Madigan Michael T, Bender Kelly S, Parenteau Mary N, Kimura Yukihiro, Wang-Otomo Zheng-Yu, Sattley W Matthew
School of Biological Sciences, Program in Microbiology, Southern Illinois University, Carbondale, Illinois, USA.
Exobiology Branch, NASA Ames Research Center, Moffett Field, California, USA.
Extremophiles. 2025 Jan 25;29(1):12. doi: 10.1007/s00792-025-01380-8.
Rhodothalassium (Rts.) salexigens is a halophilic purple nonsulfur bacterium and the sole species in the genus Rhodothalassium, which is itself the sole genus in the family Rhodothalassiaceae and sole family in the order Rhodothalassiales (class Alphaproteobacteria). The genome of this phylogenetically unique phototroph comprises 3.35 Mb and is highly chimeric, with nearly half of its genes originating from families other than the Rhodothalassiaceae, many of which lack phototrophic species. Photosynthesis genes in Rts. salexigens are not arranged in a typical photosynthesis gene cluster but are scattered across the genome, suggesting an origin from horizontal transfers. Despite an encoded RuBisCO, autotrophy has not been observed in Rts. salexigens, and enzymes that oxidize common inorganic electron donors are not encoded. Phospholipid biosynthesis in Rts. salexigens is restricted, and phosphoglycerolipids are the only phospholipids present in its intracytoplasmic membranes. Rts. salexigens fixes nitrogen using a Mo-containing nitrogenase and uses ammonia despite previous results that indicated it was a glutamate auxotroph. Glycine betaine is the sole osmolyte in Rts. salexigens, and enzymes are encoded that facilitate both its uptake and its biosynthesis from glycine. The genomic data also support chemotactic swimming motility, growth over a range of salinities, and the production of membrane-strengthening hopanoids.
嗜盐红钾菌（Rhodothalassium (Rts.) salexigens）是一种嗜盐紫色非硫细菌，是红钾菌属中的唯一物种，而红钾菌属本身是红钾菌科中的唯一属，红钾菌科又是红钾菌目（α-变形菌纲）中的唯一科。这种在系统发育上独特的光合生物的基因组由335万个碱基对组成，且高度嵌合，其近一半的基因源自红钾菌科以外的家族，其中许多家族缺乏光合物种。嗜盐红钾菌中的光合作用基因并非排列在典型的光合作用基因簇中，而是分散在基因组中，这表明其起源于水平转移。尽管编码了核酮糖-1,5-二磷酸羧化酶/加氧酶（RuBisCO），但在嗜盐红钾菌中未观察到自养现象，且未编码氧化常见无机电子供体的酶。嗜盐红钾菌中的磷脂生物合成受到限制，磷酸甘油脂是其胞内膜中仅有的磷脂。嗜盐红钾菌使用含钼固氮酶固定氮并利用氨，尽管先前的结果表明它是谷氨酸营养缺陷型。甘氨酸甜菜碱是嗜盐红钾菌中唯一的渗透溶质，并且编码了促进其摄取和从甘氨酸生物合成的酶。基因组数据还支持趋化性游动运动、在一系列盐度范围内生长以及产生增强膜的藿烷类化合物。
