Noorian Parisa, Hu Jie, Chen Zhiliang, Kjelleberg Staffan, Wilkins Marc R, Sun Shuyang, McDougald Diane
School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
The ithree Institute, University of Technology Sydney, Sydney, NSW 2007, Australia.
FEMS Microbiol Ecol. 2017 Dec 1;93(12). doi: 10.1093/femsec/fix147.
Protozoan predation is one of the main environmental factors constraining bacterial growth in aquatic environments, and thus has led to the evolution of a number of defence mechanisms that protect bacteria from predation. These mechanisms may also function as virulence factors in infection of animal and human hosts. Whole transcriptome shotgun sequencing of Vibrio cholerae biofilms during predation by the amoebae, Acanthamoeba castellanii, revealed that 131 transcripts were significantly differentially regulated when compared to the non-grazed control. Differentially regulated transcripts included those involved in biosynthetic and metabolic pathways. The transcripts of genes involved in tyrosine metabolism were down-regulated in the grazed population, which indicates that the tyrosine metabolic regulon may have a role in the response of V. cholerae biofilms to A. castellanii predation. Homogentisate 1, 2-dioxygenase (HGA) is the main intermediate of the normal L-tyrosine catabolic pathway which is known to auto-oxidize, leading to the formation of the pigment, pyomelanin. Indeed, a pigmented mutant, disrupted in hmgA, was more resistant to amoebae predation than the wild type. Increased grazing resistance was correlated with increased production of pyomelanin and thus reactive oxygen species (ROS), suggesting that ROS production is a defensive mechanism used by bacterial biofilms against predation by amoebae A. castellanii.
原生动物捕食是限制水生环境中细菌生长的主要环境因素之一，因此导致了许多保护细菌免受捕食的防御机制的进化。这些机制在感染动物和人类宿主时也可能作为毒力因子发挥作用。在被变形虫卡氏棘阿米巴捕食期间，对霍乱弧菌生物膜进行全转录组鸟枪法测序发现，与未被啃食的对照相比，有131个转录本受到显著差异调节。差异调节的转录本包括那些参与生物合成和代谢途径的转录本。在被啃食的群体中，参与酪氨酸代谢的基因转录本下调，这表明酪氨酸代谢调节子可能在霍乱弧菌生物膜对卡氏棘阿米巴捕食的反应中起作用。尿黑酸1,2-双加氧酶（HGA）是正常L-酪氨酸分解代谢途径的主要中间产物，已知其会自动氧化，导致色素焦黑素的形成。事实上，一个在hmgA基因上发生突变的色素突变体比野生型对变形虫捕食更具抗性。对变形虫捕食的抗性增加与焦黑素产量增加以及活性氧（ROS）增加相关，这表明ROS的产生是细菌生物膜对抗卡氏棘阿米巴捕食的一种防御机制。
