Cloning of pectate lyase gene pel from Pseudomonas fluorescens and detection of sequences homologous to pel in Pseudomonas viridiflava and Pseudomonas putida

Pectate lyase (PL) depolymerizes pectin and other polygalacturonates (PGAs) and is thought to play a role in bacterial invasion of plants. Production of PL by the soft-rotting pathogen Pseudomonas fluorescens CY091 is regulated by Ca2+. In the presence of Ca2+, this bacterium constitutively synthesizes PL in media containing glucose, glycerol, or PGA and excretes over 87% of total PL into culture fluids. In the absence of Ca2+, the organism fails to use PGA as a carbon source and produces very low levels of PL in media containing glucose or glycerol. Of the small amount of PL produced by the bacterium in Ca(2+)-deficient media, over 78% was detected within the cells, indicating that Ca2+ is critical not only for the production but also for the secretion of PL. The pel gene, encoding an alkaline PL (pI 10.0, Mr 41,000) was cloned and located on the overlapping region of a 4.3-kb SalI and a 7.1-kb EcoRI fragment. The 7.1-kb EcoRI fragment appears to contain a promoter for pel gene expression. A 1.7-kb SalI-XhoI subfragment of the 4.3-kb SalI fragment was cloned into pUC18 to give pROTM2. Escherichia coli cells carrying pROTM2 produce 50 to 100 times more PL than do cells carrying other pectolytic constructs. Production of PL by E. coli (pROTM2) was not affected by carbon sources or by Ca2+. The pI and Mr of PL from E. coli corresponded to values for its counterpart from P. fluorescens. A 0.7-kb BglII-ClaI fragment encoding the pel structural sequence was used to detect pel homologs in various species of fluorescent pseudomonads. Homologous sequences were observed in 10 of 11 strains of P. fluorescens, P. viridiflava, and P. putida. The pel gene in fluorescent pseudomonads is well conserved and may exist and remain repressed in certain strains or species which exhibit nonpectolytic phenotypes under laboratory conditions.

The histological maturity of regenerating mucosa of healed duodenal ulcer and ulcer recurrence after treatment with H2-antagonist

We investigated the relationship between the histological maturity of regenerating mucosa of healed duodenal ulcer and ulcer recurrence, after treatment with an H2-antagonist. Duodenal ulcer patients were given H2-antagonists (either cimetidine or famotidine) for 4 wk of therapy. Fifty-two (77.6%) of the 67 patients were healed endoscopically. The histological state of the regenerating mucosa of healed duodenal ulcer was divided into three categories: good, fair, and poor patterns. Of the 52 healed patients, 15 achieved a good histological pattern. None of these 15 patients had a recurrence 3 months later. However, nine of the 37 patients with a fair or poor pattern of regenerating mucosa had a recurrence 3 months after healing (p = 0.034). We concluded that a duodenal ulcer should be treated until the regenerating mucosa of the healed ulcer reaches a good histological pattern, so as to prevent the recurrence of the ulcer.

Analysis of pectate lyases produced by soft rot bacteria associated with spoilage of vegetables

Isoelectric focusing (IEF) profiles of pectate lyases (PLs) produced by five different groups of soft rot bacteria were analyzed by using the combined techniques of thin-layer polyacrylamide gel IEF and agarose-pectate overlay activity staining. Four strains of soft rot Erwinia spp. produced three or more PL isozymes. All of eight Pseudomonas viridiflava strains examined produced one single PL with a pI of 9.7. All 10 of Pseudomonas fluorescens strains produced two PLs; the major one had a pI of 10.0 and the minor one had a pI of 6.7. A single PL with a pI of greater than or equal to 10.0 was detected in one strain each of Xanthomonas campestris and Cytophaga johnsonae. PLs of six representative strains were purified from culture supernatants by ammonium sulfate precipitation and anion-exchange chromatography. All purified PL samples macerated potato slices, but to different degrees. The Mrs of alkaline PLs produced by P. viridiflava, P. fluorescens, X. campestris, and C. johnsonae were estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis to be 42,000, 41,000, 41,500, and 35,000, respectively. IEF profiles of PLs were distinct among the bacterial species. Profiles of non-Erwinia spoilage bacteria were considerably simpler than those of Erwinia spp. The PL with an alkaline pI appeared to be the principal or the sole enzymatic factor involved in tissue maceration caused by most strains of soft rot bacteria.

Ellagic acid effects on the carcinogenicity, DNA-binding and metabolism of 7,12-dimethylbenz(a)anthracene (DMBA)

Naturally-occurring components of the human food supply have recently received attention as possible agents for cancer chemoprevention. The plant phenol ellagic acid has been reported to be an effective inhibitor of carcinogen metabolism and certain chemically-induced tumors. Therefore, we evaluated the efficacy of ellagic acid in inhibiting DMBA metabolism, DNA-binding and the initiation of DMBA-induced carcinogenesis in rat mammary tissue. Mammary epithelial cell aggregates were isolated from rats fed control and ellagic acid (0.4 and 0.8%) containing diets. When incubated with DMBA, aggregates from ellagic acid-fed rats exhibited a significant but modest inhibition of DMBA metabolism and DNA-binding. An inhibition of DMBA-DNA binding and DMBA metabolism in secondary cultures of mammary epithelial cells also was detected only when ellagic acid was added at 150 molar excess compared to DMBA. The feeding of ellagic acid (0.8%) to rats for 28 days prior to the administration of DMBA resulted in a 21% reduction in mammary tumor incidence at 21 weeks which was, however, not statistically significant. Together, these results indicate that, in contrast to its effects with other carcinogens in other tissues, ellagic acid is not a potent inhibitor of DMBA metabolism, DNA-binding and carcinogenicity with rat mammary tissue.

Effects of hydralazine on guanosine cyclic 3', 5'-monophosphate levels in rat aorta

The mechanism of the vasodilator effect of hydralazine on isolated rat aorta was studied. Results demonstrated that the vasodilator effect of hydralazine was greater on intact aortas than on endothelium-denuded preparations, particularly at low concentrations of between 0.1 mM and 0.5 mM. In addition, hydralazine did not have any effect on cyclic GMP levels. We also found that methylene blue, an inhibitor of guanylate cyclase, completely abolished the vasorelaxant action of nitroglycerin but not that of hydralazine. These results indicate that the vasodilator effect of hydralazine was not due to elevating the cyclic GMP levels. On the other hand, hydralazine significantly inhibited both the contractions induced by norepinephrine and/or high-potassium. In conclusion, a part of the vasodilator effect of hydralazine seems to depend on the integrity of the vascular endothelium. However, this vasodilator effect was not associated with any elevation in cyclic GMP level. Thus, the direct vasodilator action of hydralazine may be related to its interference with the movement and/or translocation of calcium across the cell membrane.

Urbanization in Taiwan: 1900-1985

This paper reviews previous research and statistical data concerning urbanization and its relationship to migration in Taiwan from 1900-1985. The level of urbanization was very low when Taiwan was under Japanese rule. The low level of industrialization and the difficulty of communication and transportation in the early stage of development may have impeded migration. Beginning in 1953, Taiwan began a series of economic construction plans. Modern industries have burgeoned in many large cities and their peripheral townships, thus accelerating the urbanization process. The data clearly show that the growth rate of the urban population has been much faster than the rate of change in the proportion that is urban. During the 1920-1940 period, the population of Taiwan gradually moved from places of early settlement to new city centers or newly developed areas. It is quite clear that the process of metropolitan dispersion has increased with the development of urbanization in Taiwan. The pattern of city growth was not consistent from period to period. It was reverse U-shaped for the 1950-1960 period, upward-wave-shaped for the 1960-1970 period, and J-shaped for the 1970-1985 period. If a longer period (e.g., 1947-1985) was observed, then it became upward-wave-shaped again. It is quite clear that there is no simple relationship between city size and city growth. This relationship is affected by stage of development; it also appears to be affected by duration of observation. Generally, the longer the interval observed, and the later the period analyzed, the more the upward-wave-shape holds for the relationship. Many scholars maintain that urban growth in developing countries results primarily from the natural increase of urban populations. However, judging from the rapid urban growth in Taiwan during the 1953-1985 period, and considering the natural increase contributed by migrants in urban areas, it is likely that rural-urban migration is a more important source of urban growth.

Properties of Cytophaga johnsonae strains causing spoilage of fresh produce at food markets

Two strains of gliding, orange-pigmented bacteria, isolated from fresh bell pepper and watermelon, respectively, showing soft-rot lesions, were identified as Cytophaga johnsonae. They differed from seven type strains of C. johnsonae deposited at the American Type Culture Collection (ATCC) in some properties, such as the ability to utilize glucose, xylose, trehalose, rhamnose, and sucrose. Spherical bodies resembling microcysts of Sporocytophaga sp. in addition to short rods and long filaments were observed in two strains (ATCC 29583 and 29588) throughout the growth cycle and also in aged cultures of other strains. All strains examined were shown to degrade five natural or synthetic polymers (pectin, chitin, starch, protein, and carboxymethyl cellulose). Only six strains (including ATCC 17061, 29587, 29589, and 19366) were able to infect and macerate artificially wounded potato tubers and fruits of pepper, squash, and tomato. The pathogenic strains secreted more pectate lyase in broth medium than the nonpathogenic strains. C. johnsonae, generally known as a soil saprophyte, might occasionally act as an opportunistic pathogen, causing decay of fresh produce in storage or in transit.

Polymyxin resistance in Agrobacterium tumefaciens and its effect on crown gall tumor induction

Polymyxin-resistant (PBLr) mutants of Agrobacterium tumefaciens A6, B6, and B6M were isolated from polymyxin-sensitive (PBLs) parent strains in a defined medium containing 600 microgram of polymyxin B sulfate per millilitre. The weight and number of tumors induced by PBLr mutants on a variety of host plants such as carrot, potato, and pinto bean were 45--75% less than those induced by PBLs wild types. The crude cell envelopes (CCE) prepared from both PBLs and PBLr bacteria were inhibitory for tumor initiation when they were applied before or during the inoculation of viable tumorigenic bacteria, but not when they were applied 30 min after the inoculation of infectious bacteria. The potency to inhibit the tumor initiation by the CCE prepared from PBLs cells was approximately 50% higher than that by the equal amount of the CCE prepared from PBLr cells. The concentration of CCE preparations required to reduce tumor induction 50% in carrot and pinto bean was determined to be 2.6 mg/mL and 4.0--6.2 mg/mL for the CCE derived from PBLs and PBLr cells, respectively. These data suggest that the envelope structure or composition of PBLs and PBLr cells is distinct, and that the acquisition of resistance to polymyxin by agrobacteria modifies envelope structure or components which are essential for tumor initiation.

Effect of osmotic potential, pH, and temperature on the growth of a helical, motile mycoplasma causing corn stunt disease

Growth characteristics of corn stunt spiroplasma, a helical, motile mycoplasma, were studied over a range of osmolality, pH, and temperature in a simple medium containing 20% (v/v) agamma horse serum, 1.5% (w/v) PPLO broth, and various concentrations of sucrose. The spiroplasma was able to grow in a wide spectrum of osmolalities from 360 to 1120 mosm. Optimal growth was observed in media that contained 0.25-0.35 M sucrose. The organism became longer and thinner in media adjusted to 0.65 M sucrose or more. The spiroplasma lost helicity and motility immediately after transfer to media at pH 5.4 or lower. Optimal pH for growth was 7.2. No growth was observed at pH lower than 5.4 or higher than 8.0. Optimal temperature for growth was 32 degrees C. Very little or no growth was observed at temperatures lower than 15 degrees C or higher than 35 degrees C.