Indicators of the Ecological Impact of Bottom-Trawl Disturbance on Seabed Communities

The Ecosystem Approach to Fisheries requires that managers take account of the environmental impacts of fishing. We develop linked state and pressure indicators that show the impact of bottom-trawling on benthic communities. The state indicator measures the proportion of an area where benthic invertebrate biomass (B) or production (P) is more than 90% of pristine benthic biomass (B _0.9) or production (P_0.9). The pressure indicator measures the proportion of the area where trawling frequency is sufficiently high to prevent reaching predicted B_0.9 or P_0.9. Time to recovery to B_0.9 and P_0.9 after trawling, depending on the habitat, was estimated using a validated size-based model of the benthic community. Based on trawling intensity in 2003, 53.5% of the southern North Sea was trawled too frequently for biomass to reach B_0.9, and 27.1% was trawled too frequently for production to reach P_0.9. As a result of bottom-trawling in 2003, in 56% of the southern North Sea benthic biomass was below B_0.9, whereas in 27% of the southern North Sea benthic production was below P_0.9. Modeled recovery times were comparable to literature estimates (2.5 to more than 6 years). The advantages of using the area with an ecological impact of trawling as a pressure indicator are that it is conceptually easy to understand, it responds quickly to changes in management action, it can be implemented at a relevant scale for fisheries management, and the necessary effort distribution data are centrally collected. One of this approach’s greatest utilities, therefore, will be to communicate to policy makers and fishing enterprises the expected medium- to long-term ecological benefits that will accrue if the frequency of trawling in particular parts of fishing grounds is reduced.     

Photosynthetic activity of phytoplankton and its relation to environmental factors in hypersaline Mono Lake,California

The photosynthetic activity of phytoplankton in hypersaline Mono Lake, California was measured over the three year period, 1983–1985. The maximum chlorophyll-specific rate of carbon uptake (P_m ^B) and the light-limited slope (alpha) were derived from laboratory measurements of photosynthesis vs. irradiance (P-I) relationships. Annual estimates of primary production were 340–540 g C m^-2 yr^-1. Production was two to three times higher during the spring of 1983 than in the springs of 1984 and 1985; higher standing biomass of algae occurred in 1983. While P_m ^B rates followed water temperatures and varied over 40-fold over the year, integral primary production varied less since periods of high P_m ^B occurred when algal biomass was low. Sixty-eight percent of the seasonal variation in the P_m ^B was explained by a regression on temperature (53%), chlorophyll a (12%), and the carbon:chlorophyll a ratio (3%). Light-saturated and light-limited rates of photosynthesis generally covaried, evidenced by the strong seasonal correlation between P_m ^B and alpha. Sixty-one percent of variation in alpha was explained by a regression on P_m ^B, temperature, grazing, water column stability, and self-shading. There was no correlation of carbon uptake with ambient levels of inorganic nitrogen. The regression coefficient of the dependence of P_m ^B on the seasonal temperature trend was much larger than that determined from individual samples incubated at several different temperatures; this indicates that uptake is limited by more than low temperatures in the spring. Regression equations including only temperature, chlorophyll and depth were sufficient to estimate patterns of seasonal and year to year variation in integral primary productivity.     

A new model estimating stonefly species production in the West Carpathian torrents

Samples of stoneflies were collected from 15 streams of Slovakia during 1976–2000. The model of growth rate is based on 219 data of 50 stonefly species. The non-linear relationship among growth rate (G) of stoneflies and monthly mean water temperature (T) and body mass (W) is described by equation: G = 0.014W ^−0.19 T ^0.25. The model estimates the species production of the families Taeniopterygidae, Nemouridae, Capniidae, Leuctridae and Perlodidae. This model is combined with Morin’s & Dumont’s (1994) model for Perlidae and Chloroperlidae. There is positive evidence that the total stonefly production of mountain and submountain streams increases with discharge. On the other hand, increasing altitude has a negative influence on production.     

Primary electron transfer in reaction centers of YM210L and YM210L/HL168L mutants of <Emphasis Type="Italic">Rhodobacter sphaeroides</Emphasis>

The role of tyrosine M210 in charge separation and stabilization of separated charges was studied by analyzing of the femtosecond oscillations in the kinetics of decay of stimulated emission from P* and of a population of the primary charge separated state P⁺B_A⁻ in YM210L and YM210L/HL168L mutant reaction centers (RCs) of Rhodobacter sphaeroides in comparison with those in native Rba. sphaeroides RCs. In the mutant RCs, TyrM210 was replaced by Leu. The HL168L mutation placed the redox potential of the P⁺/P pair 123 mV below that of native RCs, thus creating a theoretical possibility of P⁺B_A⁻ stabilization. Kinetics of P* decay at 940 nm of both mutants show a significant slowing of the primary charge separation reaction in comparison with native RCs. Distinct damped oscillations in these kinetics with main frequency bands in the range of 90–150 cm⁻¹ reflect mostly nuclear motions inside the dimer P. Formation of a very small absorption band of B_A⁻ at 1020 nm is registered in RCs of both mutants. The formation of the B_A⁻ band is accompanied by damped oscillations with main frequencies from ∼10 to ∼150 cm⁻¹. Only a partial stabilization of the P⁺B_A⁻ state is seen in the YM210L/HL168L mutant in the form of a small non-oscillating background of the 1020-nm kinetics. A similar charge stabilization is absent in the YM210L mutant. A model of oscillatory reorientation of the OH-group of TyrM210 in the electric fields of P⁺ and B_A⁻ is proposed to explain rapid stabilization of the P⁺B_A⁻ state in native RCs. Small oscillatory components at ∼330–380 cm⁻¹ in the 1020-nm kinetics of native RCs are assumed to reflect this reorientation. We conclude that the absence of TyrM210 probably cannot be compensated by lowering of the P⁺B_A⁻ free energy that is expected for the double YM210L/HL168L mutant. An oscillatory motion of the HOH55 water molecule under the influence of P⁺ and B_A⁻ is assumed to be another potential contributor to the mechanism of P⁺B_A⁻ stabilization.     

Habitual physical activity and peak anaerobic power in elderly women

The aim of this study was to investigate the relationship between maximal anaerobic power (P _max) and corresponding optimal velocity (V _opt) and habitual physical activity (PA) on the one hand and with maximal oxygen consumption (V˙O_2max) on the other hand, in elderly women. Twenty-nine community dwelling, healthy women aged 66–82 years participated in the study. PA was evaluated using the Questionnaire d'Activite Physique Saint-Etienne (QAPSE) and expressed using two QAPSE activity indices: mean habitual daily energy expenditure (MHDEE) and daily energy expenditure corresponding to leisure time sports activities (sports activity). The subjects' P _max and V _opt were measured while they cycled on a friction-loaded non-isokinetic cycle ergometer. P _max was expressed relative to body mass [P _max/kg(W · kg⁻¹)], and relative to the mass of two quadriceps muscles [P _{max /Quadr}(W·kg_Quadr ⁻¹)]. A negative relationship between P _max/kg (Spearman's r = −0.56; P < 0.01), P _max/Quadr (r = −0.53; P < 0.01) and V _opt (r = −0.45; P < 0.05) and age was found. P _max/kg was positively associated with MHDEE (r = 0.51; P < 0.01) and sports activity (r = 0.58; P < 0.01), as were P _max/Quadr and V _opt (r = 0.55; P < 0.01 and r = 0.54; P < 0.01, respectively). P _max/kg, P _max/Quadr and V _opt correlated positively with V˙O_2max. The positive relationship between ergometer measurements and PA indices was similar to that between V˙O_2max and PA. P _max/kg was, moreover, closely related to V _opt (r = 0.77; P < 0.001). When a multiple stepwise regression analysis was used to select the variables influencing ergometer measurements, MHDEE contributed significantly to P _max/kg variance, whereas sports activity contributed to P _max/Quadr and V _opt variances. In conclusion, the data from this cross-sectional study suggest that in healthy elderly women habitual PA, and especially leisure time PA, alleviates the decline of the P _max of the quadriceps muscles. Accepted: 30 January 1997     

Phytoplankton biomass,P-I relationships and primary production in the Weddell Sea,Antarctica, during the austral autumn

An investigation into the changing phytoplankton biomass and total water column production during autumn sea ice formation in the eastern Weddell Sea, Antarctica showed reduced biomass concentrations and extremely low daily primary production. Mean chlorophyll-a concentration for the entire study period was extremely low, 0.15±0.01 mg.m⁻³ with a maximum of 0.35 mg.m⁻³ found along the first transect to the east of the grid. Areas of low biomass were identified as those either associated with heavy grazing or with deep mixing and corresponding low light levels. In most cases phytoplankton in the <20-μm size classes dominated. Integrated biomass to 100 m ranged from 7.1 to 28.0 mg.m⁻² and correlated positively with surface chlorophyll-a concentrations. Mean P^Bmax (photosynthetic capacity) and α^B (initial slope of the photosynthesis-irradiance curve) were 1.25±0.19 mgC. mgChla ⁻¹.h⁻¹ and 0.042±0.009 mgC.mgChla ⁻¹.h⁻¹.(μmol.m⁻².s⁻¹)⁻¹ respectively. The mean index of photoadaptation,I _k, was 32.2±4.0 μmol.m⁻².s⁻¹ and photoinhibition was found in all cases. Primary production was integrated to the critical depth (Z _cr) at each production station and ranged from 15.6 to 41.5 mgC.m⁻².d⁻¹. It appears that, other than grazing intensity, the relationship between the critical depth and the mixing depth (Z _mix) is an important factor as, ultimately, light availability due both to the late season and growing sea ice cover severely limits production during the austral autumn.     

Temporal and vertical variation of chlorophyll a concentration, phytoplankton photosynthetic activity and light attenuation in Lake Kinneret: possibilities and limitations for simulation by remote sensing

The relationship between chlorophyll a (Chl a) and primary productivity(PP) in the uppermost water layer and the water column-based(0–15 m) integral values of those variables were examinedusing measurements taken in Lake Kinneret (Israel) from 1990to 2003. In 81% of all Chl a profiles examined, the distributionwas fairly uniform within the entire 0–15 m water column,and 12.3% of instances showed a prominent subsurface maximum,when the lake phytoplankton was dominated by the dinoflagellatePeridinium gatunense. Chl a can be reliably estimated by remotesensing techniques in the productive and turbid water of LakeKinneret, since Chl a concentration at surface layers can beextrapolated to the entire water column. Light vertical attenuationcoefficient average for wavelengths from 400 to 700 nm, K_d,ranged from 0.203 to 1.954 m^–1 and showed high degreeof temporal variation. The maximal rate of photosynthetic efficiency,P_B^opt [average 3.16 (±1.50)], ranged from 0.25 to 8.85mg C m^–3 h^–1 mg Chl a^–1. Using measured dataof Chl a, P_B^opt, and light as an input, a simple depth-integratedPP model allowed plausible simulation of PP. However, a lackof correlation between photosynthetic activity and temperature(or other variable with remotely sensed potential) renders theuse of models that require input of photosynthetic efficiencyto calculate integrated PP of little value in the case of productiveand turbid Lake Kinneret.     

Primary production processes and photosynthetic performance of a unique periantarctic ecosystem: the Strait of Magellan

During the late austral summer and early autumn 1995 (March–April), an oceanographic cruise was conducted along the Strait of Magellan in order to study the photosynthetic performance of phytoplankton assemblages. The high correlations between the pico–nano fractions and both the total biomass concentrations (Chla) and primary production rates emphasized the role of these fractions in driving the primary production processes. Repeated P versus E experiments were conducted in the most productive area of the Strait, Paso Ancho, in order to assess the influence of the tidal currents on phytoplankton photosynthetic performance. These data were compared to those available from a previous cruise (February–March, 1991) carried out along the Strait. In the Pacific–Andean sector, the primary production processes were highly controlled by wind, land forcing, and irradiance availability. In the Paso Ancho, the observed highest photosynthetic capacity P_\textm^\textB P_{\text{m}}^{\text{B}} (up to 6.5 mgC mgChla ⁻¹ h⁻¹) and the high primary production rates may due to the continuous mixing of the water column forced by the strong tidal currents within the photic layer. The non-limiting, macro-nutrient concentrations in the Strait indicate that the available irradiance and the depth of mixed layer are the main driving factors of the primary production processes. The photosynthetic performance of the phytoplankton assemblages renders the Strait a unique ecosystem, which is more similar to those of the mid-latitudes than to those of the periantarctic areas.     

Electron transfer in deuterated reaction centers of Rhodobacter sphaeroides at 90 K according to femtosecond spectroscopy data

The primary act of charge separation was studied in P⁺B_A ^– and P⁺H_A ^– states (P, primary electron donor; B_A and H_A, primary and secondary electron acceptor) of native reaction centers (RCs) of Rhodobacter sphaeroides R-26 using femtosecond absorption spectroscopy at low (90 K) and room temperature. Coherent oscillations were studied in the kinetics of the stimulated emission band of P* (935 nm), of absorption band of B_A ^– (1020 nm) and of absorption band of H_A (760 nm). It was found that in native RCs kept in heavy water (D₂O) buffer the isotopic decreasing of basic oscillation frequency 32 cm ^–1 and its overtones takes place by the same factor 1.3 in the 935, 1020, and 760 nm bands in comparison with the samples in ordinary water H₂O. This suggests that the femtosecond oscillations in RC kinetics with 32 cm ^–1 frequency may be caused by rotation of hydrogen-containing groups, in particular the water molecule which may be placed between primary electron donor P_B and primary electron acceptor B_A. This rotation may appear also as high harmonics up to sixth in the stimulated emission of P*. The rotation of the water molecule may modulate electron transfer from P* to B_A. The results allow for tracing of the possible pathway of electron transfer from P* to B_A along a chain consisting of polar atoms according to the Brookhaven Protein Data Bank (1PRC): Mg(P_B)-N-C-N(His M200)-HOH-O = B_A. We assume that the role of 32-cm ^–1 modulation in electron transfer along this chain consists of a fixation of electron density at B_A ^– during a reversible electron transfer, when populations of P* and P⁺B_A ^– states are approximately equal.     

Primary production of epipsammic algal communities in Lake Balaton (Hungary)

Benthic algal communities can play an important role in matter and energy flux of shallow lakes. Their contribution to total primary production of lakes has been largely unexplored. The aim of this study was to estimate the primary production of the epipsammic algal communities at different water depths in Lake Balaton (Hungary) with photosynthetic measurements performed in laboratory. The photosynthesis of the benthic algae of different origin was studied at nine different irradiance levels, in three replicates. The maximum photosynthetic rate (P _max) was always higher in samples from the shallow parts than those from the deeper regions of the lake. Along the west–east longitudinal axis of the lake P _max decreased in the southern part and increased in the middle of the lake as a consequence of differences in the chlorophyll-a concentrations. Knowing P _max, I _k, global radiation and extinction coefficient, the primary production (mg C m⁻² day⁻¹) of the epipsammic algal community was calculated at different water depths. In the shallow regions at 0.5 and 1 m water depth 75–95% and 60–85% of the production was attributable to the epipsammon. The percentage contribution of epipsammon was at 2 m water depth 20–65%. In the deeper pelagic region (>3 m) more than 85% of the primary production originated from the phytoplankton.     

Factors driving spatial and temporal variation in production and production / biomass ratio of stream‐resident brown trout (Salmo trutta) in Cantabrian streams

1. The objective was to identify the factors driving spatial and temporal variation in annual production (P_A) and turnover (production/biomass) ratio (P/B_A) of resident brown trout Salmo trutta in tributaries of the Rio Esva (Cantabrian Mountains, Asturias, north‐western Spain). We examined annual production (total production of all age‐classes over a year) (P_A) and turnover (P/B_A) ratios, in relation to year‐class production (production over the entire life time of a year‐class) (P_T) and turnover (P/B_T) ratio, over 14 years at a total of 12 sites along the length of four contrasting tributaries. In addition, we explored whether the importance of recruitment and site depth for spatial and temporal variations in year‐class production (P_T), elucidated in previous studies, extends to annual production. 2. Large spatial (among sites) and temporal (among years) variation in annual production (range 1.9–40.3 g m^?2 per year) and P/B_A ratio (range 0.76–2.4 per year) typified these populations, values reported here including all the variation reported globally for salmonids streams inhabited by one or several species. 3. Despite substantial differences among streams and sites in all production attributes, when all data were pooled, annual (P_A) and year‐class production (P_T) and annual (P/B_A) and year‐class P/B_T ratios were tightly linked. Annual (P_A) and year‐class production (P_T) were similar but not identical, i.e. P_T = 0.94 P_A, whereas the P/B_T ratios were 4 + P/B_A ratios. 4. Recruitment (Rc) and mean annual density (N_A) were major density‐dependent drivers of production and their relationships were described by simple mathematical models. While year‐class production (P_T) was determined (R² = 70.1%) by recruitment (Rc), annual production (P_A) was determined (R² = 60.3%) by mean annual density (N_A). In turn, variation in recruitment explained R² = 55.2% of variation in year‐class P/B_T ratios, the latter attaining an asymptote at P/B_T = 6 at progressively higher levels of recruitment. Similarly, variations in mean annual density (N_A) explained R² = 52.1% of variation in annual P/B_A, the latter reaching an asymptote at P/B_A = 2.1. This explained why P/B_T is equal to P/B_A plus the number of year‐classes at high but not at low densities. 5. Site depth was a major determinant of spatial (among sites) variation in production attributes. All these attributes described two‐phase trajectories with site depth, reaching a maximum at sites of intermediate depth and declining at shallower and deeper sites. As a consequence, at sites where recruitment and mean annual density reached minimum or maximum values, annual (P_A) and year‐class production (P_T) and annual (P/B_A) and year‐class P/B_T ratios also reached minimum and maximum values.     

PHOTOSYNTHETIC RESPONSE OF NATURAL ASSEMBLAGES OF MARINE BENTHIC MICROALGAE TO SHORT-AND LONG-TERM VARIATIONS OF INCIDENT IRRADIANCE IN BAFFIN BAY,TEXAS1

This study was designed to understand the high variability characterizing primary production rates of microphytobenthos. The photosynthetic efficiency (α^B) and photosynthetic capacity (P^B_max) of the microphytobenthos were measured at different times of the day on two different dates (8 May and 7 July 1990). In July, unusually low light conditions were caused by the development of a brown tide (chrysophytes). Both light-limited and light-saturated photosynthesis changed at hourly and monthly scales. There was a linear relationship between α^B and P^B_max, suggesting a common response to environmental factors [α^B= 0.0075(±0.00063)·P^B_max+ 0.00097(±0.0071), R²= 0.94]. Incident irradiance at the sediment-water interface was the primary physical factor that explained variability of both α^B (84%) and P^B_max (92%). Temperature had a negative but minor effect that explained an extra 8% and 2% of the variance, respectively. There was no diel rhythm of α^B and P^B_max and incident irradiance was regulated by wind-induced currents. Therefore, microphytobenthos photosynthesis seemed to be primarily controlled by wind events in Baffin Bay.     

Seasonal variation in primary production of a large high altitude tropical lake (Lake Tana,Ethiopia): effects of nutrient availability and water transparency

Primary production rates, chlorophyll and phytoplankton biovolume were measured monthly from April 2003 to November 2004 in Lake Tana, a large tropical lake in the highlands of Ethiopia. The lake is characterised by low nutrient concentrations, and a low water transparency due to high silt load of the inflowing rivers during the rainy seasons (May–November) and daily resuspension of sediments in the inshore zone. The mean chlorophyll-a concentrations varied seasonally and ranged from 2.6 mg m⁻³ to 8.5 mg m⁻³ (mean: 4.5 mg m⁻³) in the offshore zone. Primary production was measured using the light–dark bottles technique. We incubated only at three depths, i.e. 0.6, 1.2 and 1.8 m. Therefore, we may have missed a substantial part of the depth production profile and probably also frequently missed P _max. Gross primary production in the openwater averaged 2.43 g O₂ m⁻² d⁻¹ and ranged between 0.03 g O₂ m⁻² d⁻¹ and 10.2 g O₂ m⁻² d⁻¹; production was significantly higher in the inshore zone. The highest production rates were observed in the post-rainy season (Oct–Nov), which coincided with a bloom of Microcystis and higher chlorophyll levels. This seasonal high production is probably caused by a relatively high nutrient availability in combination with favourable light conditions. The gross primary production rates of L. Tana are among the lowest compared with other tropical lakes. This will be partly the result of our underestimation of gross primary production by often missing P _max. Another cause is the oligotrophic nature of the lake in combination with its relatively low water transparency. The gross primary production per unit chlorophyll in the openwater zone was in the same range as in 30 other tropical lakes and reservoirs. The higher primary production in the inshore zone is probably the result of the daily water column mixing (Z _mix ≥ Z _t) in this area, enhancing nutrient recycling. A large proportion of the annual primary production is realised in one of the four seasons only. This productive post-rainy season is relatively short (2 months) and therefore efficiency of transfer of matter between the first and second trophic level of the Lake ecosystem will be poor.     

Dimensionless analysis of the microbial growth rate dependence on sub-optimal temperatures

The influence of sub-optimal temperatures (T) on the microbial growth rate (μ) has been assessed by means of dimensionless variables: T_dim = [T−T_min]/[T_opt−T_min] and μ_dim = μ/μ_opt. T_min represents the temperature at which there is no growth, T_opt the optimum temperature at which the growth rate, μ_opt, is maximum. Data sets, growth rate vs temperature, have been taken from the literature for 12 organisms (psychrotrophs, mesophiles and thermophiles). In order to compare these organisms, the power law function has been used: [μ_dim] = [T_dim]^α. The parameters μ_opt and T_opt are determined from direct readings whereas T_min and αare estimated by means of a non-linear regression. An accurate estimation of T_min is obtained providing low growth rate data are available. A wide range of optimal temperatures where the growth rate almost equals μ_opt prevents one from obtaining a narrow confidence interval forα. On the basis of the analysis hereafter developed, thermophiles are characterized by values of the power α less than mesophiles and psychrotrophs. Almost all of these values are significantly different from two, previously determined for Staphylococcus xylosus and widely used for predicting the microbial growth in foods. Received 15 May 1998/ Accepted in revised form 25 September 1998     

Thermal resistance parameters of the air environment at various altitudes

 The thermal properties of atmospheric air surrounding the human body at various altitudes are characterized with a system of parameters. This system comprises resistance of the air to convective heat transfer h _c ^–1, °C (W/m²)⁻¹ and to water vapour transfer h _D ^–1, s/m. The concept of ’evaporative resistance’h _e ^–1, hPa (W/m²)⁻¹) following the similarity of the processes is introduced. In obtaining the altitude dependencies of investigated paramters, a respective heat transfer equation expressing the rate of heat exchange at the boundary body surface – ambient air is applied. The use of the body thermal state of the established altitude dependencies is discussed. The concept of ’thermal stability’ related to the evaporative resistance parameter h _e ^–1 is introduced. This parameter is assumed as: (1) an indicator of the human body thermal stability and (2) distributor and predictor of environmental influence on the body thermal state. Received: 5 January 1996 / Accepted 5 November 1996     

Land-Use Change and Stream Water Fluxes: Decadal Dynamics in Watershed Nitrate Exports

Stream water exports of nutrients and pollutants to water bodies integrate internal and external watershed processes that vary in both space and time. In this paper, we explore nitrate (NO₃) fluxes for the 326 km² mixed-land use Fall Creek watershed in central New York for 1972–2005, and consider internal factors such as changes in land use/land cover, dynamics in agricultural production and fertilizer use, and external factors such as atmospheric deposition. Segmented regression analysis was applied independently to dormant and growing seasons for three portions of the period of record, which indicated that stream water NO₃ concentrations increased in both dormant and growing seasons from the 1970s to the early 1990s at all volumes of streamflow discharge. Dormant season NO₃ concentrations then decreased at all flow conditions between the periods 1987–1993 and 1994–2005. Results from a regression-based stream water loading model (LOADEST) normalized to mean annual concentrations showed annual modeled NO₃ concentration in stream water increased by 34% during the 1970s and 1980s (from 1.15 to 1.54 mg l⁻¹), peaked in about 1989, and then decreased by 29% through 2005 (to 1.09 mg l⁻¹). Annual precipitation had the strongest correlation with stream water NO₃ concentrations (r = −0.62, P = 0.01). Among land use factors, corn production for grain was the variable most highly correlated to stream water NO₃ concentrations (r = 0.53, P = 0.01). The strongest associative trend determined using Chi-squared Automatic Interaction Detection (CHAID) was found between stream water NO₃ concentrations and N-equivalence of dairy production (Bonferroni adjusted P value = 0.0003). Large increases in dairy production were coincident with declining nitrate concentrations over the past decade, which suggest that dairy management practices may have improved in the watershed. However, because dairy production in the Fall Creek watershed has been fueled by large increases in feed imports, the environmental costs of feed production have likely been externalized to other watersheds.     

FTIR spectroscopy of the reaction center of Chloroflexus aurantiacus: Photooxidation of the primary electron donor

Photochemical oxidation of the primary electron donor P in reaction centers (RCs) of the filamentous anoxygenic phototrophic bacterium Chloroflexus (C.) aurantiacus was examined by light-induced Fourier transform infrared (FTIR) difference spectroscopy at 95 K in the spectral range of 4000–1200 cm⁻¹. The light-induced P⁺Q_A⁻/PQ_A IR spectrum of C. aurantiacus RCs is compared to the well-characterized FTIR difference spectrum of P photooxidation in the purple bacterium Rhodobacter (R.) sphaeroides R-26 RCs. The presence in the P⁺Q_A⁻/PQ_A FTIR spectrum of C. aurantiacus RCs of specific low-energy electronic transitions at ∼2650 and ∼2200 cm⁻¹, as well as of associated vibrational (phase-phonon) bands at 1567, 1481, and 1294–1285 cm⁻¹, indicates that the radical cation P⁺ in these RCs has dimeric structure, with the positive charge distributed between the two coupled bacteriochlorophyll a molecules. The intensity of the P⁺ absorbance band at ∼1250 nm (upon chemical oxidation of P at room temperature) in C. aurantiacus RCs is approximately 1.5 times lower than that in R. sphaeroides R-26 RCs. This fact, together with the decreased intensity of the absorbance band at ∼2650 cm⁻¹, is interpreted in terms of the weaker coupling of bacteriochlorophylls in the P⁺ dimer in C. aurantiacus compared to R. sphaeroides R-26. In accordance with the previous (pre)resonance Raman data, FTIR measurements in the carbonyl stretching region show that in C. aurantiacus RCs (i) the 13¹-keto C=O groups of P_A and P_B molecules constituting the P dimer are not involved in hydrogen bonding in either neutral or photooxidized state of P and (ii) the 3¹-acetyl C=O group of P_B forms a hydrogen bond (probably with tyrosine M187) absorbing at 1635 cm⁻¹. Differential signals at 1757(+)/1749(−) and 1741(+)/1733(−) cm⁻¹ in the FTIR spectrum of C. aurantiacus RCs are attributed to the 13³-ester C=O groups of P in different environments.     

Investigation of bacterioplankton in the loess-containing lake Khanka

Some characteristics of bacterioplankton—generation time, daily (P) and specific (P/B) bacterioplankton production, and bacterial metabolic coefficientK ₂—in the loess-containing Lake Khanka were determined using five modifications of the bacterial-count procedure with the fluorescent dyes fluorescamin and erythrosin. Experiments showed that the organomineral complex (OMC) in this lake is broken down by chemoorganoheterotrophic bacteria. The increase in the loess content of the lake water intensified bacterial growth and the cycles of potassium, silicon, and other biogenic elements. The addition of starch to a loess suspension activated the breakdown of OMC due to the adsorption of starch on the OMC/water interface and stimulation of the metabolism of attached bacteria.     

Femtosecond charge separation in dry films of reaction centers of <Emphasis Type="Italic">Rhodobacter sphaeroides</Emphasis> and <Emphasis Type="Italic">Chloroflexus aurantiacus</Emphasis>

In this work, the influence of the crystallographic water on electron transfer between primary donor P and acceptor B_A was studied in reaction centers (RCs) of the purple bacterium Rhodobacter sphaeroides and the green bacterium Chloroflexus aurantiacus. For this purpose, time constants and oscillations of charge separation kinetics are compared between dry film RCs and RCs in glycerol-water buffer at 90 K. A common result of the drying of Rba. sphaeroides and Cfx. aurantiacus RCs is slowing of the charge separation process, decrease in amplitude of the oscillatory components of the kinetics, and the depletion of its spectrum. Thus, the major time constant of stimulated emission decay of P* bacteriochlorophyll dimer at 940 nm is increased from 1.1 psec for water-containing Rba. sphaeroides RCs to 1.9 psec for dry films of Rba. sphaeroides RCs. An analogous increase from 3.5 to 4.2 psec takes place in Cfx. aurantiacus RCs. In dry films of Rba. sphaeroides RCs, the amplitude of coherent oscillations of the absorption band of monomeric bacteriochlorophyll B_A⁻ at 1020 nm is 1.8 times less for the 130-cm⁻¹ component and 2.3 times less for the 32-cm⁻¹ component than the analogous amplitudes for water-containing RCs. Measurements in the analogous band of Cfx. aurantiacus RCs show that strong decrease (∼5-10 times) of the B_A⁻ absorption band and strong slowing (from ∼0.8 to ∼3 psec) of B_A⁻ accumulation together with ∼3-fold decrease in oscillation amplitude occurs on drying of these RCs. The overtones of the 32-cm⁻¹ component disappeared from the oscillations of the kinetics at 940 and 1020–1028 nm after drying of the Rba. sphaeroides and Cfx. aurantiacus RCs. The results are in agreement with the results for GM203L mutant of Rba. sphaeroides, in which the HOH55 water molecule is sterically removed, and with the results for dry films of pheophytin-modified RCs of Rba. sphaeroides R-26 and for YM210W and YM210L Rba. sphaeroides mutant RCs. The data are discussed in terms of the influence (or participation) of the HOH55 water molecule on electron transfer along the chain of polar atomic groups N-Mg(P_B)-N-C-N(HisM202)-HOH55-O=(B_A) connecting P_B and B_A in Rba. sphaeroides RCs.     

B-branch electron transfer in reaction centers of Rhodobacter sphaeroides assessed with site-directed mutagenesis

Mutants of Rhodobacter (Rba.) sphaeroides are described which were designed to study electron transfer along the so-called B-branch of reaction center (RC) cofactors. Combining the mutation L(M214)H, which results in the incorporation of a bacteriochlorophyll, β, for H_A [Kirmaier et al. (1991) Science 251: 922–927] with two mutations, G(M203)D and Y(M210)W, near B_A, we have created a double and a triple mutant with long lifetimes of the excited state P^* of the primary donor P, viz. 80 and 160 ps at room temperature, respectively. The yield of P⁺Q_A ⁻ formation in these mutants is reduced to 50 and 30%, respectively, of that in wildtype RCs. For both mutants, the quantum yield of P⁺H_B ⁻ formation was less than 10%, in contrast to the 15% B-branch electron transfer demonstrated in RCs of a similar mutant of Rba. capsulatus with a P^* lifetime of 15 ps [Heller et al. (1995) Science 269: 940–945]. We conclude that the lifetime of P^* is not a governing factor in switching to B-branch electron transfer. The direct photoreduction of the secondary quinone, Q_B, was studied with a triple mutant combining the G(M203)D, L(M214)H and A(M260)W mutations. In this triple mutant Q_A does not bind to the reaction center [Ridge et al. (1999) Photosynth Res 59: 9–26]. It is shown that B-branch electron transfer leading to P⁺Q_B ⁻ formation occurs to a minor extent at both room temperature and at cryogenic temperatures (about 3% following a saturating laser flash at 20 K). In contrast, in wildtype RCs P⁺Q_B ⁻ formation involves the A-branch and does not occur at all at cryogenic temperatures. Attempts to accumulate the P⁺Q_B ⁻ state under continuous illumination were not successful. Charge recombination of P⁺Q_B ⁻ formed by B-branch electron transfer in the new mutant is much faster (seconds) than has been previously reported for charge recombination of P⁺Q_B ⁻ trapped in wildtype RCs (10⁵ s) [Kleinfeld et al. (1984b) Biochemistry 23: 5780–5786]. This difference is discussed in light of the different binding sites for Q_B and Q_B ⁻ that recently have been found by X-ray crystallography at cryogenic temperatures [Stowell et al. (1997) Science 276: 812–816]. We present the first low-temperature absorption difference spectrum due to P⁺Q_B ⁻. This revised version was published online in June 2006 with corrections to the Cover Date.