An immunoassay for the measurement of (1-->3)-beta-D-glucans in the indoor environment

An inhibition enzyme immunoassay was developed for quantitation of (1→3)-β-D-glucans in the indoor environment. Immunospecific rabbit antibodies were produced by immunization with bovine serum albuminconjugated laminarin.The laminarin calibration curve ranged from 40 to 3000 ng/ml.Another (1→3)-β-D-glucan (curdlan) showed a similar inhibition curve, but was less reactive on a weight basis. Pustulan, presumed to be (1→3)-β-D-glucan, also showed immunoreactivity in the assay. Control experiments indicated that this was due to (1→3)-β-D-glucan structures. Other non-(1→3)-β-D-glucan polysaccharides did not react. (1→3)-β-Dglucan was detectable in dust from a variety of occupational and environmental settings. We conclude that the new assay offers a useful method for indoor (1→3)-β-Dglucan exposure assessment.

The impact of functional genomics on microbiological food quality and safety

In the food processing industry, unwanted occurrence and growth of spoilage and pathogenic microorganisms is a key concern. A prime example is the extremely heat resistant bacterial endospores, microbial survival structures, that create problems due to their ability to survive classical thermal treatments and their ability to subsequently germinate and form actively growing vegetative cells. Research on food spoilage Bacillus subtilis isolates using the Amplified Fragment Length Polymorphism (AFLP) technology and micro-array technology has identified a number of genomic factors correlated to the level of spore heat resistance. Strains could be classified according to these genomic markers. In addition, it was shown with the sequenced B. subtilis laboratory strain that sporulation in the presence of in particular calcium ions in a cocktail of calcium, magnesium, iron, manganese and potassium promotes thermal resistance of developing spores. This physiological observation correlated with an increased expression during sporulation of genes encoding small acid soluble spore proteins. Screening of ingredients using DNA-chip based techniques identifying the above indicated molecular markers, should allow in the future the identification of the occurrence of spoilage and pathogenic bacteria and prediction of their thermal preservation stress resistance. Currently various projects aiming at the integration of genomics data and micro(nano)-technology, a prerequisite if the alluded to ingredient Quality Control is going to succeed, are running or are being set-up. Information from these projects will be used together with the requirements of product organoleptic quality to derive robust integrated food safety and food quality processing parameters. Such parameters should form the basis of future food Quality Assurance systems.

Production of tissue plasminogen activator (t-PA) in Aspergillus niger

A protease-deficient strain of Aspergillus niger has been used as a host for the production of human tissue plasminogen activator (t-PA). In defined medium, up to 0.07 mg t-PA (g biomass)(-1) was produced in batch and fed-batch cultures and production was increased two- to threefold in two-phase batch cultures in which additional glucose was provided as a single pulse at the end of the first batch growth phase. Production was increased [up to 1.9 mg t-PA (g biomass)(-1)] by the addition of soy peptone to the defined medium. The rate of t-PA production in batch cultures supplemented with soy peptone (0.2 to 0.6 mg t-PA L(-1) h(-1)) was comparable to rates observed previously in high-producing mammalian or insect cell cultures. In glucose-limited chemostat culture supplemented with soy peptone, t-PA was produced at a rate of 0.7 mg t-PA L(-1) h(-1). Expression of t-PA in A. niger resulted in increased expression of genes (bipA, pdiA, and cypB) involved in the unfolded protein response (UPR). However, when cypB was overexpressed in a t-PA-producing strain, t-PA production was not increased. The t-PA produced in A. niger was cleaved into two chains of similar molecular weight to two-chain human melanoma t-PA. The two chains appeared to be stable for at least 16 h in culture supernatant of the host strain. However, in general, <1% of the t-PA produced in A. niger was active, and active t-PA disappeared from the culture supernatant during the stationary phase of batch cultures, suggesting that the two-chain t-PA may have been incorrectly processed or that initial proteolytic cleavage occurred within the proteolytic domain of the protein. Total t-PA (detected by enzyme-linked immunoassay) also eventually disappeared from culture supernatants, confirming significant extracellular proteolytic activity, even though the host strain was protease-deficient.

Identification and characterization of a family of secretion-related small GTPase-encoding genes from the filamentous fungus Aspergillus niger: a putative SEC4 homologue is not essential for growth

DNA fragments containing genetic information for five secretion-related small GTPases of Aspergillus niger (srgA-E) were isolated and identified as members of different Rab/Ypt subfamilies. This isolation and the search for similar sequences in fungal genomic and EST databases showed that, in contrast to Saccharomyces cerevisiae, filamentous fungi also possess homologues of mammalian Rab2 GTPases. Multiple transcripts with unusually long 5' and 3' untranslated regions were found for all srg genes. Their level of expression was independent of the type of carbon source used for growth. Although the transcripts of srgA and srgB were abundant to the same extent throughout the cultivation, that of the other genes peaked during the early growth phase and then declined. Two genes, srgA and srgB, were characterized further. The protein encoded by srgA exhibited relatively low identity (58%) to its closest S. cerevisiae homologue SEC4, whereas the protein encoded by srgB showed 73% identity with S. cerevisiae YPT1. In contrast to other SEC4 homologues, srgA was unable to complement an S. cerevisiae sec4 mutant, and its disruption was not lethal in A. niger. SrgA mutants displayed a twofold increase in their hyphal diameter, unusual apical branching and strongly reduced protein secretion during growth on glucose.

Measurement of beta(1-->3)-glucans in occupational and home environments with an inhibition enzyme immunoassay

beta (1-->3)-Glucans are known for their potent ability to induce nonspecific inflammatory reactions and are believed to play a role in bioaerosol-induced respiratory symptoms. An inhibition enzyme immunoassay (EIA) was developed for the quantitation of beta (1-->3)-glucans in dust samples from occupational and residential environments. Immunospecific rabbit antibodies were produced by immunization with bovine serum albumin-conjugated laminarin [beta (1-->3)-glucan] and affinity chromatography on epoxy-Sepharose-coupled beta (1-->3)-glucans. The laminarin-based calibration curve in the inhibition EIA ranged from approximately 40 to 3,000 ng/ml (15 to 85% inhibition). Another beta (1-->3)-glucan (curdlan) showed a similar inhibition curve but was three to five times less reactive on a weight basis. Pustulan, presumed to be a beta (1-->6)-glucan, showed a parallel dose-response curve at concentrations 10 times higher than that of laminarin. Control experiments with NaIO4 and beta (1-->3)-glucanase treatment to destroy beta (1-->6)- and beta (1-->3)-glucan structures, respectively, indicate that the immunoreactivity of pustulan in the assay was due to beta (1-->3)-glucan and not to beta (1-->6)-glucan structures. Other polysaccharides, such as mannan and alpha (1-->6)-glucan, did not react in the inhibition EIA. Beta (1-->3)-Glucan extraction of dust samples in water (with mild detergent) was performed by heat treatment (120 degrees C) because aqueous extracts obtained at room temperature did not contain detectable beta (1-->3)-glucan levels. The assay was shown to detect heat-extractable beta (1-->3)-glucan in dust samples collected in a variety of occupational and environmental settings. On the basis of duplicate analyses of dust samples, a coefficient of variation of approximately 25% was calculated. It was concluded that the new inhibition EIA offers a useful method for indoor beta (1-->3)-glucan exposure assessment.

Prelude to Hopf bifurcation in an epidemic model: analysis of a characteristic equation associated with a nonlinear Volterra integral equation

We discuss a simple deterministic model for the spread, in a closed population, of an infectious disease which confers only temporary immunity. The model leads to a nonlinear Volterra integral equation of convolution type. We are interested in the bifurcation of periodic solutions from a constant solution (the endemic state) as a certain parameter (the population size) is varied. Thus we are led to study a characteristic equation. Our main result gives a fairly detailed description (in terms of Fourier coefficients of the kernel) of the traffic of roots across the imaginary axis. As a corollary we obtain the following: if the period of immunity is longer than the preceding period of incubation and infectivity, then the endemic state is unstable for large population sizes and at least one periodic solution will originate.