Department of Molecular, Cellular & Developmental Biology, Ann Arbor, Michigan, USA.
Department of Microbiology & Immunology, University of Michigan, Ann Arbor, Michigan, USA.
mBio. 2022 Feb 22;13(1):e0386921. doi: 10.1128/mbio.03869-21.
The type III secretion system (T3SS) is a needle-like structure found in Gram-negative pathogens that directly delivers virulence factors like toxins and effector molecules into eukaryotic cells. The T3SS is classified into different families according to the type of effector and host. Of these, the Ysc family T3SS, found in species and Pseudomonas aeruginosa, confers high virulence to bacteria against eukaryotic hosts. Here, we present the first identification and transcriptional analyses of a Ysc T3SS in a non- Pseudomonas species, Pseudomonas lundensis, an environmental psychrotrophic bacterium and important agent of frozen food spoilage. We have identified and sequenced isolates of P. lundensis from three very distinct ecological niches (Antarctic temporary meltwater pond, U.S. supermarket 1% pasteurized milk, and cystic fibrosis lungs) and compared these to previously reported food spoilage isolates in Europe. In this paper, we show that strains of P. lundensis isolated from these diverse environments with ambient temperatures ranging from below freezing to 37°C all possess a Ysc family T3SS secretion system and a T3S effector, ExoU. Using and transcriptomics, we show that the T3SS in P. lundensis is transcriptionally active, is expressed more highly at mammalian body temperature (37°C) than 4°C, and has even higher expression levels when colonizing a host environment (mouse intestine). Thus, this Ysc T3SS-expressing psychrotrophic Pseudomonad has an even greater range of growth niches than previously appreciated, including diseased human airways. P. lundensis strains have been isolated from environments that are distinct and diverse in both nutrient availability and environmental pressures (cold food spoilage, Antarctic melt ponds, cystic fibrosis lungs). As a species, this bacterium can grow in diverse niches that markedly vary in available nutrients and temperature, and in our study, we show that these various strains share greater than 99% sequence similarity. In addition, all isolates studied here encoded complete homologs of the Ysc family T3SS seen in P. aeruginosa. Until recently, P. aeruginosa has remained as the only Pseudomonas species to have a characterized functional Ysc (Psc) family T3SS. With the identification of a complete Ysc T3SS in P. lundensis that is expressed at 37°C , it is intriguing to wonder whether this bacterium may indeed have some level of symbiotic activity, of yet unknown type, when consumed by a mammalian host.
III 型分泌系统（T3SS）是革兰氏阴性病原体中发现的一种针状结构，它直接将毒素和效应分子等毒力因子输送到真核细胞中。根据效应子和宿主的类型，T3SS 可分为不同的家族。其中，在 和铜绿假单胞菌中发现的 Ysc 家族 T3SS 使细菌对真核宿主具有高度的毒性。在这里，我们首次鉴定并分析了非铜绿假单胞菌种——嗜冷菌假单胞菌隆登斯氏菌中的 Ysc T3SS。该菌是一种环境嗜冷菌，也是冷冻食品腐败的重要因素。我们已经鉴定并测序了来自三个截然不同生态位（南极临时融水池、美国超市 1%巴氏杀菌牛奶和囊性纤维化肺）的假单胞菌隆登斯氏菌分离株，并将这些分离株与之前在欧洲报道的食品腐败分离株进行了比较。在本文中，我们表明，从这些具有从冰点到 37°C 不等的环境温度的不同环境中分离的假单胞菌隆登斯氏菌菌株都具有 Ysc 家族 T3SS 分泌系统和 T3S 效应子 ExoU。使用 和 转录组学，我们表明假单胞菌隆登斯氏菌中的 T3SS 转录活跃，在哺乳动物体温（37°C）下的表达水平高于 4°C，在定植宿主环境时的表达水平甚至更高（小鼠肠道）。因此，与之前的认知相比，这种表达 Ysc T3SS 的嗜冷假单胞菌具有更广泛的生长生态位，包括患病的人类气道。假单胞菌隆登斯氏菌菌株已从营养供应和环境压力（冷食腐败、南极融水池、囊性纤维化肺）明显不同的环境中分离出来。作为一个物种，这种细菌可以在营养物质和温度差异很大的各种小生境中生长，在我们的研究中，我们表明这些不同的菌株具有大于 99%的序列相似性。此外，本研究中所有分离株均编码了铜绿假单胞菌中存在的完整 Ysc 家族 T3SS 同源物。直到最近，铜绿假单胞菌仍然是唯一具有特征性功能 Ysc（Psc）家族 T3SS 的假单胞菌属物种。随着假单胞菌隆登斯氏菌中完整 Ysc T3SS 的鉴定，该菌在 37°C 下表达，这令人好奇的是，当被哺乳动物宿主消耗时，该菌是否确实具有某种未知类型的共生活性。
