Palmelloid-like phenotype in the alga Raphidocelis subcapitata exposed to pollutants: A generalized adaptive strategy to stress or a specific cellular response?

Features of the microalga Raphidocelis subcapitata: physiology and applications

“…When exposed to toxics, such as heavy metals (Cd or Cr) or organic compounds (MET), R. subcapitata population contains multiple nuclei (six, eight, or even more) inside the parental envelope (Machado and Soares 2014 , 2020 ; Yamagishi et al 2017 ). The exposure to Cd or MET, at environmentally relevant concentrations that arrest growth, originates a population composed mainly of living cells, in a multinucleated state, i.e., containing four (4) or more nuclei, accompanied by the accumulation of neutral lipids (Machado and Soares 2023 ). This means that under specific stress conditions, R. subcapitata undergoes repeated mitosis rounds without the rupture of the wall envelope and the release of the new cells, which provokes the increase of the size of the parental cell and the forming of clusters of cells confined by the parental cell wall (Fig.…”

“…This means that under specific stress conditions, R. subcapitata undergoes repeated mitosis rounds without the rupture of the wall envelope and the release of the new cells, which provokes the increase of the size of the parental cell and the forming of clusters of cells confined by the parental cell wall (Fig. 3 ), originating a phenotype that resembles the palmelloid-like morphology (Machado and Soares 2023 ), observed in algae belonging to the genus Chlamydomonas (de Carpentier et al 2019 ), Chlorella (Fisher et al 2016 ), Dunaliella (Borowitzka and Siva 2007 ), and Scenedesmus (Lürling and Van Donk 1997 ), when exposed to abiotic or biotic stress. The switch from a single-nucleus state to a palmelloid-like phenotype can be viewed as an adaptive response to manage/survive stress (Borowitzka 2018 ; de Carpentier et al 2019 ), which appears to be conserved in green algae.…”

“…The multinucleated state of the cell population is a transitory and a reversible phenotype, since the R. subcapitata population reverts to a unicellular lifestyle, with normal cell biovolume and shape (Fig. 3 ), upon being transferred to a fresh culture medium without pollutants (Machado and Soares 2023 ).…”

“…An increase in ROS accumulation and a decrease in enzymatic (superoxide dismutase and catalase) and non-enzymatic defenses (reduced glutathione levels) were also observed, leading to oxidative stress and consequent oxidative injury: lipid peroxidation and loss of cell membrane integrity (Machado and Soares 2021b ). Probably, the deep disturbance of the physiology of the microalga leads to the impairment of its normal reproductive cycle and autospores release, translating into slowdown/arrest of the growth of R. subcapitata , increase in biovolume, alteration of cell shape, and formation of a palmelloid-like phenotype (Machado and Soares 2020 , 2023 ).…”