Deep Learning Applied to SEM Images for Supporting Marine Coralline Algae Classification

The classification of coralline algae commonly relies on the morphology of cells and reproductive structures, along with thallus organization, observed through Scanning Electron Microscopy (SEM). Nevertheless, species identification based on morphology often leads to uncertainty, due to their general plasticity. Evolutionary and environmental studies featured coralline algae for their ecological significance in both recent and past Oceans and need to rely on robust taxonomy. Research efforts towards new putative diagnostic tools have recently been focused on cell wall ultrastructure. In this work, we explored a new classification tool for coralline algae, using fine-tuning pretrained Convolutional Neural Networks (CNNs) on SEM images paired to morphological categories, including cell wall ultrastructure. We considered four common Mediterranean species, classified at genus and at the species level (Lithothamnion corallioides, Mesophyllum philippii, Lithophyllum racemus, Lithophyllum pseudoracemus). Our model produced promising results in terms of image classification accuracy given the constraint of a limited dataset and was tested for the identification of two ambiguous samples referred to as L. cf. racemus. Overall, explanatory image analyses suggest a high diagnostic value of calcification patterns, which significantly contributed to class predictions. Thus, CNNs proved to be a valid support to the morphological approach to taxonomy in coralline algae.

PERMEABILIZATION, CELL WALL ULTRASTRUCTURE, AND GERMINATION OF BASIDIOSPORES OF THE ECTOMYCORRHIZAL FUNGUS Pisolithus microcarpus TREATED WITH DIFFERENT COMMERCIAL BRANDS OF BLEACH

ABSTRACT Basidiospores of the ectomycorrhizal fungus Pisolithus microcarpus have an impermeable cell wall, a characteristic that is possibly related to the low germination percentages of these propagules, which makes it difficult to obtain monokaryons and use these spores in inoculants. The objective of this study was to evaluate the effect of different concentrations of commercial bleach on the permeabilization of P. microcarpus basidiospores and to analyze the alterations caused in the cell wall ultrastructure and the viability and germination capacity of these propagules. Fungal basidiospores were collected in eucalyptus plantations and permeabilized using different bleach concentrations and exposure times. The basidiospores were then analyzed by scanning and transmission electron microscopy. The percentage of permeabilized basidiospores varied with the commercial brand, bleach concentration, and exposure time. Basidiospores of different basidiocarps differed in susceptibility to permeabilization treatment with bleach. Changes in the ultrastructure of permeabilized basidiospores were observed at bleach concentrations of 15 and 50 % for an exposure time of 40 s, with surface changes and loss of the spicules of the outermost layer of the wall. After permeabilization with 5 % bleach for 40 s, 80 % of the permeabilized spores were viable, resulting in the production of fungal colonies after 15 days of incubation of these propagules in the presence of Corymbia citriodora. However, the germination percentage obtained, 0.001 %, was similar to that of non-permeabilized basidiospores, indicating that other factors, besides cell wall permeability, are determinant for the germination process.

Changes in the Ultrastructure of Candida albicans Treated with Cationic Peptides

Candida albicans is becoming increasingly harmful for humans, which determines the need for new effective antifungal preparations. Currently, when testing antifungals, various morphological methods are used, among which transmission electron microscopy (TEM) is not the leading one. In this work, we used TEM to study the submicroscopic changes in C. albicans cells induced by cationic peptides R9F2 and (KFF)3K. Studies were performed on C. albicans-34 strain from the Collection of EMTC of ICBFM SB RAS in logarithmic phase. R9F2 and (KFF)3K showed an antifungal effect (MIC 10 and 20 μM) and suppressed fungal hyphal growth. Semithin and ultrathin sections of fungal suspensions incubated with 10 μM of peptides were studied at regular intervals from 15 min to 24 h. The first target of both peptides was plasmalemma, and its “alignment” was the only common morphological manifestation of their effect. Other changes in the plasmalemma and alteration of the vacuole and cell wall ultrastructure distinctly differed in cells treated with R9F2 and (KFF)3K peptides. In general, our work has shown pronounced differences of the temporal and morphologic characteristics of the effect of peptides, evidently related to their physicochemical properties. The benefit of TEM studies of ultrathin sections for understanding the mechanisms of action of antifungal drugs is shown.

Wood cell wall ultrastructure The key to understanding wood properties and behaviour

ABSTRACTIn the last 100 years, major advances have been made in understanding wood cell wall ultrastructure in tracheids, fibres, vessels and parenchyma and its relationship with xylem function and wood properties. This review will focus on how the development of imaging techniques and their application to wood cell walls has led to an understanding of cell wall organisation and the relationship between micro and macro scale properties in wood and wood-based materials. Topics such as wood formation, wood chemistry and reaction wood have recently been reviewed elsewhere and are considered only briefly in this review. Two features of wood cell walls have dominated the literature; orientation and layering of cellulose which determines the longitudinal stiffness of wood, and the distribution (topochemistry) of lignin which determines compression strength and pulping properties.

Relationship of wood cell wall ultrastructure to bacterial degradation of wood

ABSTRACT This review presents information on the relationship of ultrastructure and composition of wood cell walls, in order to understand how wood degrading bacteria utilise cell wall components for their nutrition. A brief outline of the structure and composition of plant cell walls and the degradation patterns associated with bacterial degradation of wood cell walls precedes the description of the relationship of cell wall micro- and ultrastructure to bacterial degradation of the cell wall. The main topics covered are cell wall structure and composition, patterns of cell wall degradation by erosion and tunnelling bacteria, and the relationship of cell wall ultrastructure and composition to wood degradation by erosion and tunnelling bacteria. Finally, pertinent information from select recent studies employing molecular approaches to identify bacteria which can degrade lignin and other wood cell wall components is presented, and prospects for future investigations on wood degrading bacteria are explored.