## 3 Results and Discussion
### Biofilm Formation on the Perlite Carrier
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c} \hline A1-7 & +a & + & + & + & + & ++ & + & A11-30 & +b & + & - & - & + & - & + \\ A2-2 & +a & + & - & - & ++ & + & + & A11-36 & - & ++ & + & + & + & + & + & + \\ A2-5 & - & + & + & + & + & - & ++ & A11-37 & - & ++ & + & + & + & - & ++ \\ A4-9 & - & ++ & + & + & + & + & - & A13-11 & - & ++ & + & + & + & - & ++ \\ A4-11 & +a & + & + & - & + & + & + & - & A15-11 & - & - & - & - & + & + & + \\ A4-15 & - & - & - & - & + & - & - & A16-3 & - & ++ & + & + & + & ++ & ++ \\ A4-18 & - & + & + & + & + & ++ & + & A16-4 & - & ++ & + & + & + & + & + & + \\ A4-26 & - & ++ & + & + & + & + & ++ & A16-7 & - & ++ & + & + & + & - & ++ \\ A4-31 & - & + & + & - & + & ++ & + & A16-52 & +a & ++ & + & + & + & + & ++ \\ A4-33 & +a & + & + & + & + & - & + & A18-14 & +a & ++ & + & + & + & - & ++ \\ A4-49 & - & + & + & + & + & - & + & A18-15 & - & ++ & + & + & ++ & ++ & ++ \\ A6-12 & +a & + & + & + & + & + & + & A20-1 & +a & ++ & + & + & + & ++ & ++ \\ A7-3 & - & + & + & + & ++ & + & A20-2 & +a & ++ & + & + & + & + & - & + \\ A7-13 & - & - & - & - & + & ++ & + & A20-3 & +a & ++ & + & + & + & - & + \\ A7-17 & - & ++ & + & + & + & + & + & A20-5 & +a & ++ & + & + & + & + & ++ \\ A7-22 & - & ++ & + & + & + & ++ & - & A20-6 & - & + & + & - & + & ++ & + \\ A8-4 & +b & + & - & - & + & + & - & A20-13 & +a & - & + & - & + & ++ & ++ \\ A10-3 & - & + & + & - & + & + & + & A30-7 & - & + & + & - & + & ++ & + \\ A10-13 & +b & + & + & + & + & - & ++ & A30-14 & - & ++ & + & + & + & ++ & ++ \\ A11-10 & - & ++ & + & + & + & + & - & + & A30-32 & +a & ++ & + & + & + & ++ & ++ \\ A11-29 & - & ++ & + & + & + & + & + & + & + & + & + & + & + & ++ & ++ \\ \hline \end{tabular}  
* The mean values followed by the same letter for each experimental variable are not significantly different at \(p=0.05\) compared to the positive control in the crystal violet essay at 30 °C in EMA media. \({}^{2}\)++, excellent growth. \(+\) good growth. The growth capacity in the NFB medium is related to the ability to fix nitrogen in association with the presence of diazotrophic structures and aerial mycelium.  
\end{table} 
Table 3: Results of the PGP attributes of Avocado Rhizosphere Isolates. Moreover, to verify the difference with the non-formation of a biofilm on perlite by some actinobacteria reported as non-biofilm-forming in Table 3 (i.e., the ARI_A7-3 and ARI_A13-11 strains), such isolates were randomly induced on perlite and observed using SEM. There was no successful colonization of perlite beads by actinobacteria, leaving almost all the pores exposed (Figure 2A,C). A low actinobacteria population is observed on the perlite surface without covering it with a biofilm. Furthermore, a few bacteria were found at a higher magnification but without evidence of biofilm formation (indicated by number 1 in Figure 2B,D). Most of the outer surface of the perlite was exposed without biofilm formation (indicated by number 2 in the micrographs of Figure 2B,D). Thus, it was confirmed that the CV biofilm formation tests helped to have better orientation and discrimination for the correct selection of isolates that were and were not biofilm formers. It should be emphasized that the materials were different, though, because perlite is a mineral surface, while polypropylene was used for the CV tests. Thus, it cannot be ruled out that some isolates may have an affinity for perlite and have been previously reported to be unfavorable by CV tests. However, in this case, biofilm formation on perlite was consistent with the CV tests. To some _Streptomyces_ species, the formation of the pellets is more common when bacteria have contact with smaller particles, which as a result, can become free and have large pellets with no attachment to any surface [25]. This was the case in this work with some isolates under study. _Streptomyces_ biofilm development appears to be a regular aspect of these bacteria's life cycle, albeit there exist little data on it [25].