Toxin Tolerance: Prelude to Microbial Antagonism

Toxin tolerance in fungi exposed to toxic wastes presents adilemma to science, since the vast array of toxins in municipal, medical and industrialwastes are not generally encountered in nature, other than as introduced bycurrent waste management practices.

Our observations are that of the many fungi encountered in atemperate rainforest setting in which toxic sewage sludges are disposed, only afew species demonstrate resistance or tolerance to man-made toxins, which may includemany classes of metals, chemicals, pharmaceuticals and personal care products.This observation presents the question of whether the surviving fungi arepassively tolerant of the introduced toxins or if they may utilize such toxicmaterials as nutritional substrate for their own benefit. Secondly, ourcuriosity asks if the toxin-tolerant fungi may metabolize the toxins to whichthey are exposed, perhaps as a defense mechanism of detoxification, or if theresultant metabolic products may also be toxic, with a resultant unique, independentbiological activity.

A key to understanding may be by analysis of the tissues ofthe toxin-tolerant fungi to determine which toxins from the wastes may havebeen bioassimilated, and if there may be identifiable metabolic degradantsreleased to the environment as a direct result of the active bioassimilationand metabolism of the identified toxins.

One hypothesis is that the observed toxin-tolerant fungi mayuse the toxins to synthesize novel self-protective compounds for their own defenseagainst other microbes that may seek to decompose the fungi for their own useas nutritional substrate.

These complex microbial ecology systems are nearlyundefinable. This is the arena of microbial antagonism (or microbialcompetition), wherein environmental stressors of any form, whether chemical,biological or ambient, may incite certain microbes, including fungi, to expressgene products as defense mechanisms, and that process may involve complexsynthesis pathways. Fungi are metabolic machines used extensively in industryand in agriculture to produce enzymes that degrade difficult substrates, and inmedicine to produce multiple classes of antibiotics, and so much more.

Our exploration of forest fungi that tolerate or survivetoxic insult in the form of land-disposed sewage sludge reveals several speciesof common forest fungi that may be useful for purposes of remediation of thesecontaminated and polluted forests, or for investigation of their potential asproducers of new kinds of antimicrobial agents, or for the production of otheruseful industrial or pharmaceutical products.

The summary below informs us of the idea of exploiting fungalmetabolic systems for useful human purposes. Our investigations reveal that thetoxin-tolerant forest fungi we identified are not the subject of any current orprevious investigations of commercial value, and that their genomes have not beensequenced, nor have their gene expression profiles been examined. Our currentwork is focused on determining the toxins to which these fungi are tolerant,and the nature of the metabolic or gene expression products that may resultfrom their exposure to toxic elements in forest-disposed sewage sludges.

Fungal Gene Expression on Demand: an Inducible, Tunable, andMetabolism-Independent Expression System for Aspergillus niger. Vera Meyer, etal. Appl. Environ. Microbiol. May 2011 vol. 77 no. 9 2975-2983. doi:10.1128/AEM.02740-10.The metabolic versatility of filamentous fungi makes themoutstanding cell factories in biotechnology. Important fungal metabolites thatare commercially produced include pharmaceuticals, such as antibiotics andimmunosuppressants; bulk commodities, such as organic acids; and enzymesexploited in various industrial sectors. Also, some filamentous fungi arephytopathogenic, causing huge agricultural losses, while others are causativeagents of devastating human diseases. Within the last years, genome sequencesfor most of the important industrial, agricultural, and medical filamentousfungi have been published, thus facilitating multiple research activities,including genome-mining approaches to spot new metabolites and enzymes,bioinformatics developments to reconstruct metabolic pathways, functionalgenomics attempts to study the functions of genes, and systems biology experimentsto dissect the interactions of genes and proteins.

 

Toxin tolerant fungi on the forest floor - all is well.

 

Many edible fungal species thrive in non-sludged forests.

 

Healthy fungi not exposed to sewage sludge do not host fungus mites or decomposing fungal parasites.

 

Mutual coexistence is the norm in a healthy forest in nutrient balance, not exposed to toxic sewage sludge.

 

Species diversity characterizes a healthy, non-sludged forest; a cup fungus, not yet opened.

 

Even the smallest species coexist with other life forms, such as lichens and mosses.

 

The introduction of toxic wastes changes the biological foundation of any forest or farm.

 

Up close and personal, toxic sewage sludge is no more or less that a toxic soup of chemicals and microbes, including pathogens and non-pathogenic microbes, plus a multitude of plastics, metals, fibers, bone fragments, hairs and all of the degraded industrial, medical and municipal waste materials within one's imagination.