Temporal variability in algal biomass and primary productivity in Florida lakes relative to latitudinal gradients,organic color and trophic state

Seasonal patterns in primary productivity and algal biomass in subtropical Florida lakes along increasing gradients of both dissolved organic color and phytoplankton biomass are presented. Chlorophyll a concentrations and gross primary productivity generally reached maxima during the summer and were most depressed in winter months, regardless of color or trophic classification. Primary productivity was more strongly correlated with chlorophyll a, nutrient concentrations and water clarity in clearwater (< 75 Pt units) than in colored (> 75 Pt units) systems. Amplitudes in algal biomass were considerably smaller than temperate lakes. Variability in primary production in Florida lakes was intermediate to patterns in the temperate zone and tropics, but was more closely aligned to northern latitudes. Within the Florida peninsula, variability of primary productivity decreased from north to south and corresponded to latitudinal gradients in climatic regimes.     

Dissolved oxygen and thermal regimes of a Ugandan crater lake

This paper quantifies the temporal pattern of thermal stratification and deoxygenation in Lake Nkuruba, a small (3 ha), deep (maximum depth = 38 m) crater lake in western Uganda. Dissolved oxygen penetrated to an average depth of 9 m and a maximum depth of 15 m below which the lake was permanently anoxic over the 2 years of study. Although surface oxygen levels were correlated with both surface water temperature and rainfall, seasonal cycles of dissolved oxygen were not well-defined and may have been obscured by the high frequency of short-term fluctuations and by inter-annual variations caused by shifts in rainfall. Surface water temperature averaged 23.3±0.7 °C (S.D.) and varied directly with air temperature. Both diurnal changes and top-bottom temperature differentials were small averaging 1.7±0.7 °C and 1.6±0.8 °C, respectively. Thermal stability ranged from 101.3 to 499.9 g-cm cm^-2 and was positively related to surface water temperature suggesting that this small protected lake responds rapidly to short-term meteorological changes. Because contribution to the annual heat exchange cycle was confined to upper waters, the lake's annual heat budget was low, 1,073.8 cal cm^-2 yr^-1. However, net primary productivity was relatively high averaging 1.3 g C m^-2d^-1. The region where Lake Nkuruba is situated experienced a very strong earthquake (6.2 on the Richter scale) on 4 February, 1994. Subsequently, water levels dropped markedly in the lake, falling 3.14 m over a 5-month period. This revised version was published online in September 2006 with corrections to the Cover Date.     

Applicability of planktonic biomanipulation for managing eutrophication in the subtropics

Although large-bodied cladocerans such asDaphnia can reduce algal biomass significantly in temperate lakes if freed from fish predation, the applicability of such biomanipulation techniques for eutrophication management in the subtropics and tropics has been examined only recently. Subtropical cladoceran assemblages differ from those of temperate lakes by their low species richness, early summer gameogenesis, and greatly reduced body size. Eutrophic Florida lakes are dominated by pump-filter feeding fish rather than by size selective planktivores as a temperate lakes. Cladocerans in Florida lakes can increase in abundance significantly if freed from fish but fail to have an impact on algal biomass or composition. The greatest potential for using biomanipulation to manage phytoplankton-dominated lakes in the subtropics and tropics lies with phytophagous fish. Future research should concentrate on defining the role of individual fish taxa on phytoplankton composition and community structure, nutrient cycling, and planktonic productivity before embarking on whole lake manipulation projects.     

Cysteine Scanning Mutagenesis of Transmembrane Helix 3 of a Brain Glutamate Transporter Reveals Two Conformationally Sensitive Positions

Glutamate transporters in the brain remove the neurotransmitter from the synapse by cotransport with three sodium ions into the surrounding cells. Recent structural work on an archaeal homolog suggests that, during substrate translocation, the transport domain, including the peripheral transmembrane helix 3 (TM3), moves relative to the trimerization domain in an elevator-like process. Moreover, two TM3 residues have been proposed to form part of a transient Na3′ site, and another, Tyr-124, appears close to both Na3′ and Na1. To obtain independent evidence for the role of TM3 in glutamate transport, each of its 31 amino acid residues from the glial GLT-1 transporter was individually mutated to cysteine. Except for six mutants, substantial transport activity was detected. Aqueous accessibility of the introduced cysteines was probed with membrane-permeant and membrane-impermeant sulfhydryl reagents under a variety of conditions. Transport of six single cysteine mutants, all located on the intracellular side of TM3, was affected by membrane-permeant sulfhydryl reagents. However, only at two positions could ligands modulate the reactivity. A120C reactivity was diminished under conditions expected to favor the outward-facing conformation of the transporter. Sulfhydryl modification of Y124C by 2-aminoethyl methanethiosulfonate, but not by N-ethylmaleimide, was fully protected in the presence of sodium. Our data are consistent with the idea that TM3 moves during transport. Moreover, computational modeling indicated that electrostatic repulsion between the positive charge introduced at position 124 and the sodium ions bound at Na3′ and Na1 underlies the protection by sodium.     

Balance of meprin A and B in mice affects the progression of experimental inflammatory bowel disease

MEP1A, which encodes the α subunit of meprin metalloproteinases, is a susceptibility gene for inflammatory bowel disease (IBD), and decreased intestinal meprin-α expression is associated with enhanced IBD in humans. Mice lacking meprin α (α knockout, αKO) have more severe colitis induced by dextran sulfate sodium (DSS) than wild-type (WT) mice, indicating an anti-inflammatory role for meprin A. Previous studies and those herein indicate the meprin B has proinflammatory activities. Therefore, mice lacking both meprin A and B (dKO mice) were generated to determine how their combined absence alters the inflammatory response to DSS. Unchallenged dKO mice grow and reproduce normally and have no obvious abnormal phenotype, except for a slightly elevated plasma albumin in both males and females and a lower urine creatinine level in dKO males. Upon oral administration of 3.5% DSS, the dKO mice have more severe colitis than the WT and βKO mice but significantly less than the αKO mice. The dKO mice lose more weight and have elevated MPO and IL-6 activities in the colon compared with WT mice. Systemic inflammation, monitored by plasma nitric oxide levels, is absent in DSS-treated dKO mice, unlike WT mice. The severity of experimental IBD in dKO mice is intermediate between αKO and WT mice. The data indicate that the absence of meprin A aggravates chronic inflammation and the lack of meprin B affords some protection from injury. Manipulation of the expression of meprin gene products may have therapeutic potential.     

Long, chiral polypeptide 3(10)-helices at atomic resolution

The crystal-state preferred conformation of the terminally blocked hepta- and octapeptides with the general formula -(Aib)n L-Leu-(Aib)2- (n = 4 and 5, respectively), determined by X-ray diffraction, was found to be a right-handed 3(10)-helix stabilized by five and six consecutive intramolecular NH...O = C H-bonds of the C(10)-III type, respectively. The octapeptide structure represents the first observation at atomic resolution of a regular, chiral 3(10)-helix larger than two complete turns. In both cases the right handed screw sense of the helix is dictated by the presence of the single, internal L-residue. This study confirms the propensity of short peptides rich in Aib, the prototype of the amino acid residues dialkylated at the alpha carbon, to adopt a 3(10)-helical structure and is expected to help our understanding of the conformational preferences of the membrane-active, channel-forming, ion-transporting peptaibol antibiotics.     

Modified Cysteine-Deleted Tachyplesin (CDT) Analogs as Linear Antimicrobial Peptides: Influence of Chain Length,Positive Charge,and Hydrophobicity on Antimicrobial and Hemolytic Activity

Due to increasing resistance of bacteria to traditional antibiotics, antimicrobial peptides are being investigated as a promising alternative. Tachyplesin, an antimicrobial peptide isolated from horseshoe crab, inhibits the growth of many different types of bacteria with its ability to permeabilize the cell membrane. Starting with a previously reported linear tachyplesin analog lacking cysteine (cysteine-deleted tachyplesin, CDT, KWFRVYRGIYRRR-CONH₂), this study examines the systematic deletion of the C-terminal arginines and the N-terminal lysine, addition of positively charged N-and C-terminal residues, replacement of arginine with similarly-charged lysine, and replacement of hydrophobic residues with aliphatic, aromatic, fluoro-substituted aromatic, and bicyclic amino acids to examine effects on activity. The 16 modified CDT analogs were tested for their ability to disrupt model liposomes, and minimum inhibitory concentrations were determined for gram-positive and gram-negative bacterial strains. Hemolytic activity also was assessed. Overall, results indicate that elimination of two C-terminal arginine residues results in a peptide ([des-Arg^12,13]CDT) with preserved antimicrobial activity but a reduction in hemolysis, a selectivity desirable for a therapeutic agent. Additional deletion was not tolerated, nor was addition of residues at the termini. Analysis of the 16 analogs also reveals the importance of hydrophobicity, not necessarily aromaticity, as an analog with hydrophobic isoleucine residues placed throughout the sequence ([Ile^2,3,6,10]CDT) displayed comparable antimicrobial activity to CDT with lower hemolysis, representing a promising antimicrobial peptide with lowered toxicity.     

Analysis of the community structure of planktonic ciliated protozoa relative to trophic state in Florida lakes

The planktonic ciliate populations of 30 Florida lakes constituting a broad trophic gradient were examined to determine the response of protozoan community structure to increasing eutrophication. Both ciliate abundance and biomass were strongly related to lake trophic state. Comparison of the Florida data base with a comparable north temperate lake group indicated that subtropical lakes generally possess higher ciliate abundance and biomass at a given trophic state than temperate lakes. However the equations derived for each data base were not significantly different. Community diversity and species richness increased with increasing lake productivity. Highly acidic lakes displayed significantly reduced diversity and numbers of species when contrasted with nonacidic oligotrophic lakes. Small-bodied (< 30 um) ciliates dominated all lakes but were proportionally less important in oligotrophic lakes. Presence-absence data produced three assemblages: an ubiquitous association of primarily small ciliate taxa, a group of large ciliates mainly restricted to eutrophic-hypereutrophic lakes, and a very large ciliate,Stentor niger, which dominated the protozoan communities of acidic oligotrophic lakes.     

Seasonality of planktonic ciliated protozoa in 20 subtropical Florida lakes of varying trophic state

The planktonic ciliate populations of 20 Florida lakes ranging from oligotrophic to hypereutrophic were examined monthly for one year. Oligotrophic lakes displayed abundance peaks during fall mixis and biomass peaks in late winter and fall. Mesotrophic systems exhibited a spring-fall bimodality in ciliate abundance with a biomass maxima occurring during fall. Eutrophic/hypereutrophic lakes had pronounced abundance and biomass maxima during summer, with the large ciliates Plagiopyla nasuta and Paramecium trichium often contributing heavily to the midsummer biomass peak. Members of the Oligotrichida numerically dominated abundance and biomass peaks in oligotrophic lakes while the Scuticociliatida dominated the communities of higher trophic states. Total ciliate abundance and biomass were strongly correlated with chlorophyll a concentrations as were various ciliate taxonomic groups. The relationship between ciliate seasonal distribution in these subtropical lakes with lake thermal regimes and trophic state is discussed.