180 Effects of Forage Mixtures on Rumen Fermentation Parameters as Assessed by Continuous Culture

The impact of using diverse forage mixtures on rumen performance is poorly characterized. The objective of this study was to evaluate the impact of feeding diverse pastures on rumen performance using in vitro continuous culture fermenters. Treatments were assessed using a 4 x 4 Latin square design. Each 10-d period included 7-d of adaption followed by 3-d of sample collection. Dietary treatments (DM basis) included 1) 50% orchardgrass + 50% alfalfa (OG-ALF); 2) 50% OG-ALF + 50% red clover (RC); 3) 50% OG-ALF + 50% pearl millet (MIL); and 4) 50% OG-ALF + 50% sorghum x sudangrass (SUD). Forage diets (131 g DM/ fermenter/ d) were divided into 4 portions/d (33%, 0600 h; 17%, 0720 h; 33%,1800 h; 17%, 1920 h). Fermenter pH measurements were collected every min for the entire experiment. Methane concentrations were measured using a gas probe and recorded twice daily (0530 h,1730 h) in triplicate on d 7, 8, 9, and 10. Daily total effluent samples were collected on d 8, 9, and 10 for VFA analysis. Results were analyzed using PROC MIXED of SAS. There were no differences in total VFA concentrations (P = 0.08), molar proportions (P = 0.22), or individual VFA ratios (P > 0.05) as a result of treatment. Fermenter pH did not differ between fermenters as a result of treatment (P > 0.05). Fermenters receiving OG-ALF had the greatest methane concentration (50.8 mg/dL), which was higher (P < 0.05) than methane concentrations in fermenters receiving MIL (6.2 mg/dL), SUD (6.9 mg/dL), or RC (21.2 mg/dL). Methane concentrations from the MIL, SUD and RC treatments did not differ (P > 0.05). This indicates that binary forage mixtures may have lower nutritional value compared with diverse mixtures, and this diversification could provide nutritional benefits.

Modeling of Continuous PHA Production by a Hybrid Approach Based on First Principles and Machine Learning

Polyhydroxyalkanoates (PHA) are renewable alternatives to traditional oil-derived polymers. PHA can be produced by different microorganisms in continuous culture under specific media composition, which makes the production process both promising and challenging. In order to achieve large productivities while maintaining high yield and efficiency, the continuous culture needs to be operated in the so-called dual nutrient limitation condition, where both the nitrogen and carbon sources are kept at very low concentrations. Mathematical models can greatly assist both design and operation of the bioprocess, but are challenged by the complexity of the system, in particular by the dual nutrient-limited growth phenomenon, where the cells undergo a metabolic shift that abruptly changes their behavior. Traditional, non-structured mechanistic models based on Monod uptake kinetics can be used to describe the bioreactor operation under specific process conditions. However, in the absence of a model description of the metabolic phenomena inside the cell, the extrapolation to a broader operation domain (e.g., different feeding concentrations and dilution rates) may present mismatches between the predictions and the actual process outcomes. Such detailed models may require almost perfect knowledge of the cell metabolism and omic-level measurements, hampering their development. On the other hand, purely data-driven models that learn correlations from experimental data do not require any prior knowledge of the process and are therefore unbiased and flexible. However, many more data are required for their development and their extrapolation ability is limited to conditions that are similar to the ones used for training. An attractive alternative is the combination of the extrapolation power of first principles knowledge with the flexibility of machine learning methods. This approach results in a hybrid model for the growth and uptake rates that can be used to predict the dynamic operation of the bioreactor. Here we develop a hybrid model to describe the continuous production of PHA by Pseudomonas putida GPo1 culture. After training, the model with experimental data gained under different dilution rates and medium compositions, we demonstrate how the model can describe the process in a wide range of operating conditions, including both single and dual nutrient-limited growth.

Recovery Responses of Freshwater Phytoplankton Assemblage After the Disappearance of Metal Toxicity in Semi-Continuous Cultures

The present study demonstrates the recovery of phytoplankton assemblage from metal stress. Phytoplankton assemblage consisting of different freshwater algal species isolated from a tropical pond was exposed to sublethal concentrations of Cu and Zn for 25 days in semi-continuous culture (Toxicity phase). Subsequently, algal assemblage grown in the toxicity phase were transferred to the fresh culture medium without elevated levels of the test metals for 25 days in semi-continuous culture (Recovery phase). We monitored the total biovolume of each algal species during the toxicity and recovery phases. The members of Cyanophyta were most sensitive against metal toxicity, followed by the members of Bascillariophyta. However, the members of Chlorophyta showed relatively lesser sensitivity against test metals. Among chlorophytes, Scendesmus opolinensis and Cosmarium bioculatum were tolerant to both the test metals. Metal-stressed algal species showed recovery after transferring to the basal medium depending on the concentration of metals during the toxicity phase. The members of Cyanophyta were unable to recover from metal stress. However, members of Chlorophyta showed faster recovery than others from Zn stress, and the members of Bascillariophyta showed quicker recovery from Cu stress. The differential abilities of various algal species to recover from metal stress perhaps depend on their ability to counterbalance metal toxicity. Further, research is warranted to characterize the differential ability of various algal groups to recover from metal stress. The present findings would help understand the efficiency of different algal groups to restore their position within the freshwater algal community after the disappearance for metal stress.

Recovery Responses of Freshwater Phytoplankton Assemblage After the Disappearance of Metal Toxicity in Semi-Continuous Cultures

The present study demonstrates the recovery of phytoplankton assemblage from metal stress. Phytoplankton assemblage consisting of different freshwater algal species isolated from a tropical pond was exposed to sublethal concentrations of Cu and Zn for 25 days in semi-continuous culture (Toxicity phase). Subsequently, algal assemblage grown in the toxicity phase were transferred to the fresh culture medium without elevated levels of the test metals for 25 days in semi-continuous culture (Recovery phase). We monitored the total biovolume of each algal species during the toxicity and recovery phases. The members of Cyanophyta were most sensitive against metal toxicity, followed by the members of Bascillariophyta. However, the members of Chlorophyta showed relatively lesser sensitivity against test metals. Among chlorophytes, Scendesmus opolinensis and Cosmarium bioculatum were tolerant to both the test metals. Metal-stressed algal species showed recovery after transferring to the basal medium depending on the concentration of metals during the toxicity phase. The members of Cyanophyta were unable to recover from metal stress. However, members of Chlorophyta showed faster recovery than others from Zn stress, and the members of Bascillariophyta showed quicker recovery from Cu stress. The differential abilities of various algal species to recover from metal stress perhaps depend on their ability to counterbalance metal toxicity. Further, research is warranted to characterize the differential ability of various algal groups to recover from metal stress. The present findings would help understand the efficiency of different algal groups to restore their position within the freshwater algal community after the disappearance for metal stress.