Bac­terial car­bon cyc­ling in high-lat­it­ude coastal sed­i­ments

In mar­ine sed­i­ments, het­ero­trophic mi­crobes are cent­ral to pro­cessing, ex­chan­ging and trans­form­ing or­ganic mat­ter, ul­ti­mately af­fect­ing how much of it is se­questered. To date, little is known about how these mi­cro­bial com­munit­ies change in com­pos­i­tion and sub­strate util­iz­a­tion across sea­sons. This is partly be­cause mi­cro­bial com­munit­ies in the sed­i­ment are very di­verse and com­plex, which poses meth­od­o­lo­gical chal­lenges for mi­cro­bial eco­logy in­vest­ig­a­tions. To ad­dress these chal­lenges, we de­veloped a sed­i­ment frac­tion­a­tion method that sep­ar­ates cells based on the de­gree of at­tach­ment to grains: cells in the pore­wa­ter (PW), firmly at­tached to sed­i­ment grains (FA), and those that are loosely at­tached to grains (LA). We then ap­plied this frac­tion­a­tion method to in­vest­ig­ate bac­terial car­bon cyc­ling in Arc­tic sed­i­ments. Our sampling sta­tion is loc­ated in Is­f­jorden, Sval­bard (78°N). It is within the Arc­tic Circle and is an­nu­ally sub­jec­ted to strong sea­sonal changes: dur­ing po­lar night, there are over three months with 24 hours of dark­ness, while dur­ing po­lar day, there are four months with 24 hours of sun­light. Since 2021, we have em­barked on five field cam­paigns for this pro­ject to sample sea­wa­ter and sur­face sed­i­ments across dif­fer­ent sea­sons. From our samples, we are in­vest­ig­at­ing how the above­men­tioned sed­i­ment cell frac­tions change and ad­apt to the ex­treme sea­son­al­ity in the Arc­tic. To do so, we are us­ing mul­tiple meth­od­o­lo­gical ap­proaches, such as 16S and meta­ge­n­omic se­quen­cing, fluor­es­cence in situ hy­brid­iz­a­tion and cell counts, oxy­gen con­sump­tion meas­ure­ments via mi­cro­sensors, and meas­ure­ment of poly­sac­char­ide hy­dro­lysis rates from in­cub­a­tions, among oth­ers. We have also col­lec­ted samples for the en­vir­on­mental char­ac­ter­iz­a­tion of our sampling sta­tion, which gives us in­sights into how car­bon, ni­tro­gen, and iron con­cen­tra­tions, sulfate re­duc­tion rates, pig­ments, etc., fluc­tu­ate throughout the year. Res­ults from these in­vest­ig­a­tions will provide more in­sights into the role of sed­i­ment bac­teria in the re­cyc­ling of or­ganic mat­ter in the Arc­tic.