Ahn Anne-Catherine, Cavalca Lucia, Colombo Milena, Schuurmans J Merijn, Sorokin Dimitry Y, Muyzer Gerard
Microbial Systems Ecology, Department of Freshwater and Marine Ecology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, Netherlands.
Department of Food, Environmental and Nutritional Sciences, University of Milan, Milan, Italy.
Front Microbiol. 2019 Jul 4;10:1514. doi: 10.3389/fmicb.2019.01514. eCollection 2019.
The genus includes haloalkaliphilic chemolithoautotrophic sulfur-oxidizing bacteria isolated from various soda lakes worldwide. Some of these lakes possess in addition to their extreme haloalkaline environment also other harsh conditions, to which needs to adapt. An example is arsenic in soda lakes in eastern California, which is found there in concentrations up to 3000 μM. Arsenic is a widespread element that can be an environmental issue, as it is highly toxic to most organisms. However, resistance mechanisms in the form of detoxification are widespread and some prokaryotes can even use arsenic as an energy source. We first screened the genomes of 76 strains for the presence of known arsenic oxidoreductases and found 15 putative ArxA (arsenite oxidase) and two putative ArrA (arsenate reductase). Subsequently, we studied the resistance to arsenite in detail in ALM2, and ARh2 by comparative genomics and by growing them at different arsenite concentrations followed by arsenic species and transcriptomic analysis. ALM2, which has been isolated from Mono Lake, an arsenic-rich soda lake, could resist up to 5 mM arsenite, whereas ARh2, which was isolated from a Kenyan soda lake, could only grow up to 0.1 mM arsenite. Interestingly, both species oxidized arsenite to arsenate under aerobic conditions, although ARh2 does not contain any known arsenite oxidases, and in ALM2, only B2 was clearly upregulated. However, we found the expression of a SoeABC-like gene, which we assume might have been involved in arsenite oxidation. Other arsenite stress responses for both strains were the upregulation of the vitamin B synthesis pathway, which can be linked to antioxidant activity, and the up- and downregulation of different DsrE/F-like genes whose roles are still unclear. Moreover, ALM2 induced the gene operon and the Pst system, and ARh2 upregulated the and genes as well as different heat shock proteins. Our findings for confirm previously observed adaptations to arsenic, but also provide new insights into the arsenic stress response and the connection between the arsenic and the sulfur cycle.
该属包括从世界各地不同苏打湖分离出的嗜盐碱化能自养型硫氧化细菌。这些湖泊中的一些除了极端的盐碱环境外，还存在其他恶劣条件，细菌需要适应这些条件。例如，加利福尼亚州东部苏打湖中的砷，其浓度高达3000μM。砷是一种广泛存在的元素，可能成为一个环境问题，因为它对大多数生物具有高毒性。然而，以解毒形式存在的抗性机制很普遍，一些原核生物甚至可以将砷用作能源。我们首先在76株菌株的基因组中筛选已知的砷氧化还原酶，发现了15个假定的ArxA（亚砷酸盐氧化酶）和2个假定的ArrA（砷酸盐还原酶）。随后，我们通过比较基因组学以及在不同亚砷酸盐浓度下培养它们，然后进行砷形态和转录组分析，详细研究了ALM2和ARh2对亚砷酸盐的抗性。从富含砷的莫诺湖分离出的ALM2能够抵抗高达5 mM的亚砷酸盐，而从肯尼亚苏打湖分离出的ARh2在高达0.1 mM的亚砷酸盐环境中才能生长。有趣的是，尽管ARh2不包含任何已知的亚砷酸盐氧化酶，且在ALM2中只有B2明显上调，但这两个物种在有氧条件下都能将亚砷酸盐氧化为砷酸盐。然而，我们发现了一个类似SoeABC的基因的表达，我们认为它可能参与了亚砷酸盐的氧化。这两个菌株的其他亚砷酸盐应激反应包括维生素B合成途径的上调，这可能与抗氧化活性有关，以及不同的DsrE/F样基因的上调和下调，其作用仍不清楚。此外，ALM2诱导了基因操纵子和Pst系统，ARh2上调了基因以及不同的热休克蛋白。我们对……的研究结果证实了之前观察到的对砷的适应性，但也为砷应激反应以及砷与硫循环之间的联系提供了新的见解。
