Stationary Phase Of Bacterial Growth Research Articles

Suppression of a transcriptional regulator, HexA, is essential for triggering the bacterial virulence of the entomopathogen, Xenorhabdus hominickii

A nematode-symbiotic bacterium, Xenorhabdus hominickii, exhibits two distinct lifestyles. Upon infection of its host nematode into a target insect, X. hominickii is released into the insect hemocoel and becomes pathogenic. This study examines the critical transformation in bacterial life forms concerning the activity of a transcriptional regulator, HexA. When X. hominickii was cultured in tryptic soy broth, HexA was expressed during the stationary phase of bacterial growth. Conversely, HexA was expressed in the early growth stage within the insect host, Spodoptera exigua, when infected with X. hominickii. The transient expression of HexA was succeeded by the expression of another transcriptional regulator, Lrp, which led to the production of bacterial virulent factors. Expression of HexA was manipulated by replacing its promoter with an inducible promoter controlled by the inducer, l-arabinose. In the absence of the inducer, the mutant bacteria expressed HexA at a low level, resulting in a bacterial culture broth that was more effective at suppressing insect immune responses than the wild type. When the inducer was added, HexA was expressed at high levels, rendering the culture broth ineffective in immunosuppression. Interestingly, expression of HexA inhibited the expression of another transcriptional regulator, Lrp, which in turn induced the expression of a non-ribosomal peptide synthetase, gxpS, leading to the production of an immunosuppressive metabolite, GXP. Suppression of HexA expression in mutant bacteria augmented GXP levels in secondary metabolites. This indicates that infection of X. hominickii into the insect host represses HexA expression and upregulates Lrp expression, leading to GXP production. The GXP metabolites inhibit insect immunity, thus protecting the bacteria-nematode complex. Therefore, the suppression of HexA expression in the insect hemocoel is crucial for the bacteria’s transition from a symbiotic to a pathogenic life form.

Evidence for a compact σ70 conformation in vitro and in vivo

The initiation of transcription in Escherichia coli (E.coli) is facilitated by promoter specificity factors, also known as σ factors, which may bind a promoter only as part of a complex with RNA polymerase (RNAP). By performing invitro cross-linking mass spectrometry (CL-MS) of apo-σ70, we reveal structural features suggesting a compact conformation compared to the known RNAP-bound extended conformation. Then, we validate the existence of the compact conformation using invivo CL-MS by identifying cross-links similar to those found invitro, which deviate from the extended conformation only during the stationary phase of bacterial growth. Conclusively, we provide information in support of a compact conformation of apo-σ70 that exists in live cells, which might represent a transcriptionally inactive form that can be activated upon binding to RNAP.

Logistic Model for Predicting Coliform Growth in Wastewater Effluent From the Chambo River (Ecuador)

Purpose: The objective of this work is to apply a predictive model of bacterial growth to determine the concentration of total coliforms, under controlled laboratory conditions, in wastewater from the city of Riobamba that flows into the Chambo River (Ecuador). Theoretical Framework: Wastewater pollution is a global problem that affects water quality and public health. Population growth has a drastic impact on the contamination of water bodies, particularly in Ecuador, since most of the effluents are not adequately treated, which becomes a public health and environmental problem. For this reason, over the years, total and fecal coliforms have been used as indicators of water quality. Design/Methodology/Approach: The study used a mathematical modeling approach of a logistic and deterministic type, and calculated through an executable command designed in the integrated development environment (IDE) with the Visual C# programming language (logic) and the XAML design language (interface). Findings: The results achieved are 1) the theoretical construction of a mathematical model (logistic model) starting from a differential equation and the taking of three experimental measurements, 2) the computer construction of the bacterial growth model and 3) it has been demonstrated that there is agreement between the values obtained from the model of total coliform growth and the experimental results with a margin of error of less than 1%. Research, Practical & Social Implications: This information can be used by stakeholders to determine actions that could improve current conditions. Originality/Value: The result of this study emphasizes that the model proposed can reproduce the growth of coliforms up to a maximum growth point, it is necessary to continue with the development of the same in the stationary phase of bacterial growth and then in the decay phase.

Logistic Model for Predicting Coliform Growth in Wastewater Effluent From the Chambo River (Ecuador)

Purpose: The objective of this work is to apply a predictive model of bacterial growth to determine the concentration of total coliforms, under controlled laboratory conditions, in wastewater from the city of Riobamba that flows into the Chambo River (Ecuador). Theoretical Framework: Wastewater pollution is a global problem that affects water quality and public health. Population growth has a drastic impact on the contamination of water bodies, particularly in Ecuador, since most of the effluents are not adequately treated, which becomes a public health and environmental problem. For this reason, over the years, total and fecal coliforms have been used as indicators of water quality. Design/Methodology/Approach: The study used a mathematical modeling approach of a logistic and deterministic type, and calculated through an executable command designed in the integrated development environment (IDE) with the Visual C# programming language (logic) and the XAML design language (interface). Findings: The results achieved are 1) the theoretical construction of a mathematical model (logistic model) starting from a differential equation and the taking of three experimental measurements, 2) the computer construction of the bacterial growth model and 3) it has been demonstrated that there is agreement between the values obtained from the model of total coliform growth and the experimental results with a margin of error of less than 1%. Research, Practical & Social Implications: This information can be used by stakeholders to determine actions that could improve current conditions. Originality/Value: The result of this study emphasizes that the model proposed can reproduce the growth of coliforms up to a maximum growth point, it is necessary to continue with the development of the same in the stationary phase of bacterial growth and then in the decay phase.

In-vitro assessment for the control of Fusarium species using a lactic acid bacterium isolated from yellow pitahaya (Selenicereus megalanthus (K. Schum. Ex Vaupel Moran))

The fungistatic activity of a lactic acid bacterium, which had been isolated from yellow pitahaya cultures, against fungi associated with basal rot (Fusarium oxysporum and Fusarium fujikuroi) was measured in the present study. Its activity was assessed in three fractions: fermented (S1), metabolic products (S2), and biomass (S3), using two fermentation substrates: Man Rogosa Sharpe agar (MRS) and potato dextrose agar (PDA). The bacterium was molecularly identified as Lactobacillus plantarum. S3 reduced F. fujikuroi growth by 100% over 48 h of fermentation, which occurred during the stationary phase of bacterial growth. The three fractions’ fungistatic activity against F. fujikuroi depended on the substrate employed. The fermentation kinetic parameters for L. plantarum indicated that its specific growth rate was 0.46 h–1, with 93.63% substrate consumption, 0.045 kg kg–1 cell yield, and 0.54 kg kg–1 product yield. The kinetic parameters calculated will allow for bacteria production scaling. These in-vitro trials reveal L. plantarum’s possible application as a biocontrol agent for diseases associated with Fusarium. However, further ex-vivo and in-vivo researches are required to demonstrate its behavior in crops.

Variations of Indole Metabolites and NRPS-PKS Loci in Two Different Virulent Strains of Xenorhabdus hominickii.

Xenorhabdus hominickii ANU1 is known to be an entomopathogenic bacterium symbiotic to nematode Steinernema monticolum. Another bacterial strain X. hominickii DY1 was isolated from a local population of S. monticolum. This bacterial strain X. hominickii DY1 was found to exhibit high insecticidal activities against lepidopteran and coleopteran species after hemocoelic injection. However, these two X. hominickii strains exhibited significant variations in insecticidal activities, with ANU1 strain being more potent than DY1 strain. To clarify their virulence difference, bacterial culture broths of these two strains were compared for secondary metabolite compositions. GC-MS analysis revealed that these two strains had different compositions, including pyrrolopyrazines, piperazines, cyclopeptides, and indoles. Some of these compounds exhibited inhibitory activities against phospholipase A2 to block eicosanoid biosynthesis and induce significant immunosuppression. They also exhibited significant insecticidal activities after oral feeding, with indole derivatives being the most potent. More kinds of indole derivatives were detected in the culture broth of ANU1 strain. To investigate variations in regulation of secondary metabolite production, expression level of leucine-responsive regulatory protein (Lrp), a global transcription factor, was compared. ANU1 strain exhibited significantly lower Lrp expression level than DY1 strain. To assess genetic variations associated with secondary metabolite synthesis, bacterial loci encoding non-ribosomal protein synthase and polyketide synthase (NRPS-PKS) were compared. Three NRPS and four PKS loci were predicted from the genome of X. hominickii. The two bacterial strains exhibited genetic variations (0.12∼0.67%) in amino acid sequences of these NRPS-PKS. Most NRPS-PKS genes exhibited high expression peaks at stationary phase of bacterial growth. However, their expression levels were significantly different between the two strains. These results suggest that differential virulence of the two bacterial strains is caused by the difference in Lrp expression level, leading to difference in the production of indole compounds and other NRPS-PKS-associated secondary metabolites.

English

Metabolomics based on LC-MS was used for the analysis of the fermentation of Proteiniphilum acetatigenes PSB-W treated by different culture time and different light intensity. 26 putative metabolites were detected in samples treated by different culture time. Most of the components were produced in the metabolic activity in order to participate in the whole life process of bacteria. Compared with samples treated with light intensity, a total of 37 metabolites were detected and analyzed. Only 10 compounds were detected in 1000 Lux group, which is significantly less than 1500 Lux group. The metabolite data of light groups were passed through principal component analysis (PCA) and differential metabolites were screened for each comparison group by using the Volcano Plot model. The differential metabolites were annotated by the Kyoto Encyclopedia of Genes and Genomes (KEGG) database and 7 differential metabolites related to the carotenoid synthesis enrichment pathway were screened. The results showed that carotenoids synthesis may occur during the stationary phase of bacterial growth. The precursor of carotenoid synthesis of photosynthetic bacteria is isopentenyl diphosphate (IPP) synthesized by acetyl coenzyme A under the catalysis of HMG CoA reductase. It is preliminarily clarified that it is the accumulation mechanism of bacterial carotenoid biosynthesis and provides a new clue for the comprehensive study of the synthesis and regulation mechanism of carotenoids.   Key words: Carotenoids, metabolomics analysis, Proteiniphilum acetatigenes PSB-W.

Primary selection of the prebiotic components in the complex dermatological therapeutic and preventive medicine with probiotic

The aim. Selection of optimal prebiotic components for bacteria of the genus Lactobacillus for their joint use in a complex dermatological therapeutic and preventive medicine with a probiotic.Methods. Co-cultivation of a probiotic strain in a liquid MRS nutrient medium with an active ingredient at selected concentrations. During the cultivation cycle, samples of growing culture were selected at specific intervals to determine bacterial concentration by direct seeding and acidity determination.Results. During 48 h of co-cultivation of lactobacilli with selected components, were observed a significant increase of viable cells, both in control and with the addition of vitamins at selected concentrations (exponential bacterial growth phase), from 48 h to 60 h - decrease of the rate of cell growth as in control group, and in experiments, the number of cells remains almost constant (stationary phase of bacterial growth), after 60 h - decrease of the number of cells (phase of dying).During cultivation, the oxidation of the nutrient medium resulting from the formation of lactic acid carbohydrates and other terminal metabolites were observed; that is, the addition of components slightly increases the biochemical potential of microorganisms, as evidenced by the increase in biomass and acid potential.Although there was no significant difference between one series of experiments with different vitamin contents, the largest increase in viable cell was observed with vitamin B5 (concentration 1 %) and provitamin B5 (concentration 2.5 %).Conclusions. Optimal prebiotic components for use with lactobacilli as part of dosage form were selected. Despite the pronounced synergism of action of the vitamin B5 and D-panthenol, all other components are also promising due to the positive effects on human skin and lack of negative effects on lactobacilli

Expanding the promoter toolbox of Bacillus megaterium

Over the past decades, Bacillus megaterium has gained significant interest in the biotechnological industry due to its high capacity for protein production. Although many proteins have been expressed efficiently using the optimized xylose inducible system so far, there is a considerable demand for novel promoters with varying activities, particularly for the adjustment of protein levels in multi-enzyme cascades.Genome-wide microarray analyses of the industrially important B. megaterium strain MS941 were applied to identify constitutive and growth phase dependent promoters for the expression of heterologous proteins from the early exponential to the early stationary phase of bacterial growth. Fifteen putative promoter elements were selected based on differential gene expression profiles and signal intensities of the generated microarray data. The corresponding promoter activities were evaluated in B. megaterium via β-galactosidase screening. β-Galactosidase expression levels ranged from 15% to 130% compared to the optimized xylose inducible promoter. Apart from these constitutive promoters we also identified and characterized novel inducible promoters, which were regulated by the addition of arabinose, galactose and the commonly used allolactose analog IPTG. The potential application of the identified promoters for biotechnologically relevant processes was demonstrated by overexpression of the cholesterol oxidase II from Brevibacterium sterolicum, thus obtaining product yields of up to 1.13 g/l/d.The provided toolbox of novel promoters offers versatile promoter strengths and will significantly contribute to harmonize protein expression in synthetic metabolic pathways, thereby pushing forward the engineering of B. megaterium as microbial cell factory for the biosynthesis and conversion of valuable compounds.

Identification and characterization of a cis antisense RNA of the parC gene encoding DNA topoisomerase IV of Salmonella enterica serovar Typhi

Bacterial cis-encoded antisense RNAs are transcribed from the opposite strand of protein coding genes, and their regulatory roles adapt cells to changing environmental conditions. By deep sequencing of the transcriptome of Salmonella enterica serovar Typhi, an antisense RNA that is encoded in cis to the parC gene was found. parC encodes the subunit A component of topoisomerase IV, a class of enzymes that relax both positively and negatively supercoiled DNA and are also required for segregation of daughter chromosomes in bacteria. Transcription of the 871 nucleotide antisense RNA was confirmed by northern blot and RACE analysis to be expressed mostly in the stationary phase of bacterial growth and also upregulated in iron limitation and osmotic stress conditions. Overexpression of the antisense RNA resulted in a significant increase in parC mRNA levels. Further analysis revealed that expression of the antisense RNA stabilizes the target mRNA, probably by protecting it from endoribonucleases. Our findings confirm and add to the ever increasing knowledge of the important role that regulatory antisense RNAs play in bacteria.

The adaptation responses of bacterial cytoplasmic membrane fluidity in the presence of environmental stress factors — polychlorinated biphenyls and 3-chlorobenzoic acid

Only bacteria sufficiently resistant to the toxic compounds in their environment can be used for the efficient biodegradation process in order to eliminate a widespread contamination by polychlorinated biphenyls (PCBs). The presence of PCBs results in bacterial controlled rigidification of cytoplasmic membrane. The four bacterial isolates from long-term PCB-contaminated soil (Alcaligenes xylosoxidans, Pseudomonas stutzeri) and sediment (Ochrobactrum anthropi, Pseudomonas veronii) have been used to select the strain most adapted to the PCBs, i.e. with efficient changes in the membrane phospholipid fatty acids. PCBs and their toxic degradation products — the 3-chlorobenzoic acids (3-CBA as the most toxic one) — were added separately to the liquid medium with glucose in two experimental sets: at lag phase and in stationary phase of bacterial growth in order to evaluate the effects of chemicals to cytoplasmic membrane. The main parameter — the changes in fatty acids composition (in the total lipids and the main membrane phospholipid phosphatidyletanolamine) were studied. 3-CBA caused growth inhibition when added at lag phase. However, when added during the stationary growth, inhibition was not observed. Similarly, after addition of PCBs to the stationary growth culture, inhibition of growth was not observed with all tested strains (except for P. stutzeri). This fact indicates the importance of time contact of bacteria during growth phase with xenobiotics. O. anthropi and A. xylosoxidans appeared to be the most adapted to the presence of PCBs (with sufficient membrane adaptation), active under the adverse conditions, and able to survive in the contaminated environment.

Distribution and Functions of TonB-Dependent Transporters in Marine Bacteria and Environments: Implications for Dissolved Organic Matter Utilization

BackgroundBacteria play critical roles in marine nutrient cycles by incorporating and redistributing dissolved organic matter (DOM) and inorganic nutrients in the ocean. TonB-dependent transporter (TBDT) proteins allow Gram-negative bacteria to take up scarce resources from nutrient-limiting environments as well as siderophores, heme, vitamin B12, and recently identified carbohydrates. Thus, the characterization of TBDT distribution and functions is essential to better understand the contribution TBDT to DOM assimilation and its consequences on nutrient cycling in the environment.Methodology/Principal FindingsThis study presents the distribution of encoded known and putative TBDT proteins in the genomes of microorganisms and from the Global Ocean Survey data. Using a Lek clustering algorithm and substrate specificities, the TBDT sequences were mainly classified into the following three groups: (1) DOM transporters; (2) Siderophores/Vitamins transporters; and (3) Heme/Hemophores/Iron(heme)-binding protein transporters. Diverse TBDTs were found in the genomes of oligotroph Citromicrobium bathyomarinum JL354 and Citromicrobium sp JLT1363 and were highly expressed in the stationary phase of bacterial growth. The results show that the Gammaproteobacteria and the Cytophaga-Flavobacterium-Bacteroides (CFB) group bacteria accounted for the majority of the TBDT gene pool in marine surface waters.Conclusions/SignificanceThe results of this study confirm the ecological importance of TBDTs in DOM assimilation for bacteria in marine environments owing to a wide range of substrate utilization potential in the ubiquitous Gammaproteobacteria and CFB group bacteria.

Do bacteria age?

Aging, a progressive deterioration of the physical functions necessary for survival and fertility, resulting from deleterious changes, is one of the most fundamental features of Eukaryotes. Bacteria are thought to be examples of organisms that do not age. They divide by binary fission, which is assumed to be a symmetrical division, such that both daughter cells produced from the parent bacterium have the same constituents with no obvious deterioration. The two daughter cells can continue the process apparently indefinitely giving an impression of immortality. But this thinking has come under scanner in recent years. The following new observations argue that bacteria do age: occurrence of morphologically asymmetric cell division; differential cell behavior during the stationary phase of bacterial growth; and asymmetric inheritance of an older pole by one of the daughter cells during cytokinesis. Is there a loss of fitness when a bacterium eventually divides into two daughter cells? Do they initiate ageing to increase fitness under special circumstances? These issues will be the focus of this article which attempts to resolve this controversy based on current evidence.

A conserved RpoS-dependent small RNA controls the synthesis of major porin OmpD

A remarkable feature of many small non-coding RNAs (sRNAs) of Escherichia coli and Salmonella is their accumulation in the stationary phase of bacterial growth. Several stress response regulators and sigma factors have been reported to direct the transcription of stationary phase-specific sRNAs, but a widely conserved sRNA gene that is controlled by the major stationary phase and stress sigma factor, σS (RpoS), has remained elusive. We have studied in Salmonella the conserved SdsR sRNA, previously known as RyeB, one of the most abundant stationary phase-specific sRNAs in E. coli. Alignments of the sdsR promoter region and genetic analysis strongly suggest that this sRNA gene is selectively transcribed by σS. We show that SdsR down-regulates the synthesis of the major Salmonella porin OmpD by Hfq-dependent base pairing; SdsR thus represents the fourth sRNA to regulate this major outer membrane porin. Similar to the InvR, MicC and RybB sRNAs, SdsR recognizes the ompD mRNA in the coding sequence, suggesting that this mRNA may be primarily targeted downstream of the start codon. The SdsR-binding site in ompD was localized by 3′-RACE, an experimental approach that promises to be of use in predicting other sRNA–target interactions in bacteria.

Novel l-amino acid oxidase with algicidal activity against toxic cyanobacterium Microcystis aeruginosa synthesized by a bacterium Aquimarina sp.

A brownish yellow pigmented bacterial strain, designated antisso-27, was recently isolated from a water area of saltpan in Southern Taiwan. Phylogenetic analyses based on 16S rRNA gene sequences indicate that strain antisso-27 belongs the genus Aquimarina in the family Flavobacteriacea and its only closest neighbor is Aquimarina spongiae (96.6%). Based on screening for algicidal activity, strain antisso-27 exhibits potent activity against the toxic cyanobacterium Microcystis aeruginosa. Both the strain antisso-27 bacterial culture and its culture filtrate show algicidal activity against the toxic cyanobacterium, indicating that an algicidal substance is released from strain antisso-27. The algicidal activity of strain antisso-27 occurs during the late stationary phase of bacterial growth. Strain antisso-27 can synthesize an algicidal protein with a molecular mass of 190 kDa, and its isoelectric point is approximately 9.4. This study explores the nature of this algicidal protein such as l-amino acid oxidase with broad substrate specificity. The enzyme is most active with l-leucine, l-isoleucine, l-methionine and l-valine and the hydrogen peroxide generated by its catalysis mediates algicidal activity. This is the first report on an Aquimarina strain algicidal to the toxic M. aeruginosa and the algicidal activity is generated through its enzymatic activity of l-amino acid oxidase.

Sulfolipid accumulation in Mycobacterium tuberculosis disrupted in the mce2 operon

Mycobacterium tuberculosis, the causative agent of tuberculosis, has a lipid-rich cell wall that serves as an effective barrier against drugs and toxic host cell products, which may contribute to the organism's persistence in a host. M. tuberculosis contains four homologous operons called nice (mce1-4) that encode putative ABC transporters involved in lipid importation across the cell wall. Here, we analyzed the lipid composition of M. tuberculosis disrupted in the mce2 operon. High resolution mass spectrometric and thin layer chromatographic analyses of the mutant's cell wall lipid extracts showed accumulation of SL-1 and SL(1278) molecules. Radiographic quantitative analysis and densitometry revealed 2.9, 3.9 and 9.8-fold greater amount of [(35)S] SL-1 in the mce2 operon mutant compared to the wild type M. tuberculosis during the early/mid logarithmic, late logarithmic and stationary phase of growth in liquid broth, respectively. The amount of [(35)S] SL(1278) in the mutant also increased progressively over the same growth phases. The expression of the mce2 operon genes in the wild type strain progressively increased from the logarithmic to the stationary phase of bacterial growth in vitro, which inversely correlated with the proportion of radiolabel incorporation into SL-1 and SL(1278) at these phases. Since the mce2 operon is regulated in wild type M. tuberculosis, its cell wall may undergo changes in SL-1 and SL(1278) contents during a natural course of infection and this may serve as an important adaptive strategy for M. tuberculosis to maintain persistence in a host.

Enhancement of gene expression by a peptide p(CHWPR) produced by Bifidobacterium lactis BB‐12

Recently, probiotics, including Bifidobacterium, Lactobacillus, and Enterococcus, among other organisms, have been clinically applied for their enhancing effects on defense mechanisms. It is reported that gene expression in somatic cells can be activated by autoinducers, which are hormone-like molecules produced in a microbial QS system. In the present study, based on a hypothesis that a low-molecular substance related to the QS system is involved in the probiotics effects of Bifidobacterium, we intended to extract the low-molecular substance. As a result, we successfully isolated the peptide p(CHWPR), which was composed of five amino acids including Cys, His, Trp, Pro, and Arg, and found that the peptide was produced in the stationary phase of bacterial growth and that it could enhance the gene expression of oxalyl-CoA decarboxylase (Oxc). p(CHWPR) enhanced the gene expression of c-myc and interleukin (IL)-6 in an established cell line, HL-60. We demonstrated that p(CHWPR) penetrates the cell membrane and binds specifically to RORgamma, which is a cytosolic nuclear receptor. This suggests that RORgamma bound to p(CHWPR) would bind to promoter regions of the c-myc gene. Furthermore, we found that p(CHWPR) also bound to a transcriptional avtivation subunit, CRSP70; this suggests that p(CHWPR), RORgamma, and CRSP70 in combination enhance transcription activity.

The expression of Bacillus intermedius glutamyl endopeptidase gene in Bacillus subtilis recombinant strains

The gene encoding for B. intermedius glutamyl endopeptidase (gseBi) has previously been cloned and its nucleotide sequence analyzed. In this study, the expression of this gene was explored in protease-deficient strain B. subtilis AJ73 during stationary phase of bacterial growth. We found that catabolite repression usually involved in control of endopeptidase expression during vegetative growth was not efficient at the late stationary phase. Testing of B. intermedius glutamyl endopeptidase gene expression with B. subtilis spo0-mutants revealed slight effect of these mutations on endopeptidase expression. Activity of glutamyl endopeptidase was partly left in B. subtilis ger-mutants. Probably, gseBi expression was not connected with sporulation. This enzyme might be involved in outgrowth of the spore, when germinating endospore converts into the vegetative cell. These data suggest complex regulation of B. intermedius glutamyl endopeptidase gene expression with contribution of several regulatory systems and demonstrate changes in control of enzyme biosynthesis at different stages of growth.

Structure of Thermotoga maritima Stationary Phase Survival Protein SurE : A Novel Acid Phosphatase

Background: The rpoS, nlpD, pcm, and surE genes are among many whose expression is induced during the stationary phase of bacterial growth. rpoS codes for the stationary-phase RNA polymerase σ subunit, and nlpD codes for a lipoprotein. The pcm gene product repairs damaged proteins by converting the atypical isoaspartyl residues back to L-aspartyls. The physiological and biochemical functions of surE are unknown, but its importance in stress is supported by the duplication of the surE gene in E. coli subjected to high-temperature growth. The pcm and surE genes are highly conserved in bacteria, archaea, and plants. Results: The structure of SurE from Thermotoga maritima was determined at 2.0 Å. The SurE monomer is composed of two domains; a conserved N-terminal domain, a Rossman fold, and a C-terminal oligomerization domain, a new fold. Monomers form a dimer that assembles into a tetramer. Biochemical analysis suggests that SurE is an acid phosphatase, with an optimum pH of 5.5–6.2. The active site was identified in the N-terminal domain through analysis of conserved residues. Structure-based site-directed point mutations abolished phosphatase activity. T. maritima SurE intra- and intersubunit salt bridges were identified that may explain the SurE thermostability. Conclusions: The structure of SurE provided information about the protein's fold, oligomeric state, and active site. The protein possessed magnesium-dependent acid phosphatase activity, but the physiologically relevant substrate(s) remains to be identified. The importance of three of the assigned active site residues in catalysis was confirmed by site-directed mutagenesis.

Lysis of yeast cells by Oenococcus oeni enzymes

exhibited extracellular β (1→3) glucanase activity. This activity increased when cells were cultivated with glycosidic cell-wall macromolecules. In addition, the culture supernatant of the organism effectively lysed viable or dead cells of Saccharomyces cerevisiae. This lytic activity appeared in the early stationary phase of bacterial growth. Yeast cells at the end of the log phase of growth were the most sensitive. The optimum temperature for lysis of viable yeast cells was 40°C, which is very different from the temperatures observed in enological conditions (15–20°C). Moreover, the rate of the lytic activity was significantly lower in comparison with yeast cell wall-degrading activities previously measured in various other microorganisms. Therefore, yeast cell death that is sometimes observed during the alcoholic fermentation could hardly be attributed to the lytic activity of O. oeni. Journal of Industrial Microbiology & Biotechnology (2000) 25, 193–197.