Effects of surface-active medium additives on insect cell surface hydrophobicity relating to cell protection against bubble damage

Effect of pluronic block polymers and N-acetylcysteine culture media additives on growth rate and fatty acid composition of six marine microalgae species

Abstract

The efficiency of microalgal biomass production is a determining factor for the economic competitiveness of microalgae-based industries. N-acetylcysteine (NAC) and pluronic block polymers are two compounds of interest as novel culture media constituents because of their respective protective properties against oxidative stress and shear-stress-induced cell damage. Here we quantify the effect of NAC and two pluronic (F127 and F68) culture media additives upon the culture productivity of six marine microalgal species of relevance to the aquaculture industry (four diatoms-Chaetoceros calcitrans, Chaetoceros muelleri, Skeletonema costatum, and Thalassiosira pseudonana; two haptophytes-Tisochrysis lutea and Pavlova salina). Algal culture performance in response to the addition of NAC and pluronic, singly or combined, is dosage- and species-dependent. Combined NAC and pluronic F127 algal culture media additives resulted in specific growth rate increases of 38%, 16%, and 24% for C. calcitrans, C. muelleri, and P. salina, respectively. Enhanced culture productivity for strains belonging to the genus Chaetoceros was paired with an ~27% increase in stationary-phase cell density. For some of the species examined, culture media enrichments with NAC and pluronic resulted in increased omega-3-fatty acid content of the algal biomass. Larval development (i.e., growth and survival) of the Pacific oyster (Crassostrea gigas) was not changed when fed a mixture of microalgae grown in NAC- and F127-supplemented culture medium. Based upon these results, we propose that culture media enrichment with NAC and pluronic F127 is an effective and easily adopted approach to increase algal productivity and enhance the nutritional quality of marine microalgal strains commonly cultured for live-feed applications in aquaculture.

Key points

• Single and combined NAC and pluronic F127 culture media supplementation significantly enhanced the productivity of Chaetoceros calcitrans and Chaetoceros muelleri cultures.

• Culture media enrichments with NAC and F127 can increase omega-3-fatty acid content of algal biomass.

• Microalgae grown in NAC- and pluronic F127-supplemented culture media are suitable for live-feed applications.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-021-11147-8.

Effects of shear stress on microalgae - A review

Cultivation of microalgae requires consideration of shear stress, which is generated by operations such as mixing, circulation, aeration and pumping that are designed to facilitate mass and heat transfer as well as light distribution in cultures. Excessive shear stress can cause increased cell mortality, decreased growth rate and cell viability, or even cell lysis. This review examines the sources of shear stress in different cultivation systems, shear stress tolerance of different microalgal species and the physiological factors and environmental conditions that may affect shear sensitivity, and potential approaches to mitigate the detrimental effects of shear stress. In general, green algae have the greatest tolerance to shear stress, followed by cyanobacteria, haptophytes, red algae, and diatoms, with dinoflagellates comprising the most shear-sensitive species. The shear-sensitivity of microalgae is determined primarily by cell wall strength, cell morphology and the presence of flagella. Turbulence, eddy size, and viscosity are the most prominent parameters affecting shear stress to microalgal cells during cultivation.

Pluronic enhances the robustness and reduces the cell attachment of mammalian cells

The addition of the non-ionic surfactant, Pluronic F-68, to serum-free CHO cultures causes multi-functional effects that enhance cell yield in agitated cultures and reduce cell adhesion in stationary cultures. Three independent CHO cell lines were subjected to high liquid shear in assay systems that either included or excluded a liquid-gas interface. In the absence of Pluronic, there was a loss in cell viability in either assay system, although there was an intrinsic variability in sensitivity of the cell lines to shear damage. Supplementation with Pluronic prevented loss of cell viability, indicating protection in either a gas sparged or bubble-free environment. However, we found no evidence of long-term protection of cells once Pluronic was removed. Pluronic was capable of repairing trypsin-damaged cells as evidenced by enhanced growth, reduced membrane porosity, and improved robustness under liquid shear. The proportion of adherent cells was reduced to a minimal level by the presence of Pluronic although its effect was rapidly reversible with a high proportion (70%) of adherent cells observed within a few culture passages of its removal. The observed effects of Pluronic on these cultures are compatible with a mechanism in which the polymer forms a protective layer on the cell membrane, which has a significantly lower hydrophobicity.

Large-scale propagation of a replication-defective adenovirus vector in stirred-tank bioreactor PER.C6 cell culture under sparging conditions

Large-scale propagation of replication-defective adenovirus vectors has not been well studied to date. One of the challenges for efficient propagation at large scale is to overcome the sensitivity of virus infected cells to gas sparging required for oxygenation and CO(2) removal. In our initial experiments, it was observed that productivity of an adenovirus vector was significantly reduced under sparging conditions as compared to nonsparged, i.e., surface-aerated controls in serum-free cultures. Investigations led to the identification of a buffer containing surfactant (Polysorbate-80, PS-80) that was included in the virus seed stock formulation and introduced through virus infection into the culture at a very low concentration as the cause of the reduced virus productivity. This finding was not obvious and trivial, as neither uninfected sparged nor infected nonsparged PER.C6 trade mark cells in serum-free cultures were affected by the buffer at such a low PS-80 concentration of 0.00025% (v/v), which is a common component of serum-free cell culture media. These results strongly suggest that virus-infected cells behave very differently from uninfected cells under sparging conditions. To mitigate the deleterious effects of sparging, the virus seed stock was prepared in the absence of the buffer containing PS-80. At the same time, the concentration of Pluronic-F68 (PF-68) in the serum-free medium was increased to 1 g/L, at which cell growth and metabolism were unaffected, even though this measure alone did not result in virus productivity improvement. Only by implementing the two measures together was virus productivity loss completely eliminated under sparging conditions. After demonstration of the process robustness in 2-L bioreactors, this adenovirus propagation process was successfully scaled up to 250 L in a 300-L bioreactor under the worst-case sparging conditions projected for 10,000-L scale.

Stimulation of ligninolytic enzyme production in Phanerochaete chrysosporium by polyoxyalkanes

AIMS

Poly(ethylene glycol) (PEG) and some substances similar to PEG in chemical structure were tested as stimulators of ligninolytic enzyme production in shaken culture of Phanerochaete chrysosporium.

METHODS AND RESULTS

The substances that caused high enzymatic activity were linear polymers [poly(ethylene glycol), poly(propylene glycol), poly(butylene glycol) and poly(vinyl alcohol)] and cyclic polymers (crown ether). They can have terminal groups other than -OH [PEG (di)methyl ether, PEG sulphate, PEG derivative with the amino group and xanthate]. The maximum lignin peroxidase activities were compared with the surface pressure caused by the stimulator. Addition of polymers composed of charged monomer units did not increase the enzymatic activity and the fungi did not grow at all on addition of polymers having a fixed positive charge.

CONCLUSIONS

Lignin peroxidase activity was increased after the addition of polymers with uncharged monomer units. It was higher and its maximum was reached in a shorter time on addition of polymers with higher molecular weights.

SIGNIFICANCE AND IMPACT OF STUDY

Beside Tweens there are several polymers that stimulate ligninolytic enzyme production in shaken culture of P. chrysosporium. Their characteristics are: similarity to PEG in chemical structure, having uncharged monomer units and high molecular weight.

Growth of an ovarian cell line of Galleria mellonella and its response to immune-inducing factors

Antibacterial proteins are produced in the reproductive tracts of some insect species. The advent of a pupal ovarian cell line of the lepidopteran Galleria mellonella offered an opportunity for exploring the use of ovarian tissue culture to induce antimicrobial proteins in lieu of the larvae. The ovarian cell growth rates and cell yields were maximized by adjusting Grace's medium to pH 6.5, adding 15% (v/v) qualified heat-inactivated fetal calf serum, and lowering the sucrose concentration to 9.3 g/L. Five cell forms and biochemical profiles of the collective cell types were analyzed throughout the culture growth cycle. The final modified culture medium did not affect morphogenesis, whereas it increased the culture growth rate by 50% and the final cell yield threefold. The molting and immunoprotein-inducing hormone, 20-hydroxyecdysone, increased culture growth rate and altered the levels of cell types A and D. Neither 20-hydroxyecdysone nor the larval immunizing agents, apolipophorin-III or Bacillus subtilis, in combination or alone, induced antibacterial activity. The bacterium did induce immunity in both larval and adult stages.

Parameters that determine virus adsorption kinetics: toward the design of better infection strategies for the insect cell - baculovirus expression system

High productivities of bioprocesses involving viruses can be attained through infection strategies based on adequate understanding of parameters ruling cell-virus interactions. Two factors that affect virus binding and infection efficiency were studied: the utilization of an adsorption step, where infection volume at constant cell/virus ratio was varied; and the concentration of fetal bovine serum (FBS). The insect cell-baculovirus expression system and recombinant protein VP4 of rotavirus were used as models. Virus binding kinetics were adequately described by a sigmoidal response curve. The adsorption step, with or without FBS, increased virus attachment rate, whereas it increased bound virus at equilibrium only in FBS-free infections. A first-order dependance of virus attachment on cell concentration was found above 5 x 10(6) cell/mL in infections with 10% FBS. Addition of 10% FBS decreased maximum bound baculovirus and binding rate by as much as 3 times and VP4 concentration up to 4 times. In contrast, heat inactivation of FBS increased bound virus from 20% to over 90%, an increase of 1.4 times compared to FBS-free infections. A direct linear relation was found between attached virus and maximum VP4 concentration for the different FBS concentrations tested, indicating that baculovirus-cell attachment was the limiting step for recombinant protein production. Interestingly, virus progeny accumulation was not affected by differences in virus binding. In conclusion, infection strategies aimed at increasing productivity should be performed at high cell concentrations and without FBS, or with heat-inactivated FBS.

Beneficial effects of Pluronic F-68 and artificial oxygen carriers on the post-thaw recovery of cryopreserved plant cells

The storage of prokaryotic and eukaryotic cells at ultra-low temperature in liquid nitrogen (-196 degrees C) is a procedure that has assumed an increasingly important role in underpinning many aspects of biotechnology. For eukaryotic cells, the transition from a cryopreserved state to physiologically normal temperatures and oxygen tensions, induces respiratory imbalances that may stimulate the production of toxic oxygen radicals causing impaired cellular functions. Novel treatments, that focus specifically on enhancing oxygen delivery to cells, are important in maximising post-thaw recovery. Recently, several approaches have been evaluated with suspension cultured plant cells as a model, yet biotechnologically-important, totipotent eukaryotic cell system. Such treatments include non-ionic surfactants, primarily Pluronic F-68, and artificial oxygen carriers, the latter based on inert perfluorochemical liquids or chemically-modifed haemoglobin, as supplements to culture medium used during the post-thaw recovery phase of cell growth. When used either alone or in combination, such novel treatments stimulate significantly the post-thaw viability and biomass production of cultured plant cells. Many of these technologies will be exploitable in cryopreservation protocols for eukaryotic cells in general.

Animal-cell damage in sparged bioreactors

The gas sparging of culture broth causes damage to suspended animal cells. However, despite this, sparged bioreactors remain the preferred means of cell culture because sparging is a robust method of supplying oxygen, especially on a large scale. This article examines the underlying mechanisms involved in bubble-associated cell damage and the methods available for controlling such damage.

Evidence of Pluronic F-68 direct interaction with insect cells: impact on shear protection, recombinant protein, and baculovirus production*

Pluronic F-68 has been widely used to protect animal cells from hydrodynamic stress, but its mechanism of action is still debatable. Published evidence indicates that Pluronic F-68 interacts with cells, yet scarce information exists of its effect on recombinant protein and virus production by insect cells. In this work, the effect of Pluronic F-68 on production of recombinant baculovirus and rotavirus protein VP7 was determined. Evidence of Pluronic F-68 direct interaction with Sf-9 insect cells also was obtained. Maximum recombinant VP7 concentration and yield increased 10x, whereas virus production decreased by 20x, in spinner flask cultures with 0.05% (w/v) Pluronic F-68 compared to controls lacking the additive. No differences were observed in media rheology, nor kinetics of growth and infection (as inferred from cell size) between both cultures. Hence, Pluronic F-68 influenced cell physiology independently of its shear protective effect. Cells subjected to a laminar shear rate of 3000 s(-1) for 15 min, without gas/liquid interfaces, were protected by Pluronic F-68 even after its removal from culture medium. Furthermore, the protective action was immediate in vortexed cells. The results shown here indicate that Pluronic F-68 physically interacts with cells in a direct, strong, and stable mode, not only protecting them from hydrodynamic damage, but also modifying their capacity for recombinant protein and virus production.