Diet and feeding ecology of the diving petrels Pelecanoides georgicus and P. urinatrix at South Georgia

 The diet of the diving petrels Pelecanoides georgicus and P. urinatrix was studied during 1986 (P. georgicus) and 1987 (both species) by lavaging adults as they returned to feed chicks on Bird Island, South Georgia. The diet of both species was dominated by crustaceans, in particular euphausiids (mainly Euphausia superba and some Thysanoessa), which contributed 47–76% of the biomass of crustaceans in the diet of P. georgicus, and copepods, which contributed 71% of the biomass of crustaceans in the diet of P. urinatrix. Calanoides acutus was the most numerous copepod in the diet of both species; however, Rhincalanus gigas was more common in P. urinatrix than in P. georgicus. The dominant amphipod in the diet of P. georgicus, Primno macropa, was absent from the diet of Pelecanoides urinatrix, in which Themisto gaudichaudii (rare in Pelecanoides georgicus) dominated. Dietary differences were maintained in the period (2 weeks of a total of 10 weeks) when both species were simultaneously rearing chicks. Knowledge of the prey species and of the diving abilities and foraging habits of diving petrels suggests that at South Georgia Pelecanoides urinatrix feeds closer inshore and dives deeper than Pelecarnoides georgicus. Received: 24 August 1995/Accepted: 10 February 1996     

Stable binding of the herpes simplex virus ICP47 protein to the peptide binding site of TAP.

The herpes simplex virus (HSV) ICP47 protein inhibits the MHC class I antigen presentation pathway by inhibiting the transporter associated with antigen presentation (TAP) which translocates peptides across the endoplasmic reticulum membrane. At present, ICP47 is the only inhibitor of TAP. Here, we show that ICP47 produced in bacteria can block human, but not mouse, TAP, and that heat denaturation of ICP47 has no effect on its ability to block TAP. ICP47 inhibited peptide binding to TAP without affecting ATP binding, consistent with previous observations that the peptide binding and ATP binding sites of TAP are distinct. ICP47 bound to TAP with a higher affinity (KD approximately 5 x 10(-8) M) than did peptides, and ICP47 did not dissociate from TAP. ICP47 was not transported by TAP and remained sensitive to proteases added from the cytosolic surface of the membrane. Peptides acted as competitive inhibitors of ICP47 binding to TAP, and this inhibition required a 100- to 1000-fold molar excess of peptide. These results demonstrate that ICP47 binds to a site which includes the peptide binding domain of TAP and remains bound to this site in a stable fashion.     

Regulated copper uptake in Chlamydomonas reinhardtii in response to copper availability.

A saturable and temperature-dependent copper uptake pathway has been identified in Chlamydomonas reinhardtii. The uptake system has a high affinity for copper ions (Km approximately 0.2 microM) and is more active in cells that are adapted to copper deficiency than to cells grown in a medium containing physiological (submicromolar to micromolar) copper ion concentrations. The maximum velocity of copper uptake by copper-deficient cells (169 pmol h-1 10(6) cells-1 or 62 ng min-1 mg-1 chlorophyll) is up to 20-fold greater than that of fully copper-supplemented cells, and the Km (approximately 2 x 10(2) nM) is unaffected. Thus, the same uptake system appears to operate in both copper-replete and copper-deficient cells, but its expression or activity must be induced under copper-deficient conditions. A cupric reductase activity is also increased in copper-deficient compared with copper-sufficient cells. The physiological characteristics of the regulation of this cupric reductase are compatible with its involvement in the uptake pathway. Despite the operation of the uptake pathway under both copper-replete and copper-deficient conditions, C. reinhardtii cells maintained in fully copper-supplemented cells do not accumulate copper in excess of their metabolic need. These results provide evidence for a homeostatic mechanism for copper metabolism in C. reinhardtii.     

mtDNA control-region sequence variation suggests multiple independent origins of an "Asian-specific" 9-bp deletion in sub-Saharan Africans.

The intergenic COII/tRNA(Lys) 9-bp deletion in human mtDNA, which is found at varying frequencies in Asia, Southeast Asia, Polynesia, and the New World, was also found in 81 of 919 sub-Saharan Africans. Using mtDNA control-region sequence data from a subset of 41 individuals with the deletion, we identified 22 unique mtDNA types associated with the deletion in Africa. A comparison of the unique mtDNA types from sub-Saharan Africans and Asians with the 9-bp deletion revealed that sub-Saharan Africans and Asians have sequence profiles that differ in the locations and frequencies of variant sites. Both phylogenetic and mismatch-distribution analysis suggest that 9-bp deletion arose independently in sub-Saharan Africa and Asia and that the deletion has arisen more than once in Africa. Within Africa, the deletion was not found among Khoisan peoples and was rare to absent in western and southwestern African populations, but it did occur in Pygmy and Negroid populations from central Africa and in Malawi and southern African Bantu-speakers. The distribution of the 9-bp deletion in Africa suggests that the deletion could have arisen in central Africa and was then introduced to southern Africa via the recent "Bantu expansion."     

Effect of enhanced UV-B radiation on pollen quantity,quality, and seed yield in Brassica rapa (Brassicaceae)

We conducted three experiments to examine the influence of ultraviolet-B radiation (UV-B; 280–320 nm) exposure on reproduction in Brassica rapa (Brassicaceae). Plants were grown in a greenhouse under three biologically effective UV-B levels that simulated either an ambient stratospheric ozone level (control), 16% (“low enhanced”), or 32% (“high enhanced”) ozone depletion levels at Morgantown, WV, USA in mid-March. In the first experiment, we examined whether UV-B level during plant growth influenced in vivo pollen production and viability, and flower production. Pollen production and viability per flower were reduced by ≈50% under both enhanced UV-B levels relative to ambient controls. While plants under high-enhanced UV-B produced over 40% more flowers than plants under the two lower UV-B treatments, whole-plant production of viable pollen was reduced under high-enhanced UV-B to 17% of that of ambient controls. Whole-plant production of viable pollen was reduced under low-enhanced UV-B to 34% of ambient controls. In the second experiment, we collected pollen from plants under the three UV-B levels and examined whether source-plant UV-B exposure influenced in vitro pollen germination and viability. Pollen from plants under both enhanced-UV-B treatments had initially lower germination and viability than pollen from the ambient level. After in vitro exposure to the high-enhanced UV-B levels for 6 h, viability of the pollen from plants grown under ambient UV-B was reduced from 65 to 18%. In contrast, viability of the pollen from plants grown under both enhanced UV-B treatments was reduced to a much lesser extent: only from ≈43 to 22%. Thus, ambient source-plant pollen was more sensitive to enhanced UV-B exposure. In the third experiment, we used pollen collected from source plants under the three UV-B levels to fertilize plants growing under ambient-UV-B levels, and assessed subsequent seed production and germination. Seed abortion rates were higher in plants pollinated with pollen from the enhanced UV-B treatments, than from ambient UV-B. Despite this, seed yield (number and mass) per plant was similar, regardless of the UV-B exposure of their pollen source. Our findings demonstrate that enhanced UV-B levels associated with springtime ozone depletion events have the capacity to substantially reduce viable pollen production, and could ultimately reduce reproductive success of B. rapa.     

Adaptive acid tolerance response in Listeria monocytogenes: isolation of an acid-tolerant mutant which demonstrates increased virulence.

The ability of Listeria monocytogenes to tolerate low-pH environments is of particular importance because the pathogen encounters such environments in vivo, both during passage through the stomach and within the macrophage phagosome. In our study, L. monocytogenes was shown to exhibit a significant adaptive acid tolerance response following a 1-h exposure to mild acid (pH 5.5), which is capable of protecting cells from severe acid stress (pH 3.5). Susceptibility to pH 3.5 acid is growth phase dependent. Stationary-phase Listeria cultures are naturally resistant to the challenge pH (pH 3.5), while exponential-phase cultures require adaptation at pH 5.5 to induce acid tolerance. Adaptation requires protein synthesis, since treatment with chloramphenicol prevents the development of acid tolerance. Induction of the acid tolerance response also protects L. monocytogenes against the effect of other environmental stresses. Acid-adapted cells demonstrate increased tolerance toward thermal stress, osmotic stress, crystal violet, and ethanol. Following prolonged exposure of L. monocytogenes to pH 3.5, we isolated mutants which constitutively demonstrate increased acid tolerance at all stages of the growth cycle. These mutants do not display full acid tolerance, but their resistance to low pH can be further increased following adaptation to mild-acid conditions. The mutants demonstrated increased lethality for mice relative to that of the wild type when inoculated by the intraperitoneal route. When administered as lower inocula, the mutants reached higher levels in the spleens of infected mice than did the wild type. The data suggest that low-pH conditions may have the potential to select for L. monocytogenes mutants with increased natural acid tolerance and increased virulence.     

Distribution of sewage indicated by Clostridium perfringens at a deep-water disposal site after cessation of sewage disposal.

Clostridium perfringens, a marker of domestic sewage contamination, was enumerated in sediment samples obtained from the vicinity of the 106-Mile Site 1 month and 1 year after cessation of sewage disposal at this site. C. perfringens counts in sediments collected at the disposal site and from stations 26 nautical miles (ca. 48 km) and 50 nautical miles (ca. 92 km) to the southwest of the site were, in general, more than 10-fold higher than counts from an uncontaminated reference site. C. perfringens counts at the disposal site were not significantly different between 1992 and 1993, suggesting that sewage sludge had remained in the benthic environment at this site. At stations where C. perfringens counts were elevated (i.e., stations other than the reference station), counts were generally higher in the top 1 cm and decreased down to 5 cm. In some cases, C. perfringens counts in the bottom 4 or 5 cm showed a trend of higher counts in 1993 than in 1992, suggesting bioturbation. We conclude that widespread sludge contamination of the benthic environment has persisted for at least 1 year after cessation of ocean sewage disposal at the 106-Mile Site.     

Pyruvate metabolism in mitochondria from cucumber cotyledons during early seedling development

Mitochondria were isolated from cucumber cotyledons during earlyseedling growth, and their capacity for pyruvate metabolisminvestigated. The rate of pyruvate oxidation was low. Evidenceis presented that suggests that this is due to low activitiesof the pyruvate transporter. Key words: Cotyledon, cucumber, germination, pyruvate oxidation