A group of students and professors from Yale University have found a fungi in the Amazon rainforest that can degrade and utilize the common plastic polyurethane (PUR). As part of the university’s Rainforest Expedition and Laboratory educational program, designed to engage undergraduate students in discovery-based research, the group searched for plants and cultured the micro-organisms within their tissue.
Several active organisms were identified, including two distinct isolates of Pestalotiopsis microspora with the ability to efficiently degrade and utilize PUR as the sole carbon source when grown anaerobically, a unique observation among reported PUR biodegradation activities.
Polyurethane is a big part of our mounting waste problem and this is a new possible solution for managing it. The fungi can survive on polyurethane alone and is uniquely able to do so in an oxygen-free environment.
Tremendous increases in the manufacture and consumption of plastics over recent decades have led to numerous ecological and economic concerns. The persistence of synthetic polymers introduced into the environment by human industry poses a major threat to natural ecological systems. The low cost and ease of manufacture have increased global plastic demand more than 150-fold, with the production of 1.5 million tons in 1950 and 245 million tons as of 2006. Despite recognition of the persistent pollution problems posed by plastic, global production is still increasing, with the largest increases expected in developing nations. The sheer volume of plastics produced each year presents a problem for waste disposal systems. The scale of this problem and the recalcitrance of some polymers to degradation necessitate investigation into effective methods for biodegradation of plastics. By gaining an understanding of the mechanisms of polymer degradation, a more efficient technique for the biodegradation of plastic waste can be achieved. To accomplish this goal, researchers need greater knowledge of how compounds are metabolized by existing organisms, an investigation of new organisms with bioremediation potential, and the characterization of novel metabolic capabilities.
Bioremediation is an important approach to waste reduction that relies on biological processes to break down a variety of pollutants. This is made possible by the vast metabolic diversity of the microbial world. The group found that in screening several dozen endophytic fungi for their ability to degrade the synthetic polymer polyester polyurethane (PUR). Several organisms demonstrated the ability to efficiently degrade PUR in both solid and liquid suspensions. Particularly robust activity was observed among several isolates in Pestalotiopsis.
The group found that the broad distribution of activity observed and the unprecedented case of anaerobic growth using PUR as the sole carbon source suggest that endophytes are a promising source of biodiversity from which to screen for metabolic properties useful for bioremediation.
In an effort to identify new organisms with novel metabolic capabilities for polymer degradation, the group embarked on an effort to explore the biological and chemical diversity of endophytes. This was achieved as part of an educational program to engage undergraduate students in discovery-based research through Rain Forest Expedition and Laboratory Course. Endophytes are hyperdiverse microorganisms, including bacteria and fungi, that live within the inner tissues of plants without causing overt disease symptoms. These organisms enter their hosts by penetrating exterior surfaces, and some play a key role in plant decomposition following host tissue death . Indeed, fungi such as these contribute to decomposition of lignocellulose polymers and are major contributors to the carbon cycle. The ability of these microorganisms to degrade a polymer as complex as lignocellulose would suggest that these organisms offer promise for their ability to degrade other complex polymers, such as those present in plastics.
In the study, endophytes were isolated from plant stems collected in the Ecuadorian rainforest. A subset of these organisms was screened for their ability to degrade polyurethane. Several active organisms were identified, including two distinct isolates of Pestalotiopsis microspora with the ability to efficiently degrade and utilize PUR as the sole carbon source when grown anaerobically, a unique observation among reported PUR biodegradation activities.
The results of the initial PUR clearance scree:
Impranil DLN, a polyester polyurethane (PUR), is an opaque milky suspension that becomes transparent upon degradation. Organisms capable of degrading this polymer display a zone of clearance around the growing culture . A collection of 59 fungal endophytic organisms isolated from plant samples in the Ecuadorian Amazon were screened for their ability to grow on and degrade polyester polyurethane using the PUR halo assay as the initial screen. Of the organisms screened, 18 organisms produced a halo of clearance such as that shown in Fig. 1. Two other organisms, identified by ITS sequencing as Guignardia mangiferae (E2702C) and Zopfiella karachiensis(E2719A), could grow on but not degrade PUR-A medium. These were used as negative controls in their subsequent studies.
Example of PUR-A plates initially used to screen for polyurethane-degrading activity after 2 weeks of fungal growth. (A) Negative control. (B)Pleosporales sp. strain E2705B.
Read the full explorative paper here