Evgeniy Gusev

Molecular phylogeny of monoraphid diatoms and raphe significance in evolution and taxonomy

The phylogenetic position of the genera Rossithidium and Psammothidium was studied using the plastid gene rbcL. The genus Rossithidium is not an independent taxon and should be transferred to Psammothidium. Taxa from Psammothidium genus formed a sister, but independent clade to taxa with Achnanthidium. Our data has shown that the order Achnathales was not the natural taxon and should be reduced, but the three families included in it were natural. Genera like Psammothidium (including Rossithidium) and Lemnicola should be included into the family Achnanthidiaceae. Therefore, raphe does not play an important role in diatom taxonomy and its loss occurred many times during the evolution of diatoms.

Planothidium lanceolatum and Planothidium frequentissimum reinvestigated with molecular methods and morphology: four new species and the taxonomic importance of the sinus and cavum

Molecular data (rbcL and 18S) of 36 Planothidium strains were analysed. Twenty-seven strains were also studied morphologically by light microscopy and scanning electron microscopy: six strains from Berlin, two strains from the Faroe Islands, four strains from Lake Baikal, seven strains from Korea and eight strains from Mexico. The findings were compared to International Nucleotide Sequence Database Collaboration data of strains from New Zealand, Germany, France and the USA. The molecular and morphological data differentiated eight species, and the molecular trees underlined the clear differentiation between the two clades, with taxa possessing an asymmetrical central area on the sternum valve which is devoid of striae, either in the form of a sinus or of a cavum clustering together, versus the one taxon lacking a sinus or a cavum. In addition to Planothidium lanceolatum and P. cf. subantarcticum, the clade with a sinus contains two new species, P. cryptolanceolatum and P. taeansa, whereas the other clade with a cavum contains, in addition to P. frequentissimum and the recently described P. victori and P. caputium, the new species P. naradoense. The species without a sinus or cavum is also described as new, P. suncheonmanense. With respect to their distribution, P. victori is the most common, with 11 strains from the studied continents, Europe (Berlin), Asia (Lake Baikal), Americas (Mexico, USA), Australia/Oceania (New Zealand), whereas P. frequentissimum, represented by 5 strains, was restricted to Germany, France and New Zealand. A different geographical pattern seems to apply to the P. lanceolatum clade, with four strains occurring in Germany, the Faroe Islands, USA and Lake Baikal. Planothidium cryptolanceolatum (eight strains) only occurred in Korea, Mexico and USA. One strain from the Faroe Islands, morphologically very similar to P. subantarcticum and recently described as new from the Subantarctic, was also identified.

Exploring Cryptic Diversity and Distribution Patterns in the Mallomonas kalinae/rasilis Species Complex with a Description of a New Taxon – Mallomonas furtiva sp. nov

A complex of closely related Mallomonas taxa belonging to the section Papillosae, M. kalinae Řezáčová and M. rasilis Dürrschmidt, has been studied in detail by molecular and morphometric methods. Our investigations uncovered the existence of a new species found in water bodies in Vietnam, which we describe here as Mallomonas furtiva sp. nov. This taxon is morphologically very similar to M. kalinae, from which it differs by minute, but statistically significant morphological differences on the structure of silica scales. Indeed, the principal component analysis of morphological traits measured on silica scales significantly separates all three species in the complex. Mallomonas kalinae and M. furtiva differ by number of papillae on the shield and the dome, as well as by the scale sizes. Likewise, Mallomonas rasilis and M. furtiva are primarily differentiated by the absence of submarginal anterior ribs on silica scales of the former species. Phylogenetic analyses showed that Mallomonas furtiva is closely related to M. kalinae, with which it formed a highly supported lineage. Distribution patterns of all three studied taxa are further discussed.

Simultaneous increase in cellular content and volumetric concentration of lipids in Bracteacoccus bullatus cultivated at reduced nitrogen and phosphorus concentrations

Manipulation of the nutrient concentration is an inexpensive and efficient method for increasing lipid and TAG accumulation in algal cells. However, high volumetric production requires finding a proper balance between the decrease of biomass production and the increase in the total lipid content. We isolated a strain of green microalga Bracteacoccus bullatus and increased its lipid content from 17 to 59% of biomass dry weight by manipulating of nitrogen and phosphorus content in the medium. The 10-fold reduction of the nitrogen and phosphorus concentration in the medium was the most efficient method of the lipid induction compared to nutrient deplete and high nutrient conditions. The oleic (48–64% mass of total fatty acids) and linoleic (14–24% mass of total fatty acids) acids dominated in the fatty acid profile, thus making this strain a suitable candidate for biodiesel production.