Browsing by Author "Alcaman-Arias, Maria E."

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    Dark Diazotrophy during the Late Summer in Surface Waters of Chile Bay, West Antarctic Peninsula
    (2022) Alcaman-Arias, Maria E.; Cifuentes-Anticevic, Jeronimo; Castillo-Inaipil, Wilson; Farias, Laura; Sanhueza, Cynthia; Fernandez-Gomez, Beatriz; Verdugo, Josefa; Abarzua, Leslie; Ridley, Christina; Tamayo-Leiva, Javier; Diez, Beatriz
    Although crucial for the addition of new nitrogen in marine ecosystems, dinitrogen (N-2) fixation remains an understudied process, especially under dark conditions and in polar coastal areas, such as the West Antarctic Peninsula (WAP). New measurements of light and dark N-2 fixation rates in parallel with carbon (C) fixation rates, as well as analysis of the genetic marker nifH for diazotrophic organisms, were conducted during the late summer in the coastal waters of Chile Bay, South Shetland Islands, WAP. During six late summers (February 2013 to 2019), Chile Bay was characterized by high NO3- concentrations (similar to 20 mu M) and an NH4+ content that remained stable near 0.5 mu M. The N:P ratio was approximately 14.1, thus close to that of the Redfield ratio (16:1). The presence of Cluster I and Cluster III nifH gene sequences closely related to Alpha-, Delta- and, to a lesser extent, Gammaproteobacteria, suggests that chemosynthetic and heterotrophic bacteria are primarily responsible for N-2 fixation in the bay. Photosynthetic carbon assimilation ranged from 51.18 to 1471 nmol C L-1 d(-1), while dark chemosynthesis ranged from 9.24 to 805 nmol C L-1 d(-1). N2 fixation rates were higher under dark conditions (up to 45.40 nmol N L-1 d(-1)) than under light conditions (up to 7.70 nmol N L-1 d(-1)), possibly contributing more than 37% to new nitrogen-based production (>2.5 g N m(-2) y(-1)). Of all the environmental factors measured, only PO43--exhibited a significant correlation with C and N-2 rates, being negatively correlated (p < 0.05) with dark chemosynthesis and N-2 fixation under the light condition, revealing the importance of the N:P ratio for these processes in Chile Bay. This significant contribution of N-2 fixation expands the ubiquity and biological potential of these marine chemosynthetic diazotrophs. As such, this process should be considered along with the entire N cycle when further reviewing highly productive Antarctic coastal waters and the diazotrophic potential of the global marine ecosystem.
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    Proteorhodopsin Phototrophy in Antarctic Coastal Waters
    (2021) Cifuentes-Anticevic, Jeronimo; Alcaman-Arias, Maria E.; Alarcon-Schumacher, Tomas; Tamayo-Leiva, Javier; Pedros-Alio, Carlos; Farias, Laura; Diez, Beatriz
    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.
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    Surface Ammonia-Oxidizer Abundance During the Late Summer in the West Antarctic Coastal System
    (2022) Alcaman-Arias, Maria E.; Cifuentes-Anticevic, Jeronimo; Diez, Beatriz; Testa, Giovanni; Troncoso, Macarena; Bello, Estrella; Farias, Laura
    Marine ammonia oxidizers that oxidize ammonium to nitrite are abundant in polar waters, especially during the winter in the deeper mixed-layer of West Antarctic Peninsula (WAP) waters. However, the activity and abundance of ammonia-oxidizers during the summer in surface coastal Antarctic waters remain unclear. In this study, the ammonia-oxidation rates, abundance and identity of ammonia-oxidizing bacteria (AOB) and archaea (AOA) were evaluated in the marine surface layer (to 30 m depth) in Chile Bay (Greenwich Island, WAP) over three consecutive late-summer periods (2017, 2018, and 2019). Ammonia-oxidation rates of 68.31 nmol N L-1 day(-1) (2018) and 37.28 nmol N L-1 day(-1) (2019) were detected from illuminated 2 m seawater incubations. However, high ammonia-oxidation rates between 267.75 and 109.38 nmol N L-1 day(-1) were obtained under the dark condition at 30 m in 2018 and 2019, respectively. During the late-summer sampling periods both stratifying and mixing events occurring in the water column over short timescales (February-March). Metagenomic analysis of seven nitrogen cycle modules revealed the presence of ammonia-oxidizers, such as the Archaea Nitrosopumilus and the Bacteria Nitrosomonas and Nitrosospira, with AOA often being more abundant than AOB. However, quantification of specific amoA gene transcripts showed number of AOB being two orders of magnitude higher than AOA, with Nitrosomonas representing the most transcriptionally active AOB in the surface waters. Additionally, Candidatus Nitrosopelagicus and Nitrosopumilus, phylogenetically related to surface members of the NP-epsilon and NP-gamma clades respectively, were the predominant AOA. Our findings expand the known distribution of ammonium-oxidizers to the marine surface layer, exposing their potential ecological role in supporting the marine Antarctic system during the productive summer periods.