# Bacterial Therapy of Cancer: A Way to the Dustbin of History or to the Medicine of the Future?
## 6 Future Perspectives: Bacteriobots? The term \"bacteriobot\"--bacterial microrobot--has been used in some articles to denote a new innovative thermostic methodology of bacteria-based fabrication for tumor therapy. However, in a more general sense, it can be used to refer to any bacterium that has been in any way intentionally modified [77; 126; 127]. It is worth noting that recent years are characterized by an explosive increase in the number of articles devoted to the creation of modified bacteria suitable for use as antitumor agents. This is due to the rapid development of genetic engineering methods; in particular, genome editing methods. Therefore, it is very likely to expect that, in the near future, we will observe a qualitative shift in this field of science. In this article, rather, retrospective, we did not set out to cover this issue in detail, so we will only touch on general trends. This topic is described in more detail in a number of excellent recent reviews [128; 129; 130]. One of the biggest challenges in cancer research is an efficient drug delivery to the tumor regions. To solve this problem, miniature devices would be suitable, characterized by active motion towards the tumor, penetration inside, and the accumulation in the tumor or nearby tissues. Such devices can be completely synthetic (chemically and/or physically actuated) containing only man-made materials, structures, and components, or cellular microrobots (biologically actuated) that exclusively consist of cell-made components and which are precision-engineered to exhibit anticancer effects. Moreover, hybrid versions consisting of both artificial and cell-made components that can be propelled by biological or artificial means (usually biologically actuated) can be constructed. The use of natural bacteria, particularly human commensals, as a vector for transferring a chemotherapeutic agent directly into the tumor could significantly reduce the side effects of treatment that usually accompany traditional chemotherapy [131; 132]. Bacteria can reach the target passively by blood flow or more actively, for example, with the help of flagella. Bacterial flagella rotate in a propeller-like fashion and can achieve swimming speeds up to 300 \(\upmu\)m/s. An attractive idea appears to be to use magnetic fields for guiding magnetic particles from their application site to the cancer, independently of the tumor localization. In this case, bacteria must be sensitive to magnetic fields. An interesting example includes magnetotactic bacteria, which contain naturally synthesized magnetic particles (magnetosomes), allowing them to sense magnetic fields and align their swimming directions along them [72; 128]. Thus, _Magnetococcus marinus_ (MC1) is a Gram-negative coccus found in the Atlantic Ocean. This microorganism has cilia arranged in two bundles located at one pole, which enable the bacteria to move (300 \(\upmu\)m/s). Magnetosomes of this bacterium are special elements which are magnetite particles (Fe\({}_{3}\)O\({}_{4}\)) surrounded by membranes, forming chains in the cytosol. The presence of magnetite orients the bacteria with the Earth's magnetic field. Using a powerful magnetic field, the same as in the MRI (magnetic resonance imaging) technique, it would be possible to direct bacteria containing magnetosomes to the tumor. Indeed, in a recent study, magnetic guidance led to significantly enhanced tumor accumulation of peritumally injected MC1-based hybrid microrobots in living mice compared to nonguided MC1 bacteria [133; 134]. Recently, magnetic-sensing _E. coli_ was engineered in [135] by driving the formation of iron-rich bodies into bacterial cells. Enhancing the tumor targeting is other important task that can be solved with the help of bacterial microrobots. As a result of mutations and other genetic/epigenetic aberrations, cancer cells and their microenvironments acquire chemical and physical characteristics that differ from normal cells.