Mature Pseudomonas aeruginosa biofilms undergo specific developmental events. Using a bacteriophage mutant, generated by deletion of the entire filamentous Pf4 prophage, we show that the phage is essential for several stages of the biofilm life cycle and that it significantly contributes to the virulence of P. aeruginosa in vivo. Here, we show for the first time that biofilms of the Pf4 phage-deficient mutant did not develop hollow centres or undergo cell death, typical of the differentiation process of wild-type (WT) P. aeruginosa PAO1 biofilms. Furthermore, microcolonies of the Pf4 mutant were significantly smaller in size and less stable compared with the WT biofilm. Small colony variants (SCVs) were detectable in the dispersal population of the WT biofilm at the time of dispersal and cell death, whereas no SCVs were detected in the effluent of the Pf4 mutant biofilm. This study shows that at the time when cell death occurs in biofilms of the WT, the Pf4 phage converts into a superinfective form, which correlates with the appearance of variants in the dispersal population. Unexpectedly, mice infected with the Pf4 mutant survived significantly longer than those infected with its isogenic WT strain, showing that Pf4 contributes to the virulence of P. aeruginosa. Hence, a filamentous prophage is a major contributor to the life cycle and adaptive behaviour of P. aeruginosa and offers an explanation for the prevalence of phage in this organism.

To examine the contributions of impaired gut microbial community development to childhood undernutrition, we combined metabolomic and proteomic analyses of plasma samples with metagenomic analyses of fecal samples to characterize the biological state of Bangladeshi children with severe acute malnutrition (SAM) as they transitioned, after standard treatment, to moderate acute malnutrition (MAM) with persistent microbiota immaturity. Host and microbial effects of microbiota-directed complementary food (MDCF) prototypes targeting weaning-phase bacterial taxa underrepresented in SAM and MAM microbiota were characterized in gnotobiotic mice and gnotobiotic piglets colonized with age- and growth-discriminatory bacteria. A randomized, double-blind controlled feeding study identified a lead MDCF that changes the abundances of targeted bacteria and increases plasma biomarkers and mediators of growth, bone formation, neurodevelopment, and immune function in children with MAM.

SUMMARY Pseudomonas aeruginosa strains exhibit significant variability in pathogenicity and ecological flexibility. Such interstrain differences reflect the dynamic nature of the P. aeruginosa genome, which is composed of a relatively invariable “core genome” and a highly variable “accessory genome.” Here we review the major classes of genetic elements comprising the P. aeruginosa accessory genome and highlight emerging themes in the acquisition and functional importance of these elements. Although the precise phenotypes endowed by the majority of the P. aeruginosa accessory genome have yet to be determined, rapid progress is being made, and a clearer understanding of the role of the P. aeruginosa accessory genome in ecology and infection is emerging.

BACKGROUND Environmental enteric dysfunction (EED) is an enigmatic disorder of the small intestine postulated to play a role in childhood undernutrition, a pressing global health problem. Defining the incidence of EED, its pathophysiology, and its contribution to impaired linear and ponderal growth has been hampered by the difficulty in directly sampling the small intestinal mucosa and microbial community (microbiota). METHODS Slum-dwelling Bangladeshi children aged 18±2 months, with linear growth-faltering (stunting) who failed a nutritional intervention underwent endoscopy to obtain duodenal biopsies and aspirates. Levels of 4077 plasma proteins and 2619 duodenal proteins were quantified in 80 children with histopathologic evidence of EED, and the abundances of bacterial strains in their duodenal microbiota were determined using culture-independent methods. Young germ-free mice, fed a Bangladeshi diet, were colonized with bacterial strains cultured from the duodenal aspirates. RESULTS The absolute abundances of a shared group of 14 bacterial strains recovered from the duodenums of children with EED and not typically classified as enteropathogens were negatively correlated with linear growth (length-for-age Z-score;β=-0.38±0.12(SEM);ρ=-0.49;p=0.003), and positively correlated with duodenal proteins involved in immunoinflammatory responses. Representation of these 14 duodenal taxa was significantly different in fecal microbiota from EED versus healthy children (p<0.001;PERMANOVA). Gnotobiotic mice colonized with cultured EED-donor duodenal strains develop a small intestinal enteropathy. CONCLUSIONS These results provide evidence of a causal relationship between components of the small intestinal microbiota, enteropathy and stunting and offer a rationale for developing therapeutics that target what must no longer remain terra incognita-the small intestinal microbiota. ClinicalTrials.gov identifier: NCT02812615