Transition from infant- to adult-like gut microbiota.

Transition from an infant to an adult associated gut microbiota with age through establishment of strict anaerobic bacteria remains one of the key unresolved questions in gut microbial ecology. Here a comprehensive comparative analysis of stool microbiota in a large cohort of mothers and their children sampled longitudinally up until 2 years of age using sequencing analysis tool was presented that allows realistic microbial diversity estimates. In this work, evidence for the switch from children to adult associated microbial profile between 1 and 2 years of age was provided, suggestively driven by Bifidobacterium breve. An Operational Taxonomic Unit (OTU) belonging to B. breve was highly prevalent in the population throughout the first year of life, and was negatively associated with detection of a range of adult-like OTUs. Although an adult profile was not fully established by 2 years of age, it was demonstrated that with regards to the most prevalent OTUs, their prevalence in the child population by then already resembled that of the adult population. Taken together, it was proposed that late-colonizing OTUs were recruited at a later stage and were not acquired at birth with the recruitment being controlled by gatekeeping OTUs until the age of 1 year.

Confusion about the species richness of human gut microbiota.

A key message from a range of high profile next generation sequencing studies on the human microbiota is that it composes a tremendously rich community of more than 1000 species within each one of us. Although more recent studies have shown estimates of between 100 and 200 species per individual, this has not yet been made clear in the literature. Currently, the most widely accepted estimate of species richness is therefore five to ten times too high. Here, we will review the different estimates of species richness in the literature, address potential sources of artefacts, the reluctance to correct these, and provide suggestions for future directions.

Correlation between the human fecal microbiota and depression.

BACKGROUND: Depression is a chronic syndrome with a pathogenesis linked to various genetic, biological, and environmental factors. Several links between gut microbiota and depression have been established in animal models. In humans, however, few correlations have yet been demonstrated. The aim of our work was therefore to identify potential correlations between human fecal microbiota (as a proxy for gut microbiota) and depression. METHODS: We analyzed fecal samples from 55 people, 37 patients, and 18 non-depressed controls. Our analyses were based on data generated by Illumina deep sequencing of 16S rRNA gene amplicons. KEY RESULTS: We found several correlations between depression and fecal microbiota. The correlations, however, showed opposite directions even for closely related Operational Taxonomic Units (OTU's), but were still associated with certain higher order phylogroups. The order Bacteroidales showed an overrepresentation (p = 0.05), while the family Lachnospiraceae showed an underrepresentation (p = 0.02) of OTU's associated with depression. At low taxonomic levels, there was one clade consisting of five OTU's within the genus Oscillibacter, and one clade within Alistipes (consisting of four OTU's) that showed a significant association with depression (p = 0.03 and 0.01, respectively). CONCLUSIONS & INFERENCES: The Oscillibacter type strain has valeric acid as its main metabolic end product, a homolog of neurotransmitter GABA, while Alistipes has previously been shown to be associated with induced stress in mice. In conclusion, the taxonomic correlations detected here may therefore correspond to mechanistic models.

Is it who you are or what you do that is important in the human gut?

The current leading view is that functionality and not phylotype is the most important determinant for the services provided by the gut microbiota. Here we present an alternative opinion, advocating the importance of phylotype in addition to function. We believe the literature is misled by technical artifacts in defining operational taxonomic units (OTUs), which are binned groups of bacteria based on sequence homology. Furthermore, the current metagenomic approaches where the total DNA in a sample is mixed prior to sequencing and subsequently resolved by a bioinformatics approach, are highly error prone with respect to both functional and phylotype assignments. We argue that the directions of the OTU and metagenome errors are such that stable phylotypes are overlooked, while functional stability is overestimated. Taking these errors into account, we propose that phylotype represents an interface for functionality, and is for this reason an important determinant for the services provided by the gut microbiota to the host.

Bifidobacterial succession and correlation networks in a large unselected cohort of mothers and their children.

Bifidobacteria are a major microbial component of infant gut microbiota, which is believed to promote health benefits for the host and stimulate maturation of the immune system. Despite their perceived importance, very little is known about the natural development of and possible correlations between bifidobacteria in human populations. To address this knowledge gap, we analyzed stool samples from a randomly selected healthy cohort of 87 infants and their mothers with >90% of vaginal delivery and nearly 100% breast-feeding at 4 months. Fecal material was sampled during pregnancy, at 3 and 10 days, at 4 months, and at 1 and 2 years after birth. Stool samples were predicted to be rich in the species Bifidobacterium adolescentis, B. bifidum, B. dentium, B. breve, and B. longum. Due to high variation, we did not identify a clear age-related structure at the individual level. Within the population as a whole, however, there were clear age-related successions. Negative correlations between the B. longum group and B. adolescentis were detected in adults and in 1- and 2-year-old children, whereas negative correlations between B. longum and B. breve were characteristic for newborns and 4-month-old infants. The highly structured age-related development of and correlation networks between bifidobacterial species during the first 2 years of life mirrors their different or competing nutritional requirements, which in turn may be associated with specific biological functions in the development of healthy gut.

[Hormonal regulation of sodium excretion by the kidneys during hunger therapy of obese patients]. / Gormonal'naia reguliatsiia ékskretsii natriia pochkami pri lechenii golodaniem bol'nykh ozhireniem.

Sodium excretion and the blood levels of aldosterone, renin, atrial natriuretic peptide (ANP), and insulin were investigated in 9 women with obesity of alimentary-constitutional type during hunger therapy and resumed nutrition. It has been assumed that restricted sodium excretion with the kidneys during fasting is mainly caused by activation of the renin-angiotensin-aldosterone system, with ANP contributing to it, insulin not playing the major role in this process.