Plastics are a serious source of marine pollution and thousands of tonnes find their way into our oceans in various forms. These can cause serious damage or death to many sea creatures such as birds and turtles, as well as introducing toxic chemicals into the wider environment and transporting these around the world. In an attempt to reduce our contribution of dangerous plastics to the environment we have manufactured biodegradable plastics such as polycaprolactone (PCL) which is used in a variety of products; however, even these substances are not thought to be totally biodegradable as the hydrocarbons are very difficult to break down biologically and instead are reduced to microplastic particles. Many of these particles find their way to the sea floor and this is the environment which takes the spotlight in this study.
In a previous paper, the authors reported discovery of PCL degrading bacteria found between 300 and 600m below sea level, however here, they aimed to investigate the presence and degrading ability of bacteria found much deeper, between 5000 and 7000m. Samples were taken from the Kurile and Japan Trenches and indeed, 13 strains of PCL degrading bacteria were found. These were isolated and characterised using PCR to amplify the 16S rRNA genes which were then sequenced. The degrading ability of the strains was determined by the formation of clear zones around the colonies when grown on PCL enriched agar. However, when tested on other plastic enriched agars, none of the strains produced clear zones (which indicate biodegradation).
By using the gene sequence analysis the authors found that the strains were related to previously described species. 8 of the strains were closely related to Moritella sp., 3 were closely related to Shewanella sp. and the final 2 were closely related to Psychrobacter sp. and Pseudomonas sp., respectively. As none of these related species have previously been reported as plastic biodegraders, this is the first discovery of PCL degrading bacteria in the deep sea, capable of withstanding the low-temperature, high-pressure conditions.
This study has a positive message as plastic biodegradation, which was relatively understudied and not well understood, is obviously possible to an extent and if we continue to use predominantly aliphatic-polyesters such as PCL which are biodegradable, we could help to reduce the effects of plastics on the environment. Furthermore, as these bacteria have been genetically sequenced, it may be that with the help of metagenomics we can identify other species with the same biodegrading capabilities in other habitats. However, the positive message should be taken with caution as the study does not take into account macro plastics which are the form that most commonly kills marine vertebrates.
A review of: Sekiguchi T, Sato T, Enoki M, Kanehiro H, Uematsu K, and Kato C (2010) Isolation and characterisation of biodegradable plastic degrading bacteria from deep-sea environments. JAMSTEC Rep. Res. Dev. 11: 33-41.
3 comments:
I forgot to mention that the study doesn't take into account the different elements of the plastic and just talks about it as a whole. Therefore I have assumed that these bacteria have the ability to degrade even the hydrocarbon element of the plastic, however this strictly speaking remains to be seen as the study did not differentiate. Although if I assumed right this would be a massive step forward for the oceans health!
Hi Natasha,
Various bacteria produce biosurfactants through carbon sources from hydrocarbons, these biosurfactants emulsify the hydrocarbons increasing their availability for microbial degradation. I found a paper that describes the use of protease and esterase enzymes which are then thought to be involved in the degradation of polyurethane through hydrolysis. Similarly I found a paper which discusses the use of lipases to degrade some plastics too. So yes, I guess the process works by breaking down the hydrocarbons making up the plastic. I think there is a blog posted previously describing how they degrade the hydrocarbons of crude oil, so I'm assuming it uses the same mechanisms to degrade the various hydrocarbons of some plastics. Potentially very useful, however I read how surfactants were used in the Gulf of Mexico oil spill and only resulted in the break up and then further dispersal of the oil, disturbing even more of the surrounding ecosystem, so perhaps some more work needs to be done to make them effective on a large scale!
Hi Jelena,
Yeah I've read similar things about the break down and further dispersal of the hydrocarbons as well as their degradation, hence why it would be interesting to know whether these bacteria are actually degrading the PCL hydrocarbons or just breaking it down further. Assuming that they are degrading the hydrocarbon as well as the nasty chemicals, as you said it would seem logical that these bacteria use the same mechanism as those that degrade crude oil hydrocarbons. However, I think there may be more variation in this mechanism also as these bacteria could only degrade one type of plastic, which might suggest that different tactics are needed for different materials even though they are partly made up of similar products. Also, if they do not fully degrade the plastic and just it break down leaving the hydrocarbons it would be useful to know whether there are other strains of bacteria living under the same low-temp high-pressure conditions which could carry out the remainder of the degradation process. So like you say - lots more work to do!
Post a Comment