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• Leu and Phe clearly inhibited the growth and MCs production in M. aeruginosa. • Leu and Phe increased the abundance of MCs variants with relevant structures. • Quotas of Chl-a, PC, and APC in M. aeruginosa reduced when exposed to amino acids. • The expression of pipX was upregulated while mcyD was downregulated when exposed to amino acids. Dissolved free amino acids are a significant component of dissolved organic nitrogen (DON) in natural waterbodies. The effects of four amino acids (glutamic acid, phenylalanine, leucine, and arginine) on the growth and microcystins (MCs) production of Microcystis aeruginosa were studied in batch culture. The profiles of five MCs variants and the expression levels of target genes involved in MCs biosynthesis and nitrogen metabolism were measured. When amino acids were used as the sole nitrogen source instead of nitrate at different levels (0.5, 2.0 and 8.0 mg/L based on N) in BG-11 medium, algal cell growth and intracellular MCs quotas were inhibited slightly by the treatments with glutamic acid and arginine. The treatments with phenylalanine and leucine, on the other hand, had a strong inhibitory effect on algal cell growth and MCs production. Moreover, the concentrations of Chlorophyll a , phycocyanin and allophycocyanin in cells cultured in glutamic acid, leucine and phenylalanine were lower than those in the control group with nitrate as nitrogen source. The existence of leucine or phenylalanine can lead to a significant increase in the relative abundance of MCs variants structured with the corresponding amino acids. The expression of microcystin-producing gene mcyD was downregulated while the gene pipX associated with nitrogen metabolism was upregulated during the cultivation of M. aeruginosa with amino acids as sole nitrogen source. M. aeruginosa undergoes significant alterations due to exogenous amino acids and exhibits advanced strategies for MCs production. [ABSTRACT FROM AUTHOR]

Water-soluble amino acids have been confirmed as effective cloud condensation nuclei (CCN) materials. While their influence on the hygroscopicity of nitrates is still scarcely known. In this work, ammonium nitrate (AN) was mixed with glycine and alanine at various mole ratios to form internally mixed particles deposited onto a solid substrate, whose hygroscopic properties and phase states of ingredients were investigated using microscope and attenuated total reflection-Fourier transformed infrared spectroscopy (ATR-FTIR). For mixed AN/amino acid particles with abundant inorganic, AN crystallizes at lower RH than that of pure AN, while deliquescence relative humidities (DRHs) were close to pure AN. On hydration, the mixture composed of bis(amino acid) nitrates and mono(amino acid) nitrates formed at 14.6–60.8% RH and 23.6%–60.0% RH for AN/glycine and AN/alanine particles, respectively. When the inorganic and organic components were mixed with equal mole ratio, gradual water uptake and release took place due to the hygroscopic interplay between components. In the mixed particles with abundant amino acids, glycine and alanine still kept solid at highest RH on hydration. Hydrogen bonding interaction should account for the mutual suppression on individual crystal formation. The present hygroscopic study would help people understanding cloud condensation nuclei (CCN) ability of amino acids in atmosphere. [Display omitted] • Addition of ammonium nitrate promotes the water-uptake of amino acid in mixture particles. • The amino acid nitrate was formed on hydration because intermolecular interaction in presence of little water. • The ammonium nitrate/amino acid mixed particles in equimolar ratio exhibited continuous water absorption and loss. • The amino acids inhibited the water uptake of ammonium nitrate. • The morphologies of the mixed particles depended on the chemical composition. [ABSTRACT FROM AUTHOR]

Although nitrates and amino acids are ubiquitous in the atmosphere, the interactions of amino acids with nitrates on the hygroscopicity of aerosols are still not clear. We studied the hygroscopic properties and compositional evolution of three atmospherically relevant species, sodium nitrate (NaNO 3), glycine and L-alanine (alanine). The investigations on the NaNO 3 , glycine, alanine and their internally NaNO 3 /amino acid mixed particles with molar ratios of 3:1, 1:1 and 1:3 were conducted using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The mixed NaNO 3 /glycine droplets with molar ratios of 3:1, 1:1 and 1:3 exhibited efflorescence transition at 52.3%, 62.6% and 63.2%RH, respectively. For the NaNO 3 /alanine mixed systems with molar ratios of 3:1, 1:1 and 1:3, the efflorescence relative humidity (ERH) was measured to be 50.2%, 59.8% and 69.3%, respectively. These results suggested that in each of the systems studied the addition of amino acids to aerosols could promote the crystallization of mixed droplets. However, the higher deliquescence relative humidity (DRH) with increased fraction of glycine for the mixed NaNO 3 /glycine (3:1, 79.2%RH; 1:1, 86.3%RH; 1:3, 86.5%RH) also indicated that glycine could inhibit the deliquescence phase transition of mixed systems. In the case of NaNO 3 /alanine systems, the DRH for 3:1 and 1:3 mixed particles was 78.2% and 82.7% while no deliquescence transition occurred for the 1:1 mixed particles. The hygroscopic properties of mixed NaNO 3 /amino acids droplets were modified due to the formed amino acid-NaNO 3 complex salts from the interactions of amino acids with NaNO 3 in aerosols during dehydration process. The discrepancies in water content for the mixed NaNO 3 /amino acids with molar ratios of 1:1 and 1:3 between dehydration and hydration processes at high RH could be attributed to the crystallization of amino acid-NaNO 3 complex salts during dehydration and the residual amino acids. • The chemical composition evolution of NaNO 3 /amino acid was investigated. • The amino acid-NaNO 3 complex salts can be formed. • The water content decreases after a dehydration-hydration process. • Amino acids promote the crystallization of droplets. [ABSTRACT FROM AUTHOR]