*6.2.2 Influence of nitrogen-substances on microbial growth and development of biofilm*

Influence of nitrogen on biofilm development has been assessed with a specific test. **Figure 4**. shows that organic nitrogen promotes cell growth much more than mineral nitrogen, whose different concentration does not significantly affect the

**Figure 3.** *Biofilm development – Attachment tests in sugar-broth.*

**Figure 4.** *Microbial growth with nitrogen-compounds.*

growth. However, the bigger growth is accompanied by a significant foam formation. This has not been observed when ammonium chloride has been adopted, along with a good clarification, as shown in **Figure 5**. Microscopic observation of the plate fragments collected from the various tests has provided unexpected results (**Figure 6**). Notably, no difference has been detected between biofilms developed with organic and inorganic nitrogen. This disagrees with Mittelman [40] and is in agreement with Abbott et al. [41], according to which the availability of an organic layer next to the attachment surface would be substantially uninfluential, as this would be controlled mainly by electrostatic interactions. Filamentous forms have resulted to be absent in all four tests.
