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Coming full circle on diazotrophy in the marine cyanobacterium Trichodesmium
Friday, 2021/11/26 | 07:13:49
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Douglas G. Capone; PNAS November 23, 2021 118 (47) e2117967118
The marine, nonheterocystous cyanobacterium Trichodesmium has long been chronicled as a prominent and cosmopolitan feature of the surface waters of many tropical and subtropical areas of the ocean. Indeed, reports of its accumulation in blooms at the surface appear in the journals and logs of Charles Darwin, Captain James Cook, and his botanist, Joseph Banks (1⇓–3). Phycologists mapped its distribution in the sea beginning with the first major ocean plankton survey, the Great Plankton Expedition of 1899 (4). However, it was only in the early 1960s that Trichodesmium was first reported to be diazotrophic based on uptake of enriched 15N2 (i.e., capable of fixing dinitrogen) (5). This observation was met with some skepticism by cyanobacteriologists at the time as only those with heterocysts, the specialized cells which permit oxygen-sensitive nitrogenase activity in otherwise oxic environments, were then recognized to be diazotrophic (6). However, subsequent work demonstrating the presence of nitrogenase within cells of cultured Trichodesmium with immunological approaches (7, 8) and detection of the nif operon in its genome settled the matter (9). Research on Trichodesmium and other marine diazotrophs has since been ongoing and intense, expanding the diversity of known diazotrophs and the habitats within which this process occurs as well as the general importance of this process in the sea (10). Recent reports have confirmed the quantitative significance of Trichodesmium in many areas of the ocean and the marine nitrogen cycle (11) and satellite images document its wide global distribution (12) (Fig. 1). Indeed, it has been tacitly assumed that all Trichodesmium forms are diazotrophic. Now, Delmont (13) in PNAS brings us full circle with the discovery that several extant species of Trichodesmium in the sea are indeed lacking the apparatus for dinitrogen fixation.
See more https://www.pnas.org/content/118/47/e2117967118
Fig. 1. Images of Trichodesmium spp. from the wild at different scales. (A) Epifluorescent photomicrograph of Trichodesmium filaments with blue (450 to 490 nm) excitation for chlorophyll. (Scale bar, ∼100 µm.) (B) Epifluorescent image of the two most common colonial forms in parallel (“tufts”) and radial (“puffs”) alignment using green (510 to 560 nm) excitation for phycobiliproteins. (Scale bar, ∼1 mm.) (C) Surface photograph of a Trichodesmium bloom in the Capricorn Channel of the southern Great Barrier Reef. (D) Image from the International Space Shuttle of the coast of northwest Australia showing blooms of Trichodesmium at the surface on 3 December 2002. A and B image credit: Rachel Foster (Stockholm University, Stockholm, Sweden). D image credit: Earth Science and Remote Sensing Unit, NASA Johnson Space Center, Astronaut photograph ISS005-E-21572. |
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(176).png "Coming full circle on diazotrophy in the marine cyanobacterium Trichodesmium")
