Christmas Island lagoonal lakes, models for the deposition of carbonate–evaporite–organic laminated sediments

The atoll of Christmas Island (now known as Kiritimati) in the Kiribati Republic (Central Pacific) lies at about 2°N in the intertropical convergence zone. Much of the surface area of the atoll (ca. 360 km2) is occupied by numerous lakes in which carbonate, evaporite (calcium sulfate, halite) and organic layers are deposited. Observations suggest that deposition of these different laminae is controlled by climatic and biologic factors. It is thought that periodic climatic variations, such as El Niño-Southern Oscillations (ENSO) events which bring heavy rainfall to the atoll, result in the succession of the precipitation of carbonate minerals (during periods after dilution of hypersaline waters by heavy rains), followed by evaporitic minerals (carbonate, calcium sulfate, halite) when salinity increases through evaporation. Thick (up to 5 cm) microbial (essentially cyanobacterial) mats develop continuously on the lake bottom surfaces providing the sediment with an important (total organic carbon 2–5%) organic contribution in the form of an internal, geometrically structured, network in which the authigenic minerals precipitate. The high bioproductivity of these microbial populations is reflected in low δ13C values of sedimentary organic carbon (−14 to −17‰), interpreted as being the result of high atmospheric CO2 demand (Geochim. Cosmochim. Acta, 56 (1992) 335). The well-laminated organic layers present in the sediment profile result from the death and burial of microbial populations at the time of severe climatic events (storms, heavy rainfall). These lagoonal lakes provide a model for the deposition of carbonate and organic matter in an evaporitic environment. The high ratio of deposited carbonate vs. sulfate+chloride, when compared to low ratio in evaporitic salinas, results from both a lack of limitation of calcium, magnesium and carbonate ions (in a carbonate reef environment) and active processes of high-Mg calcite precipitation (organomineralization)

Posaconazole treatment of refractory eumycetoma and chromoblastomycosis Tratamento com posaconazol de casos de cromoblastomicose e micetoma maduromicótico resistentes a outros antifúngicos

Eumycetoma and chromoblastomycosis are chronic, disfiguring fungal infections of the subcutaneous tissue that rarely resolve spontaneously. Most patients do not achieve sustained long-term benefits from available treatments; therefore, new therapeutic options are needed. We evaluated the efficacy of posaconazole, a new extended-spectrum triazole antifungal agent, in 12 patients with eumycetoma or chromoblastomycosis refractory to existing antifungal therapies. Posaconazole 800 mg/d was given in divided doses for a maximum of 34 months. Complete or partial clinical response was considered a success; stable disease or failure was considered a nonsuccess. All 12 patients had proven infections refractory to standard therapy. Clinical success was reported for five of six patients with eumycetoma and five of six patients with chromoblastomycosis. Two patients were reported to have stable disease. As part of a treatment-use extension protocol, two patients with eumycetoma who initially had successful outcome were successfully retreated with posaconazole after a treatment hiatus of > 10 months. Posaconazole was well tolerated during long-term administration (up to 1015 d). Posaconazole therapy resulted in successful outcome in most patients with eumycetoma or chromoblastomycosis refractory to standard therapies, suggesting that posaconazole may be an important treatment option for these diseases.<br>Eumicetoma e cromoblastomicose são infecções fúngicas crônicas do tecido subcutâneo que evoluem com aspecto desfigurado, raramente involuindo espontaneamente. A maioria dos pacientes não apresenta melhora sustentada por longo tempo com os tratamentos disponíveis, sendo de grande importância as novas opções terapêuticas. A eficácia do posaconazol, um novo agente antifúngico de amplo espectro do grupo dos triazóis, foi estudada em 12 pacientes com eumicetoma ou cromoblastomicose refratária às terapêuticas antifúngicas disponíveis. Os pacientes receberam por no máximo 34 meses, doses divididas de 800 mg/dia de posaconazol. Resposta clínica parcial ou completa foi considerada como sucesso; doença estável ou falha terapêutica foi considerada como insucesso. Todos os 12 pacientes tinham infecções comprovadas ou prováveis, refratárias à terapêutica padrão preconizada. Sucesso clínico foi registrado em cinco de seis pacientes com eumicetoma e cinco de seis pacientes com cromoblastomicose. Em dois pacientes observou-se doença estável. Como parte do protocolo de extensão do tratamento, dois pacientes com eumicetoma que inicialmente tinham tido sucesso terapêutico e que após um intervalo maior de 10 meses apresentaram recidiva da micose, foram retratados com sucesso com posaconazol. Posaconazol foi bem tolerado durante o longo período de administração (até 1015 dias). A terapêutica com posaconazol foi seguida de sucesso na maioria dos pacientes com eumicetoma ou cromoblastomicose refratária à terapêutica padrão, sugerindo que tal droga possa ser uma importante opção no tratamento de tais doenças