Aliidiomarina minuta sp. nov., a haloalkaliphilic bacterium that forms ultra-small cells under non-optimal conditions

An aerobic haloalkaliphilic bacterium, designated strain MLST1(T), was isolated from filtered (0.22 µm) Mono Lake (USA) waters. The isolate was observed to grow primarily on yeast extract, peptone and tryptone. Optimal growth occurred in media at pH 9.5 containing 5-11 g/l yeast extract, and 70-100 g/l NaCl. When in log phase of growth, cells were found to be mostly curved motile rods (1-3 µm length by 0.4-1 µm diameter). Phylogenetic analysis of the 16S rRNA gene and chemotaxonomic data revealed that the isolate belonged to the family Idiomarinaceae, and is closely related to Aliidiomarina maris (96.67 % sequence similarity). The major fatty acids were identified to be iso-C17:1 ω9c (27.1 %), iso-C17:0 (21.3 %) and iso-C15:0 (12.2 %). Predominant polar lipids included phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylglycerol, and the major respiratory quinone was identified as Q8. The DNA base composition was 46.3 mol% G+C. Survival studies indicated that strain MLST1(T) remains viable after exposure to adverse conditions, particularly in the prolonged absence of a carbon source, at low temperatures and with no NaCl. Under these conditions, the cells shrunk to around 0.2 µm in length by 0.1 µm in diameter and passed through 0.22 µm filters. The ultra-small cells could only be resuscitated in media with low levels of yeast extract, up to 0.6 g/l. Once resuscitated, cells were able to grow to full size. Strain MLST1(T) is clearly a unique bacterium in the waters of Mono Lake and the name Aliidiomarina minuta sp. nov. is proposed. The type strain is MLST1(T) (=JCM 17425(T) = KCTC 23357(T)).