Abstract
AbstractThe cyanobacterium Prochlorococcus is the most abundant photosynthetic cell on Earth and contributes to global ocean carbon cycling and food webs. Prochlorococcus is known for its extensive diversity that falls into two groups of ecotypes, the low‐light (LL) and high‐light (HL) adapted ecotypes. Previous work has shown niche partitioning of the very abundant HL adapted ecotypes and subecotypes across oceanographic gradients including temperature, nutrients, and day length. However, niche partitioning of subecotypes within the LL adapted ecotypes has not been studied as well because they are less abundant and less accessible than surface, HL populations. Through high‐throughput, cyanobacterial‐specific, sequencing of high‐resolution depth profiles from three stations across the North Pacific Subtropical Front, we discovered extensive diversity and strong latitudinal partitioning of subecotype populations within LL ecotypes, in contrast to fairly consistent patterns at the broader level of LL Prochlorococcus ecotypes. These results indicate that both shallow and deep‐water processes shape microbial community structure in this region despite strong connectivity in microbial communities across the North Pacific Subtropical Front, supported by a few HL and LL sequences found ubiquitously across stations. This study expands understanding of the diversity and complexity of Prochlorococcus community structure over oceanographic gradients.
Highlights
Author Contribution Statement: A.W.T. conceived of the research project and carried out data analysis and writing
We examined the positioning of the three stations relative to temperature and salinity transitions that define the subtropical domain, subtropical front, and subtropical to subarctic transition zone according to Roden (1991)
This work expands to the low light” (LL) Prochlorococcus ecotypes the understanding that ecologically distinct taxa occur within coherent ecotypes of picocyanobacteria as shown previously for Synechococcus (Pittera et al 2014; Farrant et al 2016; Ahlgren et al 2019) and HL Prochlorococcus (Larkin et al 2016)
Summary
Author Contribution Statement: A.W.T. conceived of the research project and carried out data analysis and writing. K.K. carried out sampling during the cruise, chose sampling locations based on oceanographic conditions, processed samples, and contributed to the writing of the manuscript. Prochlorococcus HLII subecotype patterns are apparent at the single cell level. In. Low light Prochlorococcus terms of gene content, single cells form cohesive subpopulations that have distinct and complementary shifts in abundance with seasonal changes in ocean conditions (Kashtan et al 2014, 2017). Subecotypes of the closely related picocyanobacterium Synechococcus have distinct abundance patterns across oceanographic gradients and time (Tai et al 2011; Farrant et al 2016; Ahlgren et al 2019)
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