We investigated whether TiO$_2$ nanoparticles (NPs) with different size ranges and crystalline forms could affect iron homeostasis in $Pseudomonas\ brassicacearum$. In the $Pseudomonas\ species$, regulation of iron homeostasis involves two sRNAs known as PrrF. We identified two sRNA-encoding genes $prrF1$ and $prrF2$ in the $P.\ brassicacearum$ genome. To investigate the cytotoxicity of TiO$_2$ NPs, we prepared two shapes of anatase titania particles for physico-chemical characterization before and after $in\ vitro$ use. We determined their biological activity by analyzing the TiO$_2$ NPs-bacteria interaction using hyperspectral microscopy, as well as their impact on the intracellular iron content. Overall, our results demonstrate that under dark conditions, TiO$_2$ NPs do not have any impact on bacterial growth. We investigated the adaptive response of bacteria and showed that TiO$_2$ NPs induced oxidant stress and consequently altered iron homeostasis. Furthermore, the bacterial iron content significantly decreased, whereas adsorption of TiO$_2$ NPs on bacterial cells increased. Although we used two different crystalline forms that differ in size and shape, they displayed nearly identical mechanisms of toxicity towards bacteria. Finally, we found that the expression of prrF RNA represents a good indicator of intracellular iron status, yielding new insights into the mechanism underlying TiO$_2$ NP toxicity towards bacteria.