Proteorhodopsin Phototrophy in Antarctic Coastal Waters

• Published in: mSphere
• Main Authors: Cifuentes-Anticevic, Jerónimo, Alcamán-Arias, María E., Alarcón-Schumacher, Tomás, Tamayo-Leiva, Javier, Pedrós-Alió, Carlos, Farías, Laura, Díez, Beatriz
• Format: Text
• Language: English
• Published: American Society for Microbiology 2021
• Subjects: Research Article; Antarctic; Southern Ocean; Austral; South Shetland Islands; Antarc*; Antarctica
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8386455/; http://www.ncbi.nlm.nih.gov/pubmed/34406852; https://doi.org/10.1128/mSphere.00525-21

Microbial proton-pumping rhodopsins are considered the simplest strategy among phototrophs to conserve energy from light. Proteorhodopsins are the most studied rhodopsins thus far because of their ubiquitous presence in the ocean, except in Antarctica, where they remain understudied. We analyzed proteorhodopsin abundance and transcriptional activity in the Western Antarctic coastal seawaters. Combining quantitative PCR (qPCR) and metagenomics, the relative abundance of proteorhodopsin-bearing bacteria accounted on average for 17, 3.5, and 29.7% of the bacterial community in Chile Bay (South Shetland Islands) during 2014, 2016, and 2017 summer-autumn, respectively. The abundance of proteorhodopsin-bearing bacteria changed in relation to environmental conditions such as chlorophyll a and temperature. Alphaproteobacteria, Gammaproteobacteria, and Flavobacteriia were the main bacteria that transcribed the proteorhodopsin gene during day and night. Although green light-absorbing proteorhodopsin genes were more abundant than blue-absorbing ones, the latter were transcribed more intensely, resulting in >50% of the proteorhodopsin transcripts during the day and night. Flavobacteriia were the most abundant proteorhodopsin-bearing bacteria in the metagenomes; however, Alphaproteobacteria and Gammaproteobacteria were more represented in the metatranscriptomes, with qPCR quantification suggesting the dominance of the active SAR11 clade. Our results show that proteorhodopsin-bearing bacteria are prevalent in Antarctic coastal waters in late austral summer and early autumn, and their ecological relevance needs to be elucidated to better understand how sunlight energy is used in this marine ecosystem. IMPORTANCE Proteorhodopsin-bearing microorganisms in the Southern Ocean have been overlooked since their discovery in 2000. The present study identify taxonomy and quantify the relative abundance of proteorhodopsin-bearing bacteria and proteorhodopsin gene transcription in the West Antarctic Peninsula’s coastal waters. This ...