Saturating growth rate against phosphorus concentration explained by macromolecular allocation.

IMPORTANCE: The Monod equation has been used to represent the relationship between growth rate and the environmental nutrient concentration under the limitation of this respective nutrient. This model often serves as a means to connect microorganisms to their environment, specifically in ecosystem and global models. Here, we use a simple model of a marine microorganism cell to illustrate the model's ability to capture the same relationship as Monod, while highlighting the additional physiological details our model provides. In this study, we focus on the relationship between growth rate and phosphorus concentration and find that RNA allocation largely contributes to the commonly observed trend. This work emphasizes the potential role our model could play in connecting microorganisms to the surrounding environment while using realistic physiological representations.

Schindler's legacy: from eutrophic lakes to the phosphorus utilization strategies of cyanobacteria.

David Schindler and his colleagues pioneered studies in the 1970s on the role of phosphorus in stimulating cyanobacterial blooms in North American lakes. Our understanding of the nuances of phosphorus utilization by cyanobacteria has evolved since that time. We review the phosphorus utilization strategies used by cyanobacteria, such as use of organic forms, alternation between passive and active uptake, and luxury storage. While many aspects of physiological responses to phosphorus of cyanobacteria have been measured, our understanding of the critical processes that drive species diversity, adaptation and competition remains limited. We identify persistent critical knowledge gaps, particularly on the adaptation of cyanobacteria to low nutrient concentrations. We propose that traditional discipline-specific studies be adapted and expanded to encompass innovative new methodologies and take advantage of interdisciplinary opportunities among physiologists, molecular biologists, and modellers, to advance our understanding and prediction of toxic cyanobacteria, and ultimately to mitigate the occurrence of blooms.

Biological treatment of volatile organic compounds (VOCs)-containing wastewaters from wet scrubbers in semiconductor industry.

This study investigated biological treatment for two kinds of volatile organic compounds (VOCs)-containing wastewaters collected from wet scrubbers in a semiconductor industry. Batch test results indicated that one wastewater containing highly volatile organic compounds was not suitable for aerated treatment conditions while the other containing much lower volatile organic compounds was suitable for aerobic treatment. Accordingly, two moving bed bioreactors, by adding commercial biocarrier BioNET, were operated under aerobic and anoxic conditions for treating low volatility wastewater (LVW) and high volatility wastewater (HVW), respectively. During 280 days of operation, the aerobic LVW bioreactor attained the highest chemical oxygen demand (COD) removal rate of 98.9 mg-COD/L/h with 81% of COD removal efficiency at hydraulic retention time (HRT) of 1 day. The anoxic HVW bioreactor performed above 80% of COD removal efficiency with the highest COD removal rate of 16.5 mg-COD/L/h at HRT of 2 days after 380 days of operation. The specific COD removal rates at different initial substrate-to-biomass (S0/X0) ratios, using either suspended sludge or microorganisms attached onto BioNET from both bioreactors, followed the Monod-type kinetics, while the half-saturation coefficients were generally higher for the microorganisms onto BioNET due presumably to relatively poor mass transfer efficiency. Based on the results of microbial community analysis using the next generation sequencing technique, the dominant communities of suspended sludge and BioNET, including nitrifiers, denitrifiers, and degraders for polycyclic aromatic hydrocarbons, were similar in the corresponded bioreactors, but microbial community shifts were observed with increased organic loadings.

Respirometry as a tool to quantify kinetic parameters of microalgal mixotrophic growth.

Modeling microalgal mixotrophy is challenging, as the regulation of algal metabolism is affected by many environmental factors. A reliable tool to simulate microalgal behavior in complex systems, such as wastewaters, may help in setting the proper values of operative variables, provided that model parameters have been properly evaluated. In this work, a new respirometric protocol is proposed to quickly obtain the half-saturation constant values for several nutrients. The protocol was first verified for autotrophic exploitation of ammonium and phosphorus (Monod kinetics), as well as of light intensity (Haldane model), further elaborated on specific light supply basis. It was then applied to measure the kinetic parameters of heterotrophic growth. The half-saturation constants for nitrogen and phosphorus resulted comparable with autotrophic ones. The dependence on acetate and dissolved oxygen concentration was assessed. Mixotrophy was modeled as the combination of autotrophic/heterotrophic reactions, implemented in AQUASIM, and validated on batch curves with/without bubbling, under nutrient limitation, and different light intensities. It was shown that the reliability of the proposed respirometric protocol is useful to measure kinetic parameters for nutrients, and therefore to perform bioprocess simulation.

Combination of Logistic and modified Monod functions to study Microcystis aeruginosa growth stimulated by fish feed.

The ecological health of aquaculture water is threatened by wasted fish feed and herbicides. In order to study the effect of prometryn and fish feed on Microcystis aeruginosa growth based on Monod and Logistic functions, four different concentrations of prometryn (0, 50, 100 and 200 µg L-1) and two different dosages of fish feed (0.075 g, 0.15 g; d < 0.85 mm) were added into the culture medium, and the fish feed was the source of nitrogen and phosphorus in the MII medium. Results showed that Microcystis aeruginosa growth can be fitted well by Logistic and modified Logistic functions with 0-200 µg L-1 prometryn (R2 = 0.981-0.998 and R2 = 0.989-0.999, respectively). With the same concentration of prometryn, the maximum algae density (Nmax) of Microcystis aeruginosa calculated by both Logistic and modified Logistic functions increased with increasing dosage of fish feed and with the same dosage of fish feed, Nmax declined with increasing concentrations of prometryn. Inhibition of prometryn on algae growth stimulated by fish feed is of double concentration-dependence, inhibition rates (I) are lower in 0.15 g fish feed medium than 0.75 g ones generally, implying that more nutrients can alleviate the stress caused by prometryn on algae. Derived formula for the specific growth rate, growth rate and inhibition rate using modified Logistic function agreed reasonably well with measured data. Jointly application of modified Monod and Logistic functions can better describe the relationship between specific growth rates and nutrients concentrations compared to combination of Monod and Logistic functions. In addition, equations for describing variations of nutrients concentrations (PO43--P and NH4+-N) with time were also derived based on both modified Monod and Logistic functions, which agree reasonably well with the measured data. In sum, the combination of modified Monod and Logistic functions provides a promising and robust method in studying algal growth stimulated by fish feed in incubator experiments.

The mechanistic-holistic divide revisited: The case of the lac operon.

In this paper, I revisit the development of the repression model of genetic regulation in the lac operon to challenge a common application of a conceptual framework in the history of biology. I take Allen's (1978) account of the changes in the life sciences during the early and mid-twentieth century as an example of a common application of a framework based on the dichotomy between a mechanistic, or reductionist, approach to science and a holistic one. From this conceptual framework, Allen infers two general claims about the process of science and its goals: (1) that "mechanistic materialism" has often presented a more practical way to begin the study of complex phenomena in the life sciences, and (2) that the approach described as "holistic materialism" provides a more complete or accurate description of the natural world. The development of the lac operon model does not fit Allen's generalizations about scientific developments, and it can be used to cast some doubt on the scope of application of that conceptual framework. I argue that a better framework to interpret particular episodes in the history of molecular biology is to consider the ways in which biologists prioritize and track different aspects of the phenomena under study, rather than to focus on whether certain scientific practices are best described as developing from mechanistic to more holistic approaches. I end with some implications for the historiography of science by considering the appropriateness of different conceptual frameworks for different grains of resolution in the history of biology.