Circumpolar synchrony in big river bacterioplankton.

Natural bacterial communities are extremely diverse and highly dynamic, but evidence is mounting that the compositions of these communities follow predictable temporal patterns. We investigated these patterns with a 3-year, circumpolar study of bacterioplankton communities in the six largest rivers of the pan-arctic watershed (Ob', Yenisey, Lena, Kolyma, Yukon, and Mackenzie), five of which are among Earth's 25 largest rivers. Communities in the six rivers shifted synchronously over time, correlating with seasonal shifts in hydrology and biogeochemistry and clustering into three groups: winter/spring, spring freshet, and summer/fall. This synchrony indicates that hemisphere-scale variation in seasonal climate sets the pace of variation in microbial diversity. Moreover, these seasonal communities reassembled each year in all six rivers, suggesting a long-term, predictable succession in the composition of big river bacterioplankton communities.

Temporal changes in cellular energy following burn injury.

Availability of ADP is a predominant influence on respiratory control. Associated with severe burn injury is an increase in energy expenditure. The purpose of this study was to determine the temporal changes in ATP, ADP, NAD, and NADH following severe burn and thereby assess any related alterations in respiratory control and energy deficit. During isoflurane anesthesia and following intraperitoneal injection of saline, 32 mice were flame burned at 40% body surface area. Twelve mice served as controls. At 12, 24, 72, and 168 h post-burn, groups of mice underwent celiotomy with determination of hepatic surface blood flow using laser Doppler and oxygen saturation using pulse oximetry. Biopsies of liver were then frozen in liquid nitrogen for subsequent quantification of ATP, ADP, AMP, NAD, and NADH by HPLC. Mortality was 12.5% at 72 h post-burn and 25% at 1 week. Oxygen saturation and hepatic surface blood flow remained similar to control values throughout the week after burn. ATP, ADP, and energy charge decreased progressively following burn reaching a significant decrease from unburned controls at 72 h. Availability of NADH remained statistically similar to unburned controls throughout the week after burn. These results demonstrate that despite maintenance of baseline oxygen delivery, there was a nadir in ATP and ADP availability and energy charge in the liver at 72 h after burn. This finding supports the concept of a limitation in phosphorylation after injury. Availability of NADH remained at or above pre-burn concentrations suggesting that the rate of fuel oxidation was not a limiting factor for ongoing oxidative phosphorylation for energy.

Sepsis-induced failure of hepatic energy metabolism.

HYPOTHESIS: Recent evidence suggests that sepsis may induce an uncoupling of oxidative phosphorylation. The purpose of this study was to quantify temporal changes in hepatic oxygen consumption and cellular energy state with increasing severity of sepsis and thus assess the interrelationship of these parameters as either primary defect or compensatory response. MAIN OUTCOME MEASURES: Pseudomonas aeruginosa was infused intravenously in eight instrumented anesthetized swine inducing a progressive severity of sepsis to shock. Eight other animals served as instrumented controls. Hepatic blood flow, oxygen use, and concentrations of ATP, ADP, AMP, NAD(+), and NADH were measured at baseline and then sequentially during the study. RESULTS: Except for an increase in heart rate, there were no temporal changes in measured values for the control animals. For swine receiving P. aeruginosa, hepatic oxygen delivery and consumption increased with early sepsis whereas there were no alterations in the concentrations of adenine nucleotides or NAD(+)/NADH within liver. Septic shock was notable for a decrease in oxygen delivery yet oxygen consumption remained elevated because of an increase in percent oxygen extraction. The hepatic concentrations of ATP and NADH decreased during septic shock. CONCLUSIONS: These findings suggest that any sepsis-induced limitation in phosphorylation may be initially compensated by an increase in oxygen use. This study also suggests that decreases in NADH availability may be a principal factor in the decompensation of sepsis to shock.