Canadian Journal of Microbiology

The relationship of polyketide melanogenesis molecular biology to that of nonmelanin-producing pathways in a wide range of fungi and other organisms is discussed. Analytical methods and fundamental properties of melanins are discussed and fungal melanin properties are compared with those of animal and bacterial melanins. The enzymatic degradation of melanins by lignin peroxidases is described.Key words: fungal melanin, polyketide melanin, DHN melanin, melanin degradation, melanin properties, melanin analysis.

Oxytetracycline, axit oxolinic và flumequine hiện là những tác nhân kháng khuẩn được sử dụng phổ biến nhất trong điều trị cá nuôi ở biển tại Na Uy. Những chất này được cung cấp qua các viên thức ăn, một lượng đáng kể đến cuối cùng nằm trong trầm tích dưới các lồng cá. Các tác động của những chất kháng khuẩn này đối với cộng đồng vi sinh vật trong trầm tích đã được nghiên cứu thực nghiệm trong các bể chứa trầm tích, nơi đã được bổ sung oxytetracycline, axit oxolinic hoặc flumequine, và được cung cấp dòng nước ổn định. Trong 20 ngày đầu của thí nghiệm, khoảng một phần ba lượng tác nhân kháng khuẩn đã biến mất khỏi trầm tích. Trong 165 ngày tiếp theo, thêm 25% lại biến mất. Có sự gia tăng số lượng vi khuẩn kháng lại oxytetracycline và axit oxolinic chỉ vài ngày sau khi bắt đầu thí nghiệm. Độ kháng phát triển đối với oxytetracycline cao hơn và kéo dài lâu hơn so với oxolinic acid và flumequine. Trong số các quinolone, flumequine có vẻ ít khả năng gây kháng nhất. Số lượng vi khuẩn trong tất cả các trầm tích đã điều trị giảm xuống còn 50–67% so với số lượng trong trầm tích đối chứng sau 2 ngày điều trị. Bảy ngày sau khi điều trị, tỷ lệ giảm sulfat trong các trầm tích đã điều trị giảm xuống dưới 10% so với tỷ lệ tìm thấy ở nhóm đối chứng. Hiệu ứng này kéo dài ít nhất 29 ngày, nhưng sau 70 ngày, sự ức chế giảm sulfat trong các trầm tích đã điều trị đã biến mất. Từ khóa: tác nhân kháng khuẩn, trầm tích, sự kháng vi khuẩn, giảm sulfat.

A series of tests is available to study the biodegradation of plastic materials under either laboratory or field conditions. Most of the standard methods have been published by the American Society for Testing and Materials. All of them describe techniques to investigate the biodegradation of plastics under laboratory conditions. Microbially formed polyhydroxyalkanoates (PHAs) have been marketed recently as biodegradable plastics. However, currently only a few articles made from PHAs (e.g., bottles) are commercially available. A series of microorganisms (prokaryotes as well as eukaryotes) has been characterized as being able to degrade PHAs. With one exception (Ilyobacter delafieldii), all of them were isolated from aerobic environments. So far, over 10 different extracellular PHA depolymerases have been purified and characterized. Depolymerases that preferentially attack PHAs with monomer units other than 3-hydroxybutyrate have been found only in Pseudomonas fluorescens and Pseudomonas lemoignei.Key words: poly(3-hydroxybutyrate), polyhydroxyalkanoates, biodegradation, industrial applications.

The use and performance of an improved diagnostic and selective medium, PEMBA (polymyxin pyruvate egg yolk mannitol bromothymol blue agar), for the detection of Bacillus cereus in foods is described. The distinct colonial appearance of B. cereus on PEMBA permitted the recognition of both strains: those that do precipitate egg yolk and those that do not react with egg yolk. A staining procedure, used to demonstrate microscopically both the presence of lipid globules in vegetative cells and spore morphology of isolates, proved a rapid and reliable confirmatory test which gave complete agreement with a battery of biochemical tests used for this purpose. The quantitative recovery of B. cereus on PEMBA from 143 food samples was not significantly different from counts on KG (Kim and Goepfert), MYP (mannitol egg yolk phenol red), and McClung's media, and the selectivity of PEMBA was generally superior.

In this study a collection of rhizobial strains were isolated from effective nodules of Phaseolus vulgaris in a wide region of northern Spain, which is the major producer region of this legume in Spain. The analysis of their core genes, rrs, atpD, and recA, and the 16S–23S intergenic spacer showed that all isolates belong to the phylogenetic group of Rhizobium leguminosarum and some of them were identical to those of strains nodulating Vicia or Trifolium . None of the isolates was identified as Rhizobium etli ; however, all of them carry the nodC alleles α and γ harboured by American strains of this species. These alleles were also found in strains nodulating P. vulgaris in southern Spain identified as R. etli. These results suggest that R. etli was carried from America to Spain with common bean seeds, but that they could have found difficulties persisting in the soils of northern Spain, probably because of the climatic conditions. The symbiotic genes of this species could have been transferred, after the arrival of P. vulgaris, to strains of R. leguminosarum already present in northern Spanish soils.

Trifolium species are the most common legumes present in wild Spanish soils; however, there are no studies to date on the diversity of rhizobia nodulating clover in Spain. Twenty strains from different Spanish soils with acidic, neutral, and basic pH were selected to study their genotypic, phenotypic, and symbiotic features. The results showed that the isolates were genotypically diverse, displaying 12 different DNA fingerprint patterns and also 14 different plasmid profiles. Although they have 16S rRNA gene sequences that are nearly identical to that of the type strain of Rhizobium leguminosarum , their recA and atpD gene sequences were phylogenetically divergent from those of R. leguminosarum reference strains, and phenotypic divergence as well as different host ranges were also found. Although most of them nodulated both Trifolium and Phaseolus , only 5 strains were also able to nodulate Pisum . The results of the effectiveness analysis showed a high variability in the symbiotic characteristics of our strains and suggested that Pisum is the more restrictive host of this group. Interestingly, some of the Trifolium isolates showed an ability to promote growth of Pisum in the absence of nodulation.

Individuals of Artemia salina, the brine shrimp, were captured from the Great Salt Lake, a highly saline (330–340 g ℓ⁻¹ solids content) terminal lake in Utah. Electron microscopy revealed the presence of intracellular procaryotic symbionts in the epithelial lining of the midgut. Fine structure and possible role of the symbiont are discussed.

Fluoride and a variety of other weak acids acted to reduce reversibily the acid tolerance of glycolysis by intact cells of Streptococcus mutans GS-5 as shown by higher final pH values in acid-drop experiments with glucose in excess. The order of effectiveness was fluoride > indomethacin > ibuprofen > ketoprofen > salicylate > sorbate > cinnamate > p-hydroxybenzoate > benzoate > ascorbate. Only fluoride also acted as an inhibitor of the glycolytic enzyme enolase. However, enolase in permeabilized cells was also inhibited by acidification with a sharp drop-off in activity between pH 6 and 5. It was proposed that the weak acids, including fluoride, acted to reduce glycolytic acid tolerance by enhancing cytoplasmic acidification and thereby inhibiting enzymes such as enolase. The potencies of the acids could not be predicted accurately from knowledge of pK_avalues, octanol–water partition coefficients, and molecular weights. It was concluded that their modes of action in acid sensitization involved perturbations of membrane function in addition to their acting as transmembrane carriers of protons. Methylparaben (methyl ester of p-hydroxybenzoate) was also a sensitizer but was less effective than the parent acid.Key words: fluoride, weak acids, enolase, Streptococcus mutans, glycolysis.

River bottom sediments, which were washed free of loosely associated chemical nutrients, were further eluted with phosphate buffer. Chemical analyses of the eluates indicated that 0.3 M buffer (pH 7.0) eluted hexose, protein, and ammonia nitrogen in concentrations 4–6 times that found in the free-flowing water. Respiration experiments showed that selected strains of Enterobacteriaceae, including pathogens, had the ability to metabolize these substrates. These studies indicate that bottom sediments can have a high adsorptive capacity and suggest that they can regulate basic nutrient concentration and eutrophication in situ.