Carbon demand,utilization, and metabolic diversity of bacterioplankton in the frontal regimes of the Indian sector of the Southern Ocean

Bacterial production, respiration and metabolic diversity were measured up to 120 m depth in the Sub-Antarctic Front (SAF) and Polar Fronts I and II (PFI and PFII) of the Indian Ocean sector of the Southern Ocean during 2010 Austral Summer. Prokaryotic cell count was maximum at PFI and PFII (~109 cells L−1) and minimum at SAF (~107 cells L−1). Furthermore, integrated bacterial production was higher at PFI (1.07 mg C m−2 h−1) and PFII (0.72 mg C m−2 h−1) compared to SAF (0.61 mg C m−2 h−1). At PFII, integrated bacterial growth efficiency was higher (8.96) compared to PFI (7.42) and SAF (7.17), signifying that the net contribution of PFII to the microbial loop could be relatively pronounced. Enhanced cell numbers and production at polar fronts indicate that the dissolved organic matter could be converted to secondary biomass through the microbial loop. However, integrated bacterial respiration rate at PFII (0.83 mg C m−2 h−1) was lower than that at PFI (1.84 mg C m−2 h−1) resulting in higher growth efficiency at PFII. Metabolic flexibility at SAF was clearly brought about by utilization of carboxylic acids like D-malic acid and itaconic acid, and carbohydrates like N-acetyl D-glucosamine, D-cellobiose and D-lactose. Utilization of amino acids like glycyl L-glutamic acid and L-threonine, and an amine, phenylethylamine, was critical in determining the metabolic variability at PFI. PFII hosted microbes that utilized phenolic compounds (2-hydroxy benzoic acid and 4-hydroxy benzoic acid) and polymers (like Tween 80). Utilization of polyols over carbohydrates in polar waters indicates a niche with lesser influence of the Antarctic melt waters on the bacterioplankton metabolism.     

Novel opportunity for understanding origin and evolution of life: perspectives on the exploration of subglacial environment of Lake Vostok, Antarctica

The year 2012 began with reports on the completion of drilling over the largest subglacial lake of Antarctica, Lake Vostok. It has been sealed from free exchange with the atmosphere for ～420,000 years, making it a potentially rich and largely unexplored storehouse of genetic information for solving evolutionary queries. Indirect evidence suggests that many impediments exist in the subglacial environment, such as high oxygen tension, low inorganic and organic nutrient concentrations, etc., whereas analysis of glacial and accretion ice from Vostok also implies that the elemental requirements for microbial growth could be satisfied in the lake by many possible electron donors (like H₂, Fe²⁺ and NO ₂ ^? ). Recent reports on the recovery of the longest ever ice core of ～3,769 m open up a new window for answering many questions about microbiological life in extremes, evolution, and adaptations. This review attempts to present an updated understanding on the potential significance of subglacial environments in unraveling the mystery of evolution of life.     

A glimpse of the diversity of complex polysaccharide-degrading culturable bacteria from Kongsfjorden,Arctic Ocean

Cold-adapted, complex polysaccharide-degrading marine bacteria have important implications in biogeochemical processes and biotechnological applications. Bacteria capable of degrading complex polysaccharide substrates, mainly starch, have been isolated from various cold environments, such as sea ice, glaciers, subglacial lakes, and marine sediments. However, the total diversity of polysaccharide-degrading culturable bacteria in Kongsfjorden, Arctic Ocean, remains unexplored. In the study reported here, we tested 215 cold-adapted heterotrophic bacterial cultures (incubated at 4 and 20 °C, respectively) isolated from Kongsfjorden, for the production of cold-active extracellular polysaccharide-degrading enzymes, including amylase, pectinase, alginase, xylanase, and carboxymethyl (CM)-cellulase. Our results show that 52 and 41% of the bacterial isolates tested positive for extracellular enzyme activities at 4 and 20 °C, respectively. A large fraction of the bacterial isolates (37% of the positive isolates) showed multiple extracellular enzyme activities. Alginase and pectinase were the most predominantly active enzymes, followed by amylase, xylanase, and CM-cellulase. All isolates which tested positive for extracellular enzyme activities were affiliated to microbial class Gammaproteobacteria. The four genera with the highest number of isolates were Pseudomonas, followed by Psychrobacter, Pseudoalteromonas, and Shewanella. The prevalence of complex polysaccharide-degrading enzymes among the isolates indicates the availability of complex polysaccharide substrates in the Kongsfjorden, likely as a result of glacial melting and/or macroalgal load. In addition, the observed high functional/phenotypic diversity in terms of extracellular enzyme activities within the bacterial genera indicates a role in regulating carbon/carbohydrate turnover in the Kongsfjorden, especially by reducing recalcitrance.     

Roseitranquillus sediminis gen. nov., sp. nov. a novel genus and species of the family Rhodobacteraceae,isolated from sediment of an Arctic fjord

Antonie van Leeuwenhoek - A Gram-negative, aerobic, non-motile, oxidase-positive, catalase-positive, rod-shaped bacterium, designated strain MCCB 386T was isolated from sediment samples collected...     

Pelagic nitrification and denitrification rates in an Arctic fjord during early spring

This study addresses factors governing nitrification and denitrification rates, along with the abundance of the bacterial groups likely involved in these activities, in Kongsfjorden, an Arctic fjord at Ny-Ålesund, Svalbard. The fjord was sampled three times during the month of March 2008 as day length and direct solar radiation increased. Although initially well mixed, cooler and more saline, the fjord became stratified, warmer and less saline during late March. The concentrations of NH₄ ⁺ (4.4?±?1.6 to 6?±?1.6 μM) and NO₂ ^? (1?±?0.3 to 1.2?±?0.4 μM) increased progressively with the decrease in NO₃ ^? (6.1?±?1.3 to 3.8?±?1.5 μM), reflecting the onset of primary productivity. Nitrification rates and the culturable population of nitrifiers decreased significantly from 1.6?±?0.9 to 0.4?±?0.1 ng at NH₄ ⁺-N l^?1 h^?1 and 5.1?±?0.3?×?10² to 29?±?14 cells l^?1, respectively. In contrast, denitrification rates increased (2.4?±?0.5 to 4.6?±?1.3 ng-at NO₃ ^?-N l^?1 h^?1), although the abundance of culturable denitrifiers did not vary significantly. A significant correlation of nitrifiers with NO₃ ^? during early March (p?<?0.01, r?=?0.51) indicated that nitrifiers may play an important role in regulating the NO₃ ^? pool and thereby in controlling the abundance of denitrifiers. However, the contribution of nitrification to the total NO₃ ^? pool decreased with time. Experimental simulations were also set up to understand the impact of change in duration of light and progressive increase in temperature on these processes. The application of 24 h light inhibited nitrification, suggesting that during peak Arctic summer the contribution of nitrification to the nitrate pool is minimal. It was also observed that a brief exposure to light (≤6 h) was enough to hamper nitrification rates. Experimental simulations suggested that a gradual increase in temperature in the fjord may enhance the magnitude of nitrification and denitrification in the fjord.     

Marine Group-II archaea dominate particle-attached as well as free-living archaeal assemblages in the surface waters of Kongsfjorden,Svalbard, Arctic Ocean

Antonie van Leeuwenhoek - Marine archaea are a significant component of the global oceanic ecosystems, including the polar oceans. However, only a few attempts have been made to study archaea in...