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1.
Algae released from fast-ice in Ellis Fjord, eastern Antarctica, made little contribution to subsequent phytoplankton growth.
Dominant taxa in the interior ice community included Nitzschia cylindrus (Grun) Hasle, Navicula glaciei V.H. and a dinoflagellate cyst. Diatom mortality within the ice was high. The algal contribution to the phytoplankton from
the fast ice was estimated by calculating the difference between algal biomass in ice cores taken on 14 November with those
taken on 18 December 1992. The biomass of sedimenting phytoplankton was estimated using sediment traps; weekly cell counts
of water were used to monitor net phytoplankton growth. The low contribution from the fast-ice of Ellis Fjord to the phytoplankton
is similar to results from other Antarctic fast-ice communities but is not necessarily reflective of processes occurring within
either Antarctic or Arctic pack ice communities. An algal mat growing on the base of the fast-ice had a carbon standing crop
of between 0.231 gC m -2 and 0.022 gC m -2. Much of this was delivered to the water column as the ice melted while the remainder was exported.
Received: 15 March 1995/Accepted: 4 September 1995 相似文献
2.
The porous medium of sea ice, a surface-rich environment characterized by low temperature and high salinity, has been proposed
as a favorable site for horizontal gene transfer, but few measurements are available to assess the possibility of this mode
of evolution in ice. Here, we report the first measurements of dissolved DNA in sea ice, measured by fluorescent dye staining
of centrifugal-filter-concentrated samples of melted ice. Newly formed landfast and pack ice on the Canadian Arctic Shelf
(ca. 71°N, 125°W) contained higher concentrations (scaled to volume of brine) of the major components of dissolved DNA—extracellular
DNA and viruses—than the underlying seawater. Dissolved DNA was dominated by extracellular DNA in surface seawater (up to
95%), with viruses making up relatively larger fractions at depths below 100 m (up to 27%) and in thick sea ice (66–78 cm;
up to 100%). Extracellular DNA was heterogeneously distributed, with concentrations up to 135 μg DNA L −1 brine detected in landfast sea ice, higher than previously reported from any marine environment. Additionally, extracellular
DNA was significantly highly enriched at the base of ice of medium thickness (33–37 cm), suggestive of in situ production.
Relative to underlying seawater, higher concentrations of extracellular DNA, viruses, and bacteria, and the availability of
numerous surfaces for attachment within the ice matrix suggest that sea ice may be a hotspot for HGT in the marine environment. 相似文献
3.
The seasonal distribution of sympagic amphipods was investigated in the Chesterfield Inlet area of northwestern Hudson Bay
(63°30′N). Amphipod abundance was measured by photographic samples and species composition was determined by sweep net samples.
Twelve species of amphipods were collected, the most common being Ischyrocerus anguipes, Pontogeneia inermis, Apherusa megalops and Weyprechtia pinguis. The major environmental variable affecting amphipod distribution was water depth. Amphipod abundance was highest near 20
m and near zero past 50 m. The maximum recorded abundance was 1367 m −2. A minor factor affecting the distribution of amphipods was snow depth, through its modifying effect on light and thereby
the growth of ice algae. Amphipods began to inhabit the sea ice shortly after its formation. From the beginning of March,
the number of amphipods on the ice increased steadily to about the 3rd week of April, after which numbers declined. This pattern
coincided with the seasonal ice algae abundance. Amphipods reduced ice algal biomass over 20-m depth by 63%. No evidence of
diurnal changes in abundance was observed.
Received: 15 May 1996 / Accepted: 4 November 1996 相似文献
4.
Abundance and reproductive biology (gonad maturation and egg production) of the Arctic copepod Calanus glacialis were studied in the Laptev Sea and adjacent Arctic Ocean in September 1993 and from July to September 1995. Both abundance
and reproductive activity were subject to strong spatial and seasonal variability, which was related to the ice cover, feeding
conditions and circulation pattern. Maximum abundance of the C. glacialis population was generally confined to the outer shelf and slope with depths between 50 and 1000 m. During both cruises, highest
egg production rates and largest number of young copepodite stages were observed in the eastern Laptev Sea, where the development
of the C. glacialis population seems to follow the opening of the “Siberian Polynya”. In the western part, which is usually covered by pack ice,
females were all immature, and no young stages were found. However, females responded quickly to a temporary opening of the
ice there in 1995 and spawned. Starvation experiments showed that food-independent reproduction fuelled by internal energy
resources was at least partly responsible for relatively high egg production rates at low ambient food concentrations. Egg
production rates in starved females were considerably higher than those previously reported.
Accepted: 14 June 2000 相似文献
5.
Epibenthic brittle star assemblages were investigated on the northwestern Barents Sea shelf between 81° and 77°N in July
1991. At 9 drift stations in water depths between 80 and 360 m, series of 35–71 photographs, each depicting about 1 m 2 of the seabed, were taken along transects of about 150- to 300-m length to assess abundances and spatial distribution patterns
of adult brittle stars (disc diameter ≥1 mm). Biomass values were derived by combining abundances with size-weight relationships
and size frequencies established using specimens from trawl catches. Six brittle star species were identified on the seabed
images. Ophiocten sericeum was the most abundant species on shallow shelf banks (≤100 m). Up to 2,800 individuals were counted on a single photograph;
median abundances per station ranged from 32 to 524 ind.m -2 and biomass from 0.3 to 5.0 g ash-free dry weight (AFDW) m -2. The spatial distribution along the transects (i.e. on the 100-m scale) was, however, extremely patchy. Disc diameters of
O. sericeum ranged between 1.6 mm and 15.4 mm. In deeper shelf habitats (>150 m), O. sericeum was rare or absent, and Ophiacantha bidentata dominated the brittle star fauna with median densities and biomasses of 2–49 ind.m -2 and 0.07–1.9 g AFDW m -2, respectively. Its disc diameters ranged from 2.9 to 14.4 mm. The other species ( Ophiura sarsi, Ophiopholis aculeata, Ophioscolex glacialis, Ophiopleura borealis) occurred in distinctly lower numbers. Our findings provide further evidence that brittle stars dominate epibenthic communities
on Arctic shelves and locally reach very high abundances. Dense beds of Ophiocten sericeum seem to be a general phenomenon on high-Arctic shallow shelf banks.
Received: 30 March 1995/Accepted: 30 June 1995 相似文献
6.
To improve our knowledge of flagellates inhabiting the Baltic Sea ice and water column during the winter, material was obtained
from northern Bothnian Bay in March/April 1995. Light microscopical observations on live and fixed material and further transmission
electron microscopy of whole mounts revealed 47 nanoflagellate taxa. In addition, detached scales of eight taxa were encountered.
It is now evident that nearly all nanoflagellate classes are present within Bothnian Bay sea ice. The most common groups were
cryptomonads, dinoflagellates, chrysophytes, prasinophytes, choanoflagellates and heterotrophic flagellates of unknown systematic
position (Protista incertae sedis). Most flagellates in Baltic Sea ice biota apparently thrive in both the water column and
the sea ice, while some, e.g. Paraphysomonas spp. (Chrysophyceae), heterotrophic euglenids, volvocalean chlorophytes, and some taxa of uncertain systematic affinity,
are more frequently found within the sea ice.
Received: 9 February 1997 / Accepted: 23 September 1997 相似文献
7.
Renal cell carcinomas (RCC) exhibit marked differences in susceptibility towards anticancer drug- and TRAIL-induced apoptosis.
However, the underlying mechanisms determining apoptosis-sensitivity or -resistance are not well understood. The purpose of
this study was to compare gene expression patterns induced by DNA-damage- and death receptor-induced apoptosis and to detect
differentially expressed genes responsible for differences in apoptosis-susceptibility. Therefore, we performed a comparative
cDNA-array analysis in an apoptosis-resistant and an apoptosis-sensitive RCC cell line. In the sensitive cell line an upregulation
of multiple E2F1- and p53-inducible proapaptotic and cell-cycle regulating target genes by Topotecan as well as TRAIL was
observed. Interestingly, several antiapoptotic NFκB-dependent target genes were also induced. In the resistant cell line,
however, only a small number of E2F1-, p53- and NFκB-dependent target genes were differentially regulated. Conclusively, anticancer
drug- as well as TRAIL-sensitivity go along with an upregulation of multiple proapoptotic genes. In contrast, the mechanisms
of apoptosis-resistance are—at least in part—located upstream of gene induction and seem not to depend upon upregulation of
de-novo-synthesized antiapoptotic genes. Conclusively, the proapoptotic stimuli are confronted with a cellular context which
allows apoptosis to be conducted—in the sensitive cell line—or not—in the resistant cell line.
Electronic Supplementary Material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.
Sebastian Heikaus and Ercan Casliskan contributed equally to this work.
This work was supported by the ’Deutsche Forschungsgemeinschaft (DFG). 相似文献
8.
Nutrient concentrations, chlorophyll- a, bacterial biomass and relative activity of denitrifying organisms were investigated from ice-core, brine and underlying
water samples in February 1998 in the Gulf of Bothnia, Baltic Sea. Examined sea ice was typical for the Baltic Sea; ice bulk
salinity varied from 0.1 to 1.6 psu, and in underlying water salinity was from 4.2 to 4.7 psu. In 2- to 3-months-old sea ice
(thickness 0.4–0.6 m), sea-ice communities were at the winter stage; chl- a concentrations were generally below 1 mg m −3 and heterotrophic organisms composed 7–20% of organism assemblage. In 1-month-old ice (thickness 0.2–0.25 m), an ice spring
bloom was already developing and chl- a concentrations were up to 5.6 mg m −3. In relation to low salinity, high concentrations of NH +
4, NO −
2, PO 3+
4 and SiOH 4 were found in the ice column. The results suggest that the upper part of ice accumulates atmospheric nutrient load during
the ice season, and nutrients in the upper 10–20 cm of ice are mainly of atmospheric origin. The most important biological
processes controlling the sea-ice nutrient status are nutrient regeneration, nutrient uptake and nitrogen transformations.
Nutrient regeneration is specially active in the middle parts of the 50- to 60-cm-thick ice and subsequent accumulation of
nutrients probably enhances the ice spring bloom. Nitrite accumulation and denitrifying activity were located in the same
ice layers with nutrient regeneration, which together with the observed significant correlation between the concentrations
of nitrogenous nutrients points to active nitrogen transformations occurring in the interior layers of sea ice in the Baltic
Sea.
Accepted: 12 June 2000 相似文献
9.
We investigated the shade adaptation of a seasonally well-developed ice algal community in thin sea ice at Saroma-Ko Lagoon,
Hokkaido, Japan on 3–4 March 2006 and 4–5 March 2007, by examining photosynthetic pigment concentrations, the chlorophyll
a-specific light-absorption coefficient ( a
ph
*), and the light-saturation index ( E
k
). The high proportions of photosynthetic pigments, including chlorophyll a, fucoxanthin, and chlorophyll c, and the low values of a
ph
* (440) and a
ph
* (675) suggested that the lagoon’s ice algal community was shade-adapted. The high ratio of E
k
to total photosynthetically active radiation (PAR) in the ice algal habitat suggested that the degree of shade adaptation
is weak. Scaling of E
k
to total PAR could be extended to studies of the degree of photoadaptive succession of ice algal communities in the Northern
Hemisphere. The degree of shade adaptation of ice algal communities in the Northern Hemisphere might be related to ice thickness,
regardless of latitude. 相似文献
10.
The 800-m thick glacigene Dwyka Formation was deposited along the northern margin of the Permo-Carboniferous Dwyka Basin which covered an area of approximately 2 × 10 6 km 2 in southwestern Gondwana. The palaeogeographic setting, geochemical data of the mudrocks and diamictites, and the palaeontology indicate marine conditions during sedimentation. Ice lobes from spreading centres in the north, east and south coalesced in the basin to form an extensive ice cover from the Westphalian to the late Sakmarian. Lodgement, rain-out and subaqueous debris-flow diamictons, subaqueous and subglacial melt-water sands, suspended mud, and turbidity current sands and silts accumulated in the Dwyka Basin. Sedimentation started on the continental shelf during a grounded ice sheet stage (predominantly lodgement processes), then a floating ice stage (predominantly debris rain-out), and finally an ice sheet disintegration stage (debris rain-out, sand fall-out and suspension settling of mud). The palaeogeographic setting, presence of marine conditions in the basin and the scale of glaciation indicate deposition from a predominantly mid-latitudinal marine ice sheet. The overall characteristics of the glacial sequence are neither typical of a polar nor a temperate setting and for such ancient glaciations a subpolar setting with the presence of unstable ice shelves is suggested. 相似文献
11.
The benthic megafauna from the soft bottoms of the shallow coastal zone of Martel Inlet (Admiralty Bay, King George Island,
South Shetland Islands, Antarctica) was studied during three austral summers (1989/1990, 1990/1991 and 1994/1995) in relation
to the bathymetric features. Surveying and sampling, based on specimen counting and underwater observations, were undertaken
by scuba-diving at depths down to 25 m. The depth zonation appears to be influenced by the nature of the substrate and especially
by the action of the ice. The multiple action of ice flows prevents the occurrence of sessile forms in the shallower areas,
where a low-diversity community, dominated by motile animals, was found. In the area around 18 m in depth, the action of icebergs
generated faunistic and sedimentary patches of impacted and non-impacted areas. The more stable conditions prevailing below
depths of 20–25 m allowed the establishment of a more diversified epifauna, including many sessile forms. The interannual
differences observed in the densities of the mobile isopod Serolis polita may be associated with the summer period when the sampling was undertaken.
Accepted: 1 March 2000 相似文献
12.
During an expedition of RV Polarstern in 1994, a vertical transect (about 200-, 300-, 450-, 800-, 1,500- and 2,200-m depth) and a horizontal transect (of three
stations at about 800-m depth) were sampled at 75°N off Greenland with an epibenthic sledge in order to obtain information
on the abundance, diversity and community patterns of epi- and suprabenthic peracarid crustaceans, which are known to be an
important component of the macrofauna along the Greenland continental shelf and slope. We wanted to scrutinize whether a hypothesized
enhanced primary production along the ice edges would reflect upon benthic biomass. Within the peracarid community a total
of 14,784 individuals were collected at these locations, while an additional 2,425 specimens were sampled at a 500-m station
at 79°N, in an area where samples had been also taken in 1993. For reasons of comparison, numbers of peracarids found at any
one station were calculated for 1,000-m trawled distance. These calculations accounted for 55,633 specimens on both transects.
Of these, the order Isopoda was the most numerous taxon with 28,650 specimens, followed by the Amphipoda with 15,025 specimens,
Cumacea with 7,868, Tanaidacea with 2,454 and the suprabenthic Mysidacea with 1,636 individuals collected at all stations
during this expedition, respectively. Interestingly the highest number of individuals was sampled at 1,525-depth (23,098 individuals);
however, at about 2,680-m depth the number of peracarids collected (13,557) was still much higher than at comparatively shallower
stations, for example, in 317-m depth (6,792). Possible reasons for these findings are discussed.
Received: 19 January 1996 /Accepted: 28 April 1996 相似文献
13.
How climate change will affect the community dynamics and functionality of lake ecosystems during winter is still little understood. This is also true for phytoplankton in seasonally ice‐covered temperate lakes which are particularly vulnerable to the presence or absence of ice. We examined changes in pelagic phytoplankton winter community structure in a north temperate lake (Müggelsee, Germany), covering 18 winters between 1995 and 2013. We tested how phytoplankton taxa composition varied along a winter‐severity gradient and to what extent winter severity shaped the functional trait composition of overwintering phytoplankton communities using multivariate statistical analyses and a functional trait‐based approach. We hypothesized that overwintering phytoplankton communities are dominated by taxa with trait combinations corresponding to the prevailing winter water column conditions, using ice thickness measurements as a winter‐severity indicator. Winter severity had little effect on univariate diversity indicators (taxon richness and evenness), but a strong relationship was found between the phytoplankton community structure and winter severity when taxon trait identity was taken into account. Species responses to winter severity were mediated by the key functional traits: motility, nutritional mode, and the ability to form resting stages. Accordingly, one or the other of two functional groups dominated the phytoplankton biomass during mild winters (i.e., thin or no ice cover; phototrophic taxa) or severe winters (i.e., thick ice cover; exclusively motile taxa). Based on predicted milder winters for temperate regions and a reduction in ice‐cover durations, phytoplankton communities during winter can be expected to comprise taxa that have a relative advantage when the water column is well mixed (i.e., need not be motile) and light is less limiting (i.e., need not be mixotrophic). A potential implication of this result is that winter severity promotes different communities at the vernal equinox, which may have different nutritional quality for the next trophic level and ecosystem‐scale effects. 相似文献
14.
The algal, protozoan and metazoan communities within different drift-ice types (newly formed, pancake and rafted ice) and
in under-ice water were studied in the Gulf of Bothnia in March 2006. In ice, diatoms together with unidentified flagellates
dominated the algal biomass (226 ± 154 μg ww l −1) and rotifers the metazoan and protozoan biomass (32 ± 25 μg ww l −1). The under-ice water communities were dominated by flagellates and ciliates, which resulted in lower biomasses (97 ± 25
and 21 ± 14 μg ww l −1, respectively). The under-ice water and newly formed ice separated from all other samples to their own cluster in hierarchical
cluster analysis. The most important discriminating factors, according to discriminant analysis, were chlorophyll- a, phosphate and silicate. The under-ice water/newly formed ice cluster was characterized by high nutrient and low chlorophyll- a values, while the opposite held true for the ice cluster. Increasing trends in chlorophyll- a concentration and biomass were observed with increasing ice thickness. Within the thick ice columns (>40 cm), the highest
chlorophyll- a concentrations (6.6–22.2 μg l −1) were in the bottom layers indicating photoacclimation of the sympagic community. The ice algal biomass showed additional
peaks in the centric diatom-dominated surface layers coinciding with the highest photosynthetic efficiencies [0.019–0.032 μg C (μg Chl- a
−1 h −1) (μE m −2 s −1) −1] and maximum photosynthetic capacities [0.43-1.29 μg C (μg Chl- a
−1 h −1)]. Rafting and snow-ice formation, determined from thin sections and stable oxygen isotopic composition, strongly influenced
the physical, chemical and biological properties of the ice. Snow-ice formation provided the surface layers with nutrients
and possibly habitable space, which seemed to have favored centric diatoms in our study. 相似文献
15.
The objective was to document a Process Validation on the packaging of human tissue grafts using polystyrene boxes containing
dry ice for short term storage. The aim was to give a high degree of assurance that the processed grafts would be maintained
at −20°C for a period of time to allow distribution to customers. This study was designed to comply with the Australian GMP—Human
Blood and Tissues and AATB Standards for Tissue Banking (Ed 12) American Association of Tissue Banks Section E4.141—Storage
Conditions for Commonly Transplanted Human Tissue. Four Eskies were packed with 1, 4, 10 & 20 “dummy” allografts with thermocouples
and Data Loggers attached with 3.5, 7, 15 and 20 kg of dry ice packed around the “dummy” allografts, respectively. All Eskies
were weighed six times over a 48 h period and temperatures recorded. The results showed that one allograft in an Esky with
3.5 kg of dry ice was able to be stored for up to 31 h and fifteen allografts in an Esky containing 20 kg dry ice lasted 48 h. 相似文献
16.
We examined the sub-ice algal community in the Chukchi Sea during June 1998 using a remotely operated vehicle (ROV). Ice algae
were observed on the under-ice surface at all ten stations (from 70°29′N to 72°26′N; 162°00′W to 153°56′W) and varied in abundance
and distribution from small aggregations limited to depressions in the ice to nets, curtains and strands of Melosira. There was no relationship between percent cover of sub-ice algae and physical factors at the kilometer scale, but at the
scale of individual ice floes the percent cover of sub-ice algae was positively correlated with distance from the floe edge
and negatively correlated with snow depth. A significant positive relationship between the concentration of sediment pigments
and percent cover of sub-ice could indicate a coupling between ice algal and benthic systems. Pieces of ice algae that appeared
to be Melosira were observed on the seafloor to a depth of over 100 m and cells or spores of obligate ice algal taxa were collected from
sediments from 44-m to 1,000-m deep. The large biomass of sub-ice algae observed at many stations in the Chukchi Sea and the
presence of ice algae on the seafloor indicates that the distribution and abundance of sub-ice algae needs to be understood
if we are to evaluate the role of ice algae in the Arctic marine ecosystem. 相似文献
17.
Net growth of ice algae in response to changes in overlying snow cover was studied after manipulating snow thickness on land-fast,
Arctic sea ice. Parallel laboratory experiments measured the effect of changing irradiance on growth rate of the ice diatom,
Nitzschia frigida. After complete removal of thick snow (≥9 cm), in situ ice algae biomass declined (over 7–12 days), while removal of thin
snow layers (4–5 cm), or partial snow removal, increased net algal growth. Ice bottom ablation sometimes followed snow removal,
but did not always result in net loss of algae. Similarly, in laboratory experiments, small increases in irradiance increased
algal growth rate, while greater light shifts suppressed growth for 3–6 days. However, N. frigida could acclimate to relatively high irradiance (110 μmol photons m 2 s −1). The results suggest that algal loss following removal of a thick snow layer was due to the combination of photoinhibition
and bottom ablation. The smaller relative increase in irradiance after removal of thin or partial snow layers allowed algae
to maintain high specific-growth rates that compensated for loss from physical mechanisms. Thus, the response of ice algae
to snow loss depends both on the amount of change in snow depth and algal photophysiology. The complex response of ice algae
growth and export loss to frequently changing snow fields may contribute to horizontal and temporal patchiness of ecologically
and biogeochemically important variables in sea ice and should be considered in predictions of how climate change will affect
Arctic marine ecosystems. 相似文献
18.
The thick, widely distributed lacustrine sediments in northern China may have recorded abundant information on the Asian monsoon evolution during the Late Cenozoic. However, reconstruction of such a history with these materials has been hampered by the paucity of reliable chronological constraints. In this study, systematic paleomagnetic measurements were conducted on a well-exposed, 2880-m thick fluviolacustrine sequence on the east side of the Liupan Mountains, a relatively monsoon-sensitive region. Correlation of the resultant magnetic polarity column to the Geomagnetic Polarity Timescale (GPTS) suggests that this sequence spans a time interval of 20.13–0.07 Ma and is generally continuous. The reliability of this correlation was further supported by three lines of independent evidence: i.e. Hipparion fossils, pollen assemblages and color changes of the sediments. Measurements of redness of the sedimentary succession suggest a remarkable decrease in air temperature over northern China, which may be closely associated with the global Mid-Miocene cooling caused by the extension of the Antarctic ice sheets. This event may have had an important influence on the evolution of the Asian monsoon circulation. 相似文献
19.
The zooplankton of the under-shelf-ice ecosystem at White Island (78 °10′ S, 167 °30′ E), McMurdo Sound, Antarctica was investigated during December 1976 and January 1977. The water column was sampled through
a hole in the McMurdo Ice Shelf over a water depth of 67 m. Seawater temperatures under the ice shelf ranged from −1.91 to
1.96 °C. Dissolved oxygen levels ranged from 5.0–6.05 ml l -1 in early December to 4.65–4.8 ml l -1 in late January. Current speeds of up to 0.13 m s -1 were recorded at a depth of 50 m and a predominantly northward flow was detected. Light levels under the shelf ice were low
with less than 1% of the incident light being transmitted to a depth of 3 m. No chlorophyll a was detected within the water column throughout the investigation. Mean zooplankton biomass values in the water column ranged
from 12 to 447 mg wet weight m -3 and were similar to values recorded elsewhere from Antarctic inshore waters, but were very much higher than those recorded
from under seasonal sea ice in McMurdo Sound. Thirty-two zooplankton species were recorded including 1 ostracod, 21 copepods
(10 calanoids, 3 cyclopoids and 8 harpacticoids), 4 amphipods, 2 euphausiids, a chaetognath and 3 pteropods. Larvae of polychaetes
and fish were found on some occasions. The species composition in general was similar to that recorded from McMurdo Sound
and other Antarctic inshore localities. Among the Copepoda, however, there were a number of species, especially among the
Harpacticoidea, that have not been found previously in McMurdo Sound and the Ross Sea, but that are known to be associated
with ice in other localities in Antarctica. Two recently described species are known only from White Island. They were present
in the water column but were most abundant in the surface water of the tide crack where they were the most abundant zooplankters.
The tide crack, which probably is an extension of the under-ice habitat, is apparently a significant nursery area for amphipods
and copepod species.
Received: 23 November 1994/Accepted 7 May 1995 相似文献
20.
We investigated the germicidal activity of 2,537 A ultraviolet (UV) radiation on bacteria in ice cubes of varying thickness and in aqueous suspensions beneath an ice layer. The test bacteria used were Escherichia coli, Serratia marcescens, Bacillus subtilis, and Sarcina lutea; aqueous suspensions of the selected organisms were frozen into ice cubes, 2 mm to 30 mm thick, at -20 C. The cubes were irradiated for 1 min, whereas the suspensions of bacteria were placed beneath an ice block (19 cm thick) and were irradiated for 0.5 to 15 min. In both groups of experiments, the standard plate count method was used to compare the number of bacteria surviving the UV treatment with the number of bacteria in the untreated controls. The results showed that 1 min of UV treatment killed as many as 97% of the gram-negative and at least 60% of the gram-positive test bacteria (freezing survivors) frozen in ice cubes 30-mm thick. Within 15 min, UV light transmitted through a 19-cm thick ice block inactivated 98% of the bacteria suspended in the buffer solution. We concluded that the UV rays were able to penetrate at least 19 cm of ice and still retain enough energy to kill bacteria. However, the UV penetration depended greatly on the optical quality of the ice. Although it was not the purpose of these experiments to find a practical method for sanitizing ice, the results of this study and of our other unpublished experiments indicate that UV light has adequate penetrating power to be considered practical in certain selected applications. 相似文献
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