An Eco-Organic Ode to Ethanol (Ethyl Alcohol)

June 6, 2012

ETHANOL, AN ANCIENT DISINFECTANT commonly used in today’s medical and health-care hand sanitizers, is also produced by microbes in food fermentation and natural ecosystems. A simple two-carbon molecule abbreviated EtOH by chemists, ethanol (ethyl alcohol) is also routinely used in organic chemistry and commerce as a solvent for natural essences or tinctures like perfumes, food flavorings, and medicinals.

“By far the most common natural source of ethanol is fermentation of fruit sugars by yeasts,” wrote Douglas J. Levey in The Evolutionary Ecology of Ethanol Production and Alcoholism, an article in Oxford Journals’ Integrative & Comparative Biology. “Although ethanol is an end product of fermentation, the fungi that produce it are locked in a complex set of interactions with fruiting plants, frugivorous vertebrates, and other microbes. Given that ethanol affects both vertebrates and microbes, it is likely to have at least some adaptive basis. In particular, it may be viewed as a defensive agent, used by yeasts to inhibit growth of competing microbes in much the same way as penicillin is thought to give Penicillium fungi the upper hand in competition with bacteria.”

“In an anthropological context, fermentation can be viewed as controlled spoilage of food,” wrote Levey. “The microbes responsible for the later stages of food spoilage generally cannot grow in alcoholic or acidic environments. Thus, by culturing the production of alcohols and in many cases organic acids via limited exposure to oxygen, the food is protected. Long before refrigeration and synthetic additives, fermentation was one of the most important food preservation technologies… As they discovered the inebriating qualities of some fermented foods, they focused attention on those fermentative processes, ultimately leading to the beer and wine industries of today.”

Ethanol and fermentation are part of fruit plant reproductive ecology. Ethanol molecules multi-task: Fruit pulp is protected from microbial decay by ethanol. Ethanol also attracts fruit pulp-eating (frugivorous) animals aiding plant reproduction via seed dispersal. In essence, fruit pulp is redirected in the ecological food chain from microbes to higher animals, to the benefit of fruit plant reproduction.

“The low molecular weight of ethanol and its substantial concentration within fruit pulp well suit this molecule for long-distance signaling of availability to appropriate consumers,” wrote Robert Dudley in an article titled Ethanol, Fruit Ripening, and the Historical Origins of Human Alcoholism in Primate Frugivores in a 2004 issue of Integrative & Comparative Biology. “Ripening involves production of a number of fruit volatiles, but ethanol is perhaps the only olfactory commonality to an otherwise bewildering taxonomic array of angiosperm fruits.”

“As with longevity and fitness benefits of ethanol exposure in fruit flies, epidemiological studies in modern humans demonstrate a reduction in cardiovascular risk and overall mortality at low levels of ethanol consumption relative either to abstinence or to higher intake levels,” writes Dudley. “If natural selection has acted on human ancestors to associate ethanol with nutritional reward, then excessive consumption by modern humans may be viewed as such a disease of nutritional excess. Availability of ethanol at concentrations higher than those attainable by yeast fermentation alone (i.e., 10–12%) is a very recent event in human history.”

Underscoring the importance of ethanol in ecosystems, yeast fungi survive up to 15% (v/v) ethanol concentrations that are lethal to most microbes. Distillation, a technique known to ancient alchemists that survived the transition from magical potions to modern chemical science, of course boosts ethanol concentrations to much higher and more lethal/toxic levels than those found in natural ecosystems.

Ethanol is also an ecological feedstock. Yeasts and certain bacteria further transform (oxidize) ethanol into acetic acid or vinegar, which besides being culinary is toxic to many microbes. In India and elsewhere, anti-microbial solutions of vinegar and baking soda commonly replace harsh commercial chemicals for floor and surface cleaning.

Ethanol’s role as an animal attractant can be turned to human advantage: for example, in ecological pest control as part of traps or trap crops. Christopher Ranger and Michael Reding of the USDA-ARS in Wooster, Ohio, and Peter Schultz, Director of Virginia Beach’s Hampton Roads Agricultural Research and Extension Center told the Entomological Society of America (ESA): Ethanol released by stressed (e.g. lack of water) or doped (injected with ethanol) forest or nursery trees (e.g. magnolias) attracts ambrosia beetles (Xylosandrus species). “A successful trap crop strategy might include 75ml (2.5 fl oz) of 90% ethanol injection of cull or park grade trees of an attractive species within the field production block or along the border between a woodlot and the high value nursery crop species,” said Schultz.&&

In the USA, where the federal government controversially subsidizes corn ethanol and mandates its use as a fuel, Douglas Landis and University of Illinois-Urbana colleagues Mary Gardinera, Wopke van der Werf and Scott Swinton wrote of the deleterious ecological consequences of growing too much corn in a 2008 issue of the Proceedings of the National Academy of Sciences of the USA. In contrast to intercropping strategies promoting landscape diversity and biocontrol of pests by natural enemies, increasingly large almost monoculture acreages of corn create a less diverse landscape with less biocontrol in other regional crops like soybeans. Too much corn in the landscape costs soybean producers in Iowa, Michigan, Minnesota and Wisconsin an estimated $239 million in reduced yields and increased pest control costs.

Not that planting corn need be bad. Indeed, the Native Americans traditionally interplanted corn with squash, beans, strawberries, sunflowers, and diverse weedy species that promoted ecological balance between pests and natural enemies. “Biological control of insects is an ecosystem service that is strongly influenced by local landscape structure,” wrote Landis et al. “Altering the supply of aphid natural enemies to soybean fields and reducing biocontrol services by 24%” from planting too much corn cost an estimated $58 million in soybean crop loss and control costs for just one pest, the soybean aphid.

Distiller’s dried grains (DDGs) leftover from ethanol production could potentially be utilized in innovative ways. Though with billions of gallons of corn ethanol being distilled, the emphasis is understandably on utilizing big tonnages of DDGs for animal feed, mulches, etc., rather than really innovative research that could yield niche corn-based products for medical use. Yiqi Yang, a Professor of Biological Systems Engineering and Charles Bessey Professor in the Nebraska Center for Materials and Nanoscience and the Departments of Biological Systems Engineering and Textiles, Clothing and Design at the University of Nebraska-Lincoln, believes that small research investments could yield niche innovations like medicines (e.g. corn-derived cancer-fighting molecules small enough to enter the brain) and biodegradable filters that can be left in the human body.


Fruit Flies, Ethanol, Good Health & Biocontrol

March 19, 2012

SEXUAL DEPRIVATION INCREASES Ethanol Intake in Drosophilia” was the semi-tabloid headline in the American Association for the Advancement of Science (AAAS) journal Science (16 March 2012; v. 1355, p. 1351). No fools, the AAAS knows a scientific title readily translatable into good headlines and writerly fun; parental Internet filters be damned. I was particularly impressed by Scientific American Science Sushi blog writer Christie Wilcox’s entertainingly deft mix of science, human implications and fun stuff on fruit flies with quotes from lead scientist Gilat Shohat-Ophir.

You Tube has an entertaining mix of titles on the subject, such as: 1) Flies turn to drinking after sexual refusal; 2) Study: Rejected Male Flies Turn to Alcohol; 3) Scientists Find Fruit Flies Self Medicate With Booze; and from Emory University, 4) ‘Drunken’ fruit flies use alcohol as a drug. The underlying science has a certain fascination, as there are similar neural (molecular) pathways for rewards and addiction (and their interaction with social experiences) in the two species: neuropeptide F (NPF) in fruit flies and neuropeptide Y (NPY) in humans. “Flies exhibit complex addiction-like behaviors,” write Shohat Ophir and colleagues K.R. Kaun, A. Azanchi and U. Heberlein, including “a preference for consuming ethanol-containing food, even if made unpalatable.”

In primitive natural settings, ethanol from fermentation of overripe fruit functions as a cue or lure for humans, fruit flies and other animals to locate fruit crops. Indeed, there is evidence that fruit fly larvae “have evolved resistance to fermentation products” from millennia of eating “yeasts growing on rotting fruit.” But fruit flies are not immune to alcohol-related mortality; the dose of the poison (alcohol) determining whether it is medicinal.

“The high resistance of Drosophila melanogaster (fruit fly) may make it uniquely suited to exploit curative properties of alcohol,” wrote Emory University’s Neil Milan, Balint Kacsoh, and Todd Schlenke in an article titled “Alcohol Consumption as Self-Medication against Blood-Borne Parasites in the Fruit Fly” in Current Biology (2012). “Ethanol levels found in natural D. melanogaster habitats range up to 6% ethanol by volume in rotting fruits, and 11% in wine seepages found at wineries. Fly consumption of food with moderate levels of ethanol (i.e., less than 4% by volume) results in increased fitness, but consumption of higher ethanol concentrations (i.e., greater than 4%) causes increasing fly mortality.”

One of the hazards of life for fruit flies is parasitic wasps, which sting the flies and lay eggs hatching into parasitoid larvae living inside and eventually killing the fruit fly. From the fruit fly’s perspective, biological control by natural enemies is deleterious and best prevented or overcome. “We have shown here that ethanol provides novel benefits to flies by reducing wasp infection, by increasing infection survival, and by allowing for a behavioral immune response against wasps based on consumption of it in toxic amounts,” wrote Milan and his colleagues. “To our knowledge, these data are the first to show that alcohol consumption can have a protective effect against infectious disease and in particular against blood-borne parasites. Given that alcohols are relatively ubiquitous compounds consumed by a number of organisms, protective effects of alcohol consumption may extend beyond fruit flies. Although many studies in humans have documented decreased immune function in chronic consumers of alcohol, little attempt has been made to assay any beneficial effect of acute or moderate alcohol use on parasite mortality or overall host fitness following infection.”

Scientists and students with science projects have been rearing fruit flies for over a century, and unraveling many of the mysteries of biological life. Indeed, the common fruit fly, “Drosophila melanogaster is emerging as one of the most effective tools for analyzing the function of human disease genes, including those responsible for developmental and neurological disorders, cancer, cardiovascular disease, metabolic and storage diseases, and genes required for the function of the visual, auditory and immune systems,” wrote Ethan Bier of the University of California, San Diego, in Nature Reviews Genetics (v.6, Jan. 2005). Depending on the matching criteria, anywhere from 33% to “75% of all human disease genes have related sequences” in fruit flies. Thus, “D. melanogaster can serve as a complex multicellular assay system for analysing the function of a wide array of gene functions involved in human disease.”

Something to think about next time you see those tiny (1/8 inch; 3 mm) golden or brownish fruit flies flitting around your overripe bananas, vegetable-laden bins and garbage cans.