Soil Microbes and Biosolids

Overestimating the importance of microbial processes to human well-being is nigh impossible.

I have been a follower now for a number of years of the evolving science reported by NIH’s The Human Microbiome Project. You owe it to yourself to watch the new TED talk by Rob Knight, a pioneer in studying human microbes, “How Microbes Make Us Who We Are…”. He explains that “the community of tiny single-cell organisms living inside our bodies have a huge — and largely unexplored — role in our health… The three pounds of microbes that you carry around with you might be more important than every single gene you carry around in your genome.” You will learn, for instance, sterile-bred mice implanted with the microbial community from the gut of fat humans results in the mice becoming obese, too!

Our own body’s complex relationships with microbes is no more magnificent than the complexity of microbial interactions in other domains of life. Uppermost in my mind is SOIL, and there is so much more we are learning.

You may have caught the announcement from this past year of the discovery in soil of a new antibiotic, teixobactin, one that promises to provide a desperately needed “last ditch” solution to antibiotic-resistant “superbugs.” This chemical is from the soil organism Eleftheria terrae, collected by a research microbiologist who had developed a wholly new approach to collecting “unculturable” bacterium, this organism literally coming from the researcher’s backyard soil. Reporter James Gallagher at BBC News reported this in “Antibiotics: US discovery labelled 'game-changer' for medicine.” The message for me: soil still holds scientific surprises.

I blogged a few weeks back of research by Dr. Ludek Zurek at Kansas State University. He has demonstrated that the spread of antibiotic resistance microbes has been abetted by houseflies and cockroaches, urban insects that have the nasty habit (at least in human minds) of regurgitating fecally-carried pathogens onto food surfaces. Where might these urban insects pick up pathogens with antimicrobial genes? How about farm fields spread with mostly manures, but also, plausibly, biosolids. I highly recommend the sobering 2014 paper by Dr. Zurek: “Insects represent a link between food animal farms and the urban environment for antibiotic resistance traits.” The message: we have a lot to learn about how microbes communicate and evolve, no less in soil than in humans.

The thought occurred to me that application of manures and biosolids to soil is a bit like the transfer of fecal matter between humans and mice, discussed in the TED Talk. The influence of biosolids, which is essentially a mass of microbes, when transferred to soil, which is largely a template for microbial interactions, is far more complex than the focus we generally give to it, which usually consists of estimating and tracking plant-available nitrogen. We have some research evidence of this complexity. The results are exciting and provocative.

Dr. Xunzhong Zhang of Virginia Tech made a presentation at the 2013 MABA Land Application Symposium, of his work on the release of biostimulants with biosolids applications. He demonstrated that biosolids-soil-plant interactions after biosolids incorporation conferred drought tolerance in crops. The message: we still don’t have a full grasp on the attributes of the biosolids-soil-plant interactions.

At the same symposium, Dr. Rufus Chaney emphasized the complexity of nutrient uptake in biosolids-amended soils. (see: Biosolids Phosphate: Plant Available but not Water Soluble Regulation Needs to be Based on Water Extractable P, not Soil Test P). He clarified the distinction between plant available phosphorus and water extractable phosphorus in biosolids-amended soils. A key part of phosphorus availability to plants comes from the interaction of microbes, roots and soil. The 1991 research paper Dr. N.S. Bolan gave evidence that microbe-mediated reactions bring phosphorus into plant roots. These reactions are a function of arbuscular mycorrhizal fungi (AMF, for short), a new term of art for me. Much interesting research is now in the literature on how organic amendments support vibrant AMF activities. Mineral-bound P, otherwise locked in the soil, is mobilized for crop uptake with the help of AMF. A 2012, “Fresh perspectives on the roles of arbuscular mycorrhizal fungi in plant nutrition and growth” provides an overview. Microbes do the heavy lifting in providing plant nutrients.

AMF are an important supplier of another soil component of increasing interest to soil experts. AMF release GLOMALIN, also for me a new term of art. Glomalin, very nearly a magic elixir in soils, is a protein exudate from soil fungi that helps to create resilient soil structure for good drainage and soil aeration. I first encountered that word when doing background work for the Advanced Stabilization Symposium in Alexandria, last summer. The Cornell Soil Health Assessment provides protocols for measuring glomalin as one of the attributes of healthy soil. It seems that organic matter yields fungi, which yields glomalin, which in turn yields good soil structure, meaning good soil aeration and drainage, and healthy crops.

So there has been this concern that biosolids might contain compounds that interfere with soil microbes, including AMF? With microbes so vital to so many processes, might the residue of antibacterial compounds and of pharmaceutical and personal care products (PPCPs) impede the vital functioning in the availability of phosphorus or in the formation of soil structure? Specifically, are triclosan and triclocarbam injurious to soil nutrition and building processes due to impacts on soil microbes?

A report this week provides good news. Triclosan and triclocarbam introduced with biosolids into the soil do not interfere with development of AMF colonies associated with crop roots. The report, “Effect of biosolids-derived triclosan and triclocarban on the colonization of plant roots by arbuscular mycorrhizal fungi”. Once again, humanity’s gratuitous creation of persistent poisons has been “handled” by Nature’s generous detoxification “ecosystem service” in soil.

Perhaps we too easily delude ourselves into believing that technological innovations in the biosolids field will come from advances in microchips, instrumentation, chemicals and machines. Consider, instead, that the microbiome may be a very fruitful place to look for innovations in biosolids. If you have any doubt about the exciting array of research opening up, check out the current issue of the new journal Microbiome, and learn about body odors and pets.

The time has come to give ourselves over to the Magnificent Microbes.