Local adaptation in populations of a Brachionus group plicatilis cryptic species inhabiting three deep crater lakes in Central Mexico

1. Salinity is a strong selective force for many aquatic organisms, affecting both ecological and evolutionary processes. Most of our knowledge on the effects of salinity on rotifers in the Brachionus plicatilis species complex is based mainly on populations from waterbodies that experience broad environmental changes both seasonally and annually. We tested the hypothesis that, despite the supposedly high potential for gene flow among rotifers inhabiting neighbouring environments, constant salinity has promoted local adaptation, genetic population divergence and even cryptic speciation in B. plicatilis complex populations from three deep maar lakes of distinct salinities [1.1, 6.5 and 9.0 g L^?1 total dissolved solids (TDS)] in Central Mexico. 2. To look for local adaptation, we performed common garden experiments to test the effect of different salinities on population density and intrinsic growth rate (r). Then, we evaluated the genetic divergence by sequencing the cytochrome c oxidase subunit I (COI) gene and performed reproductive trials to assess the potential gene flow among the three populations and with other closely related B. plicatilis complex species. 3. We confirmed that the rotifer populations have phenotypic plasticity in tolerance of salinity, but only rotifers from the least saline lake are adapted to low salinity. Among the populations, sequence divergence at COI was very low (just a single haplotype was found), suggesting a persistent founder effect from a relatively recent single colonisation event and a subsequent dispersal from one lake to the others, and a very restricted immigration rate. In the phylogenetic analysis, rotifers from this area of Mexico clustered in the same clade with the middle‐sized species Brachionus ibericus and B. sp. ‘Almenara’. Mexican rotifers showed successful recognition, copulation and formation of hybrids among them, but interpopulation breeding with the Spanish B. ibericus and B. sp. ‘Almenara’ was unsuccessful. 4. We conclude that the B. plicatilis complex populations from these three lakes belong to a new biological species not yet described (presently named B. sp. ‘Mexico’). To our knowledge, this is the first report of local adaptation of a natural B. plicatilis complex population living in freshwater conditions (1.1 g L^?1 TDS).     

Site-saturation mutagenesis of position V117 in OXA-1 β-lactamase: effect of side chain polarity on enzyme carboxylation and substrate turnover

Class D β-lactamases pose an emerging threat to the efficacy of β-lactam therapy for bacterial infections. Class D enzymes differ mechanistically from other β-lactamases by the presence of an active-site N-carboxylated lysine that serves as a general base to activate the serine nucleophile for attack. We have used site-saturation mutagenesis at position V117 in the class D β-lactamase OXA-1 to investigate how alterations in the environment around N-carboxylated K70 affect the ability of that modified residue to carry out its normal function. Minimum inhibitory concentration analysis of the 20 position 117 variants demonstrates a clear pattern of charge and polarity effects on the level of ampicillin resistance imparted on Escherichia coli (E. coli). Substitutions that introduce a negative charge (D, E) at position 117 reduce resistance to near background levels, while the positively charged K and R residues maintain the highest resistance levels of all mutants. Treatment of the acidic variants with the fluorescent penicillin BOCILLIN FL followed by SDS-PAGE shows that they are active for acylation by substrate but deacylation-deficient. We used a novel fluorescence anisotropy assay to show that the specific charge and hydrogen-bonding potential of the residue at position 117 affect CO(2) binding to K70, which in turn correlates to deacylation activity. These conclusions are discussed in light of the mechanisms proposed for both class D β-lactamases and BlaR β-lactam sensor proteins and suggest a reason for the preponderance of asparagine at the V117-homologous position in the sensors.     

Poor Decision Making Is a Consequence of Cognitive Decline among Older Persons without Alzheimer's Disease or Mild Cognitive Impairment

Objective

Decision making is an important determinant of health and well-being across the lifespan but is critical in aging, when many influential decisions are made just as cognitive function declines. Increasing evidence suggests that older adults, even those without dementia, often make poor decisions and are selectively vulnerable to scams. To date, however, the factors associated with poor decision making in old age are unknown. The objective of this study was to test the hypothesis that poor decision making is a consequence of cognitive decline among older persons without Alzheimer’s disease or mild cognitive impairment.

Methods

Participants were 420 non-demented persons from the Memory and Aging Project, a longitudinal, clinical-pathologic cohort study of aging in the Chicago metropolitan area. All underwent repeated cognitive evaluations and subsequently completed assessments of decision making and susceptibility to scams. Decision making was measured using 12 items from a previously established performance-based measure and a self-report measure of susceptibility to scams.

Results

Cognitive function data were collected over an average of 5.5 years prior to the decision making assessment. Regression analyses were used to examine whether the prior rate of cognitive decline predicted the level of decision making and susceptibility to scams; analyses controlled for age, sex, education, and starting level of cognition. Among 420 persons without dementia, more rapid cognitive decline predicted poorer decision making and increased susceptibility to scams (p’s<0.001). Further, the relations between cognitive decline, decision making and scams persisted in analyses restricted to persons without any cognitive impairment (i.e., no dementia or even mild cognitive impairment).

Conclusions

Poor decision making is a consequence of cognitive decline among older persons without Alzheimer’s disease or mild cognitive impairment, those widely considered “cognitively healthy.” These findings suggest that even very subtle age-related changes in cognition have detrimental effects on judgment.     

Using a Body-Fixed Sensor to Identify Subclinical Gait Difficulties in Older Adults with IADL Disability: Maximizing the Output of the Timed Up and Go

Objective

The identification and documentation of subclinical gait impairments in older adults may facilitate the appropriate use of interventions for preventing or delaying mobility disability. We tested whether measures derived from a single body-fixed sensor worn during traditional Timed Up and Go (TUG) testing could identify subclinical gait impairments in community dwelling older adults without mobility disability.

Methods

We used data from 432 older adults without dementia (mean age 83.30±7.04 yrs, 76.62% female) participating in the Rush Memory and Aging Project. The traditional TUG was conducted while subjects wore a body-fixed sensor. We derived measures of overall TUG performance and different subtasks including transitions (sit-to-stand, stand-to-sit), walking, and turning. Multivariate analysis was used to compare persons with and without mobility disability and to compare individuals with and without Instrumental Activities of Daily Living disability (IADL-disability), all of whom did not have mobility disability.

Results

As expected, individuals with mobility disability performed worse on all TUG subtasks (p<0.03), compared to those who had no mobility disability. Individuals without mobility disability but with IADL disability had difficulties with turns, had lower yaw amplitude (p<0.004) during turns, were slower (p<0.001), and had less consistent gait (p<0.02).

Conclusions

A single body-worn sensor can be employed in the community-setting to complement conventional gait testing. It provides a wide range of quantitative gait measures that appear to help to identify subclinical gait impairments in older adults.     

The role of heat shock protein 70 in mediating age-dependent mortality in sepsis

Sepsis is primarily a disease of the aged, with increased incidence and mortality occurring in aged hosts. Heat shock protein (HSP) 70 plays an important role in both healthy aging and the stress response to injury. The purpose of this study was to determine the role of HSP70 in mediating mortality and the host inflammatory response in aged septic hosts. Sepsis was induced in both young (6- to 12-wk-old) and aged (16- to 17-mo-old) HSP70(-/-) and wild-type (WT) mice to determine whether HSP70 modulated outcome in an age-dependent fashion. Young HSP70(-/-) and WT mice subjected to cecal ligation and puncture, Pseudomonas aeruginosa pneumonia, or Streptococcus pneumoniae pneumonia had no differences in mortality, suggesting HSP70 does not mediate survival in young septic hosts. In contrast, mortality was higher in aged HSP70(-/-) mice than aged WT mice subjected to cecal ligation and puncture (p = 0.01), suggesting HSP70 mediates mortality in sepsis in an age-dependent fashion. Compared with WT mice, aged septic HSP70(-/-) mice had increased gut epithelial apoptosis and pulmonary inflammation. In addition, HSP70(-/-) mice had increased systemic levels of TNF-α, IL-6, IL-10, and IL-1β compared with WT mice. These data demonstrate that HSP70 is a key determinant of mortality in aged, but not young hosts in sepsis. HSP70 may play a protective role in an age-dependent response to sepsis by preventing excessive gut apoptosis and both pulmonary and systemic inflammation.