Novel strains of facultatively aerobic, moderately alkaliphilic and facultatively halophilic bacteria were isolated from a sediment sample taken from the Southern Arm of Great Salt Lake, Utah. Cells of strain JW/BP-GSL-QD^T(and related strains JW/BP-GSL-RA and JW/BP-GSL-WB) were rod-shaped, spore-forming, motile bacteria with variable Gram-staining. Strain JW/BP-GSL-QD^Tgrew under aerobic conditions between 14.5 and 47 °C (optimum 39 °C), in the pH^{37 °C}range 6.5–10.3 (optimum pH^{37 °C}8.0), and between 0.1 and 4.5 M Na⁺(optimum 0.9 M Na⁺). No growth was observed in the absence of supplemented Na⁺. Strain JW/BP-GSL-QD^Tutilizedl-arabinose,d-fructose,d-galactose,d-glucose, inulin, lactose, maltose, mannitol,d-mannose, pyruvate,d-ribose,d-sorbitol, starch, trehalose, xylitol andd-xylose under both aerobic and anaerobic conditions, and used ethanol and methanol only under aerobic conditions. Strains JW/BP-GSL-WB and JW/BP-GSL-RA had the same profiles except that methanol was not used aerobically. During growth on glucose, the major organic compounds formed under aerobic conditions were acetate and lactate, and under anaerobic conditions, the fermentation products were formate, acetate, lactate and ethanol. Oxidase and catalase activities were not detected and cytochrome was absent. No respiratory quinones were detected. The main cellular fatty acids were iso-C_{15 : 0}(39.1 %) and anteiso-C_{15 : 0}(36.3 %). Predominant polar lipids were diphosphatidylglycerol, phosphatidylglycerol and an unknown phospholipid. Additionally, a small amount of an unknown glycolipid was detected. The DNA G+C content of strain JW/BP-GSL-QD^Twas 35.4 mol% (determined by HPLC). For strain JW/BP-GSL-QD^Tthe highest degree of 16S rRNA gene sequence similarity was found withAmphibacillus jilinensis(98.6 %),Amphibacillus sediminis(96.7 %) andAmphibacillus tropicus(95.6 %). The level of DNA–DNA relatedness between strain JW/BP-GSL-QD^TandA. jilinensisY1^Twas 58 %. On the basis of physiological, chemotaxonomic and phylogenetic data, strain JW/BP-GSL-QD^Trepresents a novel species of the genusAmphibacillus, for which the nameAmphibacillus cookiisp. nov. is proposed. The type strain is JW/BP-GSL-QD^T( = ATCC BAA-2118^T = DSM 23721^T).