Cell cycle of microalga Isochrysis galbana arrested by neurotoxin 13-N-methylamino-L-alanine and corresponding molecular mechanisms

The phycotoxin 13-N-methylamino-L-alanine (BMAA) has attracted attention due to its risks to marine organisms and human health. In this study, approximately 85 % of synchronized cells of the marine microalga Isochrysis galbana were arrested at the cell cycle G1 phase by BMAA at 6.5 mu M for a 24-h exposure. The concentration of chlorophyll a (Chl a) gradually decreased, while the maximum quantum yield of PSII (Fv/Fm), the maximum relative electron trans-port rate (rETRmax), light utilization efficiency (a) and half-saturated light irradiance (Ik) reduced early and recovered gradually in I. galbana exposed to BMAA in 96-h batch cultures. Transcriptional expression of I. galbana analyzed at 10, 12, and 16 h disclosed multiple mechanisms of BMAA to suppress the microalgal growth. Production of ammonia and glutamate was limited by the down-regulation of nitrate transporters, glutamate synthase, glutamine synthetase, cya-nate hydrolase, and formamidase. Diverse extrinsic proteins related to PSII, PSI, cytochrome b6f complex, and ATPase were influenced by BMAA at transcriptional level. Suppression of the DNA replication and mismatch repair pathways increased the accumulation of misfolded proteins, which was reflected by the up-regulated expression of proteasome to accelerate proteolysis. This study improves our understanding of the chemical ecology impacts of BMAA in marine ecosystems.

Automated summary

This study reveals that BMAA can inhibit the growth of marine microalgae, limit the production of ammonia and glutamate through down-regulation of specific genes, and affect gene expression related to photosynthesis and protein synthesis, resulting in cell cycle arrest and accumulation of misfolded proteins.