The limitation of using DNA sequence information to infer in situ activity, or even potential metabolic functions, has been looming over the field of environmental microbiology from its early days. This inherit property results from both the fact that, in some cases, two organisms with closeley-related 16S rRNA sequences might posses different metabolic capacities and because even if the function of the organism is known the presence of DNA or even RNA does not necessarily mean that the cells are active \cite{Blazewicz2013}. Using stable isotopes as an indicator of activity is one of the more popular and robust ways to bridge this gap. In environmental microbiology, stable isotopes are either traced in their natural abundance or introduced into the sample in a highly enriched form. In tracing the natural isotopic abundance the activity of microorganimsms, or even specific pathways can be deduced. This approach has been particularly useful in identifying if CH4 is of biogenic origin and through which metabloic pathway was it formed \cite{Conrad_2005}. Stable isotope probing, on the other hand, involves first incubating a sample with a highly-labelled substrate (typically fully labelled) and then using one of various physcial separation or detection methods to detect the active microorganisms and couple this information with DNA seqeunce data \cite{Dumont_2005}. Classically, either PLFA or nucleic acids were targeted in SIP and the labelled moelcules were spearated from the unlabelled ones using an IRMS (for PLFA) or a buoyant density gradient (for DNA and RNA). Following separation, the identity of the labelled organisms is determine using PLFA classification or sequencing. More modern apporaches to SIP also use a combination of Raman microspectroscopy or NanoSIMS with FISH to detect and identify isotopically labelled organisms \cite{Musat_2016,Wang_2016}. However, powerfull as it may be, SIP is unfortunatyely limited to tracing assimilatory processes only, since dissimlatory processes leave no trace in the biomass. Moreover, SIP is limited to using elements that have a stable isotope and are found in the major biomolecules of the cell. In practical terms this is limited to C, N, H or O (but not P) \cite{Angel_2019}. Using SIP, the extent of multiple microbial guilds has been extended, including methanotrophs \cite{Knief2003}, methanogens \cite{Lu_2005}, ammonia oxidisers \cite{Pratscher_2011}, diazotrophs \cite{Buckley_2007}, cellulose-degrading \cite{Pepe-Ranney2016} and many others. SIP has also been instromental in deciphering microbial interatcions \cite{Ho2016,Murase_2007}, and soil food webs \cite{Gorka_2019,DeRito_2005}.