A microbial ecosystem in which bacteria no longer live in a mutualistic association is called dysbiotic. Gut microbiota dysbiosis is a condition related with the pathogenesis of intestinal illnesses (irritable bowel syndrome, celiac disease, and inflammatory bowel disease) and extra-intestinal illnesses (obesity, metabolic disorder, cardiovascular syndrome, allergy, and asthma). Dysbiosis status has been related to various important pathologies, and many therapeutic strategies aimed at restoring the balance of the intestinal ecosystem have been implemented. These strategies include the administration of probiotics, prebiotics, and synbiotics; phage therapy; fecal transplantation; bacterial consortium transplantation; and a still poorly investigated approach based on predatory bacteria. This review discusses the various aspects of these strategies to counteract intestinal dysbiosis.

Aims:  To analyse the environmental stimuli modulating violacein and biofilm production in Janthinobacterium lividum. Methods and Results:  Violacein and biofilm production by J. lividum DSM1522T was assayed in different growth conditions. Our data suggest that violacein and biofilm production is controlled by the carbon source, being inhibited by glucose and enhanced by glycerol. J. lividum produced violacein also in the presence of different sub‐inhibitory concentrations of ampicillin. As opposite, the production of N‐acylhomoserine lactone(s), quorum sensing regulators was shown to be positively regulated by glucose. Moreover, violacein‐producing cultures of J. lividum showed higher CFU counts than violacein‐nonproducing ones. Conclusions:  Taken together, our results suggest that violacein and biofilm production could be regulated by a common metabolic pathway and that violacein as well as biofilm could represent a response to environmental stresses and a key factor in the survival mechanisms of J. lividum. Significance and Impact of the Study:  Although several recent studies disclosed a number of interesting biological properties of violacein, few data are reported on the physiologic function of violacein in J. lividum. This paper adds new information on the complex mechanisms allowing and regulating bacterial life in hostile environments.

Bdellovibrio bacteriovorus is a predator bacterial species found in the environment and within the human gut, able to attack Gram-negative prey. Cystic fibrosis (CF) is a genetic disease which usually presents lung colonization by Pseudomonas aeruginosa or Staphylococcus aureus biofilms. Here, we investigated the predatory behavior of B. bacteriovorus against these two pathogenic species with: (1) broth culture; (2) “static” biofilms; (3) field emission scanning electron microscope (FESEM); (4) “flow” biofilms; (5) zymographic technique. We had the first evidence of B. bacteriovorus survival with a Gram-positive prey, revealing a direct cell-to-cell contact with S. aureus and a new “epibiotic” foraging strategy imaged with FESEM. Mean attaching time of HD100 to S. aureus cells was 185 s, while “static” and “flow” S. aureus biofilms were reduced by 74 (at 24 h) and 46% (at 20 h), respectively. Furthermore, zymograms showed a differential bacteriolytic activity exerted by the B. bacteriovorus lysates on P. aeruginosa and S. aureus. The dual foraging system against Gram-negative (periplasmic) and Gram-positive (epibiotic) prey could suggest the use of B. bacteriovorus as a “living antibiotic” in CF, even if further studies are required to simulate its in vivo predatory behavior.

We investigated expression of acid phosphatases containing low-molecular-mass (25 to 27-ma) polypeptides (Lmmp-APs) similar to those described previously for Salmonella enterica serovar typhimurium and Morganella morganii in strains that were representatives of 43 different enterobacterial species by using a zymogram technique developed for detection of Lmmp-AP activities and for analysis of some of the properties of these enzymes. Under conditions that were suitable for detection of the previously described Lmmp-APs, production of similar enzymes appeared to be widespread but not universal among enteric bacteria, and heterogeneous patterns of expression were found among strains belonging to different genera and, in some cases, among strains belonging to different species of the same genus. We found that class A Lmmp-APs (i.e., Lmmp-Aps similar to the Morganella morganii PhoC and Salmonella enterica serovar typhimurium PhoN acid phosphatases) were also expressed in Cedecea spp., Enterobacter aerogenes, Hafiia alvei, Klebsiella spp., Providencia stuartii, Serratia plymuthica, and Yokenella regensburgei strains and that class B Lmmp-APs (i.e., Lmmp-APs similar to the Morganella morganii NapA and Salmonella enterica serovar typhimurium NapII acid phosphatases) were also expressed in strains of Citrobacter spp., Escherichia coli, Escherichia fergusonii, H a f i b alvei, Proteus mirabilis, Providenciu spp., Salmonella enterica serovar typhi, ShigeUa dysenteriae, and ShigeUa flexneri. No Lmmp-AP activity was detected in strains of Enterobacter spp. other than Enterobacter aerogenes, Escherichia hermanii, Kluyvera ascorbata, Leckrciu adecarboxyluta, Leminorella grimontii, MoellereUa wisconsensis, Proteus vulgaris, Proteus penneri, Serratia spp. other than Serratia plymuthica, and Yersinia spp. Because of the heterogeneous patterns of expression of Lmmp-APs, analysis of these enzymes could be useful for evolutionary studies of the enterobacterial genome and for precise phylogenetic positioning of enteric bacteria.Phosphatase activity occurs in all members of the family Enterobacteriaceae (18), but different patterns of phosphatase activity have been found in strains belonging to this family (2, 3, 10, 12, 13, 19). For instance, it is known that a phosphaterepressible alkaline phosphatase is widespread but not universally present in enterobacterial species (2, 13, 19). It is also known that the levels of cyclic phosphodiesterase activity and 5'-nucleotidase (UDP-sugar hydrolase) activity can be markedly different in different species (10) and that two different types of 5'-nucleotidases are produced by Escherichia coli and Salmonella spp. as a consequence of alternative silencing events in the genes that encode these enzymes (3). Moreover, only some species (Morganella morganii and Providencia stuartii) produce high levels of phosphate-irrepressible acid phosphatase activity (HPAP phenotype), while other species produce only intermediate or low levels of acid phosphatase activity when Pi is freely available in the cultu...

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