Faculty of Marine Bioscience, Fukui Prefectural University, 1-1, Gakuencho, Obama, Fukui 917-0003, Japan.
Microbes Environ. 2012;27(2):171-8. doi: 10.1264/jsme2.me11329.
Small cyanobacteria (<2 µm, pico-cyanobacteria) are abundant in waters deeper than the oxic-anoxic zone in the halocline of a saline meromictic lake, Lake Suigetsu, Fukui, Japan. We have isolated 101 strains that were grouped into six groups by means of the phycobiliprotein composition and sequence homology of the intergenic spacer between the 16S and 23S rRNA genes. Significant growth was observed under weak green light (1.5 µmol m⁻² s⁻¹, approx. 460 to 600 nm), whereas the cells died under white light at even moderate intensities. The isolates grew in a wide range of salinities (0.2 to 3.2%). Tolerance to sulfide varied: four groups grew in medium containing sulfide, however, two groups did not. None of the isolates were capable of anoxygenic photosynthetic (PS-II independent photosynthetic) growth using sulfide as an electron donor. All groups were included within fresh and brackish water of Synechococcus/Cyanobium clade, but they were not monophyletic in the 16S rRNA gene-based phylogenetic tree. The physiological properties of pico-cyanobacteria showed that they had the ability to survive in unique physicochemical environments in the halocline of this saline meromictic lake.
小型蓝藻（<2 µm，微微型蓝藻）在日本福井县的 Suigetsu 盐水分层湖中盐度跃层深处的含氧-缺氧带以下的水域中大量存在。我们通过藻胆蛋白组成和 16S 和 23S rRNA 基因之间的基因间隔区的序列同源性，将 101 株分离株分为六组。在弱绿光（1.5 µmol m⁻² s⁻¹，约 460 到 600nm）下观察到显著的生长，而在白光下即使在中等强度下细胞也会死亡。分离株在广泛的盐度范围内生长（0.2 到 3.2%）。对硫化物的耐受性不同：有四组在含有硫化物的培养基中生长，但有两组不能。没有一组分离株能够利用硫化物作为电子供体进行厌氧光合作用（PS-II 独立光合作用）。所有组都属于新鲜和微咸水的 Synechococcus/Cyanobium 进化枝，但它们在基于 16S rRNA 基因的系统发育树中不是单系的。微微型蓝藻的生理特性表明它们有能力在这种盐水分层湖的盐度跃层中独特的物理化学环境中生存。
