Anthropogenic CO2emissions are projected to lower the pH of the ocean 0.3 units by 2100. Previous studies suggested that
- NSF-PAR ID:
- 10317574
- Editor(s):
- Stewart, Frank J.
- Date Published:
- Journal Name:
- Microbiology Resource Announcements
- ISSN:
- 2576-098X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Summary Prochlorococcus andSynechococcus , the numerically dominant phytoplankton in the oceans, have different responses to elevated CO2that may result in a dramatic shift in their relative abundances in future oceans. Here we showed that the exponential growth rates of these two genera respond to future CO2conditions in a manner similar to other cyanobacteria, butProchlorococcus strains had significantly lower realized growth rates under elevated CO2regimes due to poor survival after exposure to fresh culture media. Despite this, aSynechococcus strain was unable to outcompete aProchlorococcus strain in co‐culture at elevated CO2. Under these conditions,Prochlorococcus ' poor response to elevated CO2disappeared, andProchlorococcus' relative fitness showed negative frequency dependence, with both competitors having significant fitness advantages when initially rare. These experiments suggested that the two strains should be able to coexist indefinitely in co‐culture despite sharing nearly identical nutritional requirements. We speculate that negative frequency dependence exists due to reductive Black Queen evolution that has resulted in a passively mutualistic relationship analogous to that connectingProchlorococcus with the ‘helper’ heterotrophic microbes in its environment. -
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Synechococcus cyanobacteria owe their ubiquity in part to the wide pigment diversity of their light-harvesting complexes. In open ocean waters, cells predominantly possess sophisticated antennae with rods composed of phycocyanin and two types of phycoerythrins (PEI and PEII). Some strains are specialized for harvesting either green or blue light, while others can dynamically modify their light absorption spectrum to match the dominant ambient color. This process, called type IV chromatic acclimation (CA4), has been linked to the presence of a small genomic island occurring in two configurations (CA4-A and CA4-B). While the CA4-A process has been partially characterized, the CA4-B process has remained an enigma. Here we characterize the function of two members of the phycobilin lyase E/F clan, MpeW and MpeQ, inSynechococcus sp. strain A15-62 and demonstrate their critical role in CA4-B. While MpeW, encoded in the CA4-B island and up-regulated in green light, attaches the green light-absorbing chromophore phycoerythrobilin to cysteine-83 of the PEII α-subunit in green light, MpeQ binds phycoerythrobilin and isomerizes it into the blue light-absorbing phycourobilin at the same site in blue light, reversing the relationship of MpeZ and MpeY in the CA4-A strain RS9916. Our data thus reveal key molecular differences between the two types of chromatic acclimaters, both highly abundant but occupying distinct complementary ecological niches in the ocean. They also support an evolutionary scenario whereby CA4-B island acquisition allowed former blue light specialists to become chromatic acclimaters, while former green light specialists would have acquired this capacity by gaining a CA4-A island. -
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Dubilier, Nicole (Ed.)
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