Bacterioplankton Dynamics in the McMurdo Dry Valley Lakes, Antarctica: Production and Biomass Loss over Four Seasons

Abstract Research of the microbial ecology of McMurdo Dry Valley lakes has concentrated primarily on phototrophs; relatively little is known about the heterotrophic bacterioplankton. Bacteria represent a substantial proportion of water column biomass in these lakes, comprising 30 to 60% of total microplankton biomass. Bacterial production and cell numbers were measured 3 to 5 times, within four Antarctic seasons (October to January), in Lakes Fryxell, Hoare, and Bonney. The winter-spring transition (September to October) was included during one year. Lake Fryxell was the most productive, but variable, lake, followed by Lakes Bonney and Hoare. Bacterial production ranged from 0 to 0.009 μg C ml-1 d-1; bacterial populations ranged from 3.2 x 10(4) to 4.4 x 10(7) cells ml-1. Bacterial production was always greatest just below the ice cover at the beginning of the season. A second maximum developed just above the chemocline of all the lakes, as the season progressed. Total bacterioplankton biomass in the lakes decreased as much as 88% between successive sampling dates in the summer, as evidenced by areal integration of bacterial populations; the largest decreases in biomass typically occurred in mid-December. A forward difference model of bacterial loss in the trophogenic zone and the entire water column of these lakes showed that loss rates in the summer reached 6.3 x 10(14) cells m-2 d-1 and 4.16 x 10(12) cells m-2 d-1, respectively. These results imply that bacteria may be a source of carbon to higher trophic levels in these lakes, through grazing.     

Recombinant glucagon-like peptide-1 (7-36 amide) lowers fasting serum glucose in a broad spectrum of patients with type 2 diabetes.

AIMS: To evaluate the safety and efficacy of various doses of recombinant glucagon-like peptide-1 (7-36) amide (rGLP-1) administered subcutaneously (s. c.) via bolus injection or continuous infusion to lower fasting serum glucose (FSG) levels in subjects with type 2 diabetes treated by diet, hypoglycemic drugs, or insulin injection. METHODS: rGLP-1 was administered s. c. to 40 type 2 diabetics currently treated by diet, sulfonylurea (SU), metformin, or insulin in a double-blind, placebo-controlled, cross-over trial; preexisting treatments were continued during the study. In the bolus injection protocol, 32 subjects (8 from each of the 4 treatment groups) received 0.0, 0.5, 1.0, and 1.5 nmol rGLP-1/kg per injection (two injections, two hours apart, beginning one hour after the evening meal) in a randomized order on separate days. In the continuous s. c. infusion protocol, 40 subjects received rGLP-1 at 0.0, 1.5, 2.5, 3.5, and 4.5 pmol/kg/min for 10-12 hours overnight starting one hour after the evening meal. Fasting bloods were taken the morning after for glucose, insulin, and glucagon measurements. RESULTS: In the diet, SU, and metformin cohorts, bolus rGLP-1 injections produced modest reductions in mean FSG levels, averaging 17.4 mg/dl (7.3-27.5; 95 % CI) at the highest dose (p < 0.001 vs. placebo). Reductions in FSG levels were greater by continuous infusion at up to 30.3 mg/dl (18.8 - 41.8; 95 % CI; p < 0.001 vs. placebo). The greatest reduction in mean FSG occurred in the SU cohort (up to 43.9 mg/dl, 24.7 - 63.1; 95 % CI; p < 0.001). rGLP-1 infusions resulted in significant increases in fasting plasma insulin and decreases in fasting plasma glucagon levels. There were no serious adverse events; GI-related symptoms were dose-related and more commonly associated with injections. CONCLUSIONS: rGLP-1 (7-36) amide dose-dependently lowered FSG in a broad spectrum of type 2 diabetics when added to their existing treatment. Subcutaneous infusion was more effective than injection, and the combination with SU was more effective than with metformin.     

拐芹根化学成分研究Ⅱ

从伞型科当归属植物拐芹(Angelica polymorpha Maxim)的根及根茎中又分得4个结晶性化合物。经物理常数测定、光谱分析,分别鉴定为欧前胡素Ⅰ,异氧化前胡内酯Ⅱ,Pabulenol Ⅲ,Phellopterin Ⅳ。     

How do floating aquatic weeds affect wetland conservation and development? How can these effects be minimised?

The most important floating aquatic weeds (FAWs) are Eichhornia crassipes, Salvinia molesta and Pistia stratiotes. E. crassipes and P. stratiotes reproduce sexually. All three species reproduce asexually. E. crassipes and S. molesta have particularly high growth rates. All can form dense mats and growth rates are increased by high nutrient levels and temperatures. Spread between continents and watersheds is largely the result of human activities. Spread within watersheds is mostly via floating propagules. FAWs are known to affect water resource management, the continued existence of human riverine and wetland communities, and conservation of biodiversity. Waterways can be blocked, and the efficiency of irrigation and hydro generation impaired. People are affected by reduction of the fish catch, inability to travel by boat and consequent isolation from gardens, markets and health services, and also changes in populations of vectors of human and animal diseases. Biodiversity can be reduced and conservation value affected. It is proposed that rational application of physical, chemical and biological control of FAWs, and reduction of nutrient input should be part of every strategy for the sustainable management of wetlands.     

Quantitative studies on the precursors of cytotoxic lymphocytes. I. Characterization of a clonal assay and determination of the size of clones derived from single precursors.

A microculture system for estimating the frequency of cytotoxic lymphocyte precursors (CLP) to alloantigens is described. Cytotoxic T lymphocytes (CL) were generated by culturing limiting numbers of RNC (H-2k)-nu/+lymph node (LN) cells with irradiated C3D2F1 (H-2k/d) spleen cells in the presence of RNC-nu/nu spleen cells for 7 days in microtiter trays. At the end of the culture period, individual wells were assayed for cytotoxic effector cells directed against 51CrP815 (H-2d) target cells. The effector cells generated under these conditions are sensitive to killing by rabbit anti-mouse brain serum and guinea pig complement. The process of differentiation from precursors to CL is radiation sensitive (Do approximately 180 rads). The frequency of precursors for H-2d was calculated by fitting the proportion of nonresponding cultures to the zero order term of the Poisson distribution, Po = e-vn, where Po = per cent nonresponders, v = precursor frequency, and N = number of LN cells cultured per well. The frequency of precursors in the RNC-nu/+LN population responding to the H-2d haplotype was found to be 1 in 776. Under conditions where no backstimulation is possible, the frequency of precursors responding to the H-2d haplotype is 1 in 885 for B6-nu/+LN and 1 in 2550 for B6-nu/+ spleen, respectively. In combination with a visual assay for individual CL, it was found that the average clone size per precursor after 7 days in culture is about 1040. Our assay could detect clones with as few as 40 CL/well. Since the average clone size in 26 times the detection limit, we conclude that the assay for CLP is highly sensitive and does not represent a minimum estimate.     

Effects of inhibitors of lipid synthesis on the replication of Rous sarcoma virus. A specific effect of cerulenin on the processing of major non-glycosylated viral structural proteins.

The effects of two inhibitors of lipid biosynthesis on the replication of Rous sarcoma virus Prague C strain in chick embryo fibroblasts have been examined in media containing delipidated serum. 25-Hydroxycholestetate into sterols, had no effect on the formation of infectious virions or on the synthesis and processing of intracellular virion proteins. Cerulenin strongly inhibited [1(-14C)]acetate incorporation into fatty acids and partially inhibited its incorporation into sterols in chick embryo cells. Rous sarcoma virus production as measured by focus formation and by the production of [35S]methionine-labeled virions was strongly inhibited within 5 h after cerulenin addition to infected cultures. Examinatin of extracts of these cells revealed the accumulation of the 76 000 dalton precursor (Pr76) of the major non-glycosylated virion structural proteins, p27, p19, p15 and p12. The failure to process the 76 000 dalton precursor was coincident in time with the decrease in viron production. Neither whole serum nor mixtures of fatty acids plus cholesterol were able to reverse the effects of cerulenin.     

Effects of inhibitors of lipid synthesis on the replication of rous sarcoma virus. A specific effect of cerulenin on the processing of major non-glycosylated viral structural proteins

The effects of two inhibitors of lipid biosynthesis on the replication of Rous sarcoma virus Prague C strain in chick embryo fibroblasts have been examined in media containing delipidated serum. 25-Hydroxycholesterol, which markedly inhibits the incorporation of [1-¹⁴C]acetate into sterols, had no effect on the formation of infectious virions or on the synthesis and processing of intracellular virion proteins. Cerulenin strongly inhibited [1-¹⁴C]acetate incorporation into fatty acids and partially inhibited its incorporation into sterols in chick embryo cells. Rous sarcoma virus production as measured by focus formation and by the production of [³⁵S]methionine-labeled virions was strongly inhibited within 5 h after cerulenin addition to infected cultures. Examination of extracts of these cells revealed the accumulation of the 76 000 dalton precursor (Pr76) of the major non-glycosylated virion structural proteins, p27, p19, p15 and p12. The failure to process the 76 000 dalton precursor was coincident in time with the decrease in viron production. Neither whole serum nor mixtures of fatty acids plus cholesterol were able to reverse the effects of cerulenin.     

In vitro studies of age-associated diseases.

We have carried out studies on cultured human fibroblasts in an attempt to trace the origins of age-dependent disorders to the cellular and molecular levels. Three interrelated areas are discussed. First, skin donors with diabetes mellitus (a disease complex that features inappropriate hyperglycemia) produce cultured fibroblasts with a moderate reduction in growth capacity, while two inherited disorders of inappropriate hyperglycemia and premature aging, progeria and Werner syndrome, yield fibroblast cultures with more severely impaired growth capacity. Second, there is a decreased response of progeria level and donor age; evidence is presented that this defective hormone responsiveness in aging cells may reside at the hormone receptor on the surface membrane, the cyclic AMP system, the intracellular enzymatic machinery, or all of these sites. Third, tissue factor, a procoagulant that activates the extrinsic clotting mechanism, is more abundant in cells from the premature aging syndromes of progeria and Werner syndrome. Fibroblast aging in vitro may help to explain various concomitants of normal aging and diabetes mellitus including cell dropout, impairment of hormone responsiveness, and increased atherothrombosis.