Impact of Algicidal Bacillus mycoides on Diatom Ulnaria acus from Lake Baikal

Abstract

Algae–bacteria interactions play an important role in water ecosystems. In this work, the BS2-15 algicidal strain was isolated from the bottom sediments of Lake Baikal and identified as Bacillus mycoides on the basis of 16S rDNA sequencing, its described ultrastructure, and biochemical properties. B. mycoides BS2-15 was demonstrated to have a strong algicidal effect against a freshwater diatom culture of Ulnaria acus, inhibiting its growth and increasing frustules fragility. By analyzing the impact of bacterial filtrate onto the cells of U. acus, we demonstrated that perhaps an algicidal compound is produced by bacteria independently in the presence of diatoms in a medium. Using methods of TUNEL and confocal microscopy, we revealed that the bacterial algicidal effect on the diatom cells results in DNA fragmentation, nucleus destruction, and neutral lipid accumulation. This phenomenon highlights the complexity of algae–bacteria interactions and their potential role in regulating water ecosystem microbial populations.

Differential Expression of Stress Adaptation Genes in a Diatom Ulnaria acus under Different Culture Conditions

“…Our work studied the changes in the expression of these genes during active cell proliferation and when division stopped during prolonged culturing. We also tracked the effect of a silica shortage and an algicidal strain of B. mycoides previously shown to kill U. acus cultures [68].…”

“…To study the MC, DSP, ALDH, and GSHS involvement in the physiological adaptation of U. acus to stresses, we cultured cells under Si starvation as a key division-limiting factor, in conditions of a prolonged culture where cells are known to stop division as a result of depletion in nutrients [86], and under exposure to an algicidal bacterial filtrate. We had previously demonstrated that U. acus cells stopped dividing during the first three days and perished rapidly during the next seven days after the addition of the Bacillus mycoides bacterial filtrate [68]. We suggested that the bacteria-produced algicidal agent activated mechanisms against stress.…”

“…We have previously shown that a Bacillus mycoides strain BS2-15 isolated from Lake Baikal sediments had an algicidal effect on the diatom Ulnaria acus (Kützing) Aboal (Bacillariophyceae, Fragilariophycidae, Licmophorales, Ulnariaceae, Ulnaria). Under the influence of this bacterium, the diatom culture stopped growing during the first three days of co-culture, followed by rapid death during the next seven days, during which the accumulation of neutral lipids and PCD features such as nuclear membrane injury and DNA fragmentation were observed [68]. Thus, one of the goals of this work was to study the response of U. acus with regard to the algicidal effects of this bacterium.…”

Molecular and cellular mechanisms of diatom response to environmental changes

“…algicidal bacteria leads to vacuolization, degradation of organelles, destruction of chloroplasts and mitochondria, and destruction of the cell shell. Study of the effect of Bacillus mycoides on Ulnaria acus found the destruction of the cell shell, DNA fragmentation, the accumulation of neutral lipids in diatom cells, the destruction of the nuclear membrane, but intact chloroplasts and mitochondria (Bedoshvili et al, 2021). Diatoms, in turn, are also able to produce antibacterial substances.…”

A New Perspective: Revealing the Algicidal Properties of Bacillus subtilis to Alexandrium pacificum from Bacterial Communities and Toxins

“…Bacillus sp. has also been shown to have high algicidal activity against some species of HAB organisms, including cyanobacteria, dinoflagellates, and diatoms [ 16 , 23 , 24 ]. Therefore, to quickly obtain green and efficient algicidal bacteria, this paper attempts to screen an algicidal bacterium against A. pacificum from different commercial Bacillus strains.…”