The Cyanotoxin BMAA Induces Heterocyst Specific Gene Expression in Anabaena sp. PCC 7120 under Repressive Conditions

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.

Proteomic Insights into Starvation of Nitrogen-Replete Cells of Nostoc sp. PCC 7120 under β-N-Methylamino-L-Alanine (BMAA) Treatment

“…In order to test BMAA effect on Nostoc under nitrogen-replete conditions, cyanobacterium was grown in three independent biological replicates in sodium nitrate containing BG11N medium for 48 h in two experimental settings: (1) control samples consisted of cells grown without the BMAA treatment and (2) the treated samples consisted of cells grown with addition of an aqueous solution of BMAA (20 µM), as it was performed earlier [ 22 , 23 ]. The analysis of cyanobacteria samples by using LC-MS/MS methods resulted in the identification of 1567 different proteins of Nostoc ( Supplementary Table S1 ).…”

“…For that reason, BMAA effects were studied, so far mostly in mammalian models, for review [ 15 ]. Knowledge on the synthesis mechanisms of this neurotoxic non-protein amino acid and on the functional role of BMAA in cyanobacteria cells is still scant [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. There are a few experimental studies dedicated to the notable and specific biological impact of BMAA on nitrogen-fixing filamentous cyanobacterium Nostoc (also known as Anabaena ) sp.…”

“…There are a few experimental studies dedicated to the notable and specific biological impact of BMAA on nitrogen-fixing filamentous cyanobacterium Nostoc (also known as Anabaena ) sp. PCC 7120 [ 20 , 21 , 22 , 23 ], which is known to be a favorable model organism for nitrogen fixation and heterocyst differentiation studies [ 24 ]. Its filaments contain only vegetative cells in the presence of combined nitrogen in the form of ammonium (NH 4 + ) or nitrate (NO 3− ) ions.…”

“…We have found one more unexpected regulatory effect of BMAA on Nostoc sp. PCC 7120 cells that were grown in nitrogen-replete medium [ 22 ]. In the presence of nitrogen, the addition of this cyanotoxin leads to the formation of heterocyst-like cells and to the activation of heterocyst-specific gene expression [ 22 ].…”

Microbial BMAA and the Pathway for Parkinson’s Disease Neurodegeneration

“…The fact is that the biological functions of this diamino acid in nature are still unknown. The few studies conducted on its natural producers have concluded that it interferes with nitrogen metabolism and have hypothesized an allelopathic role for BMAA, a common biological phenomenon by which metabolites produced by some organisms affect certain physiological traits of others (Lage et al, 2016b;Popova et al, 2018). In the case of the BMAA-containing paenilamicins, production of the compound was shown to impact competing bacterial populations in the larval gut thus confirming its allelopathic role (Müller et al, 2014).…”