Stationary Liquid Medium Research Articles

Synthesis of Novel ZrO2/g-C3N4/CuFe2O4 Nanocomposite and Its Efficient Photocatalytic Degradation of Amoxicillin, Chlorpyrifos and Methylene Blue

A novel ZrO2/g-C3N4/CuFe2O4 nanocomposite was synthesized by wet impregnation method and its photocatalytic degradation efficacy is studied on the organic pollutants viz. antibiotic drug (amoxicillin), pesticide (chlorpyrifos) and dye (methylene blue) under both dark and visible light conditions in liquid medium. The synthesized nanocomposite and its photocatalytic degradation studies were well characterized using XRD, TEM, EDS, XPS, UV-Vis DRS, PL, BET and EIS analytical techniques. Among three organic pollutants, the photocatalytic degradation of methylene blue pollutant is higher (99.5%, k = 0.0533 min-1) than that of chlorpyrifos (97.3% k = 0.0367 min-1) and amoxicillin (64.6%, k = 0.0109 min-1) under visible light exposure for 90 min using ZrO2/g-C3N4/CuFe2O4 nanocomposite as a photocatalyst. The nanocomposite showed excellent degradation efficiency under the irradiation of visible light while the degradation under dark condition is highly limited. As a control experiment the individual g-C3N4, ZrO2 and CuFe2O4 components of the nanocomposite under the same conditions possess limited degradation efficiency than that of ZrO2/g-C3N4/CuFe2O4 nanocomposite. A possible photo-degradation mechanism is also proposed. Efficient treatment of wastewater could be possible with this novel nanocomposite ZrO2/g-C3N4/CuFe2O4 due to its high stability and reusability.

Anatomical and physiological responses of Aechmea blanchetiana (Bromeliaceae) induced by silicon and sodium chloride stress during in vitro culture.

Salt stress is one of the most severe abiotic stresses affecting plant growth and development. The application of silicon (Si) is an alternative that can increase the tolerance of plants to various types of biotic and abiotic stresses. The objective was to evaluate salt stress's effect in vitro and Si's mitigation potential on Aechmea blanchetiana plants. For this purpose, plants already established in vitro were transferred to a culture medium with 0 or 14 µM of Si (CaSiO3). After growth for 30 days, a stationary liquid medium containing different concentrations of NaCl (0, 100, 200, or 300 µM) was added to the flasks. Anatomical and physiological analyses were performed after growth for 45 days. The plants cultivated with excess NaCl presented reduced root diameter and effective photochemical quantum yield of photosystem II (PSII) (ΦPSII) and increased non-photochemical dissipation of fluorescence (qN). Plants that grew with the presence of Si also had greater content of photosynthetic pigments and activity of the enzymes of the antioxidant system, as well as higher values of maximum quantum yield of PSII (FV/FM), photochemical dissipation coefficient of fluorescence (qP) and fresh weight bioaccumulation of roots and shoots. The anatomical, physiological and biochemical responses, and growth induced by Si mitigated the effect of salt stress on the A. blanchetiana plants cultivated in vitro, which can be partly explained by the tolerance of this species to grow in sandbank (Restinga) areas.

Effect of thermal radiation on heat transfer in plane wall jet flow of Casson nanofluid with suction subject to a slip boundary condition

A Glauert type laminar wall jet issuing into a stationary liquid medium lying above a wall has technical uses in wall cooling and flow control. It plays a vital role in industrial applications like cooling/heating by impingement of jet, turbine blades, film cooling, mass and heat transfer phenomena. In this regard, a steady incompressible two-dimensional laminar Glauert kind wall jet is scrutinized in this study by considering nanoparticles suspension in the base liquid sodium alginate with suction and wall slip boundary conditions. Further, a comparative study is done by considering aluminum alloy and single-walled carbon nanotube as nanoparticles. The reduced ordinary differential equations (ODEs) are numerically solved by applying Runge–Kutta–Fehlberg fourth fifth-order (RKF-45) technique along with the shooting method. Results reveal that Casson nanofluid shows enhanced heat transfer than Casson nanoliquid for increased values of radiation parameter. The rising values of the Casson parameter deteriorate the heat transfer rate of both nanoliquids but an inverse trend is seen for improved values of radiation parameter.

In vitro propagation and conservation of Cattleya tigrina A. Rich

ABSTRACT: Cattleya tigrina A. Rich has been suffering heavy losses in its natural habitat and it is now included in the list of plants that are vulnerable to extinction. The development of in vitro propagation and conservation methodologies, as well as acclimatization, are considered important for species at the risk of extinction, as they promote the multiplication and conservation of the species, hence avoiding the loss of their genetic variability. The present study established the protocol of micropropagation and the in vitro conservation of C. tigrina. For the in vitro propagation, the study tested two volumes of the MS medium and two medium consistencies (stationary liquid and semi-solid). For acclimatization, the substrate mixtures containing pine bark, charcoal, vermiculite, and coconut coir were analyzed. For the in vitro conservation, different concentrations of the salts were tested in the MS medium, together with the osmotic regulators (sucrose, mannitol, and sorbitol), and at two temperatures (18 and 25 °C). The results obtained inferred that the semi-solid medium was superior to the stationary liquid medium in the variables of survival and the presence of roots, while the liquid medium was superior to the semi-solid medium in the number of shoots. For acclimatization, pine bark was the substrate where the plants developed an improved height, with sprouting, and rooting. The conservation was satisfactory and the plants remained viable for a period of 730 days, with the MS medium with 25% of the salts, and at temperatures of 18 ºC or 25 ºC. The plants were propagated in the stationary liquid MS medium (10 mL) and the semi-solid medium (25 mL), while they were acclimatized in pine bark and preserved in the MS medium with 25% of the salts (18 ºC or 25 ºC).

Development of high frequency cost-effective micropropagation protocol for Juncus rigidus using liquid culture medium and extraction of cellulose from their in vitro shoots - An important rush

Juncus rigidus is important halophyte with high cellulose content, but no studies has been made on micropropagation of the plant and cellulose extraction from in vitro shoots. To optimize an effective system for shoot multiplication, explants were grown in agar medium, liquid static culture, and bioreactor. Best shoot bud induction was obtained in liquid MS medium supplemented with2.27 μM thidiazuron (TDZ) over 0.46–4.65 μM Kinetin (KN) and 2.22–6.66 μM 6-benzyl aminopurine (BAP). Maximum number of shoot bud (36 ± 1.3) were achieved in static liquid MS medium supplemented with 2.22 μM BAP and 0.57 μM indole acetic acid (IAA). Upon subsequent subcultures >80 shoot buds were achieved in static liquid MS medium supplemented with 1.11 μM BAP, 0.57 μM IAA, and 0.46 μMKN within 30 days of culture. Being halophytic plant NaCl did not have any significant effect on shoot proliferation. Elongated shoots cultured in MS medium supplemented with 0.44 μM BAP, and 0.57 μM IAA developed 97% rooting in filter paper boat culture vessel. Sapling production cost in liquid culture medium was 90% less as compared to solid medium. Cellulose was extracted from the in vitro shoots and 17.64% cellulose achieved from liquid medium cultured shoots. For the first time micro-shoots are tested for in vitro cellulose production. • Maximum shoot bud (36 ± 1.2) induction was achieved in static liquid medium. • More than 80 shoot buds generated in static liquid MS medium supplemented with BAP, IAA, and KN. • 33.4 multiplication rate was recorded in static liquid medium. • 17.64 % cellulose extracted form in vitro shoots of J. rigidus. • In vitro plant based cellulose synthesis is important with future industrial application and bioengineering.

Morphophysiological responses of Aechmea blanchetiana (Bromeliaceae) to excess copper during in vitro culture

The use of plants as bioindicators can be effective for environmental monitoring, mainly related to heavy metals such as copper (Cu). In vitro conditions are more easily controlled, to enable isolating the stress factors that can interfere in plants’ responses. The aim was to investigate the morphophysiological responses of Aechmea blanchetiana submitted to excess Cu, and to verify the degree of tolerance and potential as a bioindicator of this species. Previously cultured shoots of A. blanchetiana were transferred to agar-solidified MS medium. After 60 days, the tank system was recreated, with the addition of stationary liquid MS medium with different concentrations of Cu (0, 25, 50 and 100 μM). After 90 days with excess Cu, anatomical analysis along with quantification of the contents of nutrients, photosynthetic pigments and chlorophyll a fluorescence were carried out. Alterations in the stomatal density and chlorenchyma thickness were observed in the plants grown with excess Cu. There was an increase in the Cu content in the plants in function of the Cu levels. However, the adjustments in the content of the other nutrients were essential for tolerance to excess Cu. Aechmea blanchetiana tolerates high Cu concentrations and has potential for use as a bioindicator.

Data-driven multiscale modeling reveals the role of metabolic coupling for the spatio-temporal growth dynamics of yeast colonies

BackgroundMulticellular entities like mammalian tissues or microbial biofilms typically exhibit complex spatial arrangements that are adapted to their specific functions or environments. These structures result from intercellular signaling as well as from the interaction with the environment that allow cells of the same genotype to differentiate into well-organized communities of diversified cells. Despite its importance, our understanding how this cell–cell and metabolic coupling lead to functionally optimized structures is still limited.ResultsHere, we present a data-driven spatial framework to computationally investigate the development of yeast colonies as such a multicellular structure in dependence on metabolic capacity. For this purpose, we first developed and parameterized a dynamic cell state and growth model for yeast based on on experimental data from homogeneous liquid media conditions. The inferred model is subsequently used in a spatially coarse-grained model for colony development to investigate the effect of metabolic coupling by calibrating spatial parameters from experimental time-course data of colony growth using state-of-the-art statistical techniques for model uncertainty and parameter estimations. The model is finally validated by independent experimental data of an alternative yeast strain with distinct metabolic characteristics and illustrates the impact of metabolic coupling for structure formation.ConclusionsWe introduce a novel model for yeast colony formation, present a statistical methodology for model calibration in a data-driven manner, and demonstrate how the established model can be used to generate predictions across scales by validation against independent measurements of genetically distinct yeast strains.

Micropropagation of Piper crassinervium: an improved protocol for faster growth and augmented production of phenolic compounds

The medicinal plant Piper crassinervium is a source of bioactive compounds with potential use in agrochemical and pharmaceutical industries. However, its propagation is slow and influenced by the composition of the culture medium and growth conditions. In the genus Piper, tissue oxidation limits the biomass and recovery of bioactive compounds such as phenols. We evaluated the effect of medium formulations, sucrose, growth regulators, medium consistency, explant type, gas exchange and irradiance levels on growth and phenols and total flavonoids content in P. crassinervium in vitro plants. Murashige and Skoog (MS) and DKW/Juglans (DKW/J) media induced the highest production of chlorophyll and phenolic compounds; however, the regeneration rate of the explants in the DKW/J medium was the lowest (~75%) in comparison with the other media (90%). The maximum biomass production was achieved when half-strength MS (½MS) liquid medium was used; while the optimum sucrose level depended on the medium salt concentration used. Notably, the irradiance altered the accumulation of biomass and phenolic compounds. The presence of one remaining leaf in the nodal segments, used as explants, produced taller plants in ½MS liquid medium, combined or not with 2-iP. The optimal growth conditions for biomass and phenolic compound production in P. crassinervium in vitro plants established were: nodal explant with a preexisting leaf cultured on ½MS stationary liquid medium, 15 g L−1 sucrose, using lids with one PTFE 0.45-µm-pore size membrane and an irradiance of 100 µmol m−2 s−1. Medium formulation, sucrose concentration, irradiance levels, gas exchange and explants with preexisting leaf improved the in vitro propagation and phenolic compounds production in Piper crassinervium.

Effects of 6-benzylaminopurine on photosystem II functionality and leaf anatomy of in vitro cultivated Aechmea blanchetiana

Cytokinins (CKs) are often used during the in vitro cultivation of plant species. However, it is not clear how CKs, such as 6-benzylaminopurine (BAP), affect photosystem PS) II functionality and leaf anatomy over a long period of in vitro plant propagation. The aim of this study was to analyze the residual effects of BAP on the photosynthetic performance and leaf anatomy of Aechmea blanchetiana after 120 d without exposure to CKs. Aechmea blanchetiana plants previously grown in vitro were transferred to Murashige and Skoog (MS) culture media containing 0, 5, 10, 15, or 20 μM BAP. After 60 d on the MS medium with BAP, explants were subcultivated twice on the MS medium without growth regulators, first in a stationary liquid medium for 60 d and then in a solidified medium with 6 g dm-3 agar for 60 d. Leaf anatomy, pigment content, and chlorophyll a fluorescence were assessed for plants from each treatment after 120 d on the CK-free medium. Stomatal density presented a negative linear correlation with BAP concentration. Pigment content decreased in plants subjected to previous BAP exposure. An increase in absorbed energy flux per reaction center (ABS/RC) and a sharp decrease in energy transport flux (ETo/RC) followed by an increase in energy dissipation flux (DIo/RC) also occurred. Furthermore, maximum quantum yield (FV/FM) decreased as a function of BAP concentration. Thus, the use of BAP during in vitro propagation of A. blanchetiana induced long-term physiological defects.

Denitrifying nirK-containing alphaproteobacteria exhibit different electrode driven nitrite reduction capacities

Biocathodic electrode-driven denitrification has been proved experimentally in complex biofilms. However, experimentation with isolated bacteria in pure culture is still limited. In this paper, six Alphaproteobacteria (Rhizobiales), found to be dominant in a denitrifying biocathode, have been characterized bioelectrochemically. Bacteria were isolated using strict autotrophic conditions in the presence of nitrate or nitrite. Six representative isolates were selected and proven able to denitrify under autotrophic and heterotrophic conditions in liquid media. Bioelectrochemical reduction of nitrate, nitrite and nitrous oxide was tested using cyclic voltammetry. Electrode-driven nitrite reduction was only detected in four of the six isolates. However, no electrode-driven nitrate or nitrous oxide reduction could be detected for any of them. In the presence of nitrite, estimated midpoint potentials for bioelectrocatalyzed reactions ranged from −500 to −534 mV vs. SHE. Two of the isolates exhibited midpoint potentials at −450 and −486 mV vs. SHE when incubated in the absence of any external nitrogenous electron acceptor. These redox peaks were attributed to electrode-driven hydrogen production in the biofilm. We have proven that electrode-driven nitrite reduction is feasible in monospecific biofilms. However, significant variability in relation to electrode-driven nitrogen reduction processes was observed in closely related species, confirming a strain-specific behavior.

Enhanced production of diosgenin through elicitation in micro-tubers of Chlorophytum borivilianum Sant et Fernand

Diosgenin, one of the steroidal sapogenin, is a chief bioactive compound, commercially known for its pharmaceutical application to treat sexual dysfunction. The biosynthesis of plant secondary metabolites in vitro cultures is usually manipulated by different elicitors that lead to higher production than non-elicited cultures. In the present investigation, in vitro tubers of Chlorophytum borivilianum were produced on semisolid and stationary liquid Murashige and Skoog (MS) medium supplemented with various concentrations of sucrose. To elicit diosgenin contents, these micro-tubers were exposed in vitro to different concentrations of jasmonic acid (JA) and salicylic acid (SA) for 1-month. An optimum number of micro-tuber was obtained on MS semisolid medium containing 60 g/L of sucrose. However, the stationary liquid medium consisting of same sucrose level was found more suitable for increased production of micro-tubers than semisolid medium. Exposure to the lower doses of JA and SA individually induced the improved production of diosgenin in the micro-tubers of C. borivilianum. A 2.1-fold higher production of diosgenin was obtained after the 1-month exposure of micro-tubers to 25 μM of JA; while after the 25 μM of SA elicitation, 1.5-fold higher diosgenin in micro-tubers was obtained in comparison to diosgenin present in tubers of the mother plant. The results suggest that JA and SA have the considerable ability to stimulate the production of valuable diosgenin in the micro-tubers of C. borivilianum.

Somatic embryogenesis enhancement of date palm cultivar Sewi using different types of polyamines and glutamine amino acid concentration under in-vitro solid and liquid media conditions

Somatic embryogenesis enhancement of date palm cultivar Sewi using different types of polyamines and glutamine amino acid concentration under in-vitro solid and liquid media conditions

Analysis of resistance of T91 steel under load in liquid PbBi

Abstract This paper describes behaviour of the ferritic-martensitic steel T91 after long-term exposure in liquid eutectic PbBi. Small specimens of the steel were pre-loaded according to the ISO Standard No. 7539-2 and subsequently exposed to PbBi. The experiment was carried out in a flowing and static liquid metal medium at 350°C. The experimental time was selected for the flowing environment at 1000 hours and for static environment at 2000 hours. After exposure, the specimens were analysed by use SEM and EDX. Surface changes of the specimens from different experimental conditions were compared and discussed. The initiation of the cracks wasn´t observed in the monitored expositions.

Micropropagation of axillary shoots of hybrid chestnut (Castanea sativa × C. crenata) in liquid medium in a continuous immersion system

A protocol for culturing chestnut axillary shoots with the basal sections continuously immersed in liquid medium was developed and the influence of various parameters was assessed: explant type and size, support material, bioreactor size and aeration regime. Shoots excised from eight selected chestnut genotypes were successfully cultured in 10 L bioreactors in liquid Murashige and Skoog medium with half strength nitrates and supplemented with 0.05 mg/L N 6-benzyladenine and 30 g/L sucrose. Forced ventilation and the use of a support material were essential for producing healthy, non-hyperhydric shoots. High proliferation rates were achieved and good quality shoots ready for multiplication, rooting and acclimatization were obtained. Larger leaves showing higher levels of photosynthetic pigments were observed in shoots cultured in bioreactors, suggesting a certain degree of photoautotrophy in shoots cultured under forced ventilation. This is the first demonstration of the production of chestnut shoots in stationary liquid medium, indicating the feasibility of the method for large-scale propagation of the species.

Effect of Hormone Types and Concentrations on In Vitro Multiplication and Growth of Pineapple (Ananas Comosus (L.) Merr.) Cv Moris on Liquid MS Medium

The effect of two cytokinins, 6-benzyleaminopurine (BAP) and kinetin (KN) and two auxins, naphthalene acetic acid (NAA) and indole acetic acid (IAA) each applied at 10 concentrations with an increment of 0.5 mg/l in the in vitro shoot formation of Moris pineapple was evaluated in static liquid MS medium. The highest shoot formation (9 shoots per explant) was obtained in medium enriched with NAA but at high concentration (4.5 mg/l). The second best was 8 shoots per explant obtained in medium enriched with BAP at 2.0 mg/l. Out of 10 concentrations, NAA was better than BAP at the highest 5 and less at lowest 5 concentrations and at all concentrations both hormones resulted in production of more shoots per explant than hormone free medium. Except at two concentrations, NAA and BAP were better than KN. Either one of these three hormones, BAP, NAA, KN could be claimed, depending on the tested range of concentrations, better than the others for in vitro shoot formation of Moris pineapple. All of the IAA concentrations, on the other hand, failed to produce more shoots than hormone free medium. But, the longest shoot (56 mm) obtained in medium enriched with IAA at 2.5 mg/l and the shortest shoots (6 mm) on medium enriched with KN at 4.0 mg/l. Seven of the IAA concentrations resulted in shoots longer than hormone free medium (27 mm) while the shoots length on the BAP, NAA and KN contained media was two times shorter than hormone free medium. BAP at 2.0 mg/l was the best treatment for multiplication and IAA at 2.5 mg/l was the best for elongation of Moris pineapple.

Effect of medium states and pH on in vitro shoot formation and growth of pineapple (Ananas comosus L. Merr) cv Moris Effect of medium states and pH on in vitro shoot formation and growth of pineapple (Ananas comosus L. Merr) cv Moris

Abstract In vitro shoots formation, shoot weight and length of Moris pineapple explants cultured on full strength MS medium enriched with sucrose at 20 g/ l, 6-Benzylaminopurine (BAP) at 2.0 mg/l and solidified with agar at 4 and 8 g/l were compared with semi submerged explants in static liquid medium under four different medium pH adjustments (5.0; 5.5; 6.0 and 6.5). The highest shoot formations (7 shoots/ explant) was obtained on liquid medium adjusted to pH 5.0 and the heaviest (0.36 g) and tallest (61 mm) shoots obtained also in liquid medium but adjusted to pH 6.0 . However, the superiority of liquid medium could not be maintained if the medium were adjusted to inappropriate pH. No difference in shoot formation between liquid and solid medium both adjusted to pH 6.0 (4 shoots) and between liquid media adjusted to pH 5.5 and 6.5 and solid media adjusted to pH 5.0 (6 shoots). At pH 5.0; 5.5 and 6.5 liquid and solid media resulted in equal shoot weight and shoot length. Different growth parameters have different optimal pH adjustments of medium and valid comparison of states of medium could not be claimed if only one pH adjustment was made.

Gross phosphorus fluxes in a calcareous soil inoculated with Pseudomonas protegens CHA0 revealed by 33P isotopic dilution

Inoculation with phosphorus (P) solubilizing bacteria is being proposed to increase P availability for plants by mineralization and solubilization of non-available soil and fertilizer P. Solubilization of inorganic P compounds by bacterial strains has repeatedly been shown on agar plates and in liquid media. However, the effects of inoculation on P availability to plants growing in soils, either in pot or field studies, are inconsistent and do not allow to separate between direct effects on P availability and indirect effects such as improved plant health. This differentiation could be achieved using 33P isotopic labeling. We applied the 33P isotopic dilution method in a pot and in an incubation experiment to study gross P fluxes in a calcareous soil inoculated with the P solubilizing bacteria Pseudomonas protegens CHA0. We hypothesized that the inoculant dilutes the specific activity (33P/31P) in the soil solution or in the plant shoots because of P solubilization beyond the P mobilization by the endogenous microbial biomass. To this end, we conducted a plant growth experiment with Lolium multiflorum var. Gemini and an incubation experiment. In both experiments, the soil was amended or not with a calcium P rich sewage sludge ash, and both treatments were conducted with and without inoculation. The inoculant was able to solubilize P from sewage sludge ash under controlled conditions in liquid media. However, it did not enhance P release from soil or from sewage sludge ash in the incubated soil. Inoculation of the soil reduced organic P mineralization by the soil microbial biomass, which was supported by a simultaneous decrease in soil respiration. Thus, any inorganic P solubilized by the inoculant might have been offset by less basal organic P mineralization. Increased P uptake of inoculated Lolium multiflorum at first harvest was attributed to an indirect effect, since the specific activity in shoots of inoculated Lolium multiflorum was not decreased. Although sewage sludge ash contained very little water-soluble P, an increase in P availability following sewage sludge ash addition could be shown using 33P isotopic dilution, while biological processes remained unchanged. While in this study, the inoculant did not increase P availability, the approach presented here can give insight into the mechanisms underlying beneficial effects of inoculants.

Editorial: Exploring Bacterial Colonies in Solid Foods or Model Foods Using Non-Destructive Techniques.

Bacteria are present in all foods, whether they are indigenous or inoculated. They can be beneficial to the quality of foods, responsible for food spoilage, or even pathogens. In solid food products, bacteria are immobilized. They thus grow as colonies entrapped within the food products or on the food surfaces. In both cases, bacteria interact with the solid matrix, sometimes facing difficulties to access the nutrients as nutrients have to diffuse from the matrix to the bacterial colonies. Bacterial development can thus be impaired in solid matrices in comparison to planktonic growth. To control the growth of bacteria in solid foods is then of major importance. In the case of pathogens, it is crucial for safety issues to predict how the bacteria present as initial contaminants will develop. In the case of inoculated bacteria, such as lactic acid bacteria, it is also crucial to control their development because they are responsible for the final quality of the food products. However, studies on the growth of bacteria have been essentially focused on growth in liquid media. Resolute techniques, which include both microcopy approaches and quantitative techniques, have now been developed to observe colonies at the microscopic scale. They allow studying the variation of growth in different contexts either in model growth culture media or in model foods. This Research Topic starts with four review papers. A first comprehensive review about bacterial colonies redraws the history of the studies on colonies, synthetizes the conditions of growth in which growth in colonies differs from planktonic growth, and finally presents concepts of the interaction of bacterial colonies with the food matrix in which they grow, with cheese as an example (Jeanson et al.). The second review demonstrates the importance of modeling the growth of bacterial colonies in solids foods despite a lack of knowledge. The different types of models and their potential consequences on decisions are presented and discussed (Skandamis and Jeanson). The third review shows how non-invasive techniques can be used to observe bacterial growth and also quantify the bacterial metabolism in colonies at the microscopic scale (Lobete et al.). The last review paper shows how microscopy techniques are particularly valuable to increase knowledge about bacterial colonies in model foods and foods. Fluorescent microscopy allows targeting metabolites and understand the physiology of bacteria within colonies (Hickey et al.). The five following papers present original results in the field. Using an automated microscope coupled with fluorescence dyes, it was possible to demonstrate that the exposure to an oxidizing disinfectant led to different morphologies of cells depending on the strains and that dead cells were randomly distributed within the micro-colonies (Zhao et al.). The following study demonstrates the accuracy of a phenotyping technology based on laser-induced speckle scatter patterns in Bacillus colonies. The authors showed that the distribution of speckle size is modified during the growth of colonies (Kim et al.). The three following studies investigate bacterial colonies of lactic acid bacteria in their food environment in model cheeses or investigate the pH in their surrounding micro-environment in Cheddar cheeses. Physiology and growth of Streptococcus thermophilus colonies was compared in liquid milk and renneted milk using microcalorimetry. The results showed that above a threshold size of colonies (low inoculation levels), growth rates and metabolism in renneted milk differed from the one observed in liquid milk (Stulova et al.). The use of fluorescence lifetime imaging was shown to be relevant to investigate the pH micro-heterogeneity in Cheddar cheeses (Burdikova et al.). These results suggest that the surroundings of bacterial colonies within cheeses could differ from homogeneous growth conditions in liquid medium. The last study questioned the access of bacteria in colonies to their nutrients, through the assessment of diffusion of solutes inside colonies. The diffusion of high molecular weight molecules was assessed inside Lactococcus lactis colonies grown in a model cheese. The results led to the conclusion that diffusion of molecules inside bacterial colonies depends on the physicochemical properties of the molecules (Floury et al.). In conclusion, since bacteria mainly grow in colonies in foods, increase knowledge on growth and physiology of bacteria growing as colonies is now a crucial issue. This is achieved by the recent development of non-invasive techniques that allows investigating at the microscopic scale with time lapse and quantitative analyses. Knowledge about the growth and the adaptive response of bacteria to the food environment will continue to grow by addressing the remaining questions about interactions between bacterial colonies and their food environment.

Effect of growth conditions on Ophiostoma piceae (Münch) H. & P. Syd. and Ophiostoma floccosum Math-Käärik albino strains culture morphology

Blue stain in Pinus radiata D. Don wood is predominantly caused by Ophiostoma genus fungi. Stained wood causes significant economic losses to forestry and timber industries. Currently, different chemical fungicides are used to prevent the occurrence of blue stain fungi. However, recent reports have questioned the environmental friendliness of these fungicides. For this reason, the use of biological control, in particular with albino strains of the Ophiostoma genus, appears to be an environmentally safe and a technically feasible alternative to work with. The potential field application of this technology would use a formulation containing the albino fungus-the bioactive ingredient- in its yeast like form. However, some Ophiostoma strains cultures present a marked filamentous morphology in liquid culture medium, affecting the efficiency in the production of the bioactive ingredient. The hypothesis of this work presumed the possibility to control the morphology of Ophiostoma cultures, through the modification of growth conditions in liquid medium. The effect of inoculum size, growth temperature and agitation rate on the morphology of PcF2A29 Ophiostoma piceae and FlF1A55 Ophiostoma floccosum albino strains in liquid culture medium, was studied. A 23 factorial design was employed. The results showed that the initial inoculum size had a statistically significant effect on yeast-like growth morphology in both strains, whereas the temperature only produced a significant effect in PcF2A29 O. piceae strain.

Optimiza of cultural conditions in liquid media of Schizochytrium sp. PQ6 isolated from Phu Quoc island, Kien Giang province

Optimiza of cultural conditions in liquid media of Schizochytrium sp. PQ6 isolated from Phu Quoc island, Kien Giang province