEC type strain, but one that also shows virulence characteristics of EAggEC pathotypes (3).

References:

1. O'Sullivan et al., 2007. Methods for Detection and Molecular Characterisation of Pathogenic E. coli, ISBN 1 84170 506 3
2. Donnenberg, 2002. Escherichia coli: Virulence Mechanisms of a Versatile Pathogen
3. http://www.cdc.gov/ecoli/2011/ecoliO104/

Small Little Green Shiny Fellas

In the back garden of a West Cork home my brother pointed out to me the presence of a most beautiful beetle walking around on some dock plants. It was no smaller than the nail on my baby finger and had a green iridescence with which I was truly delighted. The insects turned out to be a pair of female Green Dock Beetles (Gastrophysa viridula).  

Gastrophysa viridula on a dock leaf

Belonging to the Order Coleoptera [Beetles], they reside in the Family Chrysomelidae which is a taxon with an enormous profusion of highly specialised herbivorous species. There are nearly 40,000 species in this taxon and most are phytophagous (plant-feeders). Some species although having specialised on a narrow range of plant species, that is choosing only to eat a few different types or even just one, have not yet entered any type of evolutionary dead-end. In fact they are able to switch to new host species if required; for example if the predation pressure on an ancestral host plant becomes too much. For a herbivore to do this it needs to contend with many different factors including locating the new plant, utilising its nutrients and dealing with its defensive mechanisms. All these abilities are conferred by  the pheno- and genotypic plasticity of the herbivore and indeed the plant. Other important herbivorous taxon such as the Lepidoptera (moths and butterflies) have different ecological niches for the larvae and adult stages but not so with the Chrysomelidae and so they need to choose a host plant suitable for egg deposition, larvae and adults. It is therefore beneficial to the insect to take note of the change of host plant quality throughout time and season and also to account for previous oviposition and feeding that has taken place. As one can see the demands on a herbivorous insect for successful choice and subsequent utilisation of a host plant are immense. The perceptive abilities for location of the host plant and the insects digestive abilities to gain adequate nutrients - when plant is encountered the beetles will be required to efficiently digest the plant material and cope with the plant toxins - as well as contending with herbivores and carnivores already present, all come into play during host choice. One must not forget too that phytopathogens are known to alter the attractiveness of the plants. (1)

Our leaf beetle, Gastrophysa virudula, fed and oviposited less on dock plants (Rumex obtusifolius) which were infected by the rust fungus Uromyces rumicis than it did in healthy plants in laboratory environments. The alteration in nitrogen contents were observed in rust-infected dock plants and were not fed on by G. viridula. The diseased plants also contained higher levels of calcium oxalate but whether these cues caused the reduced feeding is yet unclear. (1 & 2)

Beetles reared on infected dock leaves had greater larval mortality and slower development. Fecundity was also reduced and regarding oviposition few larvae survived from eggs laid on rusted leaves in the field. (2)

Having said all this I am glad to report that no such rust fungus was evident on the leaves shown in the pictures. Our fellas were happy out!!!

Note the distended black abdomen which is evident on the female species when ready for oviposition (3) and in fact is a type of sexual dimorphism. The following picture [different location] shows this dimorphism with the smaller beetle being the male:

Sexual Dimorphism in Green Dock Beetle

And so we went our separate ways and the beetles had their dock leaves and I my coffee and pizza and custard and what not.It's funny what you'll find in a garden and exciting to know that multitudes of life cycles are turning around every single second on this earth. For them it is a matter of survival and for us merely a more than trifling curiosity. Still it was great to see them.

Later,

Ken.


1. Fernandez and Hilker, Host plant location by Chrysomelidae, Basic and Applied Ecology, Volume 8, Issue 2, 1 March 2007, Pages 97-116


2. Hatcher, Paul, Ayres and Whittaker, The effect of foliar disease (rust) on the development of Gastrophysa viridula
(Coleoptera: Chrysomelidae). Ecological Entomology, 19, November 1994, Pages 349–360

3. Insectoid.Info, Green Dock Beetle, http://www.insectoid.info/beetles/leaf-beetle/green-dock-beetle/

Soil Organisms Determining Plant Growth

When considering an organism within an ecosystem, the most important influences taken into account are above ground plant-plant interactions and animal-plant interactions and prevalent abiotic factors. However increasing evidence suggests that plant-microbial interactions in the rhizosphere play just as important a role. Take for example growth of the Hedge Woundwort, Stachys sylvatica. This unpleasant smelling perennial is generally found in hedgerows and forest verges, preferring humid soil and intermediate light (1). It can reproduce clonally by means of runners, and produces spikes of reddish-purple flowers from June to October.

Hedge Woundwort, Stachys sylvatica

In order to investigate the effect of different soil biota on S. sylvatica, plants were grown in artificial soil inoculated with soil the rhizospheres of two different locations: a hedgerow and a forest understory (2). The innocula were processed to remove soil fauna, leaving only the mycorrhizal ans microbial communities. Strikingly, the two different innocula produced two very different plant growth responses. The S. sylvatica plants grown in the presence of the hedgerow innoculum produced plants with a higher biomass and clonal runners than those with the forest verge innoculum. In addition, the forest verge innoculum plants showed a higher number of flower infloresences than the hedgerow innoculum plants. For S. sylvatica, this shows that soil biota drive possible adaptive growth strategies.

References:

1. Sterry Collins Complete Guide to Irish Wildlife p. 236
2. Peña and Bonte, 2011. Acta Oceologica 37 pp. 110-116

Colour Changing Spider

Misumena vatia

Misumena vatia is a common crab spider (Thomisidae), one of 14 species of crab spiders in Ireland (1). Resembling crabs in their appearance and in their movements sideways and backwards, the larger females can be found sitting on flowers, waiting to pounce on prey such as hoverflies and bees that feed on the flowers (2). M. vatia is most often seen on white or yellow flowers and quite amazingly the spider can change its colour, chameleon like, to camouflage to its background (3). Colour change occurs over a period of days and this ability is due to the presence of ommochromes in the spider, a group of pigments that are of widespread occurrence in insects and some other arthropods (4). There is some debate whether the ommochromes actually act primarily as a protection against photodestruction by intense UV light (4), but the fact that M. vatia possesses the physiological ability to distinguish between certain colours in its environment (5) lends credence to them playing a role in mimicry.

Misumena vatia

References:

1. Ferriss et al. 2009, Irish Biodiversity: A Taxonomic Inventory of Fauna p. 38
2. Sterry 2004, Collins Complete Guide to Irish Wildlife p. 152
3. Gibbons, 1999. Collins Nature Guide Insects of Britain and Europe p. 229
4. Théry and Casas, 2009. Philosophical Transactions of the Royal Society 364 pp. 471-480
5. Defrize et al., 2011. Journal of Insect Physiology 57 pp. 508–513

Know Your Neuropterans

Chrysoperla carnea

Very often I have come across species, of plant, animal and fungus, that upon searching the literature, reveal themselves to be actually a species complex, a number of species that are identical in many respects but are genetically distinct. The levels of these distinctions are often quite striking, as in the case of the Green Lacewing Chsysoperla carnea (Insecta: Neuroptera: Chrysopidae). This is a common insect of the summer months that is most recognisible from its almost ponderous flight and transparent, well veined wings. In the autumn time, the green adults hibernate, often indoors, their bodies turning a pinkish colour (1). The larvae feed on aphids and are used commercially to control aphid.

Chrysoperla carnea

C. carnea has been shown to be a complex of many cryptic species, based on the songs they make to attract mates (2). When sexually receptive, members of the C. carnea group vibrate their abdomens, which in turn causes the substrate (generally a leaf) on which it stands to vibrate, generating a song. This process is known as tremulation. Both sexes tremulate, so only individuals with the same songs will be attracted to each other, and since song is genetically determined, this results in reproductive isolation of populations charactrerised by song. At least 15 groups within the C. carnea group have been described, differentiated by song (3).

Chrysoperla carnea

As Neuropterans, lacewings are considered some of the oldest insects with complete metamorphosis (4). Ancient, extinct Neuropterans can be traced back to the Late Permian period, 260-251 million years ago. Of the current c. 6000 species of Neuropterans described, about 1200 belong to the family Chrysopidae, to which the C. carnea group belong.

References:

1. Sterry, 2004. Collins Complete Guide to Irish Wildlife p. 132
2. Henry et al., 2002. Annals of the Entomological Society of America 95 pp. 172-191
3. Henry et al., 1999. Evolution 53 pp. 1165-1179
4. Tauber et al., 2009. Neuroptera in Encycolpedia of Insects, Resh and Cardé eds, pp. 695-707

Industrialisation of a Mushroom

Dryad's Saddle, Polyporus squamosus

The Dryad's Saddle mushroom (Polyporus squamosus) is a large, fleshy agaricomycete that grows in a semi-circular or saddle shaped fashion on a range of both living and dead broad-leaved trees, such as  ash, elm, sycamore and beech (1). Its upper surface is creamy yellow in colour which is marked with concentric rings of brown scales. The under surface appears as a network of pale yellow, polygonal spores.

Underside of Dryad's Saddle, Polyporus squamosus

While P. squamosus is edible, it needs to be picked young as the older mushroom is quite tough and corky. However, if processed, the resultant biomass may present a viable animal, and possible human, source of nutrition (2). In addition, P. squamosus produces pectinases (3), enzymes that degrade pectin and that are used in the fruit industry to improve juice extraction from apples, etc. (4). A polymer-polymer two phase system has been successfully used to produce both P. squamosus biomass and resultant secondary metabolites (5). This method consists of two mutually incompatible structural polymers (namely polyethylene glycol and crude dextran) in solution which brings about a spontaneous separation of phases. This reduces the need for mechanical separation of cells. P. squamosus fungal growth is restricted to the bottom phase, leaving the top phase free.  

Dryad's Saddle, Polyporus squamosus

P. squamosus has also been shown to produce useful xylanase (6) as well as a lectin that shows great potential for usein glycobiological studies in biomedical and cancer research (7), making this method of growth a useful biotechnological tool.

References:

1. Harding et al., 1996. How To Identify Edible Mushrooms p. 143
2. Antov and Peričin, 2000. APTEFF 31 pp. 567-573
3. Antov and Peričin, 2001. Enzyme and Microbial Technology 28 pp. 467-472
4. Antov, 2004. Carbohydrate Polymers 56 pp. 295-300
5. Antov et al., 2001. Journal of Biotechnology 91 pp. 83-87
6. Antov et al., 2006. Process Biochemistry 41pp. 232-235
7. Ho et al., 2000. The Journal of Biological Chemistry 275 pp. 10623-10629.

Its a Sawfly, But Not Really

Tenthredo livida is a common sawfly of holartic distribution that is often found in hedgerows and woodlands. The female lays eggs into plant tissue, using saw-like ovipositor to make the inscision. Larvae are polyphagus, feeding on a variety of plats such as hazel, willow and even bracken. The adults will hunt flies and take nectar from plants (1).

Tenthredo livida

Interestingly, calling T. livida a sawfly, or "Symphyta", is now considered incorrect. The Symphyta are a basal grade that leads to the long waisted hymenoptera. Therefore Symphyta is not a monophyletic group, that is within the group not all relatives are included (2). The terms "Symphyta" and saw fly are still used however, in an informal way.
References:

1. Calmasur and Ozbek, 2006. Proceedings of the Entomological Society of Washington 108 pp. 139-144
2. Resh and Carde, 2009. Encyclopedia of Insects p. 474