Proliferation of hydrocarbon-degrading microbes at the bottom of the Mariana Trench

Background: The Mariana Trench is the deepest known site in the Earth’s oceans, reaching a depth of ~ 11,000m 20 at the Challenger Deep. Recent studies reveal that hadal waters harbor distinctive microbial planktonic communities. However, the genetic potential of microbial communities within the hadal zone is poorly understood. Results: Here, implementing both culture-dependent and culture-independent methods, we perform extensive analysis of microbial populations and their genetic potential at different depths in the Mariana Trench. Unexpectedly, we observed an abrupt increase in the abundance of hydrocarbon-degrading bacteria at depths > 10,400m in the Challenger Deep. Indeed, the proportion of hydrocarbon-degrading bacteria at > 10,400m is the highest observed in any natural environment on Earth. These bacteria were mainly Oleibacter, Thalassolituus, and Alcanivorax genera, all of which include species known to consume aliphatic hydrocarbons. This community shift towards hydrocarbon degraders was accompanied by increased abundance and transcription of genes involved in alkane degradation. Correspondingly, three Alcanivorax species that were isolated from 10,400m water supplemented with hexadecane were able to efficiently degrade n-alkanes under conditions simulating the deep sea, as did a reference Oleibacter strain cultured at atmospheric pressure. Abundant n-alkanes were observed in sinking particles at 2000, 4000, and 6000m (averaged 23.5 μg/gdw) and hadal surface sediments at depths of 10,908, 10,909, and 10,911m (averaged 2.3 μg/gdw). The δ2H values of n-C16/18 alkanes that dominated surface sediments at near 11,000-m depths ranged from − 79 to − 93‰, suggesting these alkanes may derive from an unknown biological source. Conclusions: These results reveal that hydrocarbon-degrading microorganisms are present in great abundance in the deepest seawater on Earth and shed a new light on potential biological processes in this extreme environment

A novel tri-unsaturated highly branched isoprenoid (HBI) alkene from the marine diatom Navicula salinicola

A novel tri-unsaturated C25 highly branched isoprenoid (HBI) alkene has been identified in a laboratory culture of the diatom Navicula salinicola and its structure determined using a combination of NMR spectroscopy and gas chromatography–mass spectrometry (GC–MS). This represents the first report of a C25 HBI in a marine diatom from the Navicula genus, although a different tri-unsaturated C25 HBI has been reported previously in the freshwater species N. sclesvicensis and unspecified HBIs have been identified in the brackish N. phyllepta. The newly characterised HBI contains a relatively unusual conjugated diene sub-unit, a structural feature only previously reported in some HBIs biosynthesised by a further marine diatom, Haslea ostrearia

Arctic Land-Ocean Interactions - Permafrost land-ocean interactions in the Arctic: from coastal to submarine permafrost including gas hydrates

Most Arctic coasts are permafrost coasts. There is regional evidence in northern Alaska and the Laptev Sea area for recent acceleration in the rate of coastal erosion. This is related in part to more open water and higher wave energy due to reduced sea ice coverage, rising sea level, and more rapid thermal abrasion along coasts with high volumes of ground ice. Nearshore zones are a sensitive source and temporary storage for terrigenous matter inputs onto the shelves via coastal erosion, river discharge, and sea ice. Recent flux estimates of sediment and organic carbon from coastal erosion into the Arctic Ocean are around 430 Tg (Tg = 10^12 gram) sediment per year and 4.9-14.0 Tg organic carbon per year. However, the fate of the terrestrial material, the contribution to greenhouse gas emissions and ocean acidification, and the impact on nearshore ecosystems is poorly constrained. As sea levels in the Arctic continue to rise, warming ocean water and seawater intrusion enhance the degradation of submarine permafrost. Submarine permafrost is thought to act as a barrier to rising gases from depth, thus, as permafrost degrades, it allows the release of methane gas from dissociating gas hydrates into the water column. Because the Arctic coastal waters are very shallow, escaping greenhouse gases may pass through the water column, and enter the atmosphere directly. Apart from regional to global consequences of a changing environment along Arctic coasts, immediate local implications for coastal communities and indigenous peoples are becoming more apparent. Nearshore ecosystems located in traditional hunting and fishing grounds might be impacted by high loads of sediments and nutrients released from eroding coasts. Coastal retreat leads to a loss of natural habitat for flora and fauna and of cultural heritage from the early explorers and indigenous peoples. In the Arctic coastal zone, the impacts of environmental change on local communities, on ecosystem services, and socioeconomic dynamics have not been quantified yet

Stable isotope analysis of plant-derived nitrate - Novel method for discrimination between organically and conventionally grown vegetables

The lack of reliable markers for the discrimination between organic and conventional products makes the organic food market susceptible to attempted fraud. Robust analytical methodologies for organic food authentication are urgently needed. In this study a new approach, compound-specific nitrogen and oxygen isotope analysis of plant-derived nitrate, has been applied alongside bulk nitrogen isotope analysis for discrimination between organically and conventionally greenhouse-grown lettuce and retail potatoes and tomatoes. The method revealed significant differences between conventional and organic fertilisation. An intra-plant isotopic variation as well as significant impact of the fertiliser application rate on the nitrogen and oxygen isotope values of plant-derived nitrate has been observed. Nitrogen and oxygen isotope analysis of nitrate has a potential for differentiation between organic and conventional crops. Further analysis is needed to improve our understanding of the scope of application and robustness of this compound-specific approach. © 2014 Elsevier Ltd. All rights reserved

Leaf wax and bulk stable carbon isotope records of plant type assemblages and palaeoenvironment changes in Mfabeni Peatland (South Africa), since the late Pleistocene

As a consequence of the regional topography and semi-arid climate of southern Africa, there is a general lack of continuous terrestrial palaeoenvironmental archives and, therefore, ambiguity prevails over how terrestrial ecosystems responded to past climate fluctuations in the region. Leaf wax stable carbon isotope (δ13Cwax) signatures of peat-forming plants are primarily controlled by the C fixation pathways employed during photosynthesis. Consequently, observed changes in peat δ13Cwax trends can best be explained by the changes in relative abundances between C3 and C4 plant inputs at the time of deposition. It is still not clear how the balance between competing southern African tropical woodlands / rainforests (C3) and grasslands (predominantly C4) were affected by changes in temperature, moisture and pCO2 in the past. Regional palynology studies have gone some way to elucidate changes in past plant assemblages. However, these records do not extend as far back as the last glacial maximum (LGM) and tend to suffer from temporal discontinuities, pollen dispersal range and dating uncertainties. In this study, we employed bulk and compound-specific isotope analyses of terrestrial plant lipids extracted from the Mfabeni Peatland, KwaZulu-Natal, South Africa. The 14C age of the basal peat is c. 47 kcal yr BP, making this setting one of the oldest continuous coastal peatlands on the African continent. This unique archive allowed us to directly reconstruct the changes in local plant type assemblages. We used bulk and compound-specific δ13C records to explore the changes in proportions of C3 and C4 plant input into the Mfabeni and to compare them with local palynology and peatland chronology records to infer the changes in the palaeoenvironment since the late Pleistocene. Our results suggest shifts between the two dominant competing plant types, in general correlation with the fossil pollen incidence and peat stratigraphy, through C4 plant dominant input being exhibited from c.44.5 to 39.0 kcal yr BP and the late Holocene, while c. 46.9 – 45.7, 38.0, 14.8 kcal yr BP and early Holocene periods demonstrated C3 dominant plant input. These trends advocate that the local Mfabeni plant population responded relatively rapidly to changes in local palaeoenvironment, mainly as a consequence of fluctuations in peatland hydrology. Furthermore, our data showed that there was a poor correlation between the changes in plant type assemblages and known regional and global climate events, which suggests that the local palaeohydrological forcings could have overprinted the regional climate influences on peatland plant communities in the Mfabeni since its inception

The impact of environmental factors on molecular and stable isotope compositions of n-alkanes in Mediterranean extra virgin olive oils

The impact of climatic factors on the molecular and stable carbon and hydrogen isotope compositions of n-alkanes in extra virgin olive oils from eight Mediterranean countries is studied, and the applicability of these data for olive oil regional classification is discussed. n-Alkane average chain length values are positively correlated with the amount of precipitation and are the lowest in olive oils from Morocco and Greece and the highest in oils from Spain and Portugal. Stable carbon and hydrogen isotope compositions of n-alkane C show significant correlation with climatic parameters and are significantly more positive in olive oils from the southern compared with northern Mediterranean countries

Climatic variability in Mfabeni peatlands (South Africa) since the late Pleistocene

It has been postulated that a bipolar seesaw interhemispheric mechanism dominated the relationship between the Northern and Southern hemisphere climates since the late Pleistocene. A key test for this proposition would be to undertake palaeoenvironmental studies on terrestrial archives in climatically sensitive regions. Southern Africa's contemporary C-3 and C-4 terrestrial plant distributions display a definitive geographical pattern dictated by different growing season rainfall and temperature zones; however, the region is generally archive poor due to its overall semi-arid climate and high relief topography. The Mfabeni peatland, with a basal age of c. 47 k yrs calibrated before present (kcal yr BP), is one of the oldest continuous coastal peat deposits in Southern Africa. Molecular leaf wax isotopes (delta C-13(wax)) were generated for a 810 cm long core, and combined with previously published bulk geochemical (delta C-13(bulk), %TOC), palynological, and stratigraphic data, to reconstruct the late Pleistocene and Holocene palaeoenvironments. We interpreted environmental shifts associated with the Heinrich 4, Last Glacial Maximum, deglacial and Holocene periods, which are consistent with adjacent Indian Ocean sea surface temperature records. However, the other shorter climate perturbations during the Heinrich 5, 3, 2, 1, Antarctic cold reversal and Younger Dryas, were muted, most likely due to local hydrological overprinting on the Mfabeni record. A general anti-phase sequence was observed between the Mfabeni record and better established Northern Hemisphere events, underpinning the bipolar seesaw interhemispheric mechanism proposed for global climate forcing since the Late Pleistocene