Some sulfur, and other halogen and nitrogen compounds are also found. It has been established that microbiota produce organic metabolic products characteristic of the organism. Very likely, the amount and possibly even the kind of metabolites produced are affected by the temperature, moisture level and possibly other environmental factors. It also seems that the kind of metabolites produced are very much dependent on the nature of the substrate upon which the organism grows. Many microorgainsms are known to grow preferentially upon certain substrates.
Some organisms seem to prefer wood or other cellulosic substrates.
Others thrive on gypsum or wallboard. Some grow well in metal or fiberglass ducts using only the debris in the duct for their nutrients. All molds may produce toxins at some time under certain conditions. Some molds such as Penicillum and Fusarium species, as well as Aspergillus fumigatus and Aspergillus versicolor and Stachybotrys, when found growing indoors, should always be of concern. Essential for all microbial growth, in addition to adequate nutrients, is enough water and sufficient warmth.