The steady-state performance of a multistage fermentor with cell filtering through a membrane and recycling of concentrated cells is studied numerically for continuous production of acetic acid. The tanks-in-series odel is used to describe the flow behaviour of culture broth in the multistage fermentor. Kinetic expressions and parameter values are taken from the literature. The effects of the total number of stages, the dilution rate, the bleed ratio, the recycle ratio and the feed concentrations as operating conditions on fermentor characteristics such as the concentrations of total and viable cells as well as substrate and product in each stage, the cell viability, the acetic acid productivity and the substrate conversion were examined under the conditions of equal tank volumes and a recycle ratio equal to or greater than one. An increase in the number of stages and decreases in the bleed and recycle ratios and in the feed concentration of product enhance the productivity. The relations between the maximum productivity and the corresponding optimum dilution rate and between the corresponding outlet concentrations of the four components and the optimum dilution rate are presented as figures. Equations for the average cell viability and the critical dilution rate causing cell washout are also obtained. Furthermore, the minimum feed concentration of substrate for its complete consumption is mentioned. Compared to a single tank fermentor, staging and cell recycle increase substrate utilisation and acetic acid productivity. The computed performance of the fermentor configuration proposed in this study is sufficiently promising for the continuous production of acetic acid that it should now be checked experimentally.
The effects of cell wall phenolics, lignins and fungal metabolites on end products of simulated rumen fermentations were studied. Monomeric phenolics, selected to represent the products of aerobic oxidation of lignin by fungi, slightly enhanced carbon dioxide output at low concentrations (0.05%) but had no stimulatory effect on acetate production. Higher concentrations (0.5%) of industrial and Klason lignin decreased carbon dioxide, methane, acetate and propionate production. Secondary metabolites from toxigenic strains of Aspergillus flavus, which were used to simulate the presence of contaminated feedstuff arising from non-sterile fungal bioconversion systems (fermentations), stimulated carbon dioxide, methane, acetate and propionate production but not when extracts were boiled or autoclaved. Acetate, propionate, methane and carbon dioxide production were only slightly reduced in the presence of purified aflatoxin. With spruce sawdusts pretreated with fungi, it was found that accumulation of soluble compounds from lignin and polysaccharide depolymerisations in rumen simulations were markedly higher with sawdusts pretreated with fungi under non-sterile conditions. It was concluded that fungal pretreatment of lignocellulosic substrates had no adverse effects on the end products of rumen fermentations.
The genetic relatedness among thirty-three natural isolates of an edible mushroom, Pleurotus ostreatus, collected from Japan, Europe, U.S.A. and Korea was characterized by isoelectric focusing on polyacrylamide gels. The activities of acid phosphatase, alcohol dehydrogenase, esterase, laccase and malate dehydrogenase displayed 19, 9, 32, 11 and 10 distinct isozyme patterns, respectively. By combining the isozyme patterns obtained with the five enzymes, every isolate showed its own distinct electrophoretic phenotype. A distance matrix calculated between all pairs of the 33 electrophoretic phenotypes based on the presence or absence of isozyme bands was analyzed by the group-average method. Results of the cluster analysis assigned the 33 phenotypes into four major groups, each of which coincided with geographically distinct populations. These results suggest that geographical distance between natural populations of P. ostreatus is correlated with the genetic divergence.
Wild Saccharomyces sensu stricto yeasts isolated by K. Mikata and M. Yoneyama in Japan were reidentified by genetic hybridization analysis and molecular karyotyping. Besides known S. cerevisiae and S. paradoxus biological sibling species, two new genetically isolated populations of Saccharomyces sensu stricto complex have been found.
The DNA polymerase (Pol, 66 kDa, product of gene 2) and the primer protein (PP, 31 kDa, product of gene 3) of Bacillus subtilis phage φ29 are indispensable, together with the other phage-encoded DNA binding proteins, for the protein-primed DNA replication of φ29. Immediately after infection, genes of these essential proteins are transcribed in a polycistronic fashion. For the further investigation of these essential proteins, genes 2 and 3 of φ29 were cloned together into an Escherichia coli expression-vector system with T7 promoter. At the same time, gene 1, located downstream of gene 2, was incidentally cloned in the same segment with genes 2 and 3 due to the site of the restriction enzymes used. Though gene 1 belongs to dna genes, its function is still unclear. Upon induction of these cloned genes, we observed a very limited amount of Pol and PP in comparison to the product of gene 1 (gp1). To determine the reason for this large difference in gene expression between these three polycistronic genes, highly expressed gene, gene 1 was removed. As the deletion of gene 1, a reasonably high level of expression from the genes of both Pol and PP appeared. Efficient expression was also observed when gene 1 was substituted with its suppressor-sensitive allele, demonstrating that gp1 affected the expression of its upstream genes 2 and 3 in E. coli. This evidence is consistent with the very small amount of both Pol and PP detected in the φ29-infected cells of B. subtilis, and implies that gp1 acts as a regulator of protein synthesis of the DNA replication genes.