Characterization of the molecular mechanisms of silicon uptake in coccolithophores.

Coccolithophores are an important group of calcifying marine phytoplankton. Although coccolithophores are not silicified, some species exhibit a requirement for Si in the calcification process. These species also possess a novel protein (SITL) that resembles the SIT family of Si transporters found in diatoms. However, the nature of Si transport in coccolithophores is not yet known, making it difficult to determine the wider role of Si in coccolithophore biology. Here, we show that coccolithophore SITLs act as Na+ -coupled Si transporters when expressed in heterologous systems and exhibit similar characteristics to diatom SITs. We find that CbSITL from Coccolithus braarudii is transcriptionally regulated by Si availability and is expressed in environmental coccolithophore populations. However, the Si requirement of C. braarudii and other coccolithophores is very low, with transport rates of exogenous Si below the level of detection in sensitive assays of Si transport. As coccoliths contain only low levels of Si, we propose that Si acts to support the calcification process, rather than forming a structural component of the coccolith itself. Si is therefore acting as a micronutrient in coccolithophores and natural populations are only likely to experience Si limitation in circumstances where dissolved silicon (DSi) is depleted to extreme levels.

Role of silicon in the development of complex crystal shapes in coccolithophores.

The development of calcification by the coccolithophores had a profound impact on ocean carbon cycling, but the evolutionary steps leading to the formation of these complex biomineralized structures are not clear. Heterococcoliths consisting of intricately shaped calcite crystals are formed intracellularly by the diploid life cycle phase. Holococcoliths consisting of simple rhombic crystals can be produced by the haploid life cycle stage but are thought to be formed extracellularly, representing an independent evolutionary origin of calcification. We use advanced microscopy techniques to determine the nature of coccolith formation and complex crystal formation in coccolithophore life cycle stages. We find that holococcoliths are formed in intracellular compartments in a similar manner to heterococcoliths. However, we show that silicon is not required for holococcolith formation and that the requirement for silicon in certain coccolithophore species relates specifically to the process of crystal morphogenesis in heterococcoliths. We therefore propose an evolutionary scheme in which the lower complexity holococcoliths represent an ancestral form of calcification in coccolithophores. The subsequent recruitment of a silicon-dependent mechanism for crystal morphogenesis in the diploid life cycle stage led to the emergence of the intricately shaped heterococcoliths, enabling the formation of the elaborate coccospheres that underpin the ecological success of coccolithophores.

Embedding a trauma hospitalist in the trauma service reduces mortality and 30-day trauma-related readmissions.

BACKGROUND: Recognizing the increasing age and comorbid conditions of patients admitted to our trauma service, we embedded a hospitalist on the trauma service at our Level I trauma center.This program was initiated in January 2013. This study was designed to investigate differences in outcomes between trauma patients who received care from the trauma hospitalist (THOSP) program and similarly medically complex trauma patients who did not receive THOSP care. METHODS: There were 566 patients comanaged with THOSP between December 2013 and November 2014. These patients were matched (1:2) with propensity scores to a contemporaneous control group based on age, Injury Severity Score (ISS), and comorbid conditions. Outcomes examined included mortality, trauma-related readmissions, upgrades to the intensive care unit, hospital length of stay, the development of in-hospital complications, and the frequency of obtaining medical subspecialist consultation. Differences in outcomes were compared with Mann-Whitney U-test or χ test as appropriate. RESULTS: High-quality matching resulted in the loss of 97 THOSP patients for the final analysis. Table 1 shows the balance between the two groups after matching. While there was a 1-day increase in hospital length of stay and an increase in upgrades to the intensive care unit, there was a reduction in mortality, trauma-related readmissions, and the development of renal failure after implementation of the THOSP program (Table 2). Implementation of this program made no significant difference in the frequency of cardiology, nephrology, neurology, or endocrinology consultations. There was also no difference in the development of the complications of venous thromboembolism, pneumonia, stroke, urinary tract infection, bacteremia, or alcohol withdrawal. CONCLUSION: Our study provides evidence that embedding a hospitalist on the trauma service reduces mortality and trauma-related readmissions. A reason for these improved outcomes may be related to THOSP "vigilance." LEVEL OF EVIDENCE: Therapeutic/care management study, level IV.