Abstract：
High levels of environmental H2O2 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 H2O2. Proteomic analysis also confirmed the presence of KatA1 inside the outer membrane vesicles secreted by P. aquatica HC52 following exposure to H2O2. High light intensities (> 100 µmol m-2 s-1) 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 H2O2, thus promoting the formation of M. aeruginosa blooms under high light intensities.
摘要：
高水平的环境H2O2对许多淡水细菌物种构成威胁，包括有毒水华形成的铜绿微囊藻，特别是在高强度光条件下。在新鲜收集的铜绿分枝杆菌细胞中，从36个可培养的共生分离株中选择了具有最高的细胞外过氧化氢酶活性的水生假人HC52。过氧化氢酶活性的酶谱显示，尽管有四个推定的过氧化氢酶基因（katA1，katA2，katE，和srpA）在新测序的P.aquaticaHC52的基因组（〜6.8Mb）中鉴定。使用液相色谱-串联质谱法分析分泌的过氧化氢酶被鉴定为KatA1，缺乏典型的信号肽，尽管其分泌的潜在机制尚不清楚。分泌的KatA1的表达似乎在H2O2存在下被诱导。蛋白质组学分析还证实了在暴露于H2O2后由水牛HC52分泌的外膜囊泡内存在KatA1。已知高光照强度（>100µmolm-2s-1）可杀死无过氧化氢酶的铜绿分枝杆菌细胞，但是目前的研究发现，水曲柳杆菌细胞的存在支持了铜绿分枝杆菌的生长，而上清液或纯化形式的细胞外过氧化氢酶也在相同条件下维持铜绿分枝杆菌的生长。我们的结果表明，由P.aquaticaHC52分泌的细胞外过氧化氢酶增强了铜绿分枝杆菌对H2O2的耐受性，从而促进了高光强度下铜绿分枝杆菌花的形成。
