In order to optimize the storage conditions of heterogeneous microbial community, the trehalose influence on the survival of bacteria and yeast cells was studied. It was shown that trehalose increases survival about 20 fold at –20 ºC as compared to the control sample. Dehydration and desiccation lethal effect on the community in the presence of trehalose was significantly smaller in terms of cell viability. The dependence of the initial cell density of studied biocenoses on microbial survival in the presence of the disaccharide was revealed.

Concentrations of carbon (wheat bran), and nitrogen (soybean flour) sources, mineral salts (KH₂PO₄, MgSO₄ i CaCl₂) as well as pH of culture medium and time of cultivation were optimized within the scope of the presented work to achieve the highest yield of endoxylanase biosynthesis. Conditions of production of A. niger IBT-90 xylanase preparation with a very low cellulolytic activity and hence useful for bread-making, were optimized according to Box and Wilson [Box i Wilson, 1951]. For this purpose, two successive sets of experiments, i.e. factorial and gradient optimization procedures were carried out. In the former experiment, the linear increase in endoxylanase activity, achieved for subsequent variants of culture medium composition throughout its gradient optimization, indicated that optimum culture medium composition was not found. The latter was determined on completion of the second set of experiments and approximation of its results. Optimization of A. niger IBT-90 culture conditions resulted in 3 fold rise in the endo-1,4-β-xylanase activity (from 84.5 to 254.3 U·cm^-3) as compared to the activity observed at initial conditions. The activity of endoglucanase in the obtained preparation was low (1.5 U·cm^-3).

Mathematical optimization of culture medium composition and cultivation conditions of Antarctic bacterial strain Pseudoalteromonas sp.22b were out to increase the yield of synthesis of cold-adapted β-galactosidase. Costs of enzyme production were approximately 40% reduced and the yield of its biosynthesis, measured as a rise in specific activity, was concomitantly enhanced 2.5 fold by using the method of factorial experiment planning coupled with gradient optimization. The evidence was provided that pure lactose can be replaced in culture medium for the growth of Pseudoalteromonas sp.22b with dried protein-free whey, without of loss of β-galactosidase biosynthesis yield.

Our research was focused on pectinolytic abilities of 5 Geotrichum candidum strains. We compared activities of extra- and intracellular PG (polygalacturonase) (nKat/mg protein) in mineral media (2 variants) and barley grain. Generally, most of the strains presented higher extracellular than intracellular PG activity. Pectin was the best carbon source for G. candidum Gc1, D2 and B1, which could suggest the inductive characteristic of G candidum enzymes. Only one strain (Sc12) differed from others, because its highest biosynthesis of intracellural PG was observed with glucose as a carbon source. This could be due to constitutive characteristic of he enzymes. PG biosynthesis on barley grain confirm that G.candidum strains could be useful in malting.

Statistically based design of experiment (DOE) was applied to the optimization of synthetic medium composition for oxalic acid (OA) production by Aspergillus niger in shake-flask cultures. The Box-Wilson Central Composite Circumscribed quadratic model (CCC) was used to search the optimum levels of macroelements influencing mycelia growth and OA production. Among these variables, N, P, Mg, were found to be significant factors that affected oxalic acid production. The optimum medium composition was found to be as follows: sucrose 150 g dm^-3, NH₄NO₃ 1.3 g dm^-3, KH₂PO₄ 0.3 g dm^-3, MgSO4·7H₂O 0.64 g dm^-3. Under optimal culture conditions, the maximum oxalic acid dihydrate amounted to 85.7 g dm^-3 with confidence level 95%.

Cane and beet molasses processed via submerged methods gave citric acid (CA) synthesis approximates to 100 g dm^-3. Beet molasses can also be used for biochemical production of oxalic acid (OA) giving 38.7 g dm^-3 of product. However, molasses is not appropriate substrate for gluconic acid (GA) synthesis as only half of hydrolyzed saccharose can be converted by glucose oxidase to product. The same problems appear with reference to sugar cane bagasse and sugar beet pulp, but these solid wastes can successfully be applied for other organic acid biosynthesis by solid-state method. Enrichment them by carbon source allowed obtaining 132 and 204 g kg^-1 d.s. of CA, respectively. Hydrol bioconversion by submerged method gave high CA output approximates to 120 g dm^-3. Mixture of wastes remaining after separation of gluten and starch from wheat flour makes possible to obtain 30 g dm^-3 of citric acid. Finally, the solid wastes, i.e. wastes coming from a filtration stage in glucose syrups purification, processed by solid state fermentation, allowed obtaining 230 g of CA from approximately 1 kg of substrate used.

The effect of dissolved oxygen concentration on the growth and citric acid production by acetate mutant of Y. lipolytica GW-7 on glucose syrup in batch culture were investigated. The highest specific biomass growth rate ( 0,40–0,41 h^-1), volumetric citric acid production rate (1,0–1,1 g dm^-3h^-1) and citric acid yield (0,7–0,74 gg^-1) were obtained at dissolved oxygen concentration of 50–60% pO₂. A final citric acid concentration ranged from 43 to 52,5 g dm^-3, depending on dissolved oxygen concentration.

The aim of the work was to examine the growth of Y. lipolytica A-101 yeast in batch culture using media containing frying fats. Four different vegetable fats were used as a carbon source: sunflower oil, palm oil, rapeseed oil and modified oil (PM). Frying fats varied by the degree of degradation: fresh fats, used fats after 8h and 40h of snacks frying at 180 ^oC. The yeast of Y. lipolytica A-101 grew on all substrates. The best growing was observed in the medium containing rapeseed oil, giving biomass higher than 28.0 g_d.w · dm^-3 and high biomass productivity from 1.6 to 1.9 g×dm^-3 · h^-1. The biomass yields in processes were quite high and ranged from 0.83 to 0.94 g · g^-1. Those parameters were lower in other cultures and decreased with the degree of degradation of frying fats. Total protein content of yeast and dry matter were similar in all cultures, ranging from 26% for biomass obtained in medium with palm oil to 31% for biomass obtained in medium with rapeseed oil. The content of protein in biomass didn’t depend on the degree of degradation of fats within frying.

The aim of the study was to determine the physiological state of different acetate mutants of Yarrowia lipolytica during continuous citric acid biosynthesis in membrane reactor on glucose syrup. In investigation either Y. lipolytica mutants of rough colonies and smooth colonies were used. Experiments have shown that these strains in long time continuous process had stable morphology and phenotype acet^-. Among examined strains, smooth A-101.1.31.AWG-7 strain, with cells of smallest and equal volume, was the best producer of citric acid. In the process with above mentioned strain up to 124 g×dm^-3 of citric acid and low amount of isocitric acid, less than 5 g×dm^-3, were obtained.

The aim of the research was to evaluate the stability and kinetics of the process of continuous citric acid (CA) biosynthesis by acetate mutants of Y. lipolytica on fructose syrup in a membrane reactor. Higher yield (YCA= 0,75 gg^-1) and citric acid production rates (Q_CA= 1 gdm^-3h^-1; q_CA= 0,035gg^-1h^-1) were observed in continuous process with the rough A-101-1.31 strain. The process involving its smooth segregant A-101-1.31-K1 showed better stability and enabled to obtain significant quantities of CA. Physiological state assessment of yeasts used in the study showed their good viability and high genetic and phenotypic stability during continuous CA production in membrane reactor with cells recycle.

Bacteria from genera Bacillus and Sarcina are capable of using chicken feather keratin as a source of carbon and nitrogen in the medium. We investigated the process of feather degradation in submerged cultures, as well as cell growth and keratinase and protease synthesis levels in presence of selected reducing agents. Cysteine and Na₂SO₃ stimulated the synthesis of proteases, while Na2SO3 and Na2S, keratinases. The deterioration of keratin structure was observed by the means of scanning electron microscopy.

The aim of the research was to evaluate the influence of High Gravity fermentation on selected features of brewing yeasts. Bottom fermenting yeasts (Saccharomyces carlsbergensis 13) and top fermenting yeasts (Saccharomyces cerevisiae 51) were used as a biological material. Worts characterized by different extract content and carbohydrate profile were used for fermentation. It was observed that fermentation activity of brewing yeasts was mainly depended on composition of HG worts but sedimentation profiles was depended on genetic features of yeast strain.