Reproductive cycle progression arrest and modification of cell morphology (shape and biovolume) in the alga Pseudokirchneriella subcapitata exposed to metolachlor

Abstract

Metolachlor (MET) is an herbicide widely used and frequently found (at μg L −1) in aquatic systems. This work aimed to study the modes of action of MET on the green microalga Pseudokirchneriella subcapitata. Algae exposed to 115 or 235 μg L −1 MET, for 48 or 72 h, presented a reduction of metabolic activity, chlorophyll a and b content and photosynthetic efficiency. The exposure to 115 or 235 μg L −1 MET also induced growth yield reduction, mean cell biovolume increase and alteration of the typical algae shape (cells lunate or helically twisted) to "French croissant"-type; at these MET concentrations, algal population was mainly composed by multinucleated cells (≥ 4 nuclei), which suggest that MET impairs the normal progression of the reproductive cycle but did not hinder nuclear division. The accumulation of multinucleated cells seems to be the consequence of the incapacity of the parent cell to release the autospores. In conclusion, MET disrupts the physiology of P. subcapitata cells; the disturbance of the progression of the reproductive cycle should be in the origin of growth slowdown (or even its arrest), increase of mean cell biovolume and modification of algal shape. This work contributed to elucidate, in a systematically and integrated way, the toxic mechanism of MET on the non-target organism, the alga P. subcapitata.

CsubMADS1, a lag phase transcription factor, controls development of polar eukaryotic microalga Coccomyxa subellipsoidea C‐169

“…Cell cycle analysis to study the ploidy of the cultures revealed that WT cultures had a higher proportion of 2n cells, whereas OX cultures had a higher proportion of ≥4n cells than the WT (Figure 6b,c). In Pseudokirchneriella subcapitata , cells treated with the herbicide Metolachlor exhibit slower growth and accumulate multinucleate cells (Machado and Soares, 2020) similar to the MADS OX cultures. This phenotype results from disturbance of the reproductive cycle, where autospore release is inhibited without a disruption in nuclear division (Machado and Soares, 2020).…”

“…In Pseudokirchneriella subcapitata , cells treated with the herbicide Metolachlor exhibit slower growth and accumulate multinucleate cells (Machado and Soares, 2020) similar to the MADS OX cultures. This phenotype results from disturbance of the reproductive cycle, where autospore release is inhibited without a disruption in nuclear division (Machado and Soares, 2020). Overexpression of CsubMADS1 had a similar effect on C‐169 cells.…”

Comparative Toxicity of Herbicide Active Ingredients, Safener Additives, and Commercial Formulations to the Nontarget Alga Raphidocelis Subcapitata

“…Under less stressful conditions, algal reproduction occurs via a two‐autospore mode, which is not accompanied by an increase in cell size. In the case of SMET, researchers found that the cells’ ability to split and perform the final stage of mitosis was being inhibited, which resulted in an increase in algal size (Machado & Soares, 2020, 2021). Changes in the reproductive mode and physiology in response to stress were seen in the alga Parachlorella kessleri after exposure to SMET (Maronić et al, 2018).…”

Toxicological effects induced by the biocide triclosan on Pseudokirchneriella subcapitata

“…Photosynthetic performance of Photosystem II (PSII) of P. subcapitata, a good stress indicator, was evaluated by PAM fluorometry using a Junior PAM-fluorometer (Walz, Germany) as described by Machado and Soares (2020). PSII is the first complex protein that executes the initial reaction of photosynthesis.…”