One Hun­dred Mil­lion Year Old Polyamines

Who Would Have Thought?

by Elio

Pa­le­on­tol­o­gists are greatly helped in their work by find­ing or­ganic com­pounds that have been pre­served in fos­sils through the ages. Most use­ful among these are the amaz­ingly sta­ble poly­cyclic ter­penoid lipids, in par­tic­u­lar the bac­te­r­ial hopanoids (Click here and here), that are present in fos­sils about 2.4 bil­lion years old. But it helps to have other classes of com­pounds at hand. This is es­pe­cially true for ni­tro­gen-con­tain­ing ones, which are ab­sent in hopanoids and the like, and could be used as in­di­ca­tors of changes in the ni­tro­gen cy­cle over ge­o­logic time.

Chem­i­cal struc­ture of the most abun­dant singly charged [M+H]+ long-chain polyamine (LCPA), with n = 1–6 N‑methyl propy­leneimine re­peated units. Source

And here come the good news. A re­cent study re­ported the pres­ence of un­usu­ally long-chain polyamines in the old­est known fos­sil di­atoms, which go back to some 100 mil­lion years ago. Us­ing some ad­vanced mass spec­trom­e­try (MS) an­a­lytic tech­niques called HPLC-ESI-MS and HPLC-QToa-TOF-MS, the au­thors demon­strated that the di­atom fos­sils con­tain a large num­ber of polyamines rang­ing in chain length from 12 to 52 car­bons. The au­thors pro­pose that these mol­e­cules were pre­served by en­cap­su­la­tion as the glassy shells of the di­atoms were formed. Amaz­ingly, the fos­sils' polyamines have the same struc­ture as those formed by mod­ern di­atoms, thus, they were able with­stand the pass of time and are pre­served in­tact. The fos­silized di­atoms lived in the Lower Cre­ta­ceous, a time that was par­tic­u­larly pro­pi­tious for di­atom de­vel­op­ment due to the high con­cen­tra­tions of CO₂ in the at­mos­phere and the abun­dance of sil­ica in the oceans. It is likely that the polyamines par­tic­i­pated (as they do now) in the de­po­si­tion of the diatom's shells by com­bin­ing with sil­ica and mak­ing in­sol­u­ble ag­gre­gates. But they may have played ad­di­tional roles, based on the var­i­ous func­tions of the present day polyamines. These func­tions range from reg­u­la­tion of vir­u­lence genes in bac­te­ria and epi­ge­netic switches in eu­kary­otic cells to senes­cence in plants, just to name a few.

Scan­ning Elec­tron mi­cro­graphs of sol­vent-and acid-cleaned fos­sil di­atom shells or frus­tules show well-pre­served struc­tural de­tails that match well the shell struc­ture of mod­ern di­atoms. This demon­strates that di­a­ge­netic al­ter­ations were mi­nor dur­ing fos­siliza­tion. (Di­a­ge­n­e­sis is the term used by ge­ol­o­gists for changes af­ter sed­i­ments are de­posited). Source

Find­ing these an­cient or­ganic com­pounds has wider ram­i­fi­ca­tions. In the au­thors' own words: The use of re­cal­ci­trant long-chain polyamine bio­mark­ers of­fers a promis­ing ap­proach for re­con­struct­ing the bio­geo­chem­istry of the photic zone and to ul­ti­mately iden­tify the links be­tween nu­tri­ent cy­cling, bi­o­log­i­cal pro­duc­tiv­ity, and cli­mate change across abrupt cli­mate change events in the ge­o­log­i­cal record. Who would have thought!