Beneath our feet lies a world full of mystery—a realm where secrets of life await discovery. In

our investigation of subsurface habitats, including groundwater and seepage water from the

Hainich CZE (Critical Zone Exploratory) and a cave in Baden-Württemberg, we initiated a quest

to cultivate the hidden diversity of subsurface habitats and the untapped microbial life they

harbor. The main aim of the investigation: planctomycetes, with their complex cell structure,

multiple genes of unknown function and partly mysterious lifestyles.

Equipped with cultivation techniques that employed both oxic and anoxic approaches, we

proceeded to investigate these enigmatic environments. Each habitat with varying nutrient-,

oxygen-, and pH- conditions but with the one common factor of being completely shrouded

in darkness.

As the cultivation of these samples proceeded, a sense of anticipation arose from the

darkness. Who are these microbial players, and what secrets might they hold? And then on a

random Friday the breakthrough was achieved – The first groundwater Planctomycete was

isolated from an enormous number of plates. And there was more to come, more to

investigate and more to be fascinated by. Several isolates from the five phyla of

Actinomycetota, Bacilli, Bacteroidota, Planctomycetota, and Pseudomonadota were obtained,

including novel species that had never seen the light of the day.

An overview of these isolates and novel species for all investigated subsurface habitats and a

characterisation of all isolated planctomycetal species will be presented to uncover the buried

secrets of subsurface habitats.