Exploring the potential of Micrococcus luteus culture supernatant with resuscitation-promoting factor for enhancing the culturability of soil bacteria

A bacterial species is best characterized after its isolation in pure culture. This is an arduous endeavor for many soil microorganisms, but it can be simplified by several techniques aiming to improve culturability: for example, by using growth-promoting factors. We investigated the potential of Micrococcus luteus culture supernatant containing resuscitation-promoting factor (SRpf) to increase the number and diversity of cultured bacterial taxa from a nutrient-rich compost soil. Phosphate-buffered saline and enzyme-inactivated SRpf were included as controls. After agitation with SRpf for one day, the soil suspension was diluted and plated on two different solid, oligotrophic media: ten times diluted Reasoner 2A agar (R2A) and soil extract-based agar (SA). Colonies were collected from the plates to assess differences in diversity among different treatments and cultivation media. The diversity on both R2A and SA was higher in the SRpf-amended extracts than on the controls, yet the differences on R2A were higher. Diversity in the soil extracts was also determined by 16S rRNA amplicon sequencing, which showed an increase in the relative abundance of specific taxa before their successful cultivation. Conclusively, SRpf can effectively enhance the growth of soil bacterial species including those hitherto uncultured.