Abstract
Cyanobacteria synthesize neurotoxic β-N-methylamino-l-alanine (BMAA). The roles of this non-protein amino acid in cyanobacterial cells are insufficiently studied. During diazotrophic growth, filamentous cyanobacteria form single differentiated cells, called heterocysts, which are separated by approximately 12–15 vegetative cells. When combined nitrogen is available, heterocyst formation is blocked and cyanobacterial filaments contain only vegetative cells. In the present study, we discovered that exogenous BMAA induces the process of heterocyst formation in filamentous cyanobacteria under nitrogen-replete conditions that normally repress cell differentiation. BMAA treated cyanobacteria form heterocyst-like dark non-fluorescent non-functional cells. It was found that glutamate eliminates the BMAA mediated derepression. Quantitative polymerase chain reaction (qPCR) permitted to detect the BMAA impact on the transcriptional activity of several genes that are implicated in nitrogen assimilation and heterocyst formation in Anabaena sp. PCC 7120. We demonstrated that the expression of several essential genes increases in the BMAA presence under repressive conditions.
Highlights
Introduction βN-methylamino-L-alanine (BMAA) is synthesized by many strains of cyanobacteria [1,2,3,4,5].Biomagnifications of BMAA via food chains lead to toxin accumulation in brain tissues and Toxins 2018, 10, 478; doi:10.3390/toxins10110478 www.mdpi.com/journal/toxinsToxins 2018, 10, 478 neurodegeneration [6,7,8]
BMAA addition caused the appearance of round-shaped dark cells after 48 h of incubation and more of them could be found later (Figure 1C,E)
We found an unusual regulatory effect of BMAA that induced the transcription of several essential genes implicated in heterocyst formation, nitrogen fixation and nitrogen assimilation in Anabaena sp
Summary
Introduction βN-methylamino-L-alanine (BMAA) is synthesized by many strains of cyanobacteria [1,2,3,4,5].Biomagnifications of BMAA via food chains lead to toxin accumulation in brain tissues and Toxins 2018, 10, 478; doi:10.3390/toxins10110478 www.mdpi.com/journal/toxinsToxins 2018, 10, 478 neurodegeneration [6,7,8]. N-methylamino-L-alanine (BMAA) is synthesized by many strains of cyanobacteria [1,2,3,4,5]. Phytoplankton BMAA synthesis [3,9,10,11,12] represents a potential threat to human health [7,13]. There is no doubt about the topicality of investigations of this cyanotoxin synthesis and its functional significance within producers’ cells. Modern understanding of the regulation of BMAA synthesis and its functions in cyanobacteria is still not completed [14,15]. It is known that unicellular non-dizotrophic strains of Microcystis and Synechocystis synthesize BMAA in the course of nitrogen starvation, while the addition of ammonium or nitrate abolishes this synthesis [12,16]
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