Photoautotrophic nutrient utilization and limitation during semi‐continuous growth of Synechocystis sp. PCC6803

Microbial photosynthesis presents a valuable opportunity to capture abundant light energy to produce renewable bioenergy and biomaterials. To understand the factors that control the productivity of photosynthetic microorganisms, we conducted a series of semi‐continuous experiments using bench‐scale photobioreactor (PBR) systems, the cyanobacterium Synechocystis PCC6803 (PCC6803), and light conditions imitating actual day–night light irradiance (LI). Our results demonstrate that using normal BG‐11 medium resulted in severe phosphate (P_i) limitation for continuous operation. Mitigation of P_i‐limitation, by augmenting the P_i content of BG‐11, allowed higher biomass productivity; however, once P_i‐limitation was alleviated, limitation by inorganic carbon (C_i) or LI occurred. C_i‐limitation was detected by a low total C_i concentration (<5 mg C/L) and high and fluctuating pH. C_i‐limitation was relieved by delivering more CO₂, which led to a stable pH in the range of 7–9 and at least 5 mg/L of C_i in HCO. LI limitation, evidenced by an average LI <14 W/m² for PCC6803, was induced by a high biomass concentration of 1,300 mg/L. Thus, this work provides quantitative tools of stoichiometry and kinetics to evaluate limitation on PBRs. Biotechnol. Bioeng. 2010;106: 553–563. © 2010 Wiley Periodicals, Inc.     

Food limitation of planktonic rotifers: field experiments in two mountain ponds

1. Resource competition is thought to be important in controlling zooplankton population dynamics and structuring zooplankton communities. Resource competition requires that resources are limiting. Ten field experiments were conducted to determine the presence and intensity of resource limitation of herbivorous planktonic rotifers in two mountain ponds. The intensity of food limitation was measured as Δ r , the difference between population growth rates in food supplemented versus control enclosures.
2. Rotifers were significantly food limited (Δ r  > 0) in most experiments. The intensity of food limitation varied between species. In Grady Lake, mean Δ r was 0.26 day⁻¹ for Polyarthra vulgaris and 0.43 day⁻¹ for an unidentified Synchaeta sp. In L1 Pond, mean Δ r was 0.07 day⁻¹ for Keratella cochlearis and 0.28 day⁻¹ for S. oblonga . The frequent and intense food limitation suggests that edible phytoplankton in both ponds were often present at low densities, were of low nutritional quality, or both. The intensity of food limitation often changed rapidly over time, indicating rapid temporal variation in resource availability.
3. For P. vulgaris , Δ r was not correlated with its population growth rate in Grady Lake. Thus, although food limitation was common, population dynamics may have been more strongly affected by other factors. For K. cochlearis , Δ r increased as population density increased, suggesting the existence of intraspecific resource competition that may regulate population dynamics.     

Assessing density dependence in the transmission of lymphatic filariasis: uptake and development of Wuchereria bancrofti microfilariae in the vector mosquitoes

Understanding density dependence in the transmission of lymphatic filariasis is essential for assessing the prospects of elimination. This study seeks to quantify the relationship between microfilaria (Mf) density in human blood and the number of third stage (L3) larvae developing in the mosquito vectors Aedes polynesiensis Marks and Culex quinquefasciatus Say (Diptera: Culicidae) after blood-feeding. Two types of curves are fitted to previously published data. Fitting a linearized power curve through the data allows for correction for measurement error in human Mf counts. Ignoring measurement error leads to overestimation of the strength of density dependence; the degree of overestimation depends on the accuracy of measurement of Mf density. For use in mathematical models of transmission of lymphatic filariasis, a hyperbolic saturating function is preferable. This curve explicitly estimates the Mf uptake and development at lowest Mf densities and the average maximum number of L3 that can develop in mosquitoes. This maximum was estimated at 23 and 4 for Ae. polynesiensis and Cx. quinquefasciatus, respectively.     

Production of poly(3-hydroxybutyrate) from inexpensive substrates

Two inexpensive substrates, starch and whey were used to produce poly(3-hydroxybutyrate) (PHB) in fed-batch cultures of Azotobacter chroococcum and recombinant Escherichia coli, respectively. Oxygen limitation increased PHB contents in both fermentations. In fed-batch culture of A. chroococcum, cell concentration of 54 g l⁻¹ with 46% PHB was obtained with oxygen limitation, whereas 71 g l⁻¹ of cell with 20% PHB was obtained without oxygen limitation. The timing of PHB biosynthesis in recombinant E. coli was controlled using the agitation speed of a stirred tank fermentor. A PHB content of 80% could be obtained with oxygen limitation by increasing the agitation speed up to only 500 rpm.     

COENOBIAL CELL NUMBER IN SCENEDESMUS QUADRICAUDA (CHLOROPHYCEAE) AS A FUNCTION OF GROWTH RATE IN NITRATE-LIMITED CHEMOSTATS1

The relative numbers of cells growing as coenobia of different cell number are functions of growth rate when Scenedesmus quadricauda (Turp.) Bréb. is grown axenically in nitrate-limited, steady-state chemostats in continuous light. Unicells decreased from a maximum fraction of 0.04–0.05 of the total number of cells at 0.1 day^?1 to 0.01 or less as growth rate increased. The fraction of cells that grew as two-celled coenobia decreased from about 0.2 to 0.01–0.02. The fraction that grew as 4-celled coenobia increased from about 0.7–0.8 at 0.1 day^?1 to near unity at 0.5–0.6 day^?1, and then decreased sharply. The fraction of 8-celled coenobial cells increased from very small values below 0.6 day^?1, to ca. 0.9 at 1.0 day^?1.     

Retention of Sediments and Nutrients in the Iron Gate I Reservoir on the Danube River

This work addresses an intensively debated question in biogeochemical research: “Are large dams affecting global nutrient cycles?” It has been postulated that the largest impoundments on the Lower Danube River, the Iron Gates Reservoirs, act as a major sink for silica (Si) in the form of settling diatoms, for phosphorus (P) and to a lesser extent for nitrogen (N). This retention of P and N in the reservoir would represent a positive contribution to the nutrient reduction in the Danube River. Based on a 9-month monitoring scheme in 2001, we quantified the nutrient and the sediment retention capacity of the Iron Gate I Reservoir. The sediment accumulation corresponded to 5% TN (total nitrogen), 12% TP (total phosphorus) and 55% TSS (total suspended solids) of the incoming loading. A mass balance revealed that more N and P are leaving the reservoir than entering via the inflow. Based on these current results, the reservoir was temporarily acting as a small nutrient source. The nutrient accumulation in the sediments of the Iron Gate I Reservoir represents only 1% of the “missing” load of 10⁶ t N and 1.3 × 10⁵ t P defined as the difference between the estimated nutrient export from the Danube Basin and the measured flux entering the Black Sea. This result disproves the hypothesis that the largest impoundment on the Danube River, the Iron Gates Reservoir, plays a major role in N and P elimination.     

Effects of fire recurrence in Quercus coccifera L. shrublands of the Valencia Region (Spain): II. plant and soil nutrients

The consequences of fire recurrence (1, 2 and 3 fires in 16 years) on plant and soil C, N, P and K from Quercus coccifera garrigues were analysed in the Valencia Region (E Spain). Plant and forest floor (L horizon) nutrient concentrations either changed weakly or showed no change with fire recurrence. At the soil surface (0-2.5 cm), soil potential mineralisable nitrogen increased and available P decreased after an initial increase, whereas exchangeable K was not affected by successive fires. However, the significance of those observed trends for N and P was site-dependent. Despite the rapid formation of the L soil horizon, fire recurrence did not permit the development of the whole forest floor profile observed in the unburned garrigues. These organic layers contained a great proportion of the total nutrient pool, especially for N. Forest-floor and aboveground plant combustion by fire may produce significant losses of N and P compared with those available in mineral soil, whereas soil exchangeable K is large enough to replace these losses. Belowground nutrient reserves may account for the quick recovery of the Quercus coccifera aboveground biomass although successive fires could deplete these reserves and produce a loss of biomass and productivity in this species.     

Changes in nutrient use efficiency, status and retranslocation in young post-fire regeneration Pinus halepensis in response to sudden N and P input, irrigation and removal of competing vegetation

The capacity of Mediterranean species to adapt to variable nutrient supply levels in a global change context can be a key factor to predict their future capacity to compete and survive in this new scenario. We aimed to investigate the capacity of a typical Mediterranean tree species, Pinus halepensis, to respond to sudden changes in N and P supply in different environmental conditions. We conducted a fertilisation, irrigation and removal of competing vegetation experiment in a calcareous post-fire shrubland with an homogeneous young (5 years old) population of P. halepensis in order to investigate the retranslocation and nutrient status for the principal nutrients (N, P, Mg, K, S, Ca and Fe), and the nutrient use efficiency (NUE) of the most important nutrients linked to photosynthetic capacity (N, P, Mg and K). P fertilisation increased P concentration in needles, P, N, Mg and K retranslocations, and NUE calculated as biomass production per unit of nutrient lost in the litterfall. The P fertilisation was able to increase the aboveground biomasses and P concentration 3 years after P fertiliser application. Those responses to P fertilisation were enhanced by the removal of competing vegetation. The N needle and litterfall concentration decreased after P fertilisation and this effect was greater when the P fertilisation was accompanied by removal of competing vegetation. The increase of P availability decreased the P-NUE and increased the N-NUE when these variables were calculated as aboveground biomass production per unit of P present in the biomass. Both P-NUE and N-NUE increased when calculated as total aboveground production per unit of nutrient loss. The results show that it is necessary to calculate NUE on a different basis to have a wider understanding of nutrient use. The irrigation did not change the needle nutrient concentrations and the litterfall production, but it significantly changed the nutrient litterfall concentrations and total aboveground contents (especially P and K). These results show a high capacity of P. halepensis to quickly respond to a limiting nutrient such as P in the critical phases of post-fire regeneration. The increase in P availability had a positive effect on growth and P concentrations and contents in aboveground biomass, thus increasing the capacity of growth in future periods and avoiding immediate runoff losses and leachate. This capacity also strongly depends on neighbour competition.