Ribonuclease E(RNase E)is central to bacterial RNA metabolism.In cyanobacteria,its activity is inhibited by RebA,a key mechanism for controlling cell morphology.Here,we demonstrate that rebA is essential for diazotrop...Ribonuclease E(RNase E)is central to bacterial RNA metabolism.In cyanobacteria,its activity is inhibited by RebA,a key mechanism for controlling cell morphology.Here,we demonstrate that rebA is essential for diazotrophic growth of Anabaena PCC 7120,a filamentous cyanobacterium capable of forming heterocysts-specialized nitrogen-fixing cells-upon nitrogen starvation.The rebA mutant strain(ΔrebA)showed severe growth defects in nitrogen-deprived conditions,despite forming more heterocysts than the wild type.With a GFP fusion strain,we show that RebA is transiently upregulated during heterocyst differentiation.Microscopic and ultrastructural analyses revealed thatΔrebA heterocysts accumulated abnormally large cyanophycin granules,while vegetative cells showed reduced pigment levels and disorganized thylakoid membranes,phenotypes indicative of a severe nitrogen deficiency response.However,esculin tracer diffusion and SepJ-GFP localization inΔrebA were comparable to the wild type,suggesting that cell-cell communication via septal junctions remains functional.Thus,the growth defect likely results from impaired degradation or mobilization of fixed nitrogen.Notably,theΔrebA phenotype could be rescued only by wild-type RebA,but not by variants unable to bind RNase E,indicating that RebA's function depends on its modulation of RNase E activity.Together,these findings reveal a key posttranscriptional mechanism linking RNase E regulation to heterocyst development and intercellular nutrient transfer,highlighting the importance of regulated RNA metabolism for diazotrophic growth.展开更多
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 cya...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.展开更多
基金supported by the National Natural Science Foundation of China(32070037)the Knowledge Innovation Program of Wuhan-Basic Research(2023020201010087)+1 种基金the China Postdoctoral Science Foundation(2025M772687)the Postdoctoral Fellowship Program of CPSF(GZC20241873)。
文摘Ribonuclease E(RNase E)is central to bacterial RNA metabolism.In cyanobacteria,its activity is inhibited by RebA,a key mechanism for controlling cell morphology.Here,we demonstrate that rebA is essential for diazotrophic growth of Anabaena PCC 7120,a filamentous cyanobacterium capable of forming heterocysts-specialized nitrogen-fixing cells-upon nitrogen starvation.The rebA mutant strain(ΔrebA)showed severe growth defects in nitrogen-deprived conditions,despite forming more heterocysts than the wild type.With a GFP fusion strain,we show that RebA is transiently upregulated during heterocyst differentiation.Microscopic and ultrastructural analyses revealed thatΔrebA heterocysts accumulated abnormally large cyanophycin granules,while vegetative cells showed reduced pigment levels and disorganized thylakoid membranes,phenotypes indicative of a severe nitrogen deficiency response.However,esculin tracer diffusion and SepJ-GFP localization inΔrebA were comparable to the wild type,suggesting that cell-cell communication via septal junctions remains functional.Thus,the growth defect likely results from impaired degradation or mobilization of fixed nitrogen.Notably,theΔrebA phenotype could be rescued only by wild-type RebA,but not by variants unable to bind RNase E,indicating that RebA's function depends on its modulation of RNase E activity.Together,these findings reveal a key posttranscriptional mechanism linking RNase E regulation to heterocyst development and intercellular nutrient transfer,highlighting the importance of regulated RNA metabolism for diazotrophic growth.
基金supported by the Featured Institute Service Project from the Institute of Hydrobiology,the Chinese Academy of Sciences(Grant No.:Y85Z061601).
文摘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.
