Growth and mortality of aerobic anoxygenic phototrophs in the North Pacific Subtropical Gyre

0585423 - MBÚ 2025 RIV US eng J - Journal Article
Koblížek, Michal - Ferrera, I. - Kolářová, Eva - Duhamel, S. - Popendorf, K. J. - Gasol, J. M. - Van Mooy, B. A. S.
Growth and mortality of aerobic anoxygenic phototrophs in the North Pacific Subtropical Gyre.
Applied and Environmental Microbiology. Roč. 90, č. 4 (2024), č. článku e0003224. ISSN 0099-2240. E-ISSN 1098-5336
R&D Projects: GA ČR(CZ) GX19-28778X
Institutional support: RVO:61388971
Keywords : photoheterotrophic bacteria * photosynthetic bacterium * oligotrophic gradient * surface waters * light * diversity * rates * bacteriochlorophyll * variability * phosphorus * aerobic anoxygenic phototrophs * bacteriochlorophyll a * marine bacteria * North Pacific Subtropical Gyre * Station ALOHA
OECD category: Microbiology
Impact factor: 4.4, year: 2022
Method of publishing: Open access
https://journals.asm.org/doi/10.1128/aem.00032-24

Aerobic anoxygenic phototrophic (AAP) bacteria harvest light energy using bacteriochlorophyll-containing reaction centers to supplement their mostly heterotrophic metabolism. While their abundance and growth have been intensively studied in coastal environments, much less is known about their activity in oligotrophic open ocean regions. Therefore, we combined in situ sampling in the North Pacific Subtropical Gyre, north of O'ahu island, Hawaii, with two manipulation experiments. Infra-red epifluorescence microscopy documented that AAP bacteria represented approximately 2% of total bacteria in the euphotic zone with the maximum abundance in the upper 50 m. They conducted active photosynthetic electron transport with maximum rates up to 50 electrons per reaction center per second. The in situ decline of bacteriochlorophyll concentration over the daylight period, an estimate of loss rates due to predation, indicated that the AAP bacteria in the upper 50 m of the water column turned over at rates of 0.75-0.90 d-1. This corresponded well with the specific growth rate determined in dilution experiments where AAP bacteria grew at a rate 1.05 +/- 0.09 d-1. An amendment of inorganic nitrogen to obtain N:P = 32 resulted in a more than 10 times increase in AAP abundance over 6 days. The presented data document that AAP bacteria are an active part of the bacterioplankton community in the oligotrophic North Pacific Subtropical Gyre and that their growth was mostly controlled by nitrogen availability and grazing pressure. IMPORTANCE Marine bacteria represent a complex assembly of species with different physiology, metabolism, and substrate preferences. We focus on a specific functional group of marine bacteria called aerobic anoxygenic phototrophs. These photoheterotrophic organisms require organic carbon substrates for growth, but they can also supplement their metabolic needs with light energy captured by bacteriochlorophyll. These bacteria have been intensively studied in coastal regions, but rather less is known about their distribution, growth, and mortality in the oligotrophic open ocean. Therefore, we conducted a suite of measurements in the North Pacific Subtropical Gyre to determine the distribution of these organisms in the water column and their growth and mortality rates. A nutrient amendment experiment showed that aerobic anoxygenic phototrophs were limited by inorganic nitrogen. Despite this, they grew more rapidly than average heterotrophic bacteria, but their growth was balanced by intense grazing pressure.
Permanent Link: https://hdl.handle.net/11104/0353132