RESUMO
The physical and chemical factors that can limit or prevent microbial growth in the deep subsurface are not well defined. Brines from an evaporite sequence were sampled in the Boulby Mine, United Kingdom between 800 and 1300 m depth. Ionic, hydrogen and oxygen isotopic composition were used to identify two brine sources, an aquifer situated in strata overlying the mine, and another ambiguous source distinct from the regional groundwater. The ability of the brines to support microbial replication was tested with culturing experiments using a diversity of inocula. The examined brines were found to be permissive for growth, except one. Testing this brine's physicochemical properties showed it to have low water activity and to be chaotropic, which we attribute to the high concentration of magnesium and chloride ions. Metagenomic sequencing of the brines that supported growth showed their microbial communities to be similar to each other and comparable to those found in other hypersaline environments. These data show that solutions high in dissolved ions can shape the microbial diversity of the continental deep subsurface biosphere. Furthermore, under certain circumstances, complex brines can establish a hard limit to microbial replication in the deep biosphere, highlighting the potential for subsurface uninhabitable aqueous environments at depths far shallower than a geothermally-defined limit to life.
RESUMO
Differences in regional cerebral blood flow (rCBF) between subjects with Alzheimer's disease (AD), dementia with Lewy bodies (DLB) and healthy volunteers were investigated using statistical parametric mapping (SPM99). Forty-eight AD, 23 DLB and 20 age-matched control subjects participated. Technetium-99m hexamethylpropylene amine oxime (HMPAO) brain single-photon emission tomography (SPET) scans were acquired for each subject using a single-headed rotating gamma camera (IGE CamStar XR/T). The SPET images were spatially normalised and group comparison was performed by SPM99. In addition, covariate analysis was undertaken on the standardised images taking the Mini Mental State Examination (MMSE) scores as a variable. Applying a height threshold of P < or = 0.001 uncorrected, significant perfusion deficits in the parietal and frontal regions of the brain were observed in both AD and DLB groups compared with the control subjects. In addition, significant temporoparietal perfusion deficits were identified in the AD subjects, whereas the DLB patients had deficits in the occipital region. Comparison of dementia groups (height threshold of P < or = 0.01 uncorrected) yielded hypoperfusion in both the parietal [Brodmann area (BA) 7] and occipital (BA 17, 18) regions of the brain in DLB compared with AD. Abnormalities in these areas, which included visual cortex and several areas involved in higher visual processing and visuospatial function, may be important in understanding the visual hallucinations and visuospatial deficits which are characteristic of DLB. Covariate analysis indicated group differences between AD and DLB in terms of a positive correlation between cognitive test score and temporoparietal blood flow. In conclusion, we found evidence of frontal and parietal hypoperfusion in both AD and DLB, while temporal perfusion deficits were observed exclusively in AD and parieto-occipital deficits in DLB.
