Silica-scaled chrysophytes in large tributaries of Lake Baikal

High diversity of silica-scaled chrysophytes was recorded in the Barguzin River mouth and the Selenga River delta. Their flora was represented by 66 species and intraspecific taxa: Chrysosphaerella – 2, Paraphysomonas – 8, Clathromonas – 5, Spiniferomonas – 8, Mallomonas – 29, and Synura – 14. Eight taxa of silica-scaled chrysophytes were observed for the first time in Russia: Chrysosphaerella rotundata, Mallomonas doignonii, M. trummensis, M. corymbosa, Clathromonas poteriophora, Paraphysomonas acuminata acuminata, P. vulgaris, and Synura laticarina. In May, we found scales of Mallomonas striata with morphologically changed structure in the mouth of the Barguzin River and Srednyaya Channel of the Selenga River delta. The flora of silica-scaled chrysophytes studied differs from one tributary to another. We observed only 52 species in the Selenga River delta, whereas in the Barguzin River mouth we identified 35 species. These large rivers affect the flora of Lake Baikal diversifying silica-scaled chrysophytes in its southern and central basins. The total list of species and intra-specific taxa in the Selenga River delta, Barguzin River mouth, and in Lake Baikal includes 72 taxa. Therefore, this area may be considered as a “hotspot” of silica-scaled chrysophytes together with three hotspots observed worldwide earlier.</p

Controlled stabilisation of silicic acid below pH 9 using poly(1-vinylimidazole)

We show, for the first time, inhibition of silicic acid condensation over a wide range of pH, especially below 9 using certain molecular mass fractions of poly(1-vinylimidazole) (PVI). This is achieved by stabilisation of molybdate-active Si species, which are crucial to condensation and growth to form silica. The structure of the resulting composites depends on the molecular mass of the PVI chains. Long-chain macromolecules can ''encapsulate'' Si species giving rise to stable soluble complexes. Short PVI chains stimulate association of silica particles and at neutral pH precipitation occurs. Protonation of imidazole units in acidic pH results in dissolution of the precipitates. We believe that the results presented herein using PVI as a model system will help elucidate the mechanisms underpinning the molecular interactions between (bio) macromolecules and inorganic materials

Specific features of mandible structure and elemental composition in the polyphagous amphipod Acanthogammarus grewingkii endemic to Lake Baikal.

BACKGROUND: In crustaceans, several mechanisms provide for the mechanical strength of the cuticular "tools" (dactyli, claws, jaws), which serve to catch and crush food objects. Studies on the mandibles of the endemic Baikal amphipod Acanthogammarus grewingkii by means of electron microscopy and elemental analysis have revealed specific structural features of these mouthparts. METHODOLOGY: The fine structure of the mandible has been studied by means of SEM, TEM, and AFM; methods used to analyze its elemental and phase composition include XEPMA, XPS, SEM-EDS analysis, and XRD. CONCLUSION: Functional adaptations of the mandible in A. grewingkii provide for the optimum combination of mechanical hardness and fracture resistance, which is achieved due to a complex structure and composition of its cutting parts. Teeth of the mandible are covered by a thin layer of silica (10-20 µm). Their epicuticle is characterized by a high density, consists of three layers, and increases in thickness toward the tooth apex. The epicuticle is enriched with Br, while the concentrations of Ca and P reach the peak values in the softer internal tissues of the teeth. These data broaden the view of the diversity of adaptation mechanisms providing for the strengthening of cuticular "tools" in crustaceans

The structure of microbial community and degradation of diatoms in the deep near-bottom layer of Lake Baikal.

Insight into the role of bacteria in degradation of diatoms is important for understanding the factors and components of silica turnover in aquatic ecosystems. Using microscopic methods, it has been shown that the degree of diatom preservation and the numbers of diatom-associated bacteria in the surface layer of bottom sediments decrease with depth; in the near-bottom water layer, the majority of bacteria are associated with diatom cells, being located either on the cell surface or within the cell. The structure of microbial community in the near-bottom water layer has been characterized by pyrosequencing of the 16S rRNA gene, which has revealed 149 208 unique sequences. According to the results of metagenomic analysis, the community is dominated by representatives of Proteobacteria (41.9%), Actinobacteria (16%); then follow Acidobacteria (6.9%), Cyanobacteria (5%), Bacteroidetes (4.7%), Firmicutes (2.8%), Nitrospira (1.6%), and Verrucomicrobia (1%); other phylotypes account for less than 1% each. For 18.7% of the sequences, taxonomic identification has been possible only to the Bacteria domain level. Many bacteria identified to the genus level have close relatives occurring in other aquatic ecosystems and soils. The metagenome of the bacterial community from the near-bottom water layer also contains 16S rRNA gene sequences found in previously isolated bacterial strains possessing hydrolytic enzyme activity. These data show that potential degraders of diatoms occur among the vast variety of microorganisms in the near-bottom water of Lake Baikal

Mallomonas sibirica Bessudova & Firsova & Tomberg & Bayramova & Hilkhanova & Bedoshvili & Bashenkhaeva & Zakharova & Likhoshway 2023, sp. nov.

&lt;i&gt;Mallomonas sibirica sp. nov.&lt;/i&gt; Bessudova (Figs. 5&ndash;11) &lt;p&gt; &lt;b&gt;Description:&lt;/b&gt; Scales are 4.1&ndash;5.5 &times; 2.0&ndash;2.9 &mu;m, oval, with lateral incurvings. The dome is subcircular, its ornamentation appears to vary between samples: smooth surface or with struts or rounded depressions (up to 0.15 &mu;m in diameter) or reticulum variants were noted. The shield is covered with a thick secondary siliceous layer, marked with 8&ndash;12 regularly spaced transverse ribs with rounded depressions between them. Rounded depressions (up to 0.15 &mu;m in diameter) are evenly distributed between the transverse ribs (Fig. 5, 6, 9). There is a pore on the basal plate inside each depression. A group of 8&ndash;10 pores is located in the angle of the V-rib in the posterior part of the shield (Fig. 5). This area is lacking the secondary siliceous layer. Anterior flanges are well-developed, with 2&ndash;8 (14) struts on each side (Figs. 7, 8). The V-rib on the scales is acutely angled, slightly hooded, and continues on the anterior flanges. The posterior rim is wide and smooth, bears numerous internal struts (Fig. 5). The posterior flange contains approximately 14&ndash;20 struts and scattered rounded depressions between them, that are not evenly spaced (Fig. 5). Bristles are 3.3&ndash;8.7 &mu;m in length, slightly curved (Fig. 11). The tip is bifurcated with unequal diverging branches. One branch is short and sharp, whereas the other is wide with an acute tip and flat dorsal side. Cysts were not observed.&lt;/p&gt; &lt;p&gt; &lt;b&gt;Holotype&lt;/b&gt; (here designated): Portion of a single gathering of cells on SEM stubs No. 18075 deposited at the herbarium of the Limnological Institute, Siberian Branch of the Russian Academy of Sciences, Irkutsk (LIN). Y.R. Zakharova, Y.D. Bedoshvili and L.I. Kopyrina collected material from Ulu Lake, in the Republic of Yakutia, Russia, on April 24, 2021. Figure 6 illustrates illustrates the characteristic scales from the holotype.&lt;/p&gt; &lt;p&gt; &lt;b&gt;Type locality:&lt;/b&gt; Ulu Lake, Republic of Yakutia, Russia. Latitude/Longitude: N63&ordm;20ʹ9ʺ E141&ordm;3ʹ54ʺ.&lt;/p&gt; &lt;p&gt; &lt;b&gt;Etymology:&lt;/b&gt; The new species is named after the region of its origin, Siberia.&lt;/p&gt; &lt;p&gt; &lt;b&gt;Distribution:&lt;/b&gt; Up-to-date, &lt;i&gt;M. sibirica&lt;/i&gt; have been recorded in the type locality and in other water bodies of Eastern Siberia: &mcy;ixing zone of Yenisei River and Kara Sea waters; Vorota and Labynkyr lakes, Lake Baikal. &lt;i&gt;M. sibirica&lt;/i&gt; was found at wide ranges of environmental parameters: pH from 6.97 to 9.34, specific conductance from 5.17 to 6560 &mu;S̛ &scy;m&minus;1, and temperature of 0.4&ndash;10.2&deg;C, salinity from 0.4 to 3.8 &permil; (see Table 1).&lt;/p&gt;Published as part of &lt;i&gt;Bessudova, Anna, Firsova, Alena D., Tomberg, Irina V., Bayramova, Elvira, Hilkhanova, Diana, Bedoshvili, Yekaterina D., Bashenkhaeva, Maria, Zakharova, Lyubov I. Kopyrina Yulia R. &amp; Likhoshway, Yelena V., 2023, Two new species of silica-scaled chrysophytes (Chrysophyceae, Synurales) Mallomonas kicherica and M. sibirica water bodies of Eastern Siberia, Russia, pp. 59-69 in Phytotaxa 620 (1)&lt;/i&gt; on pages 64-65, DOI: 10.11646/phytotaxa.620.1.5, &lt;a href="http://zenodo.org/record/10015521"&gt;http://zenodo.org/record/10015521&lt;/a&gt