Chloroflexus aggregans is a thermophilic filamentous anoxygenic phototrophic bacterium frequently found in microbial mats in natural hot springs. C. aggregans often thrives with cyanobacteria that engage in photosynthesis to provide it with an organic substrate; however, it sometimes appears as the dominant phototroph in microbial mats without cyanobacteria. This suggests that C. aggregans has the ability to grow photoautotrophically. However, photoautotrophic growth has not been observed in any cultured strains of C. aggregans. We herein attempted to isolate a photoautotrophic strain from C. aggregansdominated microbial mats in Nakabusa hot spring in Japan. Using an inorganic medium, we succeeded in isolating a new strain that we designated “ACA-12”. A phylogenetic analysis based on 16S rRNA gene and 16S-23S rRNA gene internal transcribed spacer (ITS) region sequences revealed that strain ACA-12 was closely related to known C. aggregans strains. Strain ACA-12 showed sulfide consumption along with autotrophic growth under anaerobic light conditions. The deposited elemental sulfur particles observed by microscopy indicated that sulfide oxidation occurred, similar to that in photoautotrophic strains in the related species, C. aurantiacus. Moreover, we found that other strains of C. aggregans, including the type strain, also exhibited a slight photoautotrophic growing ability, whereas strain ACA-12 showed the fastest growth rate. This is the first demonstration of photoautotrophic growth with sulfide in C. aggregans. The present results strongly indicate that C. aggregans is associated with inorganic carbon incorporation using sulfide as an electron donor in hot spring microbial mats.

中文翻译：

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丝状无氧光养细菌中的硫化物依赖性光能自养，Chloroflexus aggregans

Chloroflexus aggregans 是一种嗜热丝状无氧光养细菌，常见于天然温泉的微生物垫中。C. agregans 通常与参与光合作用的蓝藻一起繁衍生息，从而为其提供有机底物；然而，它有时在没有蓝藻的微生物垫中表现为主要的光养生物。这表明 C. agregans 具有光合自养生长的能力。然而，在任何培养的聚集体 C. 菌株中都没有观察到光合自养生长。我们在此尝试从日本 Nakabusa 温泉的聚集体 C. aggregans 主导的微生物垫中分离光合自养菌株。使用无机培养基，我们成功地分离出我们命名为“ACA-12”的新菌株。基于 16S rRNA 基因和 16S-23S rRNA 基因内部转录间隔区 (ITS) 区域序列的系统发育分析表明，ACA-12 菌株与已知的聚集聚集体菌株密切相关。菌株 ACA-12 在厌氧光照条件下显示出硫化物消耗以及自养生长。通过显微镜观察到的沉积元素硫颗粒表明发生了硫化物氧化，类似于相关物种 C. aurantiacus 中的光合自养菌株。此外，我们发现其他聚集聚集体的菌株，包括类型菌株，也表现出轻微的光合自养生长能力，而菌株 ACA-12 显示出最快的生长速度。这是第一次证明聚集体中硫化物光合自养生长。目前的结果强烈表明 C.