Microscopy evidence of bacterialmicrofossils in phosphorite crusts of the Peruvian shelf: Implications for phosphogenesis mechanisms

International audiencePhosphorites are sedimentary formations enriched in Ca-phosphate minerals. The precipitation of these minerals is thought to be partlymediated by the activity of microorganisms. The vast majority of studies on phosphorites have focused on a petrological and geochemical characterization of these rocks. However, detailed descriptions are needed at the sub-micrometer scale atwhich crucial information can be retrieved about traces of past ormodern microbial activities. Here, scanning electron microscopy (SEM) analyses of a recent phosphorite crust from the upwelling-style phosphogenesis area off Peru revealed that it contained a great number of rod-like and coccus-like shaped micrometer-sized (~1.1 μm and 0.5 μm, respectively) objects, referred to as biomorphs. Some of these biomorphs were filled with carbonate fluoroapatite (CFA, a calcium-phosphate phase common in phosphorites); some were empty; some were surrounded by one or two layers of pyrite. Transmission electron microscopy (TEM) and energy dispersive X-ray spectrometry (EDXS) analyses were performed on focused ion beam(FIB)milled ultrathin foils to characterize the texture of CFA and pyrite in these biomorphs at the fewnanometer scale. Non-pyritized phosphatic biomorphswere surrounded by a thin (5-15 nmthick) rimappearing as a void on TEM images. Bundles of CFA crystals sharing the same crystallographic orientations (aligned along their c-axis) were found in the interior of some biomorphs. Pyrite formed a thick (~35-115 nm) layer with closely packed crystals surrounding the pyritized biomorphs, whereas pyrite crystals at distance from the biomorphs were smaller and distributed more sparsely. Scanning transmission X-ray microscopy (STXM) analyses performed at the C K-edge provided maps of organic and inorganic carbon in the samples. Inorganic C, mainly present as carbonate groups in the CFA lattice, was homogeneously distributed, whereas organic C was concentrated in the rims of the phosphatic biomorphs. Finally, STXM analyses at the Fe L2,3-edges together with TEMEDXS analyses, revealed that some pyritized biomorphs experienced partial oxidation. The mineralogical features of these phosphatic biomorphs are very similar to those formed by bacteria having precipitated phosphate minerals intra- and extracellularly in laboratory experiments. Similarly, pyritized biomorphs resemble bacteria encrusted by pyrite. We therefore interpret phosphatic and pyritized biomorphs present in the Peruvian phosphorite crust as microorganisms fossilized near the boundary of zones of sulfate reduction. The implications of these observations are then discussed in the light of the different possible and non-exclusive microbiallydriven phosphogenesis mechanisms that have been proposed in the past: (i) Organic matter mineralization, in particular mediated by iron reducing bacteria and/or sulfate-reducing bacteria (SRB), (ii) reduction of iron- (oxyhydr)oxides by iron-reducing bacteria and/or SRB, and (iii) polyphosphate metabolism in sulfide-oxidizing bacteria, possibly associated with SR

Resistance-associated point mutations of organophosphate insensitive acetylcholinesterase, in the olive fruit fly Bactrocera oleae

A 2.2-kb full length cDNA containing an ORF encoding a putative acetylcholinesterase (AChE) precursor of 673 amino acid residues was obtained by a combined degenerate PCR and RACE strategy from an organophosphate-susceptible Bactrocera oleae strain. A comparison of cDNA sequences of individual insects from susceptible and resistant strains, coupled with an enzyme inhibition assay with omethoate, indicated a novel glycine-serine substitution (G488S), at an amino acid residue which is highly conserved across species (13396 of Torpedo californica AChE), as a likely cause of AChE insensitivity. This mutation was also associated with a 35-40% reduction in AChE catalytic efficiency. The I199V substitution, which confers low levels of resistance in Drosophila, was also present in B. oleae (I214V) and in combination with G488S produced up to a 16-fold decrease in insecticide sensitivity. This is the first agricultural pest where resistance has been associated with an alteration in AChE, which arises from point mutations located within the active site gorge of the enzyme

Microbiome Hijacking Towards an Integrative Pest Management Pipeline

Pesticides are necessary to fight agricultural pests, yet they are often nonspecific, and their widespread use is a hazard to the environment and human health. The genomic era allows for new approaches to specifically target agricultural pests, based on analysis of their genome and their microbiome. We present such an approach, to combat Bactrocera oleae, a widespread pest whose impact is devastating on olive production. To date, there is no specific pesticide to control it. Herein, we propose a novel strategy to manage this pest via identifying novel pharmacological targets on the genome of its obligate endosymbiotic bacterium Candidatus Erwinia dacicola. Three genes were selected as pharmacological targets. The 3D models of the Helicase, Polymerase, and Protease-C gene products were designed and subsequently optimized by means of molecular dynamics simulations. Successively, a series of structure-based pharmacophore models were elucidated in an effort to pave the way for the efficient high-throughput virtual screening of libraries of low molecular weight compounds and thus the discovery of novel modulating agents. Our methodology provides the means to design, test, and identify highly specific pest control substances that minimize the impact of toxic chemicals on health, economy, and the environment. © Springer Nature Switzerland AG 2020

Magnetotactic bacteria form magnetite from a phosphate-rich ferric hydroxide via nanometric ferric (oxyhydr)oxide intermediates

The iron oxide mineral magnetite (Fe(3)O(4)) is produced by various organisms to exploit magnetic and mechanical properties. Magnetotactic bacteria have become one of the best model organisms for studying magnetite biomineralization, as their genomes are sequenced and tools are available for their genetic manipulation. However, the chemical route by which magnetite is formed intracellularly within the so-called magnetosomes has remained a matter of debate. Here we used X-ray absorption spectroscopy at cryogenic temperatures and transmission electron microscopic imaging techniques to chemically characterize and spatially resolve the mechanism of biomineralization in those microorganisms. We show that magnetite forms through phase transformation from a highly disordered phosphate-rich ferric hydroxide phase, consistent with prokaryotic ferritins, via transient nanometric ferric (oxyhydr)oxide intermediates within the magnetosome organelle. This pathway remarkably resembles recent results on synthetic magnetite formation and bears a high similarity to suggested mineralization mechanisms in higher organisms

Intracellular Ca-carbonate biomineralization is widespread in cyanobacteria.

International audienceCyanobacteria have played a significant role in the formation of past and modern carbonate deposits at the surface of the Earth using a biomineralization process that has been almost systematically considered induced and extracellular. Recently, a deep-branching cyanobacterial species, Candidatus Gloeomargarita lithophora, was reported to form intracellular amorphous Ca-rich carbonates. However, the significance and diversity of the cyanobacteria in which intracellular biomineralization occurs remain unknown. Here, we searched for intracellular Ca-carbonate inclusions in 68 cyanobacterial strains distributed throughout the phylogenetic tree of cyanobacteria. We discovered that diverse unicellular cyanobacterial taxa form intracellular amorphous Ca-carbonates with at least two different distribution patterns, suggesting the existence of at least two distinct mechanisms of biomineralization: (i) one with Ca-carbonate inclusions scattered within the cell cytoplasm such as in Ca. G. lithophora, and (ii) another one observed in strains belonging to the Thermosynechococcus elongatus BP-1 lineage, in which Ca-carbonate inclusions lie at the cell poles. This pattern seems to be linked with the nucleation of the inclusions at the septum of the cells, showing an intricate and original connection between cell division and biomineralization. These findings indicate that intracellular Ca-carbonate biomineralization by cyanobacteria has been overlooked by past studies and open new perspectives on the mechanisms and the evolutionary history of intra- and extracellular Ca-carbonate biomineralization by cyanobacteria

Magnetotactic bacteria form magnetite from a phosphate-rich ferric hydroxide via nanometric ferric (oxyhydr)oxide intermediates

The iron oxide mineral magnetite (Fe(3)O(4)) is produced by various organisms to exploit magnetic and mechanical properties. Magnetotactic bacteria have become one of the best model organisms for studying magnetite biomineralization, as their genomes are sequenced and tools are available for their genetic manipulation. However, the chemical route by which magnetite is formed intracellularly within the so-called magnetosomes has remained a matter of debate. Here we used X-ray absorption spectroscopy at cryogenic temperatures and transmission electron microscopic imaging techniques to chemically characterize and spatially resolve the mechanism of biomineralization in those microorganisms. We show that magnetite forms through phase transformation from a highly disordered phosphate-rich ferric hydroxide phase, consistent with prokaryotic ferritins, via transient nanometric ferric (oxyhydr)oxide intermediates within the magnetosome organelle. This pathway remarkably resembles recent results on synthetic magnetite formation and bears a high similarity to suggested mineralization mechanisms in higher organisms