Naked Science Forum
Life Sciences => The Environment => Topic started by: Mariana on 07/02/2019 09:23:21
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Murphy's asking:
Could someone please elucidate the difference between Plastics and PAHs (Polycyclic Aromatic Hydrocarbons)?
From my understanding, if bacteria can degrade PAH, then they might have the capability to degrade Plastic. Is that right? I am aware that PAHs can be found in plastic, but what is the molecular basis (or such) that enables bacteria to 'jump' from PAH to plastic?
What do you think?
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Could someone please elucidate the difference between Plastics and PAHs (Polycyclic Aromatic Hydrocarbons)?
PAH describes a large family of chemicals, consisting of carbon rings plus hydrogen.
- The electrons are "delocalised", which means that electrons can flow through the molecule.
- The ultimate PAH is graphene, which is a large flat sheet of carbon rings (a 2-dimensional surface)
Plastics also describes a large family of chemicals.
- Some of these do contain carbon rings (eg polystyrene), but many do not (eg polyethylene and PVC).
- Some contain just carbon and hydrogen (eg polyethylene), but others contain chlorine (PVC) or oxygen (nylon)
- Most commercial plastics are formed of long chains, which are tangled together (ie a 1-dimensional chain)
- Some plastics allow electrons to move along the chain, but most don't.
See: https://en.wikipedia.org/wiki/Polycyclic_aromatic_hydrocarbon
https://en.wikipedia.org/wiki/Plastic#Polystyrene
if bacteria can degrade PAH, then they might have the capability to degrade Plastic. Is that right?
Given the radically different chemical structures visible in PAHs and different plastics, it is highly unlikely that a bacteria which can break down PAHs could attack all other types of plastics (and vice-versa).
I think it is more feasible that a bacteria which successfully breaks down one PAH could successfully break down another PAH, since at the atomic level, the edges are carbon rings. These carbon rings are quite stable, but given the right enzymes, it should be possible to break them - and even use this as an energy source.
what is the molecular basis (or such) that enables bacteria to 'jump' from PAH to plastic?
The enzymes that break down plastics are defined by DNA sequences in the bacteria.
If you have an environment which consists of (say) PAH and PVC, and you inoculate this with one bacterium which can digest PAH and another bacterium that can digest PVC, it is possible that the bacteria will share genes defining these enzymes, resulting in a "super-bacterium" that will break down both types of plastic.
This might allow a bacterium to jump from consuming one type of plastic to another.
See: https://en.wikipedia.org/wiki/Horizontal_gene_transfer