The concept of bacterial dark matter stems from our inability to culture most microbes and represents a fundamental gap in our knowledge of microbial diversity. Herein we present the domestication of such an organism: a previously uncultured, novel species from the rare-Actinomycetes genus
Verrucosispora
. Although initial recovery took >4 months, isolation of phenotypically distinct, domesticated generations occurred within weeks. Two isolates were subjected to phenogenomic analyses, revealing domestication correlated with enhanced growth rates in nutrient-rich media, but diminished capacity to metabolize diverse amino acids. This is seemingly mediated by genomic atrophy through a mixed approach of pseudogenization and reversion of pseudogenization of amino acid metabolism genes. Conversely, later generational strains had enhanced spore germination rates, potentially through the reversion of a sporulation-associated kinase from pseudogene to true gene status. We observed that our most wild-type isolate had the greatest potential for antibacterial activity, which correlated with extensive mutational attrition of biosynthetic gene clusters in domesticated strains. Comparative analyses revealed wholesale genomic reordering in strains, with widespread SNP, indel and pseudogene-impactful mutations observed. We hypothesize that domestication of this previously unculturable organism resulted from the shedding of genomic flexibility required for life in a dynamic marine environment, parsing out genetic redundancy to allow for a newfound cultivable amenability.
Importance
The majority of environmental bacteria cannot be cultured within the laboratory. Understanding why only certain environmental isolates can be recovered is key to unlocking the abundant microbial dark matter that is widespread on our planet. In this study we present not only the culturing but domestication of just such an organism. Although initial recovery took >4 months, we were able to isolate distinct, sub-passaged offspring from the originating colony within mere weeks. A phenotypic and genotypic analysis of our generational strains revealed that adaptation to life in the lab occurred as a result of wholesale mutational changes. These permitted an enhanced ability for growth in nutrient rich media, but came at the expense of reduced genomic flexibility. We suggest that without dynamic natural environmental stressors our domesticated strains effectively underwent genomic atrophy as they adapted to static conditions experienced in the laboratory.