Culture Supernatant of the Polar Actinomycete Nocardioides antarcticus CCTCC AB 2014053T Resuscitates VBNC Cells, Promotes Bacterial Growth, and Alters Bacterial Diversity in Antarctic Soil

Resuscitation-promoting factor (Rpf) is a secreted protein of some Gram-positive bacteria that exerts significant resuscitative effects on viable but non-culturable (VBNC) microorganisms. Culture supernatants of Rpf-secreting strains, like Rpf itself, can recruit VBNC bacteria and modify soil bacterial diversity. This study investigated the resuscitative and growth-promoting effects of the culture supernatant from the polar actinomycete Nocardioides antarcticus CCTCC AB 2014053T (harboring the rpf gene) on VBNC and normal bacterial cells in Antarctic soil, as well as its impact on soil bacterial diversity. Three VBNC bacterial species—Brachybacterium paraconglomeratum, Staphylococcus edaphicus, and Pseudarthrobacter psychrotolerans—were successfully isolated from 10⁻¹⁰-fold serially diluted Antarctic soil treated with the culture supernatant. The culture supernatant, particularly its high-molecular-weight fraction, significantly promoted the growth of B. paraconglomeratum and P. psychrotolerans (growth rates: 125.0–191.7% relative to the untreated control). In contrast, the low-molecular-weight fraction inhibited the growth of S. edaphicus (growth rates: 52.9–91.7% relative to the control). High-throughput sequencing revealed that treatment with the high-molecular-weight fraction resulted in the classification of 782 soil bacterial genera, an 8.8% increase compared to the control, while the low-molecular-weight fraction reduced the number of genera to 90.9% of the control. Additionally, the culture supernatant altered the soil bacterial community composition, with distinct differences between the high- and low-molecular-weight fractions. These findings demonstrate that the N. antarcticus culture supernatant, containing Rpf, holds potential for isolating novel bacterial taxa by resuscitating VBNC cells and promoting bacterial growth in extreme environments.