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Title: Production and cross-feeding of nitrite within Prochlorococcus populations
ABSTRACT

Prochlorococcusis an abundant photosynthetic bacterium in the open ocean, where nitrogen (N) often limits phytoplankton growth. In the low-light-adapted LLI clade ofProchlorococcus, nearly all cells can assimilate nitrite (NO2−), with a subset capable of assimilating nitrate (NO3−). LLI cells are maximally abundant near the primary NO2−maximum layer, an oceanographic feature that may, in part, be due to incomplete assimilatory NO3−reduction and subsequent NO2−release by phytoplankton. We hypothesized that someProchlorococcusexhibit incomplete assimilatory NO3−reduction and examined NO2−accumulation in cultures of threeProchlorococcusstrains (MIT0915, MIT0917, and SB) and twoSynechococcusstrains (WH8102 and WH7803). Only MIT0917 and SB accumulated external NO2−during growth on NO3−. Approximately 20–30% of the NO3−transported into the cell by MIT0917 was released as NO2−, with the rest assimilated into biomass. We further observed that co-cultures using NO3−as the sole N source could be established for MIT0917 andProchlorococcusstrain MIT1214 that can assimilate NO2−but not NO3−. In these co-cultures, the NO2−released by MIT0917 is efficiently consumed by its partner strain, MIT1214. Our findings highlight the potential for emergent metabolic partnerships that are mediated by the production and consumption of N cycle intermediates withinProchlorococcuspopulations.

IMPORTANCE

Earth’s biogeochemical cycles are substantially driven by microorganisms and their interactions. Given that N often limits marine photosynthesis, we investigated the potential for N cross-feeding within populations ofProchlorococcus, the numerically dominant photosynthetic cell in the subtropical open ocean. In laboratory cultures, someProchlorococcuscells release extracellular NO2−during growth on NO3−. In the wild,Prochlorococcuspopulations are composed of multiple functional types, including those that cannot use NO3−but can still assimilate NO2−. We show that metabolic dependencies arise whenProchlorococcusstrains with complementary NO2−production and consumption phenotypes are grown together on NO3−. These findings demonstrate the potential for emergent metabolic partnerships, possibly modulating ocean nutrient gradients, that are mediated by cross-feeding of N cycle intermediates.

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Award ID(s):
2048470
NSF-PAR ID:
10492689
Author(s) / Creator(s):
; ; ; ;
Editor(s):
Dubilier, Nicole
Publisher / Repository:
American Society for Microbiology
Date Published:
Journal Name:
mBio
ISSN:
2150-7511
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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