Abstract
This study reports the discovery of Aster-Like Nanoparticles (ALNs) in pelagic environments. ALNs are pleomorphic, with three dominant morphotypes which do not fit into any previously defined environmental entities [i.e., ultramicro-prokaryotes, controversed nanobes, and non-living particles (biomimetic mineralo-organic particles, natural nanoparticles or viruses)] of similar size. Elemental composition and selected-area electron diffraction patterns suggested that the organic nature of ALNs may prevail over the possibility of crystal structures. Likewise, recorded changes in ALN numbers in the absence of cells are at odds with an affiliation to until now described viral particles. ALN abundances showed marked seasonal dynamics in the lakewater, with maximal values (up to 9.0 ± 0.5 × 107 particles·mL−1) reaching eight times those obtained for prokaryotes, and representing up to about 40% of the abundances of virus-like particles. We conclude that (i) aquatic ecosystems are reservoirs of novel, abundant, and dynamic aster-like nanoparticles, (ii) not all virus-like particles observed in aquatic systems are necessarily viruses, and (iii) there may be several types of other ultra-small particles in natural waters that are currently unknown but potentially ecologically important.
Highlights
Recent advances in environmental and nanoparticle sciences have helped to reveal an unexpected diversity of living and non-living femto-entities (0.02–0.2 μm as defined for femtoplankton by Sieburth et al, 1978) in the environment
The composition and the amorphous structure revealed by electronic microscopy (Figure 4) point out that Aster-Like Nanoparticles (ALNs) are possible organic particles (Uwins et al, 1998; Benzerara et al, 2003), or at least that their organic content may prevailed over their mineral composition known from mineral forming nanobes (Kajander et al, 2003), biomimetic mineralo-organic particles (BMOPs) or “natural nanoparticles” (Wu et al, 2016; Griffin et al, 2018), partly or totally composed of minerals
This study shows, for the first time, that aquatic ecosystems may contain abundant and dynamic nanoparticles of a novel type with ecological potentialities, especially in meso- and eutrophic waters which are predilection sites for ALN detection
Summary
Recent advances in environmental and nanoparticle sciences have helped to reveal an unexpected diversity of living and non-living femto-entities (0.02–0.2 μm as defined for femtoplankton by Sieburth et al, 1978) in the environment. Only ultramicro-prokaryotes are clearly affiliated to living organisms according to the volumetric criteria advanced by the National Research Council (1999), i.e., the theoretical minimal cell volume (TMCV) sufficient to house nucleic acids and the associated biosynthetic machinery is at 0.008 μm. Only ultramicro-prokaryotes are clearly affiliated to living organisms according to the volumetric criteria advanced by the National Research Council (1999), i.e., the theoretical minimal cell volume (TMCV) sufficient to house nucleic acids and the associated biosynthetic machinery is at 0.008 μm3 Though these new entities were described in natural environments, relatively little is known about their ecological significance. Characterizing the femtoplankton biomass and the diversity of its representatives seems crucial to our understanding of the functioning of aquatic ecosystems
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