Further notes about the morphostasis concept – split files

(17) Pathogen (Microbe) Associated Molecular Patterns (PAMPS or MAMPS)

I have been ruminating on this for some time now.

PAMPs (or, better, MAMPs) interact with Toll Like Receptors (TLRs) and this seems to bring the attention of host cells to the presence of micro-organisms. The simplistic view taken so far is that this is part of a "bug hunting and disposal process". However, this may be far too simplistic. In this section I will concentrate solely on those molecules that bacteria display and that alert sentinel cells (of whatever lineage they belong to) to the presence of "invaders". I have already emphasised that the vast mass of heterotrophic bacteria are "polite". They wait for the death of living organisms before they use them as a their nutritional source. (Heterotrophs are other-seekers or more specifically, those that eat other organisms – alive or dead).

From here on, I am going to abandon the generally popular term PAMPs in favour of MAMPs.

I can, as yet, not find easy access to information on the (bacterial) species distribution of MAMPs – like eg, LPS (lipopolysaccharide). The question is, do chemio-autotrophs display MAMPs in the same way?

An important question to raise is this. Do MAMPs have an important role to play in the identification of sick and dying cells? (This could explain their involvement in development and their close relationship to DAMPs. (DAMPs are danger associated molecular patterns – although I would prefer to rename them as "debris associated molecular patterns.) Do these molecules help the zygote derived colony to re-assimilate organic building blocks? And do they help to identify suitable nutrition for heterotrophs? Could they be giving dedicated necrotrophs (dead flesh "eaters") an "early foothold" or "head start" in the colonisation of dying tissues? If this is a valid conjecture, then – in one stroke – it would help to make better sense of the "duality" of MAMPs that has become apparent in the literature. It has become increasingly clear that TLRs (cell receptors that recognise MAMPs) can be triggered by damaged tissues. If this view is valid, TLRs themselves might be a manifestation of DAMPs – developmental cellular debris that needs clearance and re-assimilation. It is fairly obvious that sick and dying cells – like those extensively harvested everyday after apoptosis – should be dominantly shepherded away by the body's phagocytic system so that they can be used as fuel for regeneration and, also, be sequestered away from competing micro-organisms. However, once the phagocytic clearance system fails (on the death of the whole organism) this debris becomes more freely available for environmentally ubiquitous heterotrophic bacteria (and other heterotrophs, like amoeboid cells and fungi). So the MAMPs of bacteria may be dominantly displayed as receptors for TLR "ligands" that then tap into a nutritional resource that is normally commandeered and shepherded away by host cells. So, an equally valid – if not better – perspective, is that bacteria use a similar system that animal cells have integrated a new pathway – developed anciently in heterotrophic bacteria – and refined it for its own management of sick and dying cells. Now that has an immediate resonance with the centrality of mitochondria (obligate microbial symbionts in animal cells) that are intimately involved in the mechanism of apoptosis.

I am guessing that this conjecture might well be worth pursuit. The first step would be to analyse the distribution of MAMPs in all bacteria – from those that populate the vicinity of deep ocean vents to dedicated pathogenic species. So far, I have not found articles that discuss the particular distribution of MAMPs in non-heterotrophs.

A further thought: it is possible that microbes deliberately display MAMPs to saturate the Toll-receptors of debris clearing cells. In the process, although they might sacrifice a proportion of their population, they would ensure an increased persistence of self cell debris for the survivors to proliferate. This might be worthy of investigation.