Simulated Deep-sea Conditions Research Articles

How Expertise Changes Cortical Sources of EEG Rhythms and Functional Connectivity in Divers Under Simulated Deep-Sea Conditions.

Although the recent years have witnessed a growing interest in functional connectivity (FC) through brain sources, the FC in extreme situations has not been completely elucidated. This paper is aimed at investigating whether the expertise acquired during the deep-sea diving is reflected in FC in a group of professional divers (PDs) compared to a group of new divers (NDs), and how it could affect the concentration and stress levels. The sources of brain frequency rhythms, derived by the electroencephalography acquisition in a hyperbaric chamber, were extracted in different frequency bands and the corresponding FC was estimated in order to compare the two groups. The results highlighted a significant decrease of the alpha source in PDs during air breathing and a significant increase of the upper beta source over central areas at the beginning of post-oxygen air, as well as an increase of beta FC between fronto-temporal regions in the last minutes of oxygen breathing and in the early minutes of post-oxygen air. This provides evidence in support of the hypothesis that experience and expertise differences would modulate brain networks. These experiments provided the unique opportunity of investigating the impact of the neurophysiological activity in simulated critical scenarios in view of the investigation in real sea-water experiments.

Conidial germination of marine-derived fungi under simulated deep-sea conditions in the presence of inducers

The abilities of conidia of four deep-sea fungi, Aspergillus flavus NIOCC20, A. sydowii CH2, A. terreus A4636 and Penicillium sp. A4623 and one terrestrial fungus, A. terreus MTCC479 to germinate under simulated deep-sea conditions were investigated by exposing the conidia to low temperature (4 °C) and elevated hydrostatic pressures (10, 20, 30, 40, 50 and 60 MPa). The conidial germination was evaluated in presence of chemical inducers, including Thiamine, Sodium pyruvate, Hydrochloric acid, Sulphuric acid and Sucrose, in a basal medium of 1/5th strength of malt extract broth and subjected to heat treatment at 70 °C for 60 min, and incubated for 30 days under simulated deep-sea conditions. The conidia of Aspergillus flavus, A. sydowii and Penicillium sp. germinated and developed into mycelia under almost all the treatments with and without heat inducement. However, the number of germinated conidia of A. terreus A4636 and A. terreus MTCC479 was lower than the other three fungal species. This is the first study demonstrating in vitro germination of conidia of deep-sea fungi at low temperature with elevated hydrostatic pressures. Further studies are warranted to obtain insights into in situ conditions that are favourable for conidial germination and fungal activity in deep-sea niches.

Draft Genome Sequence of the Piezotolerant and Crude Oil-Degrading Bacterium Rhodococcus qingshengii Strain TUHH-12

We report here the draft genome sequence of Rhodococcus qingshengii strain TUHH-12. The ability of this piezotolerant bacterium to grow on crude oil and tetracosane as sole carbon sources at 150 × 105 Pa makes it useful in studies of hydrocarbon degradation under simulated deep-sea conditions.

Mortality and survival of cultured surface-ocean flagellates under simulated deep-sea conditions

The vast majority of the marine environment consists of dark, cold, high-pressure environments into which microbes from the surface ocean are continuously transported by advection or by attachment to sinking particles. Little is known about how the low temperature and high pressure of the deep ocean affect the abundance and activity of surface organisms, in particular microbial eukaryotes. Cultures of two flagellate species, Cafeteria roenbergensis and Neobodo designis, both isolated from surface waters where they are considered cosmopolitan, were incubated in titanium chambers for one to two weeks under typical deep-sea temperature (2°C) and pressure (50MPa, representing 5000m water depth). Samples were taken daily with minimal loss of pressure in the culture vessel, and flagellates were subsequently enumerated, along with prokaryotic prey when possible. The abundance of protists declined in all treatments, with a significantly greater rate of mortality under combined cold temperature and high pressure conditions than in the cold temperature-only conditions. However, 1.6 (SD = 3.8)% of C. roenbergensis and 10.0 (6.1)% of N. designis cells survived on average in the high pressure treatments, indicating that some fraction of sinking protists can survive transport to the deep ocean. In addition, after a period of acclimation, positive growth rates were measured in some cases, suggesting that surface-adapted flagellates cannot only survive under deep-sea conditions but are able to reproduce and potentially provide seed populations to cold, high-pressure environments.

Differentially expressed genes under simulated deep-sea conditions in the psychrotolerant yeast Cryptococcus sp. NIOCC#PY13

Microorganisms exhibit varying degrees of tolerance to extreme conditions of pressure and temperature. In the present study, the psychrotolerant deep-sea yeast, Cryptococcus sp. NIOCC#PY13, was exposed to elevated hydrostatic pressure and low temperature to explore the differentially expressed genes responsible for its survival at such extreme conditions. The suppression subtractive hybridization technique was employed for identification of expressed upregulated genes at extreme conditions of pressure and temperature. The effect of elevated pressure was found to be different than that of combined pressure and temperature exposures. Altogether, 17 and 20 upregulated genes were identified at 50 MPa and 50 MPa/5 °C, respectively. These differentially expressed genes were similar to the NCBI database ESTs (expressed sequence tags), coding for proteins such as arachidonic acid metabolism, amino acid transport and unsaturation of membrane fatty acids, which have been previously demonstrated to assist in the survival of microorganisms under stress conditions. Interestingly, about 50 % of the upregulated genes matched with hypothetical proteins at a percentage similarity of ≤96, suggesting their probability of being novel. Detailed studies of the above genes/proteins from deep-sea microorganisms are suggested for future investigations, which may shed more light on the existence and adaptation mechanisms adopted by these for their survival under such extreme conditions.

Biodegradation of Synthetic Base Fluid Surrogates in Gulf of Mexico Sediments under Simulated Deep-Sea Conditions

In this study, an anaerobic marine biodegradability test was adapted to study the fate of synthetic base fluid (SBF) surrogates, ethyl oleate and tetradecene, by deep-sea microorganisms. Sediment samples from hundreds of meters deep in the Gulf of Mexico were incubated at low temperatures (4 degrees C) and high hydrostatic pressure in steel vessels. Stimulation of indigenous microbial communities to SBF biodegradation was evident in the fact that the rate of removal of ethyl oleate was greater in sediments that had some previous exposure to SBF (first-order decay coefficient kof -0.22 +/- 0.02 week(-1)) compared to unexposed control sediments (first-order decay coefficient k of -0.11 +/- 0.02 week(-1)). When sulfate-linked tetradecene degradation occurred within the test period, the activity could also be modeled as a first-order decay following an initial lag phase, with an average decay coefficient of k = -0.05 +/- 0.01 week(-1). This study also revealed that the degradation of SBF surrogates by microorganisms collected from deep-sea sediments was not significantly effected by the hydrostatic incubation pressure.

Cultivation of fungi under simulated deep sea conditions

In order to investigate the barotolerance of marine fungi and to elucidate their ecological role in the deep sea, high-pressure equipment was built and tested. Cultures of the marine yeasts Debaryomyces hansenii, Rhodotorula rubra and Rhodosporidium sphaerocarpum were inoculated into gas-permeable plastic foil bags and incubated in pressure vessels filled with hydraulic fluid that serves also as an oxygen reservoir. The equipment was used at temperatures from 7° to 34°C and pressures from 0.1 to 80.0 MPa. Comparison of five types of plastic foil showed effects on total cell number in batch culture. An exchange of the hydraulic fluid increased yield by replenishing oxygen, the growth-limiting factor. There were no detectable growth differences between buffered (TRIS, HEPES, imidazole, MES) and unbuffered media and thus unbuffered medium was used. Yeasts were best cultivated in an unbuffered sea-water medium (glucose—peptone—yeast extract) sealed in bags made from polyethylene foil. The fluorocarbon liquid FC-77 provided the best oxygen reservoir owing to its high oxygen and carbon dioxide solubility. An exchange of the hydraulic fluid is not necessary if sensitive growth determination methods are used. All marine yeasts cultivated under simulated deep sea conditions were able to grow at least up to a pressure of 20 MPa, with Rhodotorula rubra and Rhodosporidium sphaerocarpum growing at 40 MPa, corresponding to 4000 m depth. Thus, marine yeasts are able to grow under simulated deep sea conditions and may participate in the degradation of organic matter in the deep sea.

Maintenance of abyssal benthic foraminifera under high pressure and low temperature: some preliminary results

Abyssal benthic foraminifera have been maintained alive for periods of several weeks under laboratory simulated deep-sea conditions of high pressure and low temperature. In separate experiments, bacterial-sized fluorescent microspheres and three species of microalgae were supplied as food particles. Subsequent light and electron microscopy showed that the algae had been ingested by several foraminiferal species. Furthermore, the fine structure of the foraminiferal cytoplasm was well-preserved which indicates, along with the ingestion of algal food, that they had remained in a viable condition during the incubation. Other observations indicate that abyssal benthic foraminifera ingest naturally occurring photosynthetic cells carried to the deep-sea bed by rapidly sedimenting aggregates. The ability to keep foraminifera originating from depths exceeding 4000 m alive in the laboratory paves the way for the experimental investigation of some important issues in deep-sea biology and palaeoceanography.

A barophilic flagellate isolated from 4500 m in the mid-North Atlantic

A bacterivorous, barophilic, kidney-shaped flagellate, 3.5–6 μm in length, was isolated from 4500 m in the mid-Atlantic by enrichment of water directly overlying the sediment with sterilized phytodetritus collected from the English Channel during the spring and summer. The light microscopical and electron microscopical appearances of the cell are described and used to identify it to the genus Bodo (Protozoa, Bodoninae). Bodo sp. did not grow at 1 atm and 2°C. It, however, grew under 450 atm and 2°C, with a mean relative growth rate over the exponential growth phase of 0.33 day −1, equivalent to a doubling time of 2.11 days. The flagellate was bacterivorous and had an estimated carbon conversion efficiency of bacterial carbon into flagellate carbon of 17–25%. The step in the microbial food web from bacteria to flagellate could be an important site for remineralization. Bacterial density in deep-sea phytodetritus (1–34 × 10 7 ml −1) and sediment (5–54 × 10 9 ml −1) must be sufficient to support a flagellate population. The evidence reported here of a rapidly developing bacterial and flagellate population under simulated deep-sea conditions may indicate that a microbial decomposer pathway similar to that described in shallow waters may be significant in the decomposition of sedimented biogenic particles and energy flow in the deep sea.

Effect of hydrostatic pressure and temperature on the activity and synthesis of chitinases of Antarctic Ocean bacteria

The formation of chitinases by psychrophilic and psychrotrophic marine Antarctic bacteria and the activity of these extracellular enzymes were investigated under simulated deep-sea conditions. The formation of the chitinases was affected by hydrostatic pressure of 400 bars. However, the extent of pressure inhibition differed with the bacterial strains tested and was considerably less with the extreme psychrophilic bacteria isolated from sediments of greater depth. Growth of these psychrophilic strains had a moderately barophilic character at 400 bars, whereas growth of the psychrotrophic strains was clearly restricted under simulated deep-sea conditions. With regard to the activity of the extracellular chitinases of various bacterial strains, a relatively uniform response was found. All chitinases were highly barotolerant at near neutral pH and were active up to 1000 bars. Low temperatures reduced their activity but not their barotolerance. A low pH of 5.1 diminished the barotolerance of some chitinases. The results suggest that the indigenous deep-sea bacteria are capable of decomposing chitin settled to or produced in the depth of the Antarctic Ocean.

Survival of Human Enteric and Other Sewage Microorganisms Under Simulated Deep-Sea Conditions

The survival of pure cultures of Escherichia coli, Streptococcus faecalis, Clostridium perfringens , and Vibrio parahaemolyticus under simulated deep-sea conditions of low temperature (4 C), seawater, and hydrostatic pressures ranging from 1 to 1,000 atm was determined over a period exceeding 300 h. The viability of E. coli and total aerobic bacteria in seawater-diluted raw sewage subjected to these deep-sea conditions was also measured. There was a greater survival of both E. coli and S. faecalis at 250 and 500 atm than at 1 atm at 4 C. S. faecalis was quite insensitive to 1,000 atm, whereas with E. coli there was a 10-fold die-off per 50-h exposure to 1,000 atm. In contrast, V. parahaemolyticus and C. perfringens were quite sensitive to pressures exceeding 250 atm, and with both of these species there was a total loss of viability of approximately 10 8 cells per ml within 100 h at 1,000 atm and within 200 h at 500 atm. The viability of the naturally occurring fecal coliforms in sewage exposed to moderate pressures at 4 C was found to be similar to the survival patterns demonstrated with pure cultures of E. coli . The total numbers of aerobic bacteria in these sewage samples, however, stabilized at 500 and 1,000 atm after 100 h, and at 1 and 250 atm there was significant growth of sewage-associated bacteria, which apparently utilized the organic compounds in the seawater-diluted sewage samples. A preliminary classification of some of these bacteria indicated that approximately 90% (160 isolates) of the organisms that survived over a 400-h exposure to 500 and 1,000 atm were Arthrobacter/Corynebacterium species, and the representative organisms capable of growing at 1 and 250 atm in seawater at 4 C were gram-positive cellulose digesters and an unidentified gram-negative coccus. The significance of these results with respect to the contamination of the deep ocean with human pathogens and the possibility of sewage-associated microorganisms growing and competing with indigenous marine microbial flora in situ is discussed.

Survival of Human Enteric and Other Sewage Microorganisms Under Simulated Deep-Sea Conditions1

The survival of pure cultures of Escherichia coli, Streptococcus faecalis, Clostridium perfringens, and Vibrio parahaemolyticus under simulated deep-sea conditions of low temperature (4 C), seawater, and hydrostatic pressures ranging from 1 to 1,000 atm was determined over a period exceeding 300 h. The viability of E. coli and total aerobic bacteria in seawater-diluted raw sewage subjected to these deep-sea conditions was also measured. There was a greater survival of both E. coli and S. faecalis at 250 and 500 atm than at 1 atm at 4 C. S. faecalis was quite insensitive to 1,000 atm, whereas with E. coli there was a 10-fold die-off per 50-h exposure to 1,000 atm. In contrast, V. parahaemolyticus and C. perfringens were quite sensitive to pressures exceeding 250 atm, and with both of these species there was a total loss of viability of approximately 10(8) cells per ml within 100 h at 1,000 arm and within 200 h at 500 atm. The viability of the naturally occurring fecal coliforms in sewage exposed to moderate pressures at 4 C was found to be similar to the survival patterns demonstrated with pure cultures of E. coli. The total numbers of aerobic bacteria in these sewage samples, however, stabilized at 500 and 1,000 atm after 100 h, and at 1 and 250 atm there was significant growth of sewage-associated bacteria, which apparently utilized the organic compounds in the seawater-diluted sewage samples. A preliminary classification of some of these bacteria indicated that approximately 90% (160 isolates) of the organisms that survived over a 400-h exposure to 500 and 1,000 atm were Arthrobacter/Corynebacterium species, and the representative organisms capable of growing at 1 and 250 atm in seawater at 4 C were gram-positive cellulose digesters and an unidentified gram-negative coccus. The significance of these results with respect to the contamination of the deep ocean with human pathogens and the possibility of sewage-associated microorganisms growing and competing with indigenous marine microbial flora in situ is discussed.