The bacterial community of your old chewing gum


Breaking down the microbiology world one bite at a time

The bacterial community of your old chewing gum

Microbial communities exist in surprising places. For instance, many scientists study the bacterial content of old, discarded chewing gum — the wasted chewing gum bacteriome. Why? Their hypothesis is that the bacteria which persist within wasted chewing gum microbial communities could possess biodegradation capabilities of chewing gum.

In a recent study, Satari et al. determined the bacterial contents of wasted chewing gum. To do this, they scraped off chewing gum samples from the sidewalk of five different countries: Spain, France, Singapore, Greece, and Turkey. They analyzed the bacterial diversity of each sample using a technique called Next Generation Sequencing, which enables fast and efficient DNA sequencing of thousands of samples in parallel. This method tells the researchers which bacteria are present and the relative proportion of each bacteria to other community members. Interestingly, their results showed that the samples shared many bacteria of the same genera (Figure 1). Bacteria classified within the same genus are close relatives to each other, like cousins. Importantly, the relative abundance of each genus varied significantly among the samples collected from different counties (Figure 1), suggesting that the local environment drives the community development of the wasted chewing gum bacteriome.

In many cities, the sidewalk is decorated with these dark, black residue spots. These are old pieces of chewing gum. Many chewing gums are non-biodegradable, meaning that they do not break down easily and are long-lasting. This is due to the water-insoluble component of chewing gum, a synthetic rubber-like material that gives gum its stickiness and chewy texture. The other main component of chewing gum is water-soluble and contains the sugar or sugar alcohols used to sweeten the gum and provide flavor. Wasted chewing gum is considered an environmental pollutant, and its removal is expensive and time-consuming. Thus, cost- and time-efficient solutions to removing wasted chewing gum are imperative.

Figure 1. Bacterial diversity of wasted chewing gum samples. The most abundant taxa from each location are shown in pie charts. Figure from Satari et al.

To examine the microbial succession in wasted chewing gum (i.e., the change of the microbial diversity over time), the researchers set up an experiment where they chewed gum and placed them on outdoor pavement. Over the course of 12 weeks, samples were collected for DNA sequencing to determine the dynamic changes in bacterial contents. Not surprisingly, the types of bacteria found most frequently in the first few weeks were known to be members of the oral microbiome. Their abundance decreased over time, while, in parallel, non-oral environmental bacteria abundance increased. They showed that this microbial succession eventually stabilized in the last few weeks, meaning that the rate of changes in bacterial abundances slowed. Interestingly, oral bacteria were still detected at the end of the 12 week period, albeit at low frequencies, indicating that wasted chewing gum carries oral bacteria even weeks after being discarded. Their experiment also identified genera of bacteria that were detected in their samples from different countries, suggesting that these bacteria could be fast, common colonizers of wasted chewing gum. In general, their results show that the time of outdoor exposure correlates to the bacterial profiles of wasted chewing gums.

A key aspiration of this research was to identify bacteria with the capacity to degrade chewing gum. Excitingly, DNA sequencing of gum samples harvested from their microbial succession experiment identified bacteria already reported to degrade rubbers. For example, bacteria of the genus Bacillus have been shown to break down natural and synthetic rubbers. Similarly, bacteria of the genus Corynebacterium are a component of the oral microbiome and are natural rubber degraders. In the researchers’ experiment, Bacillus species gradually increased in abundance during the outdoor incubation, and Corynebacterium species were detected at a low but stable frequency over the course of 12 weeks. Their presence, among others, suggest that they could become important for chewing gum bioremediation.

Finally, to experimentally characterize the possible gum degradation activities of chewing gum bacteria, the researchers tested the growth of various isolated species on media supplemented with chewing gum powder (prepared by grinding up Orbit and Trident gum). In each case, the only source of carbon, or food, for the bacteria is the supplemented gum powder. Their logic is that if the bacteria could grow on the chewing gum-derived carbon source, they would be able to metabolize it. Indeed, many of their cultured bacteria grew in the presence of the tested gum powders suggesting that chewing gum harbors bacteria with the capacity to degrade it (Figure 2). These results, coupled with their findings that many of the bacteria identified in their DNA sequencing of wasted chewing gum have previously been described as rubber degraders, demonstrates a promising first step in using bacteria as a bioremediation strategy of wasted chewing gum.

Figure 2. Growth of chewing gum bacterial isolates on media enriched with chewing gum powder I, II, and III, compared with growth on medium lacking a carbon source. M9 refers to the specific bacterial growth medium used. Figure from Satari et al.

This study by Satari et al. was the first report of the wasted chewing gum bacteriome. One main caveat of this study is that the researchers analyzed a small number of samples collected from different countries. Thus, going forward, more research is crucial to understand the biodegradation capacities of the wasted chewing gum bacteriome and its application in the removal of discarded chewing gum in public spaces.

Link to the original post: Satari, L., Guillén, A., Vidal-Verdú, À. et al. The wasted chewing gum bacteriome. Sci Rep 10, 16846 (2020).

Featured image: Dan Kitwood (Getty Images)