Morphological and molecular characterization of Halamphora lukasiewiczii sp. nov. (Bacillariophyceae, Amphipleuraceae), a new extremophilic diatom from petroleum seeps in the Polish Carpathians

Crude oil is toxic in high concentrations. However, several microalgae are able to proliferate in these extreme environments. In this study, we describe diatoms in natural oil seeps in the Polish Carpathians.

Only two species were found: Halamphora lukasiewiczii sp. nov. and Navicula salinarum. Cultures were established and characterized using morphological, and molecular data based on the rbc L gene with secondary support from SSU rRNA sequences. Halamphora lukasiewiczii sp. nov. was examined using light, fluorescence, and scanning electron microscopy.

This new species is closely related to Halamphora aponina, H. angustiformis, H. borealis, H. kenderoviana, H. witkowskii, and H. margalefii var. lacustris. It is distinguished by small, dorsiventral valves (8.0–22.5 µm long, 3.0–5.0 µm wide) with exceptionally dense ventral striation (approximately 55 by 10 µm), the highest among related taxa. The H-shaped chloroplast is located ventrally, with lobes extending below the valves and forming a characteristic U- to V-shaped outline in apical view.

In molecular phylogeny, Halamphora lukasiewiczii sp. nov. is closely related to H. margalefii, differing by 13 base pairs for a length of 1288 bp in the rbc L gene sequence of H. lukasiewiczii SZCZ MR 2353. The DNA sequences of the inland Polish strain of Navicula salinarum showed low genetic divergence from the available sequences from Chinese coastal waters. The adaptations that allow Halamphora lukasiewiczii sp. nov. and Navicula salinarum to proliferate in this extreme environment require further investigation.