Therapeutic food interventions have reduced mortality in children with severe acute malnutrition (SAM) but incomplete restoration of healthy growth remains a major problem1,2. The relationships between the type of nutritional intervention, the gut microbiota, and therapeutic responses are unclear. In the current study, bacterial species whose proportional representation define a healthy gut microbiota as it assembles during the first two postnatal years were identified by applying a machine-learning-based approach to 16S rRNA datasets generated from monthly fecal samples obtained from a birth-cohort of children, living in an urban slum of Dhaka, Bangladesh, who exhibited consistently healthy growth. These age-discriminatory bacterial species were incorporated into a model that computes a ‘relative microbiota maturity index’ and ‘microbiota-for-age Z-score’ that compare development (defined here as maturation) of a child’s fecal microbiota relative to healthy children of similar chronologic age. The model was applied to twins and triplets (to test for associations of these indices with genetic and environmental factors including diarrhea), children with SAM enrolled in a randomized trial of two food interventions, and children with moderate acute malnutrition. Our results indicate that SAM is associated with significant relative microbiota immaturity that is only partially ameliorated following two widely used nutritional interventions. Immaturity is also evident in less severe forms of malnutrition and correlates with anthropometric measurements. Microbiota maturity indices provide a microbial measure of human postnatal development, a way of classifying malnourished states, and a parameter for judging therapeutic efficacy. More prolonged interventions with existing or new therapeutic foods and/or addition of gut microbes may be needed to achieve enduring repair of gut microbiota immaturity in childhood malnutrition and improve clinical outcomes.

Undernourished children exhibit impaired gut microbiota development. Transplanting microbiota from 6- and 18-month old healthy or undernourished Malawian donors into young germ-free mice fed a Malawian diet revealed that immature microbiota from undernourished infants/children transmit impaired growth phenotypes. The representation of several age-discriminatory taxa in recipient animals correlated with lean body mass gain, liver, muscle, and brain metabolism, plus bone morphology. Co-housing mice shortly after receiving microbiota from healthy (H) or severely stunted/underweight (Un) infants demonstrated that invasion of age-/growth-discriminatory taxa from H to Un cagemates’ microbiota ameliorates growth faltering. Adding two invasive species, Ruminococcus gnavus and Clostridium symbiosum, to the Un microbiota also ameliorated growth and metabolic abnormalities. These results provide evidence that microbiota immaturity is causally related to undernutrition, and reveal potential therapeutic targets and agents.

Summary Identifying interventions that more effectively promote healthy growth of children with undernutrition is a pressing global health goal. Analysis of human milk oligosaccharides (HMOs) from 6-month postpartum mothers in two Malawian birth-cohorts revealed that sialylated HMOs are significantly less abundant in mothers with severely stunted infants. To explore this association, we colonized young germ-free mice with a consortium of bacterial strains cultured from the fecal microbiota of a 6-month old stunted Malawian infant and fed recipient animals a prototypic Malawian diet with or without purified sialylated bovine milk oligosaccharides (S-BMO). S-BMO produced a microbiota-dependent augmentation of lean body mass gain, changed bone morphology and altered liver, muscle and brain metabolism in ways indicative of a greater ability to utilize nutrients for anabolism. These effects were also documented in gnotobiotic piglets using the same consortium and Malawian diet. These preclinical models indicate a causal, microbiota-dependent relationship between S-BMO and growth promotion.

The nucleosomal response refers to the rapid phosphorylation of histone H3 on serine 10 and HMG-14 on serine 6 that occurs concomitantly with immediateearly (IE) gene induction in response to a wide variety of stimuli. Using antibodies against the phosphorylated residues, we show that H3 and HMG-14 phosphorylation is mediated via different MAP kinase (MAPK) cascades, depending on the stimulus. The nucleosomal response elicited by TPA is ERK-dependent, whereas that elicited by anisomycin is p38 MAPK-dependent. In intact cells, the nucleosomal response can be selectively inhibited using the protein kinase inhibitor H89. MAPK activation and phosphorylation of transcription factors are largely unaffected by H89, whereas induction of IE genes is inhibited and its characteristics markedly altered. MSK1 is considered the most likely kinase to mediate this response because (i) it is activated by both ERK and p38 MAPKs; (ii) it is an extremely efficient kinase for HMG-14 and H3, utilizing the physiologically relevant sites; and (iii) its activity towards H3/HMG-14 is uniquely sensitive to H89 inhibition. Thus, the nucleosomal response is an invariable consequence of ERK and p38 but not JNK/SAPK activation, and MSK1 potentially provides a link to complete the circuit between cell surface and nucleosome.

The induction of immediate‐early (IE) genes, including proto‐oncogenes c‐fos and c‐jun, correlates well with a nucleosomal response, the phosphorylation of histone H3 and HMG‐14 mediated via extracellular signal regulated kinase or p38 MAP kinase cascades. Phosphorylation is targeted to a minute fraction of histone H3, which is also especially susceptible to hyperacetylation. Here, we provide direct evidence that phosphorylation and acetylation of histone H3 occur on the same histone H3 tail on nucleosomes associated with active IE gene chromatin. Chromatin immunoprecipitation (ChIP) assays were performed using antibodies that specifically recognize the doubly‐modified phosphoacetylated form of histone H3. Analysis of the associated DNA shows that histone H3 on c‐fos‐ and c‐jun‐associated nucleosomes becomes doubly‐modified, the same H3 tails becoming both phosphorylated and acetylated, only upon gene activation. This study reveals potential complications of occlusion when using site‐specific antibodies against modified histones, and shows also that phosphorylated H3 is more sensitive to trichostatin A (TSA)‐induced hyperacetylation than non‐phosphorylated H3. Because MAP kinase‐mediated gene induction is implicated in controlling diverse biological processes, histone H3 phosphoacetylation is likely to be of widespread significance.