Lower Specific Growth Rate Research Articles

Dietary DHA/EPA ratio affects growth, tissue fatty acid profiles and expression of genes involved in lipid metabolism in mud crab Scylla paramamosain supplied with appropriate n-3 LC-PUFA at two lipid levels

An 8-week feeding trial was conducted to determine the optimal dietary docosahexaenoic acid/eisosapentaenoic acid (DHA/EPA) ratio of mud crab (Scylla paramamosain) supplied with optimal n-3 LC-PUFA at two dietary lipid levels. Eight isonitrogenous diets were formulated to contain 7% and 12% crude lipid, each with DHA/EPA ratios of 0.6, 1.2, 2.3 and 3.2, respectively. Each diet was randomly assigned to triplicate groups of 30 juvenile mud crabs (initial weight 20.9 ± 0.6 g) that were stocked in single crab cells. In crabs fed 7% lipid, the diet with a DHA/EPA ratio of 2.3 showed significantly higher weight gain than crabs fed the other ratios while in crabs fed 12% lipid, lower weight gain and specific growth rate were observed in crabs fed the diet with a DHA/EPA ratio of 0.6 than crabs fed the other ratios. Lipid content in hepatopancreas significantly increased as dietary DHA/EPA ratio increased from 1.2 to 2.3 in crabs fed 7% lipid, while no differences were observed among crabs fed the diets with DHA/EPA ratios higher than 0.6 when fed 12% lipid. Total fatty acid and DHA contents and DHA/EPA ratio showed increasing, and EPA decreasing, trends in muscle and hepatopancreas with increased dietary DHA/EPA ratio, at both dietary lipid levels. The hemolymph triacylglycerol and total cholesterol contents were higher in crabs fed dietary DHA/PA ratios of 1.2 and 2.3 than those fed ratios of 0.6 and 3.2 at 7% dietary lipid, and lowest low and high-density lipoprotein cholesterol contents were observed in crabs fed DHA/EPA dietary ratios of 0.6 and 3.2 at 7% and 12% lipid, respectively. The expression levels of fas, aco3 and fatp4 were significantly up-regulated, and cptI, hsl and ldlr were down-regulated, with increased dietary DHA/EPA ratio in crabs fed 7% lipid. In crabs fed 12% lipid, the expression levels of g6pd, 6pgd, srebp-1, aco1 and fatp4 were down-regulated, and fabp-1 was up-regulated, with increased dietary DHA/EPA ratio. The expression levels of elovl4 and Δ6 fad initially increased and then decreased as dietary DHA/EPA ratio increased from 0.6 to 3.2 in crabs fed both 7% and 12% lipid. Based on analysis of weight gain versus dietary DHA/EPA ratio, the optimal dietary DHA/EPA ratios of mud crab S. paramamosa were estimated to be 2.2 and 1.2 when supplied with optimal n-3 LC-PUFA at 7% and 12% lipid, respectively.

Growth kinetics of Staphylococcus aureus and background microorganisms in camel milk

Staphylococcus aureus is a common foodborne pathogen that is ubiquitous in nature. Consumption of contaminated foods, such as dairy products, can lead to food poisoning caused by heat-stable staphylococcal toxins that are not easily destroyed during pasteurization. The objective of this study was to investigate the growth kinetics of S. aureus and background microorganisms in camel milk stored at different temperatures between 8 and 43°C using one-step kinetic analysis to estimate the kinetic parameters from the observed growth curves. The growth of S. aureus showed apparent lag, exponential, and stationary phases, whereas no or negligible lag phase was observed for background microorganisms. Data analysis showed that the estimated minimum, optimum, and maximum growth temperatures were 5.9, 42.0, and 49.2°C for S. aureus, and 3.0, 38.6, and 49.2°C for the background microorganisms, respectively. The estimated optimum specific growth rate was higher for S. aureus (1.24 h-1) than for background microorganisms (0.995 h-1). This study found that camel milk may inhibit the growth of S. aureus, as it exhibits a lower specific growth rate than that in cow milk or cooked potato. It also has a longer lag phase than that in cow milk at comparable temperature ranges. This unique property is probably related to the presence of some antimicrobial compounds naturally occurring in camel milk. Validation of kinetic parameters and models showed that the root mean square error of prediction was only 0.5 log cfu/mL for S. aureus and background microorganisms, suggesting that the models are reasonably accurate. These models can be used for conducting risk assessments of S. aureus and predicting the general microbiological shelf life of camel milk to prevent foodborne staphylococcal poisoning.

Squalene-Tetrahymanol Cyclase Expression Enables Sterol-Independent Growth of Saccharomyces cerevisiae.

Biosynthesis of sterols, which are considered essential components of virtually all eukaryotic membranes, requires molecular oxygen. Anaerobic growth of the yeast Saccharomyces cerevisiae therefore strictly depends on sterol supplementation of synthetic growth media. Neocallimastigomycota are a group of strictly anaerobic fungi which, instead of containing sterols, contain the pentacyclic triterpenoid "sterol surrogate" tetrahymanol, which is formed by cyclization of squalene. Here, we demonstrate that expression of the squalene-tetrahymanol cyclase gene TtTHC1 from the ciliate Tetrahymena thermophila enables synthesis of tetrahymanol by S. cerevisiae Moreover, expression of TtTHC1 enabled exponential growth of anaerobic S. cerevisiae cultures in sterol-free synthetic media. After deletion of the ERG1 gene from a TtTHC1-expressing S. cerevisiae strain, native sterol synthesis was abolished and sustained sterol-free growth was demonstrated under anaerobic as well as aerobic conditions. Anaerobic cultures of TtTHC1-expressing S. cerevisiae on sterol-free medium showed lower specific growth rates and biomass yields than ergosterol-supplemented cultures, while their ethanol yield was higher. This study demonstrated that acquisition of a functional squalene-tetrahymanol cyclase gene offers an immediate growth advantage to S. cerevisiae under anaerobic, sterol-limited conditions and provides the basis for a metabolic engineering strategy to eliminate the oxygen requirements associated with sterol synthesis in yeasts.IMPORTANCE The laboratory experiments described in this report simulate a proposed horizontal gene transfer event during the evolution of strictly anaerobic fungi. The demonstration that expression of a single heterologous gene sufficed to eliminate anaerobic sterol requirements in the model eukaryote Saccharomyces cerevisiae therefore contributes to our understanding of how sterol-independent eukaryotes evolved in anoxic environments. This report provides a proof of principle for a metabolic engineering strategy to eliminate sterol requirements in yeast strains that are applied in large-scale anaerobic industrial processes. The sterol-independent yeast strains described in this report provide a valuable platform for further studies on the physiological roles and impacts of sterols and sterol surrogates in eukaryotic cells.

Development of a dual specific growth rate-based fed-batch process for production of recombinant human granulocyte colony-stimulating factor in Pichia pastoris.

A number of limitations exist for production of human granulocyte colony-stimulating factor (G-CSF) in Pichia pastoris. In this study, two different specific growth rates (0.015h-1, 0.01h-1) were used sequentially in the mixed substrate feeding period during methanol induction phase to enhance the G-CSF titer in the culture broth. Necessary parameters required for implementing the feeding strategy, such as specific product yield on biomass (YP/X) and maintenance coefficient (m) on glycerol, methanol, and sorbitol were estimated using continuous culture technique. Using this strategy, for the same volumetric productivity, about 20% increase in protein titer was achieved over that obtained from the run carried out at a single pre-set value of 0.015h-1 alone. Thus, implementation of higher specific growth rate (0.015h-1) set during initial stages of the methanolinductionphase followed by a lower specific growth rate (0.01h-1) helped in achieving increased protein titers.

Contribution of Complex I NADH Dehydrogenase to Respiratory Energy Coupling in Glucose-Grown Cultures of Ogataea parapolymorpha

The thermotolerant yeast Ogataea parapolymorpha (formerly Hansenula polymorpha) is an industrially relevant production host that exhibits a fully respiratory sugar metabolism in aerobic batch cultures. NADH-derived electrons can enter its mitochondrial respiratory chain either via a proton-translocating complex I NADH-dehydrogenase or via three putative alternative NADH dehydrogenases. This respiratory entry point affects the amount of ATP produced per NADH/O2 consumed and therefore impacts the maximum yield of biomass and/or cellular products from a given amount of substrate. To investigate the physiological importance of complex I, a wild-type O. parapolymorpha strain and a congenic complex I-deficient mutant were grown on glucose in aerobic batch, chemostat, and retentostat cultures in bioreactors. In batch cultures, the two strains exhibited a fully respiratory metabolism and showed the same growth rates and biomass yields, indicating that, under these conditions, the contribution of NADH oxidation via complex I was negligible. Both strains also exhibited a respiratory metabolism in glucose-limited chemostat cultures, but the complex I-deficient mutant showed considerably reduced biomass yields on substrate and oxygen, consistent with a lower efficiency of respiratory energy coupling. In glucose-limited retentostat cultures at specific growth rates down to ∼0.001 h-1, both O. parapolymorpha strains showed high viability. Maintenance energy requirements at these extremely low growth rates were approximately 3-fold lower than estimated from faster-growing chemostat cultures, indicating a stringent-response-like behavior. Quantitative transcriptome and proteome analyses indicated condition-dependent expression patterns of complex I subunits and of alternative NADH dehydrogenases that were consistent with physiological observations.IMPORTANCE Since popular microbial cell factories have typically not been selected for efficient respiratory energy coupling, their ATP yields from sugar catabolism are often suboptimal. In aerobic industrial processes, suboptimal energy coupling results in reduced product yields on sugar, increased process costs for oxygen transfer, and volumetric productivity limitations due to limitations in gas transfer and cooling. This study provides insights into the contribution of mechanisms of respiratory energy coupling in the yeast cell factory Ogataea parapolymorpha under different growth conditions and provides a basis for rational improvement of energy coupling in yeast cell factories. Analysis of energy metabolism of O. parapolymorpha at extremely low specific growth rates indicated that this yeast reduces its energy requirements for cellular maintenance under extreme energy limitation. Exploration of the mechanisms for this increased energetic efficiency may contribute to an optimization of the performance of industrial processes with slow-growing eukaryotic cell factories.

Effects of first feeding regime on growth performance, survival rate and development of digestive system in pikeperch (Sander lucioperca) larvae

This study evaluated the effects of first feeding regime on growth performance, survival rate, and development of digestive organs (intestine, liver and pancreas) in pikeperch (Sander lucioperca) larvae. The fish larvae at 5 days post-hatch (DPH), were initially fed with rotifers (Brachionus plicatilis) for 3 days and from 8 to 17 DPH were fed with rotifers/Artemia for different time periods as follows: (A) only rotifers; (B) 8–13 DPH rotifers/14–17 DPH Artemia; (C) 8–10 DPH rotifers/ 11–17 DPH Artemia; (D) only Artemia; (E) a combination of rotifers and Artemia. Growth performance, survival rate and histological features of intestine, liver and pancreas were assessed at 11, 14 and 17 DPH to examine the effects of feeding regime. The groups fed rotifers for initial 3 days followed by feeding on Artemia (group D) (53 ± 5.43%) and combination of rotifers and Artemia (group E) (68 ± 5.51%), respectively, for the following 9 days showed significantly (P < .05) higher survival rates than the other groups (36–50%). The group fed merely on rotifers (groups A) exhibited significantly lower specific growth rate (SGR) than the other groups, and the highest SGR was found in the group fed with combination of rotifers and Artemia after 3 day rotifer feeding. Moreover, the highest total length (8.57 ± 0.57 mm), myotome height (0.75 ± 0.09 mm) and eye diameter (0.58 ± 0.05 mm) were obtained by combined feeding of rotifers and Artemia after 3 day of initial rotifer feeding. Significant differences among groups were found in morphometric parameters in the anterior intestine and liver. The results of histological examination of the liver, intestine and pancreas did not show any obvious pathological changes in all groups. In conclusion, feeding with rotifers from 5 to 8 DPH and afterwards with Artemia could be suggested as an economical feeding regime for first feeding of pikeperch larvae as comparable survival and growth to co-feeding with rotifers and Artemia were achieved.

Replacement of rotifer with Artemia nauplii in clownfish larvae rearing (Amphiprion percula Lacepede, 1802)

This study was conducted to minimize the period of using rotifer in rearing percula clownfish larvae from newly hatched to 30 days. Artemia nauplii was used to replace rotifer when the larvae reached 5, 7, 9, 11 and 13 days after hatching (DAH). The results showed that larvae fed with Artemia nauplii starting from 7 DAH achieved the highest specific growth rate in standard length (4,02%/day). The later the starting point of weaning was, the lower the larval specific growth rate was. The lowest specific growth rate was at 13 DAH (3.21%/day; P &lt; 0.05). However, there were no significant differences in the specific growth rate among the weaning times at 5, 9 and 11 DAH (P &gt; 0.05). Similarly, the starting points of weaning times had no significant effects on larval survival rate, ranging from 39,6 - 48,2% (P &gt; 0.05). The results of this study helped reduce the period of using rotifer in rearing the clownfish larvae which contributes to the improvement of larval performance in artificial reproduction of this species.

Specific Growth Rate as a Predictor of Survival in Pancreatic Neuroendocrine Tumors: A Multi-institutional Study from the United States Neuroendocrine Study Group.

Pancreatic neuroendocrine tumors (PNETs) are often indolent; however, identifying patients at risk for rapidly progressing variants is critical, particularly for those with small tumors who may be candidates for expectant management. Specific growth rate (SGR) has been predictive of survival in other malignancies but has not been examined in PNETs. A retrospective cohort study of adult patients who underwent PNET resection from 2000 to 2016 was performed utilizing the multi-institutional United States Neuroendocrine Study Group database. Patients with ≥ 2 preoperative cross-sectional imaging studies at least 30days apart were included in our analysis (N = 288). Patients were grouped as "high SGR" or "low SGR." Demographic and clinical factors were compared between the groups. Kaplan-Meier and log-rank analysis were used for survival analysis. Cox proportional hazard analysis was used to assess the impact of various clinical factors on overall survival (OS). High SGR was associated with higher T stage at resection, shorter doubling time, and elevated HbA1c (all P ≤ 0.01). Patients with high SGR had significantly decreased 5-year OS (63vs 80%, P = 0.01) and disease-specific survival (72 vs 91%, P = 0.03) compared to those with low SGR. In patients with small (≤ 2cm) tumors (N = 106), high SGR predicted lower 5-year OS (79 vs 96%, P = 0.01). On multivariate analysis, high SGR was independently associated with worse OS (hazard ratio 2.67, 95% confidence interval 1.05-6.84, P = 0.04). High SGR is associated with worse survival in PNET patients. Evaluating PNET SGR may enhance clinical decision-making, particularly when weighing expectant management versus surgery in patients with small tumors.

Histologic examination and transcriptome analysis uncovered liver damage in largemouth bass from formulated diets

As a commercial carnassial fish, largemouth bass (Micropterus salmoides) consumes a large amount of forage fish as food annually. To reduce the use of forage fish, a formulated diet was utilized in a largemouth bass culture. Although they have been improved upon for 10 years, formulated diets still cannot meet the nutritional needs of largemouth bass. The formulated diet and forage fish were separately used to feed fish in an experimental group (FDG) and control group (FFG) to investigate the effects of a commercial formulated diet on the growth performance and liver histomorphology and transcriptomics of largemouth bass. After the 8-month feeding trial, fish fed the formulated diet exhibited a significantly lower weight gain rate (WGR) and specific growth rate (SGR) but a higher hepatosomatic index (HSI) and hepatocyte vacuolization score. A further transcriptomic difference analysis demonstrated all of the physiological changes in the process of liver injury caused by the formulated diet. Several key genes involved in the process of liver disease, including gk (glucokinase), pck (phosphoenolpyruvate carboxykinase), acetyl-CoA acetyltransferase cytosolic-like (acat cytosolic-like), type-2 ice-structuring protein (type-2 isp), tf (transferrin), col6a3 (collagen type VI alpha 3), and TBT-bp (tributyltin-binding protein), showed significant differences in their expression patterns between the two diet groups. KEGG analysis showed that the differentially expressed genes in both females and males were involved in important pathways, including glycolysis, the citrate cycle (the TCA cycle), pathogenic E. coli infection and fatty acid biosynthesis. The results suggest that the extra carbohydrates in the formulated diet were transformed into fatty acids and that the synthesized fatty acids with the lipids in the formulated diet accumulated heavily in the liver, leading to inflammation and liver injury in largemouth bass.

Bifidobacterium sp. 고농도 성장을 위한 환경인자 및 세포활성도 최적화

For the industrial use of Bifidobacterium sp., maintaining cell viability is crucial along with the high cell concentration through fermentation optimization. The effects of initial glucose concentration, lactic acid concentration, pH and culture temperature on cell growth were investigated to optimize the environmental factors. In addition, the batch and fed-batch cultivation were performed to evaluate the correlation between the cell concentration based on the absorbance and the viable cell number. Both B. infantis and B. bifidum showed the highest cell growth rates at low glucose levels and the specific growth rate decreased with increasing glucose concentrations. The growth rate of B. bifidum was reduced with increasing glucose concentration, but the maximum cell concentration was increased. However, B. infantis showed lower maximum cell concentration in the higher glucose concentration. The impacts of lactic acid, pH and temperature of both B. infantis and B. bifidum were similar to those of most lactic acid bacteria. However, B. bifidum showed a more resilience within the same range of each environmental factor showing continuous growing at low specific growth rate even when B. infantis stopped growing. The number of viable cells of B. infantis was dramatically reduced even though the absorbance remained constant. In particular, the number of viable cells and the number of viable cells per absorbance decreased to 1/7 and 1/10 as the fed-batch culture progressed. Meantime, once the maximum viable cell number was reached, B. bifidum maintained the constant viable cell number and viable cell number per absorbance were maintained.

Respiratory Physiology of Lactococcus lactis in Chemostat Cultures and Its Effect on Cellular Robustness in Frozen and Freeze-Dried Starter Cultures.

In this study, we used chemostat cultures to analyze the quantitative effects of the specific growth rate and respiration on the metabolism in Lactococcus lactis CHCC2862 and on the downstream robustness of cells after freezing or freeze-drying. Under anaerobic conditions, metabolism remained homofermentative, although biomass yields varied with the dilution rate (D). In contrast, metabolism shifted with the dilution rate under respiration-permissive conditions. At D = 0.1 h-1, no lactate was produced, while lactate formation increased with higher dilution rates. Thus, a clear metabolic shift was observed, from flavor-forming respiratory metabolism at low specific growth rates to mixed-acid respiro-fermentative metabolism at higher specific growth rates. Quantitative analysis of the respiratory activity, lactose uptake rate, and metabolite production rates showed that aerobic acetoin formation provided most of the NADH consumed in respiration. Moreover, the maintenance-associated lactose consumption under respiration-permissive conditions was only 10% of the anaerobic value, either due to higher respiratory yield of ATP on consumed lactose or due to lower maintenance-related ATP demand. The cultivation conditions also affected the quality of the starter cultures produced. Cells harvested under respiration-permissive conditions at D = 0.1 h-1 were less robust after freeze-drying and had lower acidification activity for subsequent milk acidification, whereas respiration-permissive conditions at the higher dilution rates led to robust cells that performed equally well or better than anaerobic cells.IMPORTANCELactococcus lactis is used in large quantities by the food and biotechnology industries. L. lactis can use oxygen for respiration if heme is supplied in the growth medium. This has been extensively studied in batch cultures using various mutants, but quantitative studies of how the cell growth affects respiratory metabolism, energetics, and cell quality are surprisingly scarce. Our results demonstrate that the respiratory metabolism of L. lactis is remarkably flexible and can be modulated by controlling the specific growth rate. We also link the physiological state of cells during cultivation to the quality of frozen or freeze-dried cells, which is relevant to the industry that may lack understanding of such relationships. This study extends our knowledge of respiratory metabolism in L. lactis and its impact on frozen and freeze-dried starter culture products, and it illustrates the influence of cultivation conditions and microbial physiology on the quality of starter cultures.

Anchovy and giant squid hydrolysates can enhance growth and the immune response of European seabass (Dicentrarchus labrax) fed plant-protein-based diets

The aim of the present study was to evaluate: 1) the in vitro bactericidal and bacteriostatic activities of four selected marine hydrolysates, from anchovy or giant squid, against several fish pathogens, and 2) if the inclusion of 3% of those hydrolysates in a plant-protein-based diet could result in similar growth, feed efficiency, humoral immune status and haematological parameters of juvenile European seabass (Dicentrarchus labrax), compared to a fish meal-based diet, during an in vivo trial. Four marine hydrolysates from anchovy (ANC) or giant squid (GS) were obtained by hydrolysis using either a single protease (P1, endopeptidase activity; or P2, endo - and exopeptidase activities) or a mixture of P1 and P2 (MIX). Bactericidal and bacteriostatic activities of each hydrolysates were evaluated in vitro against several fish pathogens. Afterwards, four experimental diets with ANC (ANC-P1 and ANC-P2) or GS (GS-MIX and GS-P2) hydrolysates, a positive control (PC) diet with a higher content of a fishmeal (25%), and a negative control (NC) diet, where 50% of fishmeal of PC diet was replaced by plant sources, were formulated for an in vivo trial. Diets were fed to triplicate groups of juvenile European seabass (7.0 ± 2.0 g) distributed into tanks of 250 L each, at a density of 3.7 kg m−3, for 60 days. At the end of the in vivo trial, growth performance, nutrient utilization, whole body composition and humoral immune status of fish were evaluated.The in vitro trial showed that all marine hydrolysates conferred resistance against fish pathogens, as they had bactericidal and bacteriostatic activities against a great number of bacteria belonging to the Vibrionaceae family. However, GS hydrolysed by a single peptidase (P2) resulted in a lower bactericidal activity (P < .050) against Vibrio harveyi than the others hydrolysates. During the in vivo trial, fish fed ANC-P1, ANC-P2 and GS-MIX diets had similar (P > .050) growth compared to fish fed PC diet, whereas fish fed GS-P2 had lower (P ≤ .001) final body weight and specific growth rate than fish fed PC. However, the experimental diets barely affected innate immunity. These results showed that the 3% inclusion of ANC and GS hydrolysates, mainly ANC hydrolysed by a single protease with both endo - and exopeptidase activities (P2) or GS hydrolysed by a protease mix (MIX), in plant-protein-based diets for juvenile European seabass could be good options to hamper the negative effects caused by plant ingredients.

Growth and osmoregulatory response of Cyprinus carpio haematopterus (Amur carp) reared in inland saline water

A 90 days experiment was designed to assess the growth and osmoregulatory response of Cyprinus carpio haematopterus (Amur carp) in inland saline water of sub-humid and semi-arid/ arid zones of Haryana, India. Two hundred forty fingerlings (avg. wt. 3.48±0.272 g) were equally distributed in 4 treatment groups (salinities; control C, 0 ppt; T1, 5 ppt; T2, 10 ppt and T3, 15 ppt) with 3 replicates in 500 L tanks followed by complete randomized design (CRD). There were no significant differences observed in physico-chemical parameters of water among different treatments and found in optimum range throughout the experimental period. The parameters, viz. total alkalinity, hardness (total, calcium and magnesium) and concentration of ions were varying with the salinity and displayed increasing trend with increase in salinity. At the end of experiment, 100% survival was obtained upto 5 ppt whereas decreasing trend was found with increasing salinity (T2 and T3). There was highest% weight gain obtained in control group followed by T1, T2 and T3 groups. The highest specific growth rate (SGR) and protein efficiency ratio (PER) along with lowest food conversion ratio (FCR) was reported in control group followed by T1 and T2 groups, while lowest SGR, PER and highest FCR were reported in T3 group. Serum and water osmolality showed significant increasing trend with increasing salinity, while osmoregulatory capacity was decreasing with increase in salinity. Based on the findings, it is suggested that Amur carp can be cultured with 100% survival up to 5 ppt with slightly lower production rate.

Impact of starvation on digestive enzymes activities and plasma metabolites in Siberian sturgeon ( Acipenser baerii , Brandt, 1869)

To increase the current knowledge about the relationship between nutritional status and the digestive capacity of Siberian sturgeon (Acipenser baerii), we addressed the effect of starvation‐refeeding and macronutrient composition on growth parameters and key digestive enzyme activities in A. baerii. Acipenser baerii juveniles were fed four different diets for 3 weeks, then starved for 2 weeks and allowed to refed for 5 weeks with the same diets. Another group of fish were fed 10 weeks with the corresponding diets. Among 10‐week fed fish, high‐protein diets promoted higher body weight values, while the lowest specific growth rate was observed in fish fed a low‐protein, medium‐carbohydrate, high‐lipid diet (p .05) and α‐amylase activity in the intestine as well as pepsin in the stomach (p < .05). Our findings suggest that A. baerii maintains a high capacity to digest proteins and lipids after 2 weeks of starvation and that α‐amylase can be used as an indicator of the nutritional status in fish submitted to starvation‐refeeding cycles. Indeed, refeeding with high‐protein and CHO:L ratio diets after starvation could improve the growth rate of A. baerii in culture.

T-2 toxin in the diet suppresses growth and induces immunotoxicity in juvenile Chinese mitten crab (Eriocheir sinensis)

The T-2 toxin is a trichothecene mycotoxin and is highly toxic to aquatic animals, but little is known on its toxic effect in crustaceans. In the present study, the crab juveniles were fed with diets containing four levels of T-2 toxin: 0 (control), 0.6 (T1), 2.5 (T2) and 5.0 (T3) mg/kg diet for 56 days to evaluate its impact on the juvenile of Chinese mitten crab (Eriocheir sinensis). The crabs fed the T-2 toxin diets had significantly lower weight gain and specific growth rate than those fed the control diet. Moreover, crab survival in T3 group was obviously lower than that in the control. Oxidative stress occurred in all the treatment groups as indicated by higher activities of total superoxide dismutase, glutathione peroxidase, and total antioxidant capacity than those in the control. The total hemocyte count, respiratory burst, phenoloxidase in the hemolymph, and phenoloxidase, acid phosphatase and alkaline phosphatase in the hepatopancreas of crabs fed T-2 toxin were significantly lower than those in the control. The transcriptional expressions of lipopolysaccharide-induced TNF-alpha factor, relish, and the apoptosis genes in the hepatopancreas were induced by dietary T-2 toxin. The genes related to detoxication including cytochrome P450 gene superfamily and glutathione S transferase were induced in low concentration, then decreased in high concentration. Dietary T-2 toxin damaged the hepatopancreas structure, especially as seen in the detached basal membrane of hepatopancreatic tubules. This study indicates that dietary T-2 toxin can reduce growth performance, deteriorate health status and cause hepatopancreas dysfunction in crabs.

An evaluation of Lux technology as an alternative methodology to determine growth rates of Listeria in laboratory media and complex food matrices

Listeria monocytogenes is a foodborne pathogen which is a significant challenge in food production, particularly for ready-to-eat (RTE) products. Incidence of Listeria in food can be reduced by the application of multiple preservative factors or “hurdles”, which include acids, water activity and salts. Studying the growth of Listeria in complex foods is often reliant on laborious plate-counting techniques, therefore alternative methodologies are required. In this study we investigated the use of bioluminescence produced by chromosomally integrated genes encoding luciferase and its substrate to determine microbial growth rates in media and complex food matrices. Five Listeria innocua strains, used as a non-pathogenic surrogate for L. monocytogenes, were transformed with plasmid pPL2luxPhelp, resulting in a collection of Lux-tagged strains. Three test matrices (BHI broth, zucchini purée and béarnaise sauce) were adjusted, testing various combinations of pH (4.7–5.3), water activity (0.96 & 0.98) and undissociated acetic and propionic acid concentrations (0-2 mM). Adjusted matrices were inoculated with a cocktail of Lux-tagged strains and growth monitored over time by both bioluminescence and viable plate counts. Specific growth rates were calculated using both the bioluminescence and plate count data and compared. Statistical analysis showed that specific growth rates determined by bioluminescence did not significantly differ from those determined by plate counts (t-test, P > 0.05), while measurements of bias and accuracy showed good agreement between growth rates determined by both methods. Although plate counts remain the method of choice for detection of very low specific growth rates, this study demonstrates the potential of bioluminescence as a rapid alternative to plate counts for determining microbial growth rates in complex foods.

Adaptive Control of Biomass Specific Growth Rate in Fed-Batch Biotechnological Processes. A Comparative Study

This article presents a comparative study on the development and application of two distinct adaptive control algorithms for biomass specific growth rate control in fed-batch biotechnological processes. A typical fed-batch process using Escherichia coli for recombinant protein production was selected for this research. Numerical simulation results show that both developed controllers, an adaptive PI controller based on the gain scheduling technique and a model-free adaptive controller based on the artificial neural network, delivered a comparable control performance and are suitable for application when using the substrate limitation approach and substrate feeding rate manipulation. The controller performance was tested within the realistic ranges of the feedback signal sampling intervals and measurement noise intensities. Considering the efforts for controller design and tuning, including development of the adaptation/learning algorithms, the model-free adaptive control algorithm proves to be more attractive for industrial applications, especially when only limited knowledge of the process and its mathematical model is available. The investigated model-free adaptive controller also tended to deliver better control quality under low specific growth rate conditions that prevail during the recombinant protein production phase. In the investigated simulation runs, the average tracking error did not exceed 0.01 (1/h). The temporary overshoots caused by the maximal disturbances stayed within the range of 0.025–0.11 (1/h). Application of the algorithm can be further extended to specific growth rate control in other bacterial and mammalian cell cultivations that run under substrate limitation conditions.

Influense of various forms of iron on growth of Chlorella vulgaris Beijer culture

A comparative study of the toxic effect of magnetic nanoparticles of iron oxide (MNPs) and ions of bivalent and trivalent iron in the composition of sulfates on the growth of an intensive culture of Chlorella vulgaris Beijer is provided. The high sensitivity of the introduced biotest is shown for the case of a standard toxicant (potassium dichromate). Using the probit-analysis, and semi-extincting specific growth rate of EC50 culture concentrations were established in four-day experiments, which amounted to 1.3 ± 0.2 mg/l for potassium dichromate, 0.8 ± 0.1 mg/l for ferrous iron, 2.0 ± 0.2 mg/l for trivalent 1 and for MNPs iron oxide – 13 ± 1 mg / l. The probit analysis features and the significantly lower semi-suppressing specific growth rate of the culture in experiments with MNPs compared with ionic iron suggests a possible manifestation of other forms of exposure that are not related to the mechanism of chemical intoxication.

Characterization of smoltification in the Tasmanian strain of Atlantic salmon (Salmo salar) in recirculation and flow-through systems

This study examined morphological, physiological and molecular indicators of smoltification in Atlantic salmon (Salmo salar) juveniles in a flow-through (FT) and recirculating aquaculture system (RAS). Fish were exposed to 24-h light to initiate smoltification, for 5 (FT) and 7 (RAS) weeks prior to transfer from freshwater (FW) to seawater (SW) and were sampled weekly preceding and following SW transfer. Mass, length, condition factor, plasma chloride, gill Na+/K+-ATPase (NKA) activity and expression of salinity-specific isoforms of NKA mRNA transcripts were monitored. Fish raised in FT had significantly lower specific growth rate (SGR) in FW than in SW and showed a significant 5-6-fold increase in gill NKA activity, and high plasma chloride levels after transfer to SW. These fish also exhibited no significant reduction in relative mRNA expression of NKAα1a in FW but a sharp significant downregulation post-SW transfer. No significant increase in NKAα1b was seen until week 8 (3 weeks post-SW transfer). The log2 ratio of NKAα1b to NKAα1a showed a significant 8-fold increase throughout the study. Fish raised in the RAS had significantly higher SGR in FW than SW, and showed significantly higher plasma chloride in saltwater challenged fish compared to the freshwater control at all weeks during the FW phase. Fish had a 50% higher initial NKA activity than in FT, increasing significantly 2-3-fold and showed an immediate down-regulation of NKAα1a after exposure to 24-hr light in FW, and a further reduction after SW-transfer. There was no significant increase in NKAα1b in the RAS-raised fish for the duration of the study, and there was a significant 8-fold increase in log2 ratio of NKAα1b to NKAα1a. Whilst there were too many varying factors to statistically compare hatchery type in this study, it's evident that there are potentially system-related effects worthy of future investigation.

Growth performance, nutrient digestibility and intestinal morphology of rainbow trout ( Oncorhynchus mykiss ) fed graded levels of the yeasts Saccharomyces cerevisiae and Wickerhamomyces anomalus

In a 10‐week study, we evaluated the effects of replacing 20%, 40% or 60% of fishmeal (present in control diet at 300 g/kg) on a digestible protein basis with yeast Saccharomyces cerevisiae or a yeast mixture of Wickerhamomyces anomalus and S. cerevisiae on growth performance, nutrient digestibility, nutrient retention and intestinal health of rainbow trout (Oncorhynchus mykiss). Triplicate tanks with 35 rainbow trout (144.7 ± 25.1 g mean ± SEM) were fed rations of 1.5% of total biomass per tank. Replacement of 60% of fishmeal with yeast mixture resulted in lower specific growth rate of 1.0% versus 1.2%/day for other diets. Apparent digestibility coefficients for crude protein and most amino acids were highest in fish fed fishmeal‐based diet, with similar values for fish fed the diet with 20% replacement with yeast mixture. Diet with 20% replacement with yeast mixture resulted in highest phosphorus digestibility. Replacement of 60% of fishmeal with S. cerevisiae resulted in oedematous mucosal fold tips in the proximal intestine. The results of this study suggest that these yeasts can replace up to 40% of fishmeal under current inclusion levels in diets for rainbow trout without compromising growth performance, nutrient digestibility or intestinal health.