Is the world poised for the end of COVID-19 pandemic? Should we lower our guard now? Well, just when we thought the COVID-19 curve is beginning to flatten and that morbidities and mortalities from COVID-19 are declining across the world, some other viral infections are posing a threat to humans and livestock. This situation may also be compounded by the possible emergence of more transmissible and more deadly SARS-CoV-2 variants. Amid these grim prospects, another worrying factor is the reports of a bovine viral disease called “lumpy skin disease” emerging in parts of India.
Although most of us blame the microorganisms-bacteria, yeasts, fungi, protozoa and viruses-for diseases in plants, animals, and humans; we must remember that the majority of microbes such as bacteria and fungi are going to give us novel kinds of fertilisers for our crops and drugs to fight infections in animals and humans.
In fact, some microbes have been found to hold promise for providing novel solutions to the plastic pollution problem in the world. Today, let’s discuss these issues: plastic-munching microbes, COVID-scenario globally, and the rise of lumpy skin disease.
Plastic Eating Microbes
According to the United Nations Environment Programme (UNEP), about 400 million tons of plastic wastes are generated globally per year, of which about 14 million tons enter our oceans every year, posing a serious threat to marine life.
On the land too, plastic wastes land up in landfills or incinerators or clog our wetlands or other ecosystems posing hazards to animal and human health. Moreover, toxic fumes from burning plastic wastes in incinerators aggravate air pollution. One solution is cutting down the use of plastics drastically, which is not going to happen in the near future.
What if bacteria and fungi, which are versatile metabolically, use plastics as their food and energy sources and degrade them into harmless end products? For a long time, this was just a pipedream. However, in the recent past, several scientific breakthroughs give us hope for a solution to our plastic problem. Let us look at some of these developments.
In 2016, a startling discovery was made by a team of Japanese scientists led by Kohei Oda, Kyoto Institute of Technology and Kenji Miyamoto, Keio University. They collected a sediment sample from a plastic bottle recycling plant in Sakai City, Japan. From this sample, they could isolate a wonderful bacterium which they named as Ideonella sakaiensis. This bacterium was later found to digest a kind of plastic called polyethylene terephthalate (PET) used most often for making bottles. By “eating” PET i.e., using it as its carbon and energy source, I. sakaiensis was found to degrade PET into harmless end products.
The Japanese bacterium degrades PET using a pair of enzymes called PETase and MHETase; converting PET into ethylene glycol and terephthalic acid (TPA). Why this bacterium could not immediately lead to degradation of PET wastes on an industrial scale? This was because the bacterium digests PET rather slowly.
Other scientists started making attempts to enable Ideonella’s PET digesting enzymes work faster. In 2018, John McGeehan and team at the University of Portsmouth, UK engineered a PETase enzyme that works better than the natural enzyme. In 2020, the process was improved even further by combining PETase and MHETase into a single “super enzyme.”
The industrial scale biodegradation of plastic wastes is still many years away. We have only found bacteria and their enzymes that can break down PET plastic. But there are many other types of plastic such as polyethylene (PE), polypropylene (PP), polystyrene (PS), polyurethane (PU), low density polyethylene (LDPE), and high-density polyethylene (HDPE) etc. However, for PET wastes, industrial scale application is in the offing.
Carbios, a French firm, has set up a demonstration plant to enzymatically biodegrade PET waste. It hopes to launch large-scale industrial operations by 2024/2025. In partnership with Nestle and PepsiCo, Carbios aims to inject large amounts of recycled materials (from PET wastes) back into fresh PET products.
Meanwhile, other groups have discovered a bacteria that “eats” other kinds of plastics. A team at the Helmholtz Centre for Environmental Research, Leipzig, Germany has found a soil bacterium, Pseudomonas sp. TDA1, that can produce enzymes able to digest polyurethanes. This bacterium was found in a soil sample around a heap of plastic waste; possibly it was feeding on polyurethane diol, which is used in plastic as a component that protects products from corrosion.
Similarly, a team of scientists, in 2017, discovered an interesting fungus from a garbage dump in Islamabad, Pakistan. This fungus, Aspergillus tubingensis, could digest polyurethane (PU). PU is used in refrigerators, fake leather and many other applications.
On the other hand, many scientists are combing through genomes of soil microbes to find genes coding for plastic-degrading enzymes. ETH Zurich has screened thousands of genomes and found several candidate genes.
Aleksej Zelezniak, Chalmers University, Sweden also identified plastic-degrading enzymes in the genomes of many soil and marine bacteria. Leipzig University researchers found an enzyme called PHL7 that breaks down PET plastic in record time. This enzyme was found in a microbe isolated from a compost heap in a cemetery in Leipzig.
More recently, scientists from Cambridge University surveyed 29 European lakes and found several bacteria that preferred to “eat” plastic wastes instead of organic matter such as decaying leaves or wood (Tanentzap, Andrew et al. Nature Communications 13, 4175, 2022).
We may look forward to the day when we would have cut down the amounts of plastics we consume as well as come up with facilities to break down existing wastes using plastic-eating bacteria and their enzymes on industrial-scale treatment plants installed across the globe!
COVID-19 Scenario
The WHO chief has recently said that the world is poised for the end of Covid-19 pandemic (Business Standard, Sep. 21, 2022). However, we still need to seriously ponder if the end of the pandemic is in sight. Should we lower our guard and do away with masking?
K Srinath Reddy, PHFI, says that there is a decline in serious Covid infections but the virus is going to stay. He also stressed the need to be vigilant about new variants from northern hemisphere in the winter. Gagandeep Kang, CMC, says that the end is still not in sight but Covid-19 will not be a serious public health problem.
There is the looming threat of new variants emerging and some areas may witness a fresh spike of infections. We must be watchful of sudden, sporadic, localized surges. The relevant authorities must be prepared to impose restrictions as and when needed.
Meanwhile, a new variant called BF.7 (B.1.1.529.5.2.1.7) has been reported from several countries including Germany, France, and Denmark (Down To Earth, Sep. 23, 2022).
As per information displayed on the WHO website (Sep. 22, 2022), the time for COVID complacency hasn’t arrived yet. Several countries have called for accelerating global rollout of vaccines, tests, and treatments. Coordinated action is needed to deliver vaccines in poorly vaccinated regions and scale up healthcare facilities in under-developed areas for ensuring adequate infrastructure for testing, treatment and saving lives as far as possible.
Lumpy Skin Disease
Lumpy skin disease is a viral disease that affects cows. This infection has killed about 75,000 cattle in India (The Hindu, Sep. 21, 2022). It has spread to over 10 states among which Rajasthan is the worst-hit.
It’s caused by lumpy skin disease virus (LSDV), a capripoxvirus belonging to poxviridae family (which includes smallpox and monkeypox viruses). It’s not a zoonotic virus (that means it cannot spread from animals to humans). It’s a contagious vector-borne disease spread by mosquitoes, some types of flies, and ticks.
While the country is hit by lumpy skin disease virus, another virus-sheep pox virus, SPV has hit Gujarat (IE, Sep. 6, 2022). 18 sheep had died from the virus. Like LSDV, SPV also belongs to the capripoxvirus genus belonging to poxviridae family.
(The views expressed are personal)
