Single-Cell Measurements and Modelling Reveal Substantial Organic Carbon Acquisition by Prochlorococcus

Author:IMBeR IPO Date:2023-02-27 Hits:29


Single-Cell Measurements and Modelling Reveal Substantial Organic Carbon Acquisition by Prochlorococcus

作者: Zhen Wu, Dikla Aharonovich, Dalit Roth-Rosenberg, Osnat Weissberg, Tal Luzzatto-Knaan, Angela Vogts, Luca Zoccarato, Falk Eigemann, Hans-Peter Grossart, Maren Voss, Michael J. Follows and Daniel Sher

期刊: Nature Microbiology

Marine phytoplankton are responsible for about half of the photosynthesis on Earth. Many are mixotrophs, combining photosynthesis with heterotrophic assimilation of organic carbon, but the relative contribution of these two lifestyles is unclear. Here single-cell measurements reveal that Prochlorococcus at the base of the photic zone in the Eastern Mediterranean Sea obtain only ~20% of carbon required for growth by photosynthesis. This is supported by laboratory-calibrated calculations based on photo-physiology parameters and compared with in situ growth rates. Agent-based simulations show that mixotrophic cells could grow tens of metres deeper than obligate photo-autotrophs, deepening the nutricline by ~20 m. Time series from the North Atlantic and North Pacific indicate that, during thermal stratification, on average 8–10% of the Prochlorococcus cells live without enough light to sustain obligate photo-autotrophic populations. Together, these results suggest that mixotrophy underpins the ecological success of a large fraction of the global Prochlorococcuspopulation and its collective genetic diversity.

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Fig. 3 a, Depth profiles of PAR, NO2 + NO3 and chlorophyll (Chl). b, Phytoplankton cell counts using flow cytometry. c, Relative abundance of different Prochlorococcus clades across the water column, determined by ITS sequencing (HLI denotes high-light-adapted clade I, HLII denotes high-light-adapted clade II, LLI denotes low-light-adapted clade I, LLII/III denotes low-light-adapted clades II and III, LLIV denotes low-light-adapted clade IV, LLVII denotes low-light-adapted clade VII, Syn denotes Synechococcus). d, Density plots of Prochlorococcus per-cell chlorophyll fluorescence (FL). Note the change in chlorophyll fluorescence (d) without a concomitant change in population structure (c) between 65 m and 100 m. Note also the presence of LL clades above 115 m and HL clades at 125 m (c) while a double population is observed only at 115 m (d). The circles in d represent the populations sorted and analysed by NanoSIMS, and are colour-coded as in ee, Density plots of the ratios of C-specific C uptake rate (μC) to N-specific N uptake rate (μN) from NanoSIMS analysis of each sorted subpopulation from 115 m, the single population from 125 m, and lab cultures. The numbers of cells measured in each population are 45 (LL 115 m), 49 (HL 115 m), 55 (125 m) and 489 (lab culture).The scatter plots and gates used for these analyses are shown in Extended Data Fig. 1