Park Yerim, Kim Wonjae, Cha Yeji, Kim Minkyung, Park Woojun
Laboratory of Molecular Environmental Microbiology, Department of Environmental Science and Ecological Engineering, Korea University, Seoul, Republic of Korea.
Laboratory of Molecular Environmental Microbiology, Department of Environmental Science and Ecological Engineering, Korea University, Seoul, Republic of Korea.
Harmful Algae. 2024 Aug;137:102680. doi: 10.1016/j.hal.2024.102680. Epub 2024 Jun 23.
High levels of environmental HO represent a threat to many freshwater bacterial species, including toxic-bloom-forming Microcystis aeruginosa, particularly under high-intensity light conditions. The highest extracellular catalase activity-possessing Pseudoduganella aquatica HC52 was chosen among 36 culturable symbiotic isolates from the phycosphere in freshly collected M. aeruginosa cells. A zymogram for catalase activity revealed the presence of only one extracellular catalase despite the four putative catalase genes (katA1, katA2, katE, and srpA) identified in the newly sequenced genome (∼6.8 Mb) of P. aquatica HC52. Analysis of secreted catalase using liquid chromatography-tandem mass spectrometry was identified as KatA1, which lacks a typical signal peptide, although the underlying mechanism for its secretion is unknown. The expression of secreted KatA1 appeared to be induced in the presence of HO. Proteomic analysis also confirmed the presence of KatA1 inside the outer membrane vesicles secreted by P. aquatica HC52 following exposure to HO. High light intensities (> 100 µmol m s) are known to kill catalase-less axenic M. aeruginosa cells, but the present study found that the presence of P. aquatica cells supported the growth of M. aeruginosa, while the extracellular catalases in supernatant or purified form also sustained the growth of M. aeruginosa under the same conditions. Our results suggest that the extracellular catalase secreted by P. aquatica HC52 enhances the tolerance of M. aeruginosa to HO, thus promoting the formation of M. aeruginosa blooms under high light intensities.
高浓度的环境过氧化氢对许多淡水细菌物种构成威胁，包括能形成有毒水华的铜绿微囊藻，尤其是在高强度光照条件下。从新鲜采集的铜绿微囊藻细胞的藻际中36种可培养的共生分离物中，挑选出具有最高胞外过氧化氢酶活性的水生假杜氏菌HC52。过氧化氢酶活性的酶谱分析表明，尽管在新测序的水生假杜氏菌HC52基因组（约6.8 Mb）中鉴定出四个假定的过氧化氢酶基因（katA1、katA2、katE和srpA），但仅存在一种胞外过氧化氢酶。使用液相色谱 - 串联质谱法对分泌的过氧化氢酶进行分析，鉴定为KatA1，它缺乏典型的信号肽，尽管其分泌的潜在机制尚不清楚。分泌型KatA1的表达似乎在过氧化氢存在时被诱导。蛋白质组学分析也证实，在暴露于过氧化氢后，水生假杜氏菌HC52分泌的外膜囊泡内存在KatA1。已知高光强度（> 100 μmol m⁻² s⁻¹）会杀死无过氧化氢酶的无菌铜绿微囊藻细胞，但本研究发现，水生假杜氏菌细胞的存在支持了铜绿微囊藻的生长，而上清液中或纯化形式的胞外过氧化氢酶在相同条件下也维持了铜绿微囊藻的生长。我们的结果表明，水生假杜氏菌HC52分泌的胞外过氧化氢酶增强了铜绿微囊藻对过氧化氢的耐受性，从而促进了高光强度下铜绿微囊藻水华的形成。
