Abstract EANA2026-108

Microorganisms govern the biogeochemical cycles of elements on Earth and likely on any other planet. Microbial growth in nature must be tightly regulated to limit their potential exponential growth which otherwise would fill up a planet in a matter of a few days. On Earth, we have tested for the general capability of a variety of prokaryotes to thrive under tight nutrient-limiting conditions allowing very slow growth. This slow growth was around 105-fold lower than the tested species optimum growth rates. This slow growth is generally named near-zero growth. All species tested were able to maintain near-zero growth rates in the laboratory showing doubling times even slower than one year. To this aim we used a retentostat which provides a continuous culturing system open for the medium and closed to the cells. This system is independent on culture medium, growth conditions and the species to be cultured, thus, representing a general approach to analyze microbial behavior and growth everywhere. RNA content per cell decreased drastically with decreasing growth rates. RNA sequencing analyses suggested specific responses by different species with a general strategy aimed to increase metabolic efficiency of resources, use non-preferential substrates, inhibition of cell division processes, reduction of biosynthetic pathways and enhancement of secondary metabolites to fight competence. When exploring life in other planets, or under extreme conditions, one should expect the possibility that microorganisms can be thriving under very reduced growth, at near-zero growth, that is, in many case scenarios, microbial growth will be asymptotically approaching maintenance or zero growth which might lead to additional difficulty to detect their activity and analyze their behavior and role in the environment under study.