## 2 Diversity of Gut Prokaryotes and the Principles of Microbiota Transfer
### Enterotypes of Human and Animal Guts
It is worth noting that some later publications oftentimes suggested different ways of characterising murine enterotypes, proposing clusters centred around _Alistipes_, _Akkermansia_, and _Clostidium_[39]; however, it has to be clarified that this particular study relied on an external dataset [40] that utilised material from murine faeces instead of caecal content, as was the case with the paper published by [PERSON] and colleagues. When it comes to bacterial clusters inhabiting porcine guts, an early study describing microbias in young pigs found two clear enterotypes: one exhibiting the domination of _Ruminococcus_ and _Treponema_, and the other, _Prevotella_ and _Mitsuokella_[41]. Apart from the interesting resemblance to human microbial profiles, it was observed that the second enterotype was associated with significantly higher growth rates and total body weight after sixty days, which has obvious implications for the economy of animal husbandry. A somewhat similar result was achieved by a different group, which managed to classify porcine enterotypes into a _Treponema_-dominated and a _Prevotella_-dominated one, observing slightly improved feed efficiency in the second group that approached the traditional threshold of statistical significance [42]. However, other publications have identified different compositions of porcine gut microbiota, with one study reporting consistent dominance of _Clostidium_ with increased presence of either _Prevotella_ or _Escherichia_[43]. Another study found two enterotypes at 52 days of age: one dominated by _Prevotella_ and _Sarcinia_ and the other by _Lactobacillus_; further divergence was observed later on, with _Lactobacillus_ and _Turicbacter-Clostidium_ enterotypes becoming the most common during subsequent measurements at 99 and 154 days of age, along with frequent enterotypic switches undergone by individual animals [44]. Studies on avian enterotypes have demonstrated their impact on host metabolism and phenotype. In broiler chickens, three enterotypes (ET1, ET2, ET3) have been identified, each dominated by distinct bacterial genera such as _Bacteroides_, _Rhodococcus_, and _Akkermansia_. ET2 was associated with increased triglyceride levels and fat deposition, with _Rhodococcus_ and _Ochroductrum_ correlating with efficient plant polysaccharide degradation and lipid metabolism. These findings highlight the role of enterotypes in avian species, extending their impact beyond metabolism to production traits [45]. In Muscovy ducks, enterotype classification has also been linked to physiological traits, particularly in relation to carcass composition. Analysis of ileal microbiota in 200 ducks identified three enterotypes (ET1, ET2, and ET3), dominated by _Streptococcus_, _Candidatus Arthromitus_, and _Bacteroides_, respectively. Unlike in broilers, where enterotypes influenced lipid metabolism, enterotypic classification in ducks correlated significantly with carcass traits, including eviscerated yield and leg muscle weight. ET3, characterized by higher microbial diversity, exhibited the highest leg muscle weight and percentage of leg muscle, suggesting potential microbiota-mediated modulation of muscle development. These findings indicate that enterotypes in avian species may influence traits beyond digestion and metabolism, with potential implications for production efficiency [46]. Enterotype differentiation in marine fish is less studied than that in terrestrial and avian species, despite the recognized role of gut microbiota in host physiology. A study on Mediterranean scorpionfishes (_Scorpaena_ spp.) revealed that both host phylogeny and geographic origin influence gut microbiota composition. Analysis of gut mucosal communities in three _Scorpaena_ species identified distinct core microbiota profiles, with _Photobacterium_, _Enterovibrio_, and _Vibrio_ dominating in _S. notata_ while _Clostridium sensu stricto 1_ was the only consistently present genus in _S. scrofa_.