Chaperones are transcriptional regulators and can co-ordinate the expression of the genes involved in a stress response and improve LAB stress tolerance [19]. Molecular chaperones also have a number of other functions, for example protein folding, preventing protein aggregation, targeting proteins for secretion, and the transfer of peptides across membranes [41, MLN8237 ic50 42]. Hsp60 (GroEL) and Hsp70 (DnaK) are both well-conserved proteins in lactobacilli and bifidobacteria and are most efficiently induced by heat [43, 44]. Some of the LAB symbionts produced DNA chaperones

extra-cellularly (Lactobacillus Hon2N, LY2874455 Hma11N, Bin4N, and Bifidobacterium Hma3N, which produced DnaK or GroEL, Additional file 1). Bifidobacterium Hma3N produced both when stressed with LPS for 3 days, while Lactobacillus Hon2N produced both of the chaperonins DnaK YH25448 price and CsaA, and also the two universal stress proteins UspA when stressed with LPS for 1 day (Additional file 1). These molecular chaperones are usually seen within the bacterial cytosol, however

there have been reports showing that bacteria can produce them extra-cellularly as “moonlighting” proteins [45]. The LAB may produce enzymes extra-cellularly to interact with their host, since many adhesion molecules are needed in such a harsh environment. Bergonzelli et al. reported that chaperonin GroEL of Lactobacillus johnsonii has been found on the surface of the cells and could interact with Helicobacter pylori, indicating a competition for binding sites in humans [41]. However, the LAB symbionts may release the chaperonins to aid in the folding of other secreted proteins that are more typically their function [40]. We did notice that 16% of the known proteins discussed in Table  2 had signal peptide

sequences however many more of the proteins produced can be transported from the cell without the need for these signals, for example bacteriocins, DNA chaperones and some enzymes. More research should be performed to investigate the mode of extra-cellular transport in order to understand the functions of these produced proteins. We can see from the majority of Non-specific serine/threonine protein kinase the extra-cellularly produced proteins secreted by the 13 symbiotic LAB, were produced under stress by LPS, which was extracted from Pseudomonas aeruginosa. Interestingly, species within the genus Pseudomonas are often isolated from flowers and introduced into bees and their crop by nectar foraging [15]. Our results show that lipotechoic acid (LA) was not as an effective stressor as LPS, however it is important to remember that during stress many LAB produce different proteins, but the production of these proteins can differ depending on the stress [19]. This is outlined in our results and is important to remember when performing any other future experiments.