Bacteria closely related to Bacilluspumilus cannot be distinguished from such other species as B.safensis,B.stratosphericus,B.altitudinis and B.aerophilus simply by 16S rRNA gene sequence.In this report,76 marine strainswere subjected to phylogenetic analysis based on 7housekeeping genes to understand the phylogeny and biography in comparison with other origins.A phylogenetic tree based on the7 housekeeping genes concatenated in the order of gyrB-rpoB-pycA-pyrE-mutL-aroE-trpBwas constructed and compared with trees based on the single genes.All these trees exhibited a similar topology structure with small variations.Our 79 strains were divided into 6 groups from A to F;Group A was the largest and contained49 strains close to B.altitudinis.An additional two large groups were presented by B.safensis and B.altitudinis.Among the housekeeping genes,gyrB and pyrE showed comparatively better resolution power and may serve as molecular markers to distinguish these closely related strains.Furthermore,arecombinant phylogenetic tree based on the gyrB gene and containing 73 terrestrial and our isolates was constructed to detect the relationship between marine and other sources.The tree clearly showed that the bacteria of marine origin were clustered together in all the large groups.In contrast,the cluster belonging to B.safensis was mainly composed of bacteriaof terrestrial origin.Interestingly,nearly all the marine isolates were at the top of the tree,indicating the possibility of the recent divergence of this bacterial group in marine environments.We conclude that B.altitudinis bacteria are the most widely spread of the B.pumilus group in marine environments.In summary,this report provides the first evidence regarding the systematic evolution of this bacterial group,and knowledge of their phylogenetic diversity will help in theunderstanding of theirecological role and distribution in marine environments.