@article{fdi:010073183,
  title = {{P}rogrammed cell death in diazotrophs and the fate of organic matter in the western tropical {S}outh {P}acific {O}cean during the {OUTPACE} cruise},
  author = {{S}pungin, {D}. and {B}elkin, {N}. and {F}oster, {R}. {A}. and {S}tenegren, {M}. and {C}aputo, {A}. and {P}ujo-{P}ay, {M}. and {L}eblond, {N}. and {D}upouy, {C}{\'e}cile and {B}onnet, {S}ophie and {B}erman-{F}rank, {I}.},
  editor = {},
  language = {{ENG}},
  abstract = {{T}he fate of diazotroph ({N}-2 fixers) derived carbon ({C}) and nitrogen ({N}) and their contribution to vertical export of {C} and {N} in the western tropical {S}outh {P}acific {O}cean was studied during {OUTPACE} ({O}ligotrophy to {U}l{T}ra-oligotrophy {PAC}ific {E}xperiment). {O}ur specific objective during {OUTPACE} was to determine whether autocatalytic programmed cell death ({PCD}), occurring in some diazotrophs, is an important mechanism affecting diazotroph mortality and a factor regulating the vertical flux of organic matter and, thus, the fate of the blooms. {W}e sampled at three long duration ({LD}) stations of 5 days each ({LDA}, {LDB} and {LDC}) where drifting sediment traps were deployed at 150, 325 and 500m depth. {LDA} and {LDB} were characterized by high chlorophyll a ({C}hl a) concentrations (0.2-0.6 mu g {L}-1) and dominated by dense biomass of the filamentous cyanobacterium {T}richodesmium as well as {UCYN}-{B} and diatom-diazotroph associations ({R}hizosolenia with {R}ichelia-detected by microscopy and het-1 nif{H} copies). {S}tation {LDC} was located at an ultra-oligotrophic area of the {S}outh {P}acific gyre with extremely low {C}hl a concentration (similar to 0.02 mu g {L}-1) with limited biomass of diazotrophs predominantly the unicellular {UCYN}-{B}. {O}ur measurements of biomass from {LDA} and {LDB} yielded high activities of caspase-like and metacaspase proteases that are indicative of {PCD} in {T}richodesmium and other phytoplankton. {M}etacaspase activity, reported here for the first time from oceanic populations, was highest at the surface of both {LDA} and {LDB}, where we also obtained high concentrations of transparent exopolymeric particles ({TEP}). {TEP} were negatively correlated with dissolved inorganic phosphorus and positively coupled to both the dissolved and particulate organic carbon pools. {O}ur results reflect the increase in {TEP} production under nutrient stress and its role as a source of sticky carbon facilitating aggregation and rapid vertical sinking. {E}vidence for bloom decline was observed at both {LDA} and {LDB}. {H}owever, the physiological status and rates of decline of the blooms differed between the stations, influencing the amount of accumulated diazotrophic organic matter and mass flux observed in the traps during our experimental time frame. {A}t {LDA} sediment traps contained the greatest export of particulate matter and significant numbers of both intact and decaying {T}richodesmium, {UCYN}-{B} and het-1 compared to {LDB} where the bloom decline began only 2 days prior to leaving the station and to {LDC} where no evidence for bloom or bloom decline was seen. {S}ubstantiating previous findings from laboratory cultures linking {PCD} to carbon export in {T}richodesmium, our results from {OUTPACE} indicate that nutrient limitation may induce {PCD} in high biomass blooms such as displayed by {T}richodesmium or diatom-diazotroph associations. {F}urthermore, {PCD} combined with high {TEP} production will tend to facilitate cellular aggregation and bloom termination and will expedite vertical flux to depth.},
  keywords = {{PACIFIQUE} {SUD}},
  booktitle = {},
  journal = {{B}iogeosciences},
  volume = {15},
  numero = {12},
  pages = {3893--3908},
  ISSN = {1726-4170},
  year = {2018},
  DOI = {10.5194/bg-15-3893-2018},
  URL = {https://www.documentation.ird.fr/hor/fdi:010073183},
}