Photo by Aqua Mechanical, Flickr
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Glyphosate is the active ingredient in the herbicide Roundup, and, not surprisingly, it is the most widely used herbicide in the world. Glyphosate functions by inhibiting the activity of a set of plant enzymes that control the synthesis of aromatic amino acids (tyrosine, tryptophan and phenylalanine). This disrupted amino acid metabolism, then, results in defective protein synthesis and ultimately causes the death of the plant. Since these glyphosate-affected enzymes are not found in animals, glyphosate, at concentrations used in herbicide applications, is alleged to have little effect on animals and is advertised as “safe” weed and grass killer. Many bacteria, though, have the enzymes that are affected by glyphosate and there is some concern that both soil bacteria and also microbiome bacteria could be affected by glyphosate applications.
Honeybee gut microbiomes have long evolutionary histories and have been strongly conserved over millions of years (see Signs of Summer 11, July 27, 2017). These gut microbiome bacteria are important as barriers against infection by pathogens and also in the chemical conversion of raw nectar into honey.
Honeybee. Photo by C.J.Sharp, Wikimedia Commons
In a paper published this past fall in the Proceedings of the National Academy of Science (September 24, 2018) a research group from the University of Texas showed that glyphosate exposure greatly reduces levels of a common gut microbiome bacterium in honeybees and causes those affected bees to be more susceptible to infections by pathogenic bacteria. These impacts may also affect the nourishment and energy levels of the bees and may even play a previously unrecognized role in the development of Colony Collapse Disorder.
These researchers also point out that glyphosate may impact the gut microbiome bacteria in many animal species. Studies looking at the impacts of glyphosate on humans, for example, should include along with possible cancer connections and neurodegenerative disorders, possible disruptions of the human microbiome.
In another paper published in Science last fall (November 8, 2018) researchers at Harvard University examined the impact of pesticide exposure on the behavior of bumblebees inside their nests. Using high performance cameras and coded markings attached to the backs of all of the individual bumblebees, the specific locations, interactions, and other behaviors of the nest bumblebees were recorded over a two week period of time. Twelve nests were set up in the laboratory with half of the nests having access to nectar sources that contained the widely used neonicotinoid pesticide imidacloprid. The other six nests were given access to nectar that did not contain imidacloprid.
Bumblebee queen. Photo by M. Cooper, Wikipedia Commons
The bumblebees that were exposed to imidacloprid were less active in the nest compared to controls and did not participate in nest maintenance or larvae care. Exposed bumblebees also had fewer social interactions with their fellow nest inhabitants. These altered behaviors were particularly noticeable at night while, interestingly, during the day especially as the experiment went on, pesticide exposed bumblebees actually behaved in increasingly normal ways.
Pesticide exposed bumblebees, though, were less able than controls to regulate the temperature of their nest. None of the bumblebees in imidacloprid exposed nests constructed the expected thermal insulating, waxy barriers that function to prevent cold temperatures from damaging developing larvae. Larval care and development, then, were significantly affected by the pesticide.
Exposure to imidacloprid has been previously show to reduce foraging activity in bumblebees with the consequential reduction in nectar and pollen gathering and the decline in the overall health and vigor of the nest. This impact has led the European Union to ban imidacloprid use in EU countries (see Signs of Summer 4, June 26, 2018).
Mexican free-tail bats. Photo by A. Froschauer, USFWS.
Bats have many very positive ecological roles. They are vital pollinators and seed dispersing agents, and they consume a vast number of potentially disease carrying and crop destroying insects (see Signs of Summer 1, June 7, 2013).
Bats also, though, have a few less positive ecological features. For example, they carry and disseminate, sometimes across vast distances, some of the most deadly viruses known to humans including Ebola, Marburg and the SARS corona virus. Bats carrying these deadly pathogens, though, never seem to be ill. Somehow they act as reservoirs for these viruses but never become victims. Virologists at China’s Wuhan Institute of Virology explored this resistance of bats to viral illnesses and published their results in Science.
Previous ideas about viral resistance in bats centered on two hypotheses: 1. Possibly a bat’s immune system can make large numbers of “naïve” antibodies (i.e. antibodies that did not yet have specific antigen recognition sites). These circulating, naive antibodies could then mediate the very rapid immune system destruction of encountered viruses. Or, 2. The high body temperatures seen in bats during flight might stimulate immune activity much like the body temperature elevations seen in fever. Unlike fever, though, this acceleration of immune activity could easily be stopped by simply landing and ceasing flight muscle contractions.
The virologists at Wuhan examined the fundamental genetic sequences of two very distantly related bat species and found a core of highly conserved (and, therefore, very important!) genes that act to regulate the bats’ immune systems. Central to the protein products of these genes was a regulator protein that is found in all vertebrate immune systems. This protein is called STING (“STimulator of INterferon Genes”).
STING detects strands of DNA and RNA that are in inappropriate cellular locations and then triggers an immune cascade that destroys them. Often these DNA’s and RNA’s are viral nucleic acids, but they can also be fragments from a cell’s own genome that may have broken loose due to metabolic disruption or stress.
Indiana bat. USFWS.
The bat version of STING triggers a much more subdued metabolic response than the STING from other vertebrates. Many pathogenic viruses, in fact, damage or even kill their hosts because of the uncontrolled immune cascades and inflammatory storms triggered by their STING proteins! Bats, possibly, can carry their wide array of pathogenic viruses because of their very mild STING response!
But why do bats have such a toned down STING response? Bats are the only flying mammal, and , apparently, the metabolic stress of flight especially through the generation of high levels of free radicals from very active mitochondria in their flight muscle cells, leads to repeated breakage of their cellular DNA with the subsequent leakage of the nucleic acid fragments out from their cellular nuclei. Bats, then, have evolved a muted STING response to enable them to tolerate these metabolic stresses of flight, and the unintended consequence of this adaptation is their ability to carry so many types of viruses in their bodies.
There may be another unintended consequence of these muted STING proteins and their extremely down-regulated inflammatory responses. Reduced inflammation may be one of the causes of the very long life spans seen in bats. Bats do live much longer than any other (non-flying) mammal of similar size.
Interesting stuff! I had not heard of glyphosate interactivity with honeybees, but it adds more to the overall picture of pesticide effects. There is evidence of synergistic reactions to pesticides that make them even more deleterious, like between neonicotinoids and fungicides. Agricultural areas are now soaked with poison and almost devoid of non-crop weed flowers, a bad combination for bees, wild or domestic.
All insect populations appear to be crashing these days. I suppose we will go on spraying ourselves to death.