Microbial ecology of the Southern Ocean

Abstract

The Southern Ocean (SO) distributes climate signals and nutrients worldwide, playing a pivotal role in global carbon sequestration. Microbial communities are essential mediators of primary productivity and carbon sequestration, yet we lack a comprehensive understanding of microbial diversity and functionality in the SO. Here, we examine contemporary studies in this unique polar system, focusing on prokaryotic communities and their relationships with other trophic levels (i.e. phytoplankton and viruses). Strong seasonal variations and the characteristic features of this ocean are directly linked to community composition and ecosystem functions. Specifically, we discuss characteristics of SO microbial communities and emphasise differences from the Arctic Ocean microbiome. We highlight the importance of abundant bacteria in recycling photosynthetically derived organic matter. These heterotrophs appear to control carbon flux to higher trophic levels when light and iron availability favour primary production in spring and summer. Conversely, during winter, evidence suggests that chemolithoautotrophs contribute to prokaryotic production in Antarctic waters. We conclude by reviewing the effects of climate change on marine microbiota in the SO.

Structure and dispersion of the conjugative mobilome in surface ocean bacterioplankton

“…Hence, it is possible to observe marine taxa with known global distribution, such as SAR11, Flavobacteriales and Rhodobacterales [ 21 , 25 ]. Consistent with the literature, the Southern Ocean is an isolated region where the conditions shape bacterioplankton communities differently from other oceanic regions (including the Arctic Ocean), as well as driven by seasonal eukaryotic phytoplankton blooms, which boost primary production in this oceanic region [ 72 ]. All of the above give rise to unique cellular OTUs [ 21 ], as also observed in the mobilome revealed by this study.…”

Phylogenomic analysis expands the known repertoire of single-stranded DNA viruses in benthic zones of the South Indian Ocean

“…Despite the importance of the SIO in modulating global climate and heat uptake in the ocean [ 1 , 42 , 98 ], we lack taxonomic insights regarding the functional roles of viruses. Using two of the most widely used pipelines [ 54 , 99 ], we explored viral communities in deep SIO waters.…”

“…Disentangling the phylogenetically diverse assemblages of bacteria, fungi, phytoplankton, and viruses and their contributions to ecosystem services in the global ocean remains a major endeavour. There is strong evidence that these assemblages influence the biological carbon pump in marine environments [ 1 , 2 ]. Among these assemblages, viruses are the most numerically abundant [ 3 ], and recent evidence has demonstrated their profound influence on prokaryotic lifestyles in the oceans [ 4–8 ].…”

Environmental control and metabolic strategies of organic‐matter‐responsive bacterioplankton in the Weddell Sea (Antarctica)

“…Numerous studies have provided insights into the species‐specific temperature responses of cultured isolates and have identified many psychrophilic specialists able to optimize their metabolism and cellular features to enable life at extremely low temperature (D'Amico et al, 2006). However, culture‐independent approaches have demonstrated that in addition to endemic specialists, many cosmopolitan bacterial taxa sufficiently tolerate the Antarctic marine environment (Castillo et al, 2022; Delmont et al, 2014; Liu et al, 2020; Luria et al, 2017; Piontek et al, 2022). Recent studies using high‐throughput sequencing technologies identified key taxa in bacterial communities of Antarctic marginal seas that were mainly assigned to genera of the orders Flavobacteriales , Chitinophagales (both Bacteroidia ), Rhodobacterales ( Alphaproteobacteria ), Cellvibrionales and Pseudomonadales (both Gammaproteobacteria ) (Delmont et al, 2014; Grzymski et al, 2012; Luria et al, 2016; Piontek et al, 2022).…”