Genomes of "Spiribacter", a streamlined, successful halophilic bacterium.
BACKGROUND
Thalassosaline waters produced by the concentration of seawater are widespread and common extreme aquatic habitats. Their salinity varies from that of sea water (ca. 3.5%) to saturation for NaCl (ca. 37%). Obviously the microbiota varies dramatically throughout this range. Recent metagenomic analysis of intermediate salinity waters (19%) indicated the presence of an abundant and yet undescribed gamma-proteobacterium. Two strains belonging to this group have been isolated from saltern ponds of intermediate salinity in two Spanish salterns and were named "Spiribacter".


RESULTS
The genomes of two isolates of "Spiribacter" have been fully sequenced and assembled. The analysis of metagenomic datasets indicates that microbes of this genus are widespread worldwide in medium salinity habitats representing the first ecologically defined moderate halophile. The genomes indicate that the two isolates belong to different species within the same genus. Both genomes are streamlined with high coding densities, have few regulatory mechanisms and no motility or chemotactic behavior. Metabolically they are heterotrophs with a subgroup II xanthorhodopsin as an additional energy source when light is available.


CONCLUSIONS
This is the first bacterium that has been proven by culture independent approaches to be prevalent in hypersaline habitats of intermediate salinity (half a way between the sea and NaCl saturation). Predictions from the proteome and analysis of transporter genes, together with a complete ectoine biosynthesis gene cluster are consistent with these microbes having the salt-out-organic-compatible solutes type of osmoregulation. All these features are also consistent with a well-adapted fully planktonic microbe while other halophiles with more complex genomes such as Salinibacter ruber might have particle associated microniches.
Mario
M
López-Pérez
Rohit
R
Ghai
Maria Jose
MJ
Leon
Ángel
Á
Rodríguez-Olmos
José Luis
JL
Copa-Patiño
Juan
J
Soliveri
Cristina
C
Sanchez-Porro
Antonio
A
Ventosa
Evolutionary Genomics Group, División de Microbiología, Universidad Miguel Hernández, Apartado 18, San Juan 03550, Alicante, Spain. frvalera@umh.es.
Francisco
F
Rodriguez-Valera
D014644:Genetic Variation; D016680:Genome, Bacterial; D056186:Metagenomics; D010802:Phylogeny; D020560:Proteobacteria / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification*; D054712:Salinity; D012623:Seawater / Q000382:microbiology*; D012965:Sodium Chloride / Q000737:chemistry; D013030:Spain; D014871:Water Microbiology
D012965:Sodium Chloride