D. Tóth

Effect of bacterial starvation on surfactant biotransformation

Effect of carbon starvation on the rate of dihexylsulfosuccinate (DHSS) biotransformation byComamonas terrigena was determined. The protein content during the starvation was stable in all variants and did not change during the transformation cycle. All starved cultures exhibited a higher biotransformation rate than a non-starved control. Cells ofC. terrigena exposed for 16 h in media with no C source showed the highest specific biotransformation rate (144% of the non-starved culture). Extension of the starvation to 2 d led to a decrease of the rate to close to that found in non-starved cells.

Comparison of culturable Gram-negative bacterial community structures in the rhizosphere of three fruit plants

This research work was oriented to outlining the diversity of Gram-negative culturable portion of the bacterial community in three fruit plants rhizosphere. Rhizosphere samples were taken from European chestnut (Castanea sativa Mill), true service tree (Sorbus domestica L.) and cornelian cherry (Cornus mas L.) plants. Experiments were conducted for three years during the vegetation period, and the bacterial community structure was assessed with cultivation-dependent approach. Many Gram-negative isolates (n = 251) from the rhizosphere survived sub culturing and were identified by biochemical tests. A total of 57 species belonging to 29 genera were identified and assigned to four broad taxonomic groups (Bacteroidetes, Alpha-, Beta- and Gamma-proteobacteria). Several specific bacterial cluster communities were identified inside all the three rhizospheres. Most of the species belonged to the genera Moraxella, Pseudomonas, Pantoea, Enterobacter and Acinetobacter. In addition, while, using the plate count analysis, large discrepancies in numbers among physiological groups of bacteria cultured from three rhizosphere samples have not been revealed, more expressive distinctions among bacterial populations were obtained concerning the relative abundance of different genera, different taxonomic groups as well as different diversity indices. Furthermore, the number of cultured bacteria and their taxonomic distribution in the rhizosphere of all three plants changed not only explicitly during vegetation period but continually during the three years of investigation. It seems that rhizosphere bacterial populations of each plant are under the influence of the specific root-released materials.

Dihexyl sulfosuccinate biodegradation by mixed cultures.

The primary biodegradation of dihexyl sulfosuccinate has been demonstrated using two single cultures and three mixed bacterial cultures ofComamonas terrigena. Primary biodegradation was found in all variants. The highest biotransformation rate and efficiency was observed in one of the single strains. No synergistic effect on degradation was found in mixed cultures.

Effect of starvation and chloramphenicol on acceleration of bacterial dihexyl sulfosuccinate biotransformation.

Starvation for carbon and energy sources accelerated the biotransformation of the anion-active surfactant dihexyl sulfosuccinate (DHS) byComamonas terrigena cells. Cloramphenicol (Cm) added at different time intervals to non-starved cells inhibited the DHS transformation. The largest difference between cells treated and non-treated by Cm was observed for a 16-h-starvation period. Protein synthesisde novo during starvation enhanced the DHS biotransformation efficiency. A partial transformation of DHS in the presence of Cm indicated the constitutive character of enzymes involved in primary DHS biodegradation.

Screening for alkyl sulfosuccinate degrading microorganisms

Publisher Summary This chapter describes screening for pure microbial cultures capable of rapid alkyl sulfosuccinate (ASS) primary biodegradation among the culture collection strains and naturally occurring microorganisms. ASS represents synthetic surfactants of a secondary alkane sulfonate type. The ASS solubilization capacities, wetting of solids, their capabilities of reduction of surface tension at the phase boundaries are the basis of commercial use of ASS in products for washing and cleaning, cosmetics, antifogging agents, inks and pesticide sprays. Searching for ASS biodegraders among culture collection strains is done by systematic screening of 85 strains for the ability of Di-n-hexyl sulphosuccinate (DHSS) primary biodegradation. Screening test shows that DHSS degraders are frequent among bacteria belonging to the genera Bacillus , Rhodococcus , Streptomyces and Nocardiae . High frequency of DHSS degrading actinomycetes confirms their reputation for potent biodegraders. Enrichment media used for cultivation of microbial cultures are designed to contain a limited number of specific substrates that preferentially promotes the growth of ASS degraders.

Metabolic activity of cadmium-stressed and/or starvedVibrio sp.

Starvation ofVibrio sp. strain S14 cells for at least 2.5 h induced an enhanced resistance to subsequently applied cadmium stress. Bacterial cultures starved for a shorter time (0–2 h) exhibited a decreased ability to incorporate glucose when exposed to Cd2+. Cyclic increase and decrease in protein synthetic activity of stressed vibrios reflect stages of starvation-induced protiens expression. Vibrio cells pre-stressed by Cd2+ addition or by starvation responded in many aspects similarly to the next stress challenge. The presence of 100 mg/L chloramphenicol significantly lowered cell resistance against the secondary stress. Proteins synthesized due to the primary stress provideVibrio S14 with an enhanced probability to survive in unfavourable environment.

Performance of immobilized cells for dihexyl sulfosuccinate biotransformation

Possibilities of using immobilized bacterial cells for waste water treatment in a continuous process was determined. Cells ofComamonas terrigena strain N3H immobilized in calcium alginate beads were successful by used in packed bead-type reactor for continuous biotransformation of the anion-active surfactant dihexyl sulfosuccinate. Absence of calcium ions from the treated medium led to the disruption of alginate beads within 8 d of usage. When the medium was supplemented with Ca2+ ions the beads were stable for at least one month in the continuous process. During the whole time period the transformation effectivity was in the range of 80–100% even at the highest, flow rate of 14 mL/min.

Protein expression in the stressed Vibrio strains.

In a conjunction process using Escherichia coli SM10 (pLOF) KmR APR as donor and Vibrio S141 SmR as recipient, several mutants were constructed: Vibrio PH 101, V. PH 106, and V. PH 109 with lowered ability to synthesize poly-beta-hydroxybutyrate. The survival and metabolic activities of parent and mutant strains were estimated when they were subjected to stress conditions (starvation of carbon and energy sources and/or cadmium treatment). Using two-dimensional electrophoresis, the synthesis of stress proteins was demonstrated. Vibrio cultures consecutively exposed to CdCl2 and then to starvation or vice versa responded similarly metabolically. These results show increased proteosynthetic activity of the stressed Vibrio cells, indicating that the primary cadmium treatment induced the expression and synthesis of the protective proteins, enabling the cells to cope with the secondary stress.

Verification of the mathematical model of nitrogen circulation with and without light access

Abstract The aim of this paper is to study a mathematical model describing the circulation of nitrogenous compounds in an aquatic environment under aerobic conditions, described in the treatises of Leonov and of Leonov and Toth. On the basis of experimental data determined under conditions with and without light access, the coefficients K 1 , …, K 4 are estimated. which express the maximum substrate uptake by living organisms. It is shown that the mathematical model for the estimated coefficients K 1 , …, K 4 reflects both the qualitative and the quantitative disparities in the behaviour of the experimental system under conditions with and without light access.

Effect of nitrate and thiosulfate concentration on the denitrification activity of bacterial isolates

The denitrification activity of five bacterial isolates was studied in samples of soil and freshwater sediments and from a wastewater treatment plant. The bacteria were exposed in a mineral medium supplied with Na2S2O3·5H2O (electron donor) and KNO3 (electron acceptor). The effect of different concentrations of donor and/or acceptor of electrons was evaluated by the method of acetylene inhibition of N2O-reductase. No positive influence on denitrification activity was observed with increased levels of individually added substrates. Three bacterial isolates exhibited a significant increase of denitrification activity when measured in the presence of both tested substances.