Attila Szentirmai

Bio: Attila Szentirmai is an academic researcher from University of Debrecen. The author has contributed to research in topics: Penicillium chrysogenum & Aspergillus nidulans. The author has an hindex of 23, co-authored 47 publications receiving 1448 citations. Previous affiliations of Attila Szentirmai include University of the Sciences.

Microbial physiology of sidechain degradation of sterols

Abstract: A large number of valuable starting materials for steroids synthesis (e.g. 4-androstene-3,17-dione, 1,4-androstadiene-3,17-dione, 9α-hydroxy-4-androsten-17-one) have been produced by microbial transformation methods. This review helps to evaluate the microbial physiological interest of the widely used sterol sidechain degradation processes. Four inducible groups of the catabolic enzymes are involved in the sterol sidechain degradation pathway; the fatty acid β-oxidation system, the ω-oxidase reaction, a methyl-crotonyl-CoA carboxylation system and the propionyl-CoA carboylase system. Altogether nine catabolic enzymes are involved in the β-sitosterol sidechain degradation pathway. They work in 14 consecutive enzymatic steps. Summing up: three molecules of FADH2, three molecules of propionyl-SCoA, three of NADH and one molecule of acetic acid are formed, while the sidechain of one mole of sitosterol is removed selectively. The metabolism of the propionates and the acetate yield 18 molecules of NADH and 7 molecules of FADH2. Taking into consideration the whole process more than 80 molecules of ATP could be formed during the sitosterol sidechain degradation process.

Phase Variation in Xenorhabdus nematophilus.

Abstract: Xenorhabdus nematophilus is a symbiotic bacterium that inhabits the intestine of entomopathogenic nematodes. The bacterium-nematode symbiotic pair is pathogenic for larval-stage insects. The phase I cell type is the form of the bacterium normally associated with the nematode. A variant cell type, referred to as phase II, can form spontaneously under stationary-phase conditions. Phase II cells do not elaborate products normally associated with the phase I cell type. To better define phase variation in X. nematophilus, several strains (19061, AN6, F1, N2-4) of this bacterium were analyzed for new phenotypic traits. An analysis of pathogenicity in Manduca sexta larvae revealed that the phase II form of AN6 (AN6/II) was significantly less virulent than the phase I form (AN6/I). The variant form of N2-4 was also avirulent. On the other hand, F1/II and 19061/II were as virulent as the respective phase I cells. Strain 19061/II was found to be motile, and AN6/II regained motility when the bacteria were grown in low-osmolarity medium. In contrast, F1/II remained nonmotile. The phase II cells did not produce the outer membrane protein, OpnB, that is normally induced during the stationary phase. Both phase I and phase II cells were able to support nematode growth and development. These findings indicate that while certain phenotypic traits are common to all phase II cells, other characteristics, such as virulence and motility, are variable and can be influenced by environmental conditions.

Isolation and activity of Xenorhabdus antimicrobial compounds against the plant pathogens Erwinia amylovora and Phytophthora nicotianae.

Abstract: Aims: Broad-spectrum antibiotics produced by symbiotic bacteria [entomopathogenic bacterium (EPB)] of entomopathogenic nematodes keep monoxenic conditions in insect cadavers in soil. This study evaluated antibiotics produced by EPB for their potential to control plant pathogenic bacteria and oomycetes. Methods and Results: Entomopathogenic bacterium produce antibiotics effective against the fire blight bacterium Erwinia amylovora, including streptomycin resistant strains, and were as effective in phytotron experiments as kasugamycin or streptomycin. Xenorhabdus budapestensis and X. szentirmaii antibiotics inhibited colony formation and mycelial growth of Phytophthora nicotianae. From X. budapestensis, an arginine-rich fraction (bicornutin) was adsorbed by Amberlite® XAD 1180, and eluted with methanol : 1 n HCI (99 : 1). Bicornutin inactivated zoospores, and inhibited germination and colony formation of cystospores at <<25 ppm. An UV-active molecule (bicornutin-A, MW = 826), separated by HPLC and thin-layer chromatography, was identified as a novel hexa-peptide : RLRRRX. Conclusions: Xenorhabdus budapestensis produces metabolites with strong antibacterial and cytotoxic activity. Individual compounds can be isolated, identified and patented, but their full antimicrobial potential may be multiplied by synergic interactions. Significance and Impact of the Study: Active compounds of two new Xenorhabdus species might control plant diseases caused by pathogens of great importance to agriculture such as Erw. amylovora and P. nicotianae.

Fungal cell wall chitinases and glucanases.

Abstract: The fungal cell wall is a complex structure composed of chitin, glucans and other polymers, and there is evidence of extensive cross-linking between these components. The wall structure is highly dynamic, changing constantly during cell division, growth and morphogenesis. Hydrolytic enzymes, closely associated with the cell wall, have been implicated in the maintenance of wall plasticity and may have roles during branching and cross-linking of polymers. Most fungal cell wall hydrolases identified to date have chitinase or glucanase activity and this short article reviews the apparent functions of these enzymes in unicellular and filamentous fungi, and the mechanisms that regulate enzyme activity in yeasts.

Cells have distinct mechanisms to maintain protection against different reactive oxygen species: Oxidative-stress-response genes

Abstract: The complete set of viable deletion strains in Saccharomyces cerevisiae was screened for sensitivity of mutants to five oxidants to identify cell functions involved in resistance to oxidative stress. This screen identified a unique set of mainly constitutive functions providing the first line of defense against a particular oxidant; these functions are very dependent on the nature of the oxidant. Most of these functions are distinct from those involved in repair and recovery from damage, which are generally induced in response to stress, because there was little correlation between mutant sensitivity and the reported transcriptional response to oxidants of the relevant gene. The screen identified 456 mutants sensitive to at least one of five different types of oxidant, and these were ranked in order of sensitivity. Many genes identified were not previously known to have a role in resistance to reactive oxygen species. These encode functions including protein sorting, ergosterol metabolism, autophagy, and vacuolar acidification. Only two mutants were sensitive to all oxidants examined, only 12 were sensitive to at least four, and different oxidants had very different spectra of deletants that were sensitive. These findings highlight the specificity of cellular responses to different oxidants: No single oxidant is representative of general oxidative stress. Mitochondrial respiratory functions were overrepresented in mutants sensitive to H2O2, and vacuolar protein-sorting mutants were enriched in mutants sensitive to diamide. Core functions required for a broad range of oxidative-stress resistance include transcription, protein trafficking, and vacuolar function.