Members of the genus Psychrobacillus are widely distributed across diverse environments, and novel representatives continue to be identified. Here, we describe the strain nc5.1T, isolated from soil near Lake Syltran-Kel in the Kabardino-Balkarian Republic, Russia. Phylogenomic analysis indicated that P. glaciei PB01T was its closest relative, placing the isolate within the genus Psychrobacillus. The average nucleotide identity (84.3%) and digital DNA-DNA hybridization (31%) values compared with PB01T suggested that the isolate represents a novel species. The strain nc5.1T was a Gram-negative, motile, rod-shaped bacterium forming circular, smooth, beige-brown colonies. No morphologically detectable endospores were observed under sporulation-inducing conditions. Optimal growth conditions were pH 6.5, 0.5% NaCl, and 30°C; however, a minor but reproducible viable fraction persisted after exposure to 80°C. Biochemical profiling revealed that the strain assimilated 46 carbon sources spanning carbohydrates, amino acids, and organic acids and exhibited growth in the presence of aztreonam, nalidixic acid, and potassium tellurite. The dominant cellular fatty acids were C14:1 (52.8%), C14:0 (16.0%), and C16:0 (7.7%), which distinguished the isolate from P. glaciei. Genomic analysis identified biosynthetic gene clusters associated with the synthesis of iturin and a streptozotocin-like moiety, suggesting the capacity for biosynthesis of secondary metabolites with beneficial properties. MTT assays showed that culture supernatants did not reduce mammalian cell viability but, conversely, moderately stimulated the proliferation of PANC-1 cells. Together, the phenotypic, chemotaxonomic, and genomic data indicate that strain nc5.1T represents a novel species with the proposed name Psychrobacillus syltrankelensis sp. nov. The type strain is nc5.1T (=RCAM 07221).IMPORTANCEThe discovery of the P. syltrankelensis species extends our understanding of diversity within Bacillaceae and reveals traits that challenge the established views of the family. Based on genomic thresholds, nc5.1ᵀ clearly represents a novel species while also displaying atypical morphological features, such as Gram-negative staining and absence of sporulation. Despite the lack of morphologically detectable endospores, the strain retained viability after exposure to elevated temperatures, further emphasizing its unusual physiological profile. These characteristics underscore the limitations of morphology-based taxonomy and the necessity of genome-guided classification. Genome analysis revealed two adaptive groups within Psychrobacillus, distinguished by mutually exclusive biosynthetic clusters responsible for the synthesis of either iturin or bacillomycin D, with nc5.1ᵀ belonging to the iturin-producing lineage. The nc5.1ᵀ isolate also harbored a highly divergent streptozotocin-like locus, indicating unexplored secondary metabolism with potential biotechnological relevance. At the same time, culture supernatants unexpectedly stimulated the growth of human pancreatic carcinoma cells, underlining the complexity of functional predictions based solely on genomic data. Together, these findings highlight the importance of combining phenotypic, ecological, and genomic approaches for accurate species delineation and provide new insights into the hidden metabolic potential of Psychrobacillus.
Romanenko et al. (Mon,) studied this question.