The AEGEAN-169 clade of bacterioplankton is synonymous with SAR11 subclade V (HIMB59) and metabolically distinct

Abstract

Bacterioplankton of the SAR11 clade are the most abundant marine microorganisms and consist of numerous subclades spanning Order level divergence (Pelagibacterales). The assignment of the earliest diverging subclade V (a.k.a. HIMB59) to thePelagibacteralesis highly controversial, with multiple recent phylogenetic studies placing them completely separate from SAR11. Other than through phylogenomics, subclade V has not received detailed examination due to limited genomes from this group. Here, we assessed the ecogenomic characteristics of subclade V to better understand the role of this group in comparison to thePelagibacterales. We used a new isolate genome, recently released single amplified genomes (SAGs) and metagenome-assembled genomes (MAGs), and previously established SAR11 genomes to perform a comprehensive comparative genomics analysis. We paired this analysis with recruitment of metagenomes spanning open ocean, coastal, and brackish systems. Phylogenomics, average amino acid identity, and 16S rRNA gene phylogeny indicate that SAR11 subclade V is synonymous with the ubiquitous AEGEAN-169 clade, and support the contention that this group represents a taxonomic Family. AEGEAN-169 shared many bulk genome qualities with SAR11, such as streamlining and low GC content, but genomes were generally larger. AEGEAN-169 had overlapping distributions with SAR11 but was metabolically distinct from SAR11 in its potential to transport and utilize a broader range of sugars as well as in transport of trace metals and thiamin. Thus, regardless of the ultimate phylogenetic placement of AEGEAN-169, these organisms have distinct metabolic capacities that likely allow them to differentiate their niche from canonical SAR11 taxa.

Emergent Metabolic Niches for Marine Heterotrophs

“…When analyzed by taxonomic order, we found that the most sensitive taxa to substrate limitation across all compound classes were the Pelagibacterales (24.9% of models showed substantial growth reduction to at least one compound class), SAR86 (21.6% showed substantial growth reduction), and AEGEAN-169 (19.1% showed substantial growth reduction) (Supplemental Figure S5a). This is consistent with these groups being classically oligotrophic organisms with streamlined genomes and limited metabolic flexibility 17–19 . By contrast, the classically copiotrophic groups (the Enterobacterales , Sphingomonadales , and Rhodobacterales ) showed the least growth sensitivity to substrate reduction, with only 5.9%, 9.1% and 9.4% of these models showing substantial growth reduction across all compound classes, respectively (Supplemental Figure S5a).…”

New isolates refine the ecophysiology of the Roseobacter CHAB-I-5 lineage

“…S5, S7). This contrasts with other abundant free-living microorganisms like SAR11 and Aegean-169 which both have subclades adapted to lower salinities [70,82]. Other Roseobacter relatives have been isolated from brackish salinities as well [18,19,83,84], and CHAB-I-5 members have been observed in equivalent abundances along the salinity gradient of the Chesapeake Bay [14].…”

The Arctic summer microbiome across Fram Strait: Depth, longitude, and substrate concentrations structure microbial diversity in the euphotic zone

“…Nitrosomonas (ammonia oxidizers) and LS‐NOB (nitrite oxidizers) might perform shared denitrification (Lehtovirta‐Morley, 2018), although probably less effective than ammonia oxidation by archaea (Rasmussen & Francis, 2022). AEGEAN‐169 (recently designated as SAR11 clade V) can potentially utilize a broader range of CHOs than other SAR11 clades, and might participate in trace metal cycling and thiamin synthesis (Getz et al, 2023).…”