Sample preparation, humidity and ash determination

Culture samples are collected and centrifuged for 10 min at 4°C, and then carefully washed twice with demineralized water. Collected biomass corresponding to 2-3 g dry weight is freeze-dried [34]. 

Since the samples are very hygroscopic, humidity determination has to be performed in parallel to elemental analyses. For that purpose, samples are equilibrated at room ambient conditions in Petri dishes for several hours just before use. Aliquots of 0.5 to 1 g are weighted and dried for 24 h at 100°C to determine the humidity content (/moisture) in triplicate. The CHN content obtained from the analyzer for each element k (/j.hum) are corrected for humidity content as follows to obtain the mass fraction of the element on dry weight. 

Hydrogen content also has to be corrected for water content. 

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