# The Viable but Non-Culturable (VBNC) State, a Poorly Explored Aspect of Beneficial Bacteria
## 6 Proteomics, Transcriptomics, and Metabolomics of Bacterial Cells in VBNC State
metallidurans_ show that during the transition from the culturable state to the VBNC state, there is a strong decrease in the expression of proteins involved in different mechanisms, such as basal bacterial metabolism, cellular processes, signaling, information storage, protein synthesis pathways, energetic processes, and cell shape regulation [49]. The proteins that show an increase in their regulation are involved in energetic processes and redox reactions. The proteomic analysis of the return to a culturable state showed that gluconate increased the expression of several proteins related to fundamental bacterial metabolism when used. Meanwhile, when only water was added to promote the return to the culturable state, the expression of only six proteins was increased. These results suggest that reduced soil carbon or water availability could initiate the bacterial VBNC state in soil-like environments. This limitation could induce gene expression and protein synthesis, leading to the VBNC state. In recent metabolomics studies of the VBNC state, it has been observed in various bacterial species that active metabolic pathways are linked to the transport and metabolism of inorganic ions, carbohydrates, and amino acids, as well as pathways involved in the synthesis of the cell wall, membrane, and envelope [128]. Additionally, it has been determined that during the VBNC state, there is an augmentation in the amino acid content, consequently leading to the alteration of specific amino acid metabolic pathways, such as the biosynthesis of aminoacyl-tRNA and the metabolism of arginine, proline, alanine, aspartate, and glutamate. Additionally, shifts were observed in D-glutamine and D-glutamate metabolism, \(\beta\)-alanine and arginine biosynthesis, and the valine, leucine, and isoleucine degradation pathways Another notable metabolic change was a substantial increase in cAMP content, which could potentially function as an inducing factor for the VBNC state [129]. Other studies suggest that the glyoxylate cycle serves as a pivotal metabolic pathway for stress resistance and in maintaining cellular metabolic balance during the VBNC state [130]. The metabolomic analysis of _Lacticasibacillus paracasei_ in the VBNC state revealed 25 differential metabolites from five major classes: amino acids, carbohydrates, lipids, vitamins, and purines and pyrimidines. The levels of L-cysteine, L-alanine, L-lysine, and L-arginine increased markedly in the cells that returned to the culturable state, while the levels of cellulose, alginose, and guanine decreased significantly. Cells that left the non-culturable state had higher levels of cysteine, L-glutamic acid, L-arginine, and L-glutamine. A compound identified at high levels was xylooligosaccharide, which probably favors the return to the cultivable state [129]. It is important to note that a universally applicable molecular or metabolic mechanism explaining the VBNC state has not yet been fully developed. Based on the above evidence, the only assertion that we can make is that bacteria exhibit a broad spectrum of possibilities and strategies to enter, persist in, and exit the culturable state. These behaviors will depend on various factors: the specific stress triggering this state, the mechanisms facilitating its reversal, and the characteristics unique to each bacterial species.