Constraints on anaerobic respiration in the hyperthermophilic Archaea Pyrobaculum islandicum and Pyrobaculum aerophilum

Pyrobaculum islandicum uses iron, thiosulfate, and elemental sulfur for anaerobic respiration, while Pyrobaculum aerophilum uses iron and nitrate; however, the constraints on these processes and their physiological mechanisms for iron and sulfur reduction are not well understood. Growth rates on sulfur compounds are highest at pH 5 to 6 and highly reduced (<-420-mV) conditions, while growth rates on nitrate and iron are highest at pH 7 to 9 and more-oxidized (>-210-mV) conditions. Growth on iron expands the known pH range of growth for both organisms. P. islandicum differs from P. aerophilum in that it requires direct contact with insoluble iron oxide for growth, it did not produce any extracellular compounds when grown on insoluble iron, and it lacked 2,6-anthrahydroquinone disulfonate oxidase activity. Furthermore, iron reduction in P. islandicum appears to be completely independent of c-type cytochromes. Like that in P. aerophilum, NADH-dependent ferric reductase activity in P. islandicum increased significantly in iron-grown cultures relative to that in non-iron-grown cultures. Proteomic analyses showed that there were significant increases in the amounts of a putative membrane-bound thiosulfate reductase in P. islandicum cultures grown on thiosulfate relative to those in cultures grown on iron and elemental sulfur. This is the first evidence of this enzyme being used in either a hyperthermophile or an archaeon. Pyrobaculum arsenaticum and Pyrobaculum calidifontis also grew on Fe(III) citrate and insoluble iron oxide, but only P. arsenaticum could grow on insoluble iron without direct contact.

Characterization of dissimilatory Fe(III) versus NO3- reduction in the hyperthermophilic archaeon Pyrobaculum aerophilum

The hyperthermophilic archaeon Pyrobaculum aerophilum used 20 mM Fe(III) citrate, 100 mM poorly crystalline Fe(III) oxide, and 10 mM KNO3 as terminal electron acceptors. The two forms of iron were reduced at different rates but with equal growth yields. The insoluble iron was reduced when segregated spatially by dialysis tubing, indicating that direct contact with the iron was not necessary for growth. When partitioned, there was no detectable Fe(III) or Fe(II) outside of the tubing after growth, suggesting that an electron shuttle, not a chelator, may be used as an extracellular mediator of iron reduction. The addition of 25 and 50% (vol vol(-1)) cell-free spent insoluble iron media to fresh media led to growth without a lag phase. Liquid chromatography analysis of spent media showed that cultures grown in iron, especially insoluble iron, produced soluble extracellular compounds that were absent or less abundant in spent nitrate medium. NADH-dependent ferric reductase activity increased approximately 100-fold, while nitrate reductase activity decreased 10-fold in whole-cell extracts from iron-grown cells relative to those from nitrate-grown cells, suggesting that dissimilatory iron reduction was regulated. A novel 2,6-anthrahydroquinone disulfonate oxidase activity was more than 580-fold higher in iron-grown cells than in nitrate-grown cells. The activity was primarily (>95%) associated with the membrane cellular fraction, but its physiological function is unknown. Nitrate-grown cultures produced two membrane-bound, c-type cytochromes that are predicted to be monoheme and part of nitrite reductase and a bc1 complex using genome analyses. Only one cytochrome was present in cells grown on Fe(III) citrate whose relative abundance was unchanged.

Are persons with cognitive impairment able to state consistent choices?

PURPOSE

This study examined the decision-making capacity of persons with cognitive impairment with respect to their everyday care preferences and choices. This is the first in a series of articles to report on findings from a larger study that examines choice, decision making, values, preferences, and practices in everyday care for community-dwelling persons with cognitive impairment and their family caregivers.

DESIGN AND METHODS

Fifty-one respondent pairs, or dyads, were interviewed, that is, persons with cognitive impairment (n = 51) and their family caregivers (n = 51). All persons with cognitive impairment were interviewed twice within a week using a parallel interview to determine stability and accuracy of responses. The family caregiver was interviewed once.

RESULTS

Persons with mild to moderate cognitive impairment (i.e., Mini-Mental State Exam scores 13-26) are able to respond consistently to questions about preferences, choices, and their own involvement in decisions about daily living, and to provide accurate and reliable responses to questions about demographics.

IMPLICATIONS

Including the perspective of persons with cognitive impairment in both research and practice has the potential to enhance their autonomy and improve their quality of life.

Depression and health in family caregivers: adaptation over time

This study examined the predictors of caregiver depression and "adaptation" over time in a sample of 202 family caregivers of cognitively impaired adults. By examining caregiver adaptation (i.e., a caregiver's ability to adjust psychologically to the demands of providing long-term in-home care), we were able to account for initial levels of depression, regression to the mean, and floor and ceiling effects. Results indicated that the strongest predictors of caregiver depression 1 year after baseline were initial levels of depression, worsening of caregiver subjective physical health status and burden, and short-term use of in-home respite assistance. These findings suggest that caregivers who experience deterioration in levels of physical health and burden and who use in-home respite on a short-term or sporadic basis may be especially vulnerable to the chronic stress of providing long-term in-home care.

A well-deserved break: respite programs offered by California's statewide system of Caregiver Resource Centers

This article describes the range of respite care options that are helping families of cognitively impaired adults under the auspices of California's statewide system of Caregiver Resource Centers. Types of respite provided include in-home care, adult day care and other group care programs, and overnight respite options outside the home, ranging from short-term care of the patient in a facility to weekend retreats designed for caregivers. The hallmarks of the program are flexibility, choice, and consumer control.