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A novel chemoheterotrophic iron-reducing micro-organism, designated as strain LSZ-M11000 T , was isolated from sediment of the Marianas Trench. Phylogenetic analysis based on the 16S rRNA gene revealed that strain LSZ-M11000 T belonged to genus Tepidibacillus , with 97 % identity to that of Tepidibacillus fermentans STGH T , a mesophilic bacterium isolated from the Severo-Stavropolskoye underground gas storage facility in Russia. The polar lipid profile of strain LSZ-M11000 T consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, as well as other unidentified phospholipids and lipids. The major fatty acids were C 16 : 0 (28.4 %), C 18 : 0 (15.8 %), iso-C 15 : 0 (12.9 %), and anteiso-C 15 : 0 (12.0 %). Strain LSZ-M11000 T had no menaquinone. Genome sequencing revealed that the genome size of strain LSZ-M11000 T was 2.97 Mb and the DNA G+C content was 37.9 mol%. The average nucleotide identity values between strain LSZ-M11000 T and its close phylogenetic relatives, Tepidibacillus fermentans STGH T and Tepidibacillus decaturensis Z9 T , were 76.4 and 72.6 %, respectively. The corresponding DNA-DNA hybridization estimates were 20.9 and 23.4 %, respectively. Cells of strain LSZ-M11000 T were rod-shaped (1.0-1.5×0.3-0.5 µm). Using pyruvate as an electron donor, it was capable of reducing KMnO 4 , MnO 2 , As(V), NaNO 3 , NaNO 2 , Na 2 SO 4 , Na 2 S 2 O 3 , and K 2 Cr 2 O 7 . Based on phenotypic, genotypic, and phylogenetic evidence, strain LSZ-M11000 T is proposed to be a novel strain of the genus Tepidibacillus , for which the name Tepdibacillus marianensis is proposed. The type strain is LSZ-M11000 T (=CCAM 1008 T =JCM 39431 T ).