On Maintenance and Metabolisms in Soil Microbial Communities

Biochemistry is an essential yet often undervalued aspect of soil ecology, especially in soil C cycling. We assume based on tradition, intuition or hope that the complexity of biochemistry is confined to the microscopic world, and can be ignored when dealing with whole soil systems. This opinion paper draws attention to patterns caused by basic biochemical processes that permeate the world of ecosystem processes. From these patterns, we can estimate activities of the biochemical reactions of the central C metabolic network and gain insights into the ecophysiology of microbial biosynthesis and growth and maintenance energy requirements; important components of Carbon Use Efficiency (CUE).The biochemical pathways used to metabolize glucose vary from soil to soil, with mostly glycolysis in some soils, and pentose phosphate or Entner-Doudoroff pathways in others. However, notwithstanding this metabolic diversity, glucose use efficiency is high and thus substrate use for maintenance energy and overflow respiration is low in these three soils. These results contradict current dogma based on four decades of research in soil ecology. We identify three main shortcomings in our current understanding of substrate use efficiency: 1) in numeric and conceptual models, we lack appreciation of the strategies that microbes employ to quickly reduce energy needs in response to starvation; 2) production of exudates and microbial turnover affect whole-soil CUE more than variation in maintenance energy demand; and 3) whether tracer experiments can be used to measure the long-term substrate use efficiency of soil microbial communities depends critically on the ability of non-growing cells to take up tracer substrates, how biosynthesis responds to these substrates, as well as on how cellular activities scale to the community level.To move the field of soil ecology forward, future research must consider the details of microbial ecophysiology and develop new tools that enable direct measurement of microbial functioning in intact soils. We submit that 13C metabolic flux analysis is one of those new tools.

PECULIARITIES OF STUDENTS' ADAPTATION TO SYSTEMATIC EXERCISES IN PHYSICAL EDUCATION AND SPORT IN THE CONDITIONS OF A CIRCUMPOLAR REGION

The article is devoted to the study of health improvement and adaptation to physical activity of students in conditions of the Arctic region. The data on the implementation of physical education and sports are were given taking into account peculiarities of maintenance energy and adaptation processes of the students' organism.

340 Relationship of Retained Energy in Lactating Beef Cows to Maintenance Energy Requirement and voluntary Feed Intake

This study’s objective was to determine the relationship between retained energy, lactation maintenance energy requirement (MER), and dry period voluntary feed intake (VOL) in beef cows. Twenty-four mature fall-calving Angus cows were used in an 82-d study during lactation to establish maintenance energy requirements followed by a voluntary feed intake study after weaning. During the lactation MER experiment, cows were housed in 2 drylot pens and limit-fed a mixed hay/concentrate diet (17.8% CP, 2.6 Mcal/kg ME, DM basis) individually once per d in a stall barn. Cows were adapted to the diet and feeding management for the first 16 d. Subsequently, cows were weighed and feed allowance adjusted at 14-d intervals to achieve BW and BCS stasis. Milk yield and composition were determined on d – 10, 49, and 77 using a milking machine. Retained energy was calculated as average daily maternal tissue energy change plus average daily milk energy yield. During the post-weaning VOL experiment, cows were provided ad libitum access to a grass hay diet for 41 d (8.15% CP, 1.8 Mcal/kg ME, DM basis) using five individual feed intake monitoring units (SmartFeed, C-Lock, Inc). Each one unit increase in metabolizable energy intake, kcal/kg BW0.75 was associated with a 0.86 ± 0.28 kcal/kg BW0.75 increase in total retained energy (P = 0.005). Using this partial efficiency coefficient, ME required for maintenance declined by 0.80 ± 0.11 kcal ME/kg BW0.75 for each additional kcal net energy retained/kg BW0.75 (P < 0.0001). There was no relationship between lactation-period retained energy and post-weaning VOL forage dry matter intake. The present study results contradict previous reports suggesting that maintenance requirements increase with increasing productivity.

PSXI-29 Effects of feed restriction on blood constituent concentrations in hair sheep

Forty-six Dorper, 47 Katahdin, and 41 St. Croix female sheep (initial body weight of 62, 62, and 51 kg, respectively, SEM=1.43; 3.8±0.18 yr of age) from 45 commercial farms in Midwest, Northwest, Southeast, and central Texas regions of the United States were used to evaluate effects of feed restriction on concentrations of blood constituents. A 50% concentrate pelleted diet was fed, with the amount varied in the first 4 wk to achieve stable BW. The amount of feed offered in wk 5–10 was set at 55% of that consumed in wk 3–4. Blood was sampled at the end of wk 3, 4, 6, 8, and 10, with constituent levels in wk 4 and 10 assumed relevant to conditions with different maintenance energy requirements (i.e., fed at maintenance and approximately 43% lower with restricted intake). There were some differences among breeds such as ones based on samples collected at all times in urea nitrogen (14.0, 13.7, and 15.4 mg/dl; SEM=0.31) and creatinine (0.945, 0.836, and 0.809 mg/dl for Dorper, Katahdin, and St. Croix, respectively; SEM=0.0253) but relatively few among regions and only one interaction between week and breed or region. There was a trend for a difference (P = 0.051) between wk 4 and 10 in the concentration of glucose (51.9 and 54.2 mg/dl; SEM=0.90), and there were differences (P < 0.05) in levels of lactate (23.9 and 20.3 mg/dl; SEM=0.89), urea N (16.4 and 13.0 mg/dl; SEM= 0.25), creatinine (0.808 and 0.919 mg/dl; SEM=0.0165), triglycerides (31.8 and 25.5 mg/dl; SEM=0.63), cholesterol (67.5 and 74.7 mg/dl; SEM=1.66), and cortisol (10.55 and 8.31 ng/ml for wk 4 and 10, respectively; SEM=0.0542). In conclusion, similar responses of different hair sheep breeds in blood constituent levels to feed restriction is in accordance with comparable effects on body weight and the maintenance energy requirement previously reported.

522 Late-Breaking: Effects of Corn Processing and Age on Energy Balance, Nutrient Digestion and Rumination in Cattle

Current library values for energy content in whole or dry-rolled corn (DRC) are identical and do not differ for cattle of different age (NASEM, 2016). Calves (295 ± 29 kg) and yearlings (521 ± 29 kg) were fed whole, DRC or steam-flaked corn (SFC) to evaluate library values of energy content in different types of processed corn among cattle of different age. Cattle were fed diets comprised of 75% corn (DM-basis) to 2.5-times maintenance energy requirements using estimates of NEm in corn and SFC (NASEM, 2016). Data were analyzed using the MIXED procedure of SAS. There was no observed interaction of corn processing and cattle age (P ≥ 0.40). Time spent ruminating (min/d) was not different between dietary treatment or age. Total tract starch digestibility was greatest (P = 0.01) for cattle fed SFC (97.5%), intermediate in cattle fed DRC (92.4%) and least in cattle fed whole corn (89.5%). Nitrogen balance was not affected (P ≥ 0.30) by corn processing or age. Digestible and metabolizable energy (Mcal/kg-DMI) were greater (P ≤ 0.05) for cattle fed SFC compared to DRC or whole. A greater proportion of DE was lost to heat production (P = 0.01) in cattle fed whole corn compared to DRC and tended to be greater (P = 0.08) in cattle fed SFC than DRC. Retained energy (Mcal/d) should have been similar if current library values correctly reflect energy content in each type of processed corn. However, retained energy was greater (P < 0.01) for cattle fed DRC compared to whole corn and tended to be greater (P = 0.06) compared to SFC indicating that library values for DRC underestimate energy available to growing cattle. Measures of retained energy for cattle fed DRC indicated that energy available for gain from DRC was 42% greater than library values (NASEM, 2016).

Energy: Protein Ratio in Ruminants: Insights from the Intragastric Infusion Technique

Studies on energy:protein ratio in ruminants are constrained by rumen fermentation since it governs nutrient metabolism and the ratio of energy:protein yielding nutrients available for absorption. By circumventing rumen fermentation, the total intragastric infusion technique (IIT) allowed objective quantification of maintenance energy and protein requirements, volatile fatty acid utilisation efficiency, efficiency of energy utilisation for maintenance (Km) and growth (Kf) and the origin of N retention responses to independent variation of energy and protein intake. This review outlines the key IIT findings and whether they are reflected in current feeding systems with implications for different production systems worldwide. Maintenance energy requirements are similar to those derived from comparative slaughter but maintenance N requirements are significantly lower. No differences in utilisation efficiency exist between acetic, propionic and butyric acids. At low energy intakes, endogenous energy reserves are utilised to retain amino acids and fuel substantial tissue protein gains. The use of fasting metabolism to measure the utilisation of nutritionally balanced diets is questioned since it is a glucose-deficient state. Inter-species differences in glucose metabolism appear to exist, suggesting that glucose requirements may be higher in cattle than sheep. The difficulty in predicting nutrient requirements, particularly protein, with any one technique is highlighted.

Standard metabolic rate does not associate with age-at-maturity genotype in juvenile Atlantic salmon

Atlantic salmon (Salmo salar) is a species with diverse life-history strategies, to which the timing of maturation contributes considerably. Recently, the genome region including the gene vgll3 has gained attention as a locus with a large effect on salmon maturation timing, and recent studies on the vgll3 locus in salmon have indicated that its effect might be mediated through body condition and accumulation of adipose tissue. However, the cellular and physiological pathways leading from vgll3 genotype to phenotype are still unknown. Standard metabolic rate is a potentially important trait for resource acquisition and assimilation and we hypothesized that this trait, being a proxy for the maintenance energy expenditure of an individual, could be an important link in the pathway from vgll3 genotype to maturation-timing phenotype. As a first step to studying links between vgll3 and the metabolic phenotype of Atlantic salmon, we measured the standard metabolic rate of 150 first year Atlantic salmon juveniles of both sexes, originating from 14 different families with either late maturing or early maturing vgll3 genotypes. No significant difference in mass-adjusted standard metabolic rate was detected between individuals with different vgll3 genotypes, indicating that juvenile salmon of different vgll3 genotypes have similar maintenance energy requirements in the experimental conditions used and that the effects of vgll3 on body condition and maturation are not strongly related to maintenance energy expenditure in either sex at this life stage.

Inclusion of maintenance energy improves the intracellular flux predictions of CHO

Chinese hamster ovary (CHO) cells are the leading platform for the production of biopharmaceuticals with human-like glycosylation. The standard practice for cell line generation relies on trial and error approaches such as adaptive evolution and high-throughput screening, which typically take several months. Metabolic modeling could aid in designing better producer cell lines and thus shorten development times. The genome-scale metabolic model (GSMM) of CHO can accurately predict growth rates. However, in order to predict rational engineering strategies it also needs to accurately predict intracellular fluxes. In this work we evaluated the agreement between the fluxes predicted by parsimonious flux balance analysis (pFBA) using the CHO GSMM and a wide range of 13C metabolic flux data from literature. While glycolytic fluxes were predicted relatively well, the fluxes of tricarboxylic acid (TCA) cycle were vastly underestimated due to too low energy demand. Inclusion of computationally estimated maintenance energy significantly improved the overall accuracy of intracellular flux predictions. Maintenance energy was therefore determined experimentally by running continuous cultures at different growth rates and evaluating their respective energy consumption. The experimentally and computationally determined maintenance energy were in good agreement. Additionally, we compared alternative objective functions (minimization of uptake rates of seven nonessential metabolites) to the biomass objective. While the predictions of the uptake rates were quite inaccurate for most objectives, the predictions of the intracellular fluxes were comparable to the biomass objective function.