Metabolic activities of the intestinal microflora of a deep-sea invertebrate

Giant sponge grounds of Central Arctic seamounts are associated with extinct seep life

The Central Arctic Ocean is one of the most oligotrophic oceans on Earth because of its sea-ice cover and short productive season. Nonetheless, across the peaks of extinct volcanic seamounts of the Langseth Ridge (87°N, 61°E), we observe a surprisingly dense benthic biomass. Bacteriosponges are the most abundant fauna within this community, with a mass of 460 g C m⁻² and an estimated carbon demand of around 110 g C m⁻² yr⁻¹, despite export fluxes from regional primary productivity only sufficient to provide <1% of this required carbon. Observed sponge distribution, bulk and compound-specific isotope data of fatty acids suggest that the sponge microbiome taps into refractory dissolved and particulate organic matter, including remnants of an extinct seep community. The metabolic profile of bacteriosponge fatty acids and expressed genes indicate that autotrophic symbionts contribute significantly to carbon assimilation. We suggest that this hotspot ecosystem is unique to the Central Arctic and associated with extinct seep biota, once fueled by degassing of the volcanic mounts.

This study reports the discovery of dense sponge gardens across the peaks of permanently ice-covered, extinct volcanic seamounts of the Langseth Ridge and on the remnants of a now extinct seep ecosystem. Using approaches to sample and infer food and energy sources to this ice-covered community, the authors suggest that the sponges use refractory organic matter trapped in the extinct seep community on which they sit.

Vertically distinct microbial communities in the Mariana and Kermadec trenches

Hadal trenches, oceanic locations deeper than 6,000 m, are thought to have distinct microbial communities compared to those at shallower depths due to high hydrostatic pressures, topographical funneling of organic matter, and biogeographical isolation. Here we evaluate the hypothesis that hadal trenches contain unique microbial biodiversity through analyses of the communities present in the bottom waters of the Kermadec and Mariana trenches. Estimates of microbial protein production indicate active populations under in situ hydrostatic pressures and increasing adaptation to pressure with depth. Depth, trench of collection, and size fraction are important drivers of microbial community structure. Many putative hadal bathytypes, such as members related to the Marinimicrobia, Rhodobacteraceae, Rhodospirilliceae, and Aquibacter, are similar to members identified in other trenches. Most of the differences between the two trench microbiomes consists of taxa belonging to the Gammaproteobacteria whose distributions extend throughout the water column. Growth and survival estimates of representative isolates of these taxa under deep-sea conditions suggest that some members may descend from shallower depths and exist as a potentially inactive fraction of the hadal zone. We conclude that the distinct pelagic communities residing in these two trenches, and perhaps by extension other trenches, reflect both cosmopolitan hadal bathytypes and ubiquitous genera found throughout the water column.

Pressure as an environmental parameter for microbial life--a review

Microbial life has been prevailing in the biosphere for the last 3.8 Ga at least. Throughout most of the Earth's history it has experienced a range of pressures; both dynamic pressure when the young Earth was heavily bombarded, and static pressure in subsurface environments that could have served as a refuge and where microbial life nowadays flourishes. In this review, we discuss the extent of high-pressure habitats in early and modern times and provide a short overview of microbial survival under dynamic pressures. We summarize the current knowledge about the impact of microbial activity on biogeochemical cycles under pressures characteristic of the deep subsurface. We evaluate the possibility that pressure can be a limiting parameter for life at depth. Finally, we discuss the open questions and knowledge gaps that exist in the field of high-pressure geomicrobiology.

Recovery and maintenance of live amphipods at a pressure of 580 bars from an ocean depth of 5700 meters

Amphipods were collected from an ocean depth of 5700 meters in a windowed pressure-retaining trap, kept alive in the trap for as long as 9 days aboard ship, and transported to a land laboratory. Observations suggest that the animals can easily tolerate decompressions of 29 percent and briefly of 70 percent of the value of 580 bars, the pressure of their natural habitat. The average pleopod beat frequency was 106 beats per minute. Evidence suggests that food (fish bait) can have at least a 4-day residence time in the gut of these animals.

Isolation of a deep-sea barophilic bacterium and some of its growth characteristics

A bacterium, a spirillum, has been isolated from a deep-sea sample and has been found to grow optimally at about 500 bars and 2 degrees to 4 degrees C. These conditions are similar to those prevailing at the 5700-meter depth from which the sample was collected. The organism grows at these pressures and temperatures with a generation time of between 4 and 13 hours; at atmospheric pressure and 2 degrees to 4 degrees C, the generation time is about 3 to 4 days.

Absence of microorganisms in crustacean digestive tracts

Two marine and one terrestrial wood-boring isopod species and one wood-inhabiting amphipod species maintain a digestive tract free of microorganisms. Digestive tracts examined in toto with the scanning electron microscope were devoid of microorganisms. In contrast, the outer exoskeleton surfaces of these crustaceans support a dense bacterialflora. Observations of the hindgut of termites revealed a diverse gut microflora as expected.

Effects of hyperbaric pressure on a deep-sea archaebacterium in stainless steel and glass-lined vessels

The effects of hyperbaric helium pressures on the growth and metabolism of the deep-sea isolate ES4 were investigated. In a stainless steel reactor, cell growth was completely inhibited but metabolic gas production was observed. From 85 to 100 degrees C, CO(2) production proceeded two to three times faster at 500 atm (1 atm = 101.29 kPa) than at 8 atm. At 105 degrees C, no CO(2) was produced until the pressure was increased to 500 atm. Hydrogen and H(2)S were also produced biotically but were not quantifiable at pressures above 8 atm because of the high concentration of helium. In a glass-lined vessel, growth occurred but the growth rate was not accelerated by pressure. In most cases at temperatures below 100 degrees C, the growth rate was lower at elevated pressures; at 100 degrees C, the growth rates at 8, 250, and 500 atm were nearly identical. Unlike in the stainless steel vessel, CO(2) production was exponential during growth and continued for only a short time after growth. In addition, relatively little H(2) was produced in the glass-lined vessel, and there was no growth or gas production at 105 degrees C at any pressure. The behavior of ES4 as a function of temperature and pressure was thus very sensitive to the experimental conditions.

Growth of a bacterium under a high-pressure oxy-helium atmosphere

Growth of a barotolerant marine organism, EP-4, in a glutamate medium equilibrated with an oxy-helium atmosphere at 500 atmospheres (atm; total pressure) (20 degrees C) was compared with control cultures incubated at hydrostatic pressures of 1 and 500 atm. Relative to the 1-atm control culture, incubation of EP-4 at 500 atm in the absence of an atmosphere resulted in an approximately fivefold reduction in the growth rate and a significant but time variant reduction in the rate constants for the incorporation of substrate into cell material and respiration. Distinct from the pressurized control and separate from potential effects of dissolution of helium upon decompression of subsamples, exposure of the organism to high-pressure oxy-helium resulted in either a loss of viability of a large fraction of the cells or the arrest of growth for one-third of the experimental period. After these initial effects, however, the culture grew exponentially at a rate which was three times greater than the 500-atm control culture. The rate constant for the incorporation of substrate into cell material was also enhanced twofold in the presence of high-pressure oxy-helium. Dissolved oxygen was well controlled in all of the cultures, minimizing any potential toxic effects of this gas.

The presence, nature, and role of gut microflora in aquatic invertebrates: A synthesis

This review of the literature concerns the gut microbiota of aquatic invertebrates and highlights the questions and processes that merit attention if an understanding of the role of gut microbes in the physiology of host invertebrates and nutrient dynamics of aquatic systems is to be gained. A substantial number of studies report the presence of gut microbes in aquatic invertebrates. Crustacea, Mollusca, and Echinodermata have received the most attention, with few studies involving other invertebrate groups. Different types of associations (e.g., ingestion, contribution of exoenzymes, incubation, parasitism) are reported to occur between gut microbes and aquatic invertebrates, and it is clear that gut bacterial communities cannot be treated as single functional entities, but that individual populations require examination. In addition, gut microbes may be either ingested transients or residents, the presence of which have different implications for the invertebrate. The most commonly reported genera of gut bacteria are Vibrio, Pseudomonas, Flavobacterium, Micrococcus, and Aeromonas. Quite a number of authors report the physiological properties of gut microbes (including enzyme activities and attributes such as nitrogen fixation), while less attention has been given to consideration of the colonization sites within the digestive tract, the density and turnover of gut bacteria, and the factors affecting the presence and nature of gut microflora. In addition, although a few studies have demonstrated a positive relationship between invertebrates and their gut microbiota, particularly with regard to nutrient gain by the invertebrate, very little conclusive evidence exists as to the role of bacteria in the physiology of host invertebrates. This has resulted from a lack of process-oriented studies. The findings for aquatic gut microbes are compared to those of gut bacteria associated with terrestrial invertebrates, where gut microbes contribute significantly to nutrient gain by the host in some environments.

Rapid bacterial growth in the hindgut of a marine deposit feeder

Antibiotic-insensitive mutants of natural sedimentary bacteria from an intertidal site were selected on gradient plates. Two of these strains, anAeromonas sp. andVibrio alginolyticus, were mixed with natural sediments from the field and fed toAbarenicola vagabunda, an intertidal lugworm characteristic of sandy beaches in the Pacific Northwest. Digestive removal was apparent in the midgut, 97% efficiency being seen forAeromonas sp. Both strains showed rapid growth in the hindgut, increasing between 2 and 3 orders of magnitude in abundance between the midgut and rectum of the polychaete, corresponding with a doubling time of about 50 min for each strain. Direct epifluorescence counts of natural bacteria in guts of animals freshly collected from the field suggest a mean doubling time that is only slightly greater (66 min) for all ingested bacteria that survive midgut digestion. These bacterial growth rates exceed by orders of magnitude the greatest rates reported for ambient marine sediments and suggest that hindgut bacterial growth, though of little immediate importance in the energetics of the animals, may strongly influence both population dynamics of marine bacteria and diagenesis of sedimentary organic matter.

Substrate Degradation and Pressure Tolerance of Free-Living and Attached Bacterial Populations in the Intestines of Shallow-Water Fish

Bacterial populations attached to intestinal linings of shallow-water fish were compared to those free in the lumen for response to hydrostatic pressure and ability to degrade a variety of substrates. Results suggested that, unlike reports on gut-associated deep-sea bacteria, the two shallow-water populations were not significantly different in their pressure or substrate responsiveness.

Barophilic Bacteria Associated with Digestive Tracts of Abyssal Holothurians

Abyssal holothurians and sediment samples were collected at depths of 4,430 to 4,850 m in the Demerara abyssal plain. Bacterial concentrations in progressive sections of the holothurian digestive tract, as well as in surrounding surface sediments, were determined by epifluorescence microscopy. Total bacterial counts in sediments recently ingested by the animals were 1.5- to 3-fold higher than in surrounding sediments at the deepest station. Lowest counts were observed consistently in the foregut, where the digestive processes of the holothurian are believed to occur. In most animals, counts increased 3- to 10-fold in the hindgut. Microbial activity at 3°C and in situ and atmospheric pressure were determined for gut and sediment samples by measuring the utilization of [ 14 C]glutamic acid, the doubling time of the mixed-population of culturable bacteria, and the percentage of the total bacterial count responsive to yeast extract in the presence of nalidixic acid, using epifluorescence microscopy. A barophilic microbial population, showing elevated activity under deep-sea pressure, was detected by all three methods in sediments removed from the hindgut. Transmission electron micrographs revealed intact bacteria directly associated with the intestinal lining only in the hindgut. The bacteria are believed to be carried as an actively metabolizing, commensal gut flora that transforms organic matter present in abyssal sediments ingested by the holothurian. Using data obtained in this study, it was calculated that sediment containing organic matter altered by microbial activity cleared the holothurian gut every 16 h, suggesting that abyssal holothurians and their associated gut flora are important participants in nutrient cycles of the abyssal benthic ocean.

Activity and growth of microbial populations in pressurized deep-sea sediment and animal gut samples

Benthic animals and sediment samples were collected at deep-sea stations in the northwest (3,600-m depth) and southeast (4,300- and 5200-m depths) Atlantic Ocean. Utilization rates of [14C]glutamate (0.67 to 0.74 nmol) in sediment suspensions incubated at in situ temperatures and pressures (3 to 5 degrees C and 360, 430, or 520 atmospheres) were relatively slow, ranging from 0.09 to 0.39 nmol g-1 day-1, whereas rates for pressurized samples of gut suspensions varied widely, ranging from no detectable activity to a rapid rate of 986 nmol g-1 day-1. Gut flora from a holothurian specimen and a fish demonstrated rapid, barophilic substrate utilization, based on relative rates calculated for pressurized samples and samples held at 1 atm (101.325 kPa). Substrate utilization by microbial populations in several sediment samples was not inhibited by in situ pressure. Deep-sea pressures did not restrict growth, measured as doubling time, of culturable bacteria present in a northwest Atlantic sediment sample and in a gut suspension prepared from an abyssal scavenging amphipod. From the results of this study, it was concluded that microbial populations in benthic environments can demonstrate significant metabolic activity under deep-ocean conditions of temperature and pressure. Furthermore, rates of microbial activity in the guts of benthic macrofauna are potentially more rapid than in surrounding deep-sea sediments.

Thermal Inactivation of a Deep-Sea Barophilic Bacterium, Isolate CNPT-3

The barophilic deep-sea bacterium, isolate CNPT-3, was inactivated by exposures to temperatures between 10 and 32�C at atmospheric pressure. Inactivation in samples from warmed cell suspensions was measured as the loss of colonyforming ability (CFA) at 10�C and 587 bars. At atmospheric pressure, there was a slow loss of CFA even at 10�C. The loss of CFA was rapid above 20�C and only slightly affected by high pressures. The first-order rate constants for thermal inactivation fit the Arrhenius equation with an activation energy of 43 kcal (ca. 179.9 kJ)/mol. Light microscopy and scanning transmission electron microscopy revealed morphological changes due to warming of the cells. The changes ensued the loss of CFA. The results supported the hypothesis from an earlier work that indigenous (autochthonous) deep-sea bacteria from cold deep seas are both barophilic and psychrophilic. If ultimately sustained, these characteristics may be useful in designing experiments to assess the relative importance of the autochthonous and allochthonous bacteria in the deep sea. The data were used to evaluate how barophilic bacteria may have been missed in many investigations because of warming of the cells during sample retrieval from the sea or during cultivation in the laboratory. The evaluation revealed the need for temperature and pressure data during retrieval of samples and cultivation in the laboratory. Most deep-ocean microbiology may be possible with thermally insulated equipment for retrieval from the sea and with high-pressure vessels for laboratory incubations.

Barophilic growth of bacteria from intestinal tracts of deep-sea invertebrates

Digestive tracts of abyssal scavenging amphipods and a deep-sea holothurian were examined for the presence of intestinal microflora capable of rapid proliferation under in situ pressures of 430 to 520 atmospheres (atm) and temperatures of 3-5°C. For two amphipod specimens, population doubling times of 5 and 6 hours were observed under in situ conditions, compared to 8 and 6 hours, respectively, at 1 atm. Growth enhancement under pressure was related inversely to initial population size and directly to concentration of available nutrient. In the case of the deposit-feeding holothurian, attached bacteria scraped from the intestinal lining showed a doubling time, under pressure, of 11 hours, compared to 36 hours for transient sediment bacteria that comprised the gut contents. These data suggest that deep-sea animals possess a commensal gut flora capable of responding to increased nutrient levels, via feeding of the host, without inhibition by the elevated hydrostatic pressures encountered in the deep ocean environment.

A pressure-retaining deep ocean sampler and transfer system for measurement of microbial activity in the deep sea

A deep ocean sampler (DOS) has been developed for microbiological sampling and is capable of aseptically collecting 400-ml water samples from any depth in the world oceans. The instrument maintains samples under in situ pressure and temperature. A hyperbaric transfer system has also been developed, enabling transfer of sample volumes up to 150 ml, without decompression or dilution, to pressurized incubation chambers. Utilization of(14)C-glutamate (21 to 96μg/l) and(14)C-acetate (4.6μg/l) by microbial populations in undecompressed water samples from the N.W. Atlantic and the Cape and Angola Basins was recorded over incubation periods of 2 to 18 weeks. Rates of substrate utilization ranged from 1 to 38×10(-2) μg/l/day.

Species Composition and Barotolerance of Gut Microflora of Deep-Sea Benthic Macrofauna Collected at Various Depths in the Atlantic Ocean

The bacterial flora of marine animals collected at depths of 570 to 2,446 m was examined for population size and generic composition, and the barotolerant characteristics of selected bacterial isolates were determined. Total numbers of culturable, aerobic, heterotrophic bacteria were found to be low in animals collected at the greatest ocean depths sampled in this study. Vibrio spp. were predominant in 10 of 15 samples examined, and Photobacterium spp. and yeasts were the major components of the remainder. Pseudomonas, Achromobacter , and Flavobacterium spp. comprised minor components of the gut flora of deep-sea fish. Forty-six pure cultures isolated from samples of seven animals were tested for growth or viability after incubation for 1 week under pressures ranging from 100 to 750 atm. Strains of bacteria isolated from samples of fish intestine were more barotolerant than those from the stomach ( P <0.01). When incubated at a pressure of 600 atm, viability of bacterial cultures originally isolated from fish caught at a depth of 570 m was significantly decreased in comparison with viability of cultures from animals caught at depths of 1,393 and 2,446 m ( P <0.01). From results of this study, it is concluded that the gut microflora of animals that dwell in the deeper regions of the ocean are adapted to an increased hydrostatic pressure environment, that is, the gut microflora is less inhibited by elevated hydrostatic pressure with increasing depth from which the host animal was collected.

Undecompressed microbial populations from the deep sea

Metabolic transformations of glutamate and Casamino Acids by natural microbial populations collected from deep waters (1,600 to 3,100 m) were studied in decompressed and undecompressed samples. Pressure-retaining sampling/incubation vessels and appropriate subsampling/incubation vessels and appropriate subsampling techniques permitted time course experiments. In all cases the metabolic activity in undecompressed samples was lower than it was when incubated at 1 atm. Surface water controls showed a reduced activity upon compression. The processes involving substrate incorporation into cell material were more pressure sensitive than was respiration. The low utilization of substrates, previously found by in situ incubations for up to 12 months, was confirmed and demonstrated to consist of an initial phase of activity, in the range of 5 to 60 times lower than the controls, followed by a stationary phase of virtually no substrate utilization. No barophilic growth response (higher rates at elevated pressure than at 1 atm) was recorded; all populations observed exhibition various degrees of barotolerance.