Kamal Ghorui
Polystyrene is one of the most highly used synthetic polymers in the world and is extremely resistant to decomposition. Therefore, it poses a glaring global environmental challenge due to its chemical stability and the vitality of accumulating in the natural environment. As for plastic biodegradation, insect species such as mealworms are demonstrating some success at degrading polystyrene; however, a significant advance in the field of bioremediation of plastics has come from the study of the cockroach species Blaptica dubia. According to the research Environmental Science and Ecotechnology, Blaptica dubia cockroaches possess a highly integrated host-microbe metabolic network that enables them to degrade approximately 54.9 per cent of polystyrene from all consumed polystyrene within 42 days.This process resembles an advanced ‘factory line’ as it proceeds through an initial oxidative degradation by gut microbial species (i.e., Pseudomonas) followed by degradation of polystyrene degradation intermediates along the cockroach’s own metabolic pathways (i.e., β-oxidation and tricarboxylic acid (TCA) cycle), providing direct usable cellular energy from these degradation intermediates. Ultimately, the synergies illustrated through the metabolomic studies of the B. dubia cockroach may result in revolutionary biorecycling and sustainable fuels industrial technologies.
Why are Dubia cockroaches better at degrading plastic than other insects
The Environmental Science and Ecotechnology indicated that mealworms and wax moths are capable of only fragmenting or degrading plastics at low levels, but the Dubia cockroach (Blaptica dubia) is an outstanding biotechnology converter of plastics. Specifically, a study identified that Dubia roaches consume polystyrene and are able to degrade 54.9 per cent (mass) of that consumed plastic through their metabolic systems within 42 days. This degradation percentage is greater than the degradation rates of any other known insect (to date) that consumes plastic, making this an important advancement in identifying biological means to break down persistent synthetic polymeric materials, such as Styrofoam.
How gut bacteria ‘unlock’ synthetic polymers
The breakdown of the polystyrene plastic begins in the gut of the cockroach, acting as a specialised bioreactor within the gut environment of the insects that were fed a plastic-based diet, as well as enrichment of the bacterial genera Pseudomonas, Citrobacter, and Stenotrophomonas in the gut of the cockroach. The bacteria utilise enzymes (e.g., oxidoreductases) to execute the initial ‘oxidative attack,’ thereby breaking apart (depolymerising) the long, tough polystyrene polymer chains into smaller, more highly oxygenated molecules. If it were not for these initial interventions by the microbes present in the gut of the cockroach, the plastic would not be chemically simple enough for the cockroach to process or absorb.
From plastic waste to biological fuel
A key characteristic of the Dubia roach is that it can truly ‘consume’ plastic. After the bacteria feast upon the polystyrene and break it down into other materials, the Dubia’s own genetics trigger them to do the same. There was a significant increase in β-oxidation and TCA Cycle activity after the study was conducted. So, not only do they process the plastic, but they also utilise the carbon from the broken down polystyrene within their mitochondrial pathways to generate cellular energy and turn what was once pollution into a source of energy.
Shrinking the global plastic carbon footprint
The end goal of such research is not to release large amounts of cockroaches into landfills, but rather to replicate their internal production process at an industrial level. By uncovering more of the precise synergies between the host enzymes and bacteria living in the Dubia’s gut, future technologies will enable synthetic bioreactors or engineered microbiomes that can produce renewable fuels and high-efficiency recycling facilities that can convert plastics back into value-added raw materials. Therefore, significant mitigation of the carbon footprint created by global polystyrene waste production is possible.
