Surface properties of mycoparasitic Pythium species and their interaction with model materials.

Pythium oligandrum, a soil-born oomycete, is an effective biological control agent exhibiting antagonistic and parasitic activity against pathogenic fungi. This study is the first attempt to characterize its surface properties and to apply models of physicochemical interactions (thermodynamic, DLVO and XDLVO) to quantify its adhesion properties to a model material, represented by magnetic beads (MB). The predictions of interaction models were based on experimental data (contact angles, zeta potentials, size). Adhesion intensities (AI) were determined experimentally taking advantage of MB with different surface properties. The role of weak physicochemical interactions was estimated by comparing experimental AI with model predictions. The results revealed that the surface properties of the three Pythium spp. studied were very similar and fell within the range for hydrophilic microorganisms (ΔGTOT > 0) with a predominantly negative surface charge. The most reliable description of AI was obtained using the DLVO model, including Lifshitz-van der Waals and electrostatic interactions. The highest AI between Pythium spp. and all three MB was observed at pH 3, which was supported by the DLVO prediction. The greater agreement between the sphere-sphere geometric version of the DLVO model and experiment suggests that the surface protrusions of the oospores increase the efficiency of adhesion. The surface properties of the pathogenic fungi, characterized in this work, fell within the range defined by MB and therefore it can be expected that their physicochemical interactions with Pythium spp. will also be favourable.

Laboratory scale cultivation of Salinispora tropica in shake flasks and mechanically stirred bioreactors.

OBJECTIVE: Marine actinomycetes from the genus Salinispora have an unexploited biotechnological potential. To accurately estimate their application potential however, data on their cultivation, including biomass growth kinetics, are needed but only incomplete information is currently available. RESULTS: This work provides some insight into the effect of temperature, salinity, nitrogen source, glucose concentration and oxygen supply on growth rate, biomass productivity and yield of Salinispora tropica CBN-440T. The experiments were carried out in unbaffled shake flasks and agitated laboratory-scale bioreactors. The results show that the optimum growth temperature lies within the range 28-30 °C, salinity is close to sea water and the initial glucose concentration is around 10 g/L. Among tested nitrogen sources, yeast extract and soy peptone proved to be the most suitable. The change from unbaffled to baffled flasks increased the volumetric oxygen transfer coefficient (kLa) as did the use of agitated bioreactors. The highest specific growth rate (0.0986 h-1) and biomass productivity (1.11 g/L/day) were obtained at kLa = 28.3 h-1. A further increase in kLa was achieved by increasing stirrer speed, but this led to a deterioration in kinetic parameters. CONCLUSIONS: Improvement of S. tropica biomass growth kinetics of was achieved mainly by identifying the most suitable nitrogen sources and optimizing kLa in baffled flasks and agitated bioreactors.

Cooking oil-surfactant emulsion in water for harvesting Chlorella vulgaris by sedimentation or flotation.

In this study, a novel harvesting emulsion (HEM) consisting of cooking oil in an aqueous solution of cetyltrimethylammonium bromide (CTAB) was tested for the harvesting of a technologically important microalga, Chlorella vulgaris. The influence of HEM dose, biomass and bovine serum albumin (BSA) (model interferer compound) on harvesting efficiency (E) were studied. The HEM E was over 90% at pH 10 (0.33% (v/v) cooking oil, 6.7 mg/L of CTAB) and 12 (0.13% (v/v) cooking oil, 2.7 mg/L of CTAB). Harvesting efficiencies at pH 4 and 7 were < 73.5% due to the absence of precipitate formation. Bovine serum albumin (10 mg/L) increased the HEM dose necessary to achieve E ˃ 90% by 1.2 (pH 10), and 3 fold (pH 12). By manipulating the dose of HEM and pH, the method of harvesting (flocculation/sedimentation or flotation) was adjustable depending on the technological requirements.

Heterotrophic cultivation of Chlorella vulgaris using saline waste water from the demineralization of cheese whey.

OBJECTIVE: Desalination of cheese whey by electrodialysis yields saline wastewater (SWW). The goal was to test this as the basis of a culture medium and to prove experimentally the concept that it was a suitable resource for heterotrophic cultivation of the freshwater green microalga Chlorella vulgaris. RESULTS: Optimization of glucose concentration, nitrogen source and medium salinity for microalgal growth was first carried out in defined medium (DM) and shake flasks. These results were then adopted in shake flask cultivation experiments using pre-treated SWW medium (PSWW). Subsequently, microalgal growth under optimized conditions was tested in bioreactors. Various media such as DM, PSWW and diluted PSWW (DPSWW) were compared. Volumetric biomass productivities decreased in the order DM (0.371 g L-1 h-1, urea) > DPSWW (0.315 g L-1 h-1, soy peptone) > PSWW (0.152 g L-1 h-1, soy peptone). Although biomass productivities in DPSWW and PSWW media were significantly lower than in DM, these media required the addition of only 66 and 33% of DM N sources, respectively. No other added DM component was necessary in (D)PSWW to achieve microalgal growth. CONCLUSIONS: Although the optimized cultivation of freshwater microalgae on alternative medium based on SWW resulted in biomass productivities lower than those on DM, the required addition of N sources was also lower. Potentially lower production costs of Chlorella biomass and the meaningful use of SWW are the main outcomes of this work.

Physico-chemical approach to adhesion of Alicyclobacillus cells and spores to model solid materials.

Acidothermophilic bacteria of the genus Alicyclobacillus are frequent contaminants of fruit-based products. This study is the first attempt to characterize the physico-chemical surface properties of two Alicyclobacillus sp. and quantify their adhesion disposition to model materials [diethylaminoethyl (DEAE), carboxyl- and octyl-modified magnetic beads] representing materials with different surface properties used in the food industry. An insight into the mechanism of adhesion was gained through comparison of experimental adhesion intensities with predictions of a colloidal interaction model (XDLVO). Experimental data (contact angles, zeta potentials, size) on interacting surfaces (cells and materials) were used as inputs into the XDLVO model. The results revealed that the most significant adhesion occurred at pH 3. Adhesion of both vegetative cells and spores of two Alicyclobacillus sp. to all materials studied was the most pronounced under acidic conditions, and adhesion was influenced mostly by electrostatic attractions. The most intensive adhesion of vegetative cells and spores at pH 3 was observed for DEAE followed by hydrophobic octyl and hydrophilic carboxyl surfaces. Overall, the lowest rate of adhesion between cells and model materials was observed at an alkaline pH. Consequently, prevention of adhesion should be based on the use of alkaline sanitizers and/or alkaline rinse water.