Local environment shapes milk microbiomes while evolutionary history constrains milk macronutrients in captive cercopithecine primates.

Milk is a complex biochemical fluid that includes macronutrients and microbiota, which, together, are known to facilitate infant growth, mediate the colonization of infant microbiomes, and promote immune development. Examining factors that shape milk microbiomes and milk-nutrient interplay across host taxa is critical to resolving the evolution of the milk environment. Using a comparative approach across four cercopithecine primate species housed at three facilities under similar management conditions, we test for the respective influences of the local environment (housing facility) and host species on milk (a) macronutrients (fat, sugar, and protein), (b) microbiomes (16S rRNA), and (c) predicted microbial functions. We found that milk macronutrients were structured according to host species, while milk microbiomes and predicted function were strongly shaped by the local environment and, to a lesser extent, host species. The milk microbiomes of rhesus macaques (Macaca mulatta) at two different facilities more closely resembled those of heterospecific facility-mates compared to conspecifics at a different facility. We found similar, facility-driven patterns of microbial functions linked to physiology and immune modulation, suggesting that milk microbiomes may influence infant health and development. These results provide novel insight into the complexity of milk and its potential impact on infants across species and environments.

Macronutrient composition of milk from captive southern pig-tailed macaques (Macaca nemestrina).

Milk composition is a fundamental aspect of mammalian reproduction. Differences in milk composition between species may reflect phylogeny, dietary ecology, lactation strategy, and infant growth patterns, but may also vary within a species due to maternal body condition. This study presents the first published data on milk macronutrient composition of southern pig-tailed macaques (Macaca nemestrina) and compares the results with data on two other Cercopithecine species. Milk samples were obtained from five dams at 10- and 14-weeks postparturition. Macronutrient composition was determined at the Smithsonian's National Zoo and Conservation Biology Institute using proven methods developed over 30 years. On average (±SEM), the milk contained 83.9 ± 0.4% water, 6.7 ± 0.4% fat, 7.6 ± 0.1% sugar, 1.8 ± 0.1% protein, and 0.22 ± 0.01% mineral content. The Ca:P ratio was 1.8; concentrations of Ca and protein were correlated. Mean gross energy was 1.02 ± 0.03 kcal/g with most of the energy coming from fat (59.6 ± 1.5%), followed by sugar (29.9 ± 1.4%) and protein (10.5 ± 0.5%). The milks at 14 weeks of infant age were higher in energy than the milks at 10 weeks, with an increase in energy from fat (p = 0.005) and decrease in energy from sugar (p = 0.018). The energy from protein did not change (p = 0.272). Compared to captive rhesus macaque (Macaca mulatta) and olive baboon (Papio anubis) milk assayed by identical methods, captive pig-tailed macaque milk was higher in energy, but after accounting for the higher milk energy there was no difference in the proportions of milk energy from protein, fat, and sugar. The captive pig-tailed dams were significantly heavier than reported values for wild pig-tailed macaques, suggesting high body condition. High body condition in captive Cercopithecines appears to result in milk higher in energy, with more energy coming from fat and less from sugar. However, variation in the proportion of milk energy from protein in captive Cercopithecine milks appears relatively constrained.

Macronutrient composition of olive baboon (Papio anubis) milk: A comparison to rhesus macaque (Macaca mulatta) milk.

This study was designed to (1) characterize the macronutrient composition of olive baboon (Papio anubis) milk, (2) compare baboon milk composition to that of rhesus macaques (Macaca mulatta), and (3) evaluate the association between the proportion of milk energy derived from protein and relative growth rate within anthropoid primates. A single milk sample was collected from each of eight lactating olive baboons ranging between 47- and 129-days postparturition and six rhesus macaques from 15- to 92-days living at the same institution under identical management conditions. Macronutrient composition (water, fat, protein sugar, and ash) was determined using standard techniques developed at the Nutrition Laboratory at the Smithsonian National Zoological Park. Baboon milk on average contained 86.0% ± 0.6% water, 4.7% ± 0.5% fat, 1.6% ± 0.04% protein, 7.3% ± 0.07% sugar, and 0.165% ± 0.007% ash. Baboon milk gross energy (GE) averaged 0.81 ± 0.04 kcal/g with 51.9% ± 2.6% from fat, 11.8% ± 0.7% from protein, and 36.2% ± 2.0% from sugar. Baboon milk demonstrated strong similarity to milk composition of the closely phylogenetically related rhesus macaque (86.1% ± 0.3% water, 4.1% ± 0.4% fat, 1.69% ± 0.05% protein, 7.71% ± 0.08% sugar, 0.19% ± 0.01% ash, and 0.78 kcal/g). There was no statistical difference between baboon and macaque milk in the proportions of energy from fat, sugar, and protein. Baboon milk can be described as a high sugar, moderate fat, and low protein milk with moderate energy density, which is consistent with their lactation strategy characterized by frequent, on-demand nursing and relatively slow life history compared to nonprimate mammal taxa. The milk energy from protein of both baboon and macaque (12.8% ± 0.3%) milk was intermediate between the protein milk energy of platyrrhine (19.3%-23.2%) and hominoid (8.9%-12.6%) primates, consistent with their relative growth rates also being intermediate. Compared to these cercopithecid monkeys, platyrrhine primates have both higher relative growth rates and higher milk energy from protein, while apes tend to be lower in both.

Switching of the folding-energy landscape governs the allosteric activation of protein kinase A.

Protein kinases are dynamic molecular switches that sample multiple conformational states. The regulatory subunit of PKA harbors two cAMP-binding domains [cyclic nucleotide-binding (CNB) domains] that oscillate between inactive and active conformations dependent on cAMP binding. The cooperative binding of cAMP to the CNB domains activates an allosteric interaction network that enables PKA to progress from the inactive to active conformation, unleashing the activity of the catalytic subunit. Despite its importance in the regulation of many biological processes, the molecular mechanism responsible for the observed cooperativity during the activation of PKA remains unclear. Here, we use optical tweezers to probe the folding cooperativity and energetics of domain communication between the cAMP-binding domains in the apo state and bound to the catalytic subunit. Our study provides direct evidence of a switch in the folding-energy landscape of the two CNB domains from energetically independent in the apo state to highly cooperative and energetically coupled in the presence of the catalytic subunit. Moreover, we show that destabilizing mutational effects in one CNB domain efficiently propagate to the other and decrease the folding cooperativity between them. Taken together, our results provide a thermodynamic foundation for the conformational plasticity that enables protein kinases to adapt and respond to signaling molecules.