Holocene stromatolites characterized by unusually positive inorganic δ(13) CPDB values (i.e. up to +16‰) are present in Lagoa Salgada, a seasonally brackish to hypersaline lagoon near Rio de Janeiro (Brazil). Such positive values cannot be explained by phototrophic fixation of CO2 alone, and they suggest that methanogenesis was a dominating process during the growth of the stromatolites. Indeed, up to 5 mm methane was measured in the porewater. The archaeal membrane lipid archaeol showing δ(13) C values between -15 and 0‰ suggests that archaea are present and producing methane in the modern lagoon sediment. Moreover, (13) C-depleted hopanoids diplopterol and 3β-methylated C32 17β(H),21β(H)-hopanoic acid (both -40‰) are preserved in lagoon sediments and are most likely derived from aerobic methanotrophic bacteria thriving in the methane-enriched water column. Loss of isotopically light methane through the water column would explain the residual (13) C-enriched pool of dissolved inorganic carbon from where the carbonate constituting the stromatolites precipitated. The predominance of methanogenic archaea in the lagoon is most likely a result of sulphate limitation, suppressing the activity of sulphate-reducing bacteria under brackish conditions in a seasonally humid tropical environment. Indeed, sulphate-reduction activity is very low in the modern sediments. In absence of an efficient carbonate-inducing metabolic process, we propose that stromatolite formation in Lagoa Salgada was abiotically induced, while the (13) C-enriched organic and inorganic carbon pools are due to methanogenesis. Unusually, (13) C-enriched stromatolitic deposits also appear in the geological record of prolonged periods in the Palaeo- and Neoproterozoic. Lagoa Salgada represents a possible modern analogue to conditions that may have been widespread in the Proterozoic, at times when low sulphate concentrations in sea water allowed methanogens to prevail over sulphate-reducing bacteria.
Objective
Maternal iron needs increase 6-fold during pregnancy, but obesity interferes with iron absorption. We hypothesized that maternal obesity impairs fetal iron status.
Study Design
316 newborns with risk factors for infantile iron deficiency anemia (IDA) were studied to examine obesity during pregnancy and neonatal iron status. Erythrocyte iron was assessed by cord blood hemoglobin (Hb), zinc protoporphyrin/heme (ZnPP/H) and reticulocyte-ZnPP/H and storage iron by serum ferritin.
Results
Women with body mass index ≥30 kg/m2, as compared with non-obese women, delivered larger offspring with higher reticulocyte-ZnPP/H, and lower serum ferritin concentrations (p<0.05 for both). With increasing BMI, estimated body iron was relatively lower (mg/kg) and the ratio of total Hb-bound iron (mg)/total body iron (mg) increased. Maternal diabetes compromised infant iron status, but multivariate analysis demonstrated that obesity was an independent predictor.
Conclusions
Obesity during pregnancy and excessive weight gain are independent risk factors for iron deficiency in the newborn.
Terra Nova, 24, 248–254, 2012
Abstract
The study of microbe‐mineral interactions and the identification of biominerals in sedimentary rocks provide crucial information on the coevolution of life and Earth surface environments. Desulfovibrio brasiliensis, a sulfate‐reducing bacterium isolated from Lagoa Vermelha (Brazil), is known for its ability to precipitate dolomite, a mineral that is common in the geological record, but difficult to obtain in laboratory experiments simulating Earth's surface conditions. Here, we report on a new bacterial strain capable of precipitating Mg‐calcite and Ca‐dolomite, isolated from a microbial mat in the sabkha of Abu Dhabi (UAE). The 16S rRNA gene sequence of the isolate revealed a 99.6% identity (i.e. same species) with Desulfovibrio brasiliensis. The presence of the same microbial species at two geographically distant dolomite‐forming locations is difficult to explain in terms of pure coincidence. Rather, it suggests that the ability of precipitating dolomite may be a unique characteristic associated with specific strains.
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