Investigation on cyanobacterial production of the proposed neurotoxinβ-N-methylamino-L-alanine(BMAA)

β-N-methylamino-L-alanine(BMAA)is an environmental neurotoxin thought to be produced by cyanobacteria.However,the cyanobacterial origin of BMAA remains controversial.The detection method and culture conditions of cyanobacteria are often cited as factors behind the discrepancy of published results.We showed previously that BMAA was highly toxic to the cyanobacterium Nostoc PCC 7120,and it is taken up via an amino acid transport system.Using a mutantΔnatAΔbgtA deficient in amino acid transport as a genetic control,we show here that BMAA taken up from the medium can be detected quantitatively at a threshold similar to,or below those reported,but was undetectable in the mutant.The BMAA isomer,2,4-diaminobutanoic acids(DAB),but not BMAA,could be detected in cell free extracts of Nostoc PCC 7120.Long-term(20 days)diazotrophic growth or nonlimiting supply of phosphate,conditions reported to enhance BMAA synthesis,did not lead to the detection of BMAA.An UPLC-MS/MS signal with a similar retention time to BMAA was found after prolonged diazotrophic incubation,but did not have fragment ions of BMAA after further analysis.When extended to 29 different cyanobacterial strains and 6 natural cyanobacterial bloom samples,none of them was found to produce BMAA.The cytotoxicity of BMAA to cyanobacteria,and the lack of a cellular protective mechanism against such toxicity,contradict the presence of a BMAA synthesis pathway in these organisms.More specific methods for BMAA detection in vivo need to be developed to clarify the cyanobacterial origin of BMAA.

“Life is short,and art is long”:RNA degradation in cyanobacteria and model bacteria

RNA turnover plays critical roles in the regulation of gene expression and allows cells to respond rapidly to environmental changes.In bacteria,the mechanisms of RNA turnover have been extensively studied in the models Escherichia coli and Bacillus subtilis,but not much is known in other bacteria.Cyanobacteria are a diverse group of photosynthetic organisms that have great potential for the sustainable production of valuable products using CO_(2)and solar energy.A better understanding of the regulation of RNA decay is important for both basic and applied studies of cyanobacteria.Genomic analysis shows that cyanobacteria have more than 10 ribonucleases and related proteins in common with E.coli and B.subtilis,and only a limited number of them have been experimentally investigated.In this review,we summarize the current knowledge about these RNAturnover-related proteins in cyanobacteria.Although many of them are biochemically similar to their counterparts in E.coli and B.subtilis,they appear to have distinct cellular functions,suggesting a different mechanism of RNA turnover regulation in cyanobacteria.The identification of new players involved in the regulation of RNA turnover and the elucidation of their biological functions are among the future challenges in this field.