Effects of Four Isothiocyanates in Dissolved and Gaseous States on the Growth and Aflatoxin Production of Aspergillus flavus In Vitro.

Aflatoxins (AFs), a class of toxins produced by certain species of the genus Aspergillus, occasionally contaminate food and cause serious damage to human health and the economy. AFs contamination is a global problem, and there is a need to develop effective strategies to control aflatoxigenic fungi. In this study, we focused on isothiocyanates (ITCs) as potential chemical agents for the control of aflatoxigenic fungi. We quantitatively evaluated the effects of four ITCs (allyl ITC (AITC), benzyl ITC (BITC), and methyl and phenylethyl ITCs) in dissolved and gaseous states on the growth and aflatoxin B1 production of Aspergillus flavus. In experiments using dissolved ITCs, BITC was found to be the strongest inhibitor of growth and aflatoxin B1 production by A. flavus. Meanwhile, in the gaseous state, AITC strongly inhibited the A. flavus growth. When the concentration of ITCs in the liquid medium was quantified over time, AITC levels decreased to below the detection limit within 24 h, whereas BITC levels remained stable even after 48 h. These results suggested that when ITCs are utilized to control aflatoxigenic fungi, it is necessary to use them in a dissolved or gaseous state, depending on their volatility.

Human factors and tidal influences on water quality of an urban river in Can Tho, a major city of the Mekong Delta, Vietnam.

In this study, we focused on water quality in an urban canal and the Mekong River in the city of Can Tho, a central municipality of the Mekong Delta region, southern Vietnam. Water temperature, pH, electrical conductivity, BOD5, CODCr, Na(+), Cl(-), NH4 (+)-N, SO4 (2-)-S, NO3 (-)-N, and NO2 (-)-N for both canal and river, and tide level of the urban canal, were monitored once per month from May 2010 to April 2012. The urban canal is subject to severe anthropogenic contamination, owing to poor sewage treatment. In general, water quality in the canal exhibited strong tidal variation, poorer at lower tides and better at higher tides. Some anomalies were observed, with degraded water quality under some high-tide conditions. These were associated with flow from the upstream residential area. Therefore, it was concluded that water quality in the urban canal changed with a balance between dilution effects and extent of contaminant supply, both driven by tidal fluctuations in the Mekong River.

Polynucleobacter rarus sp. nov., a free-living planktonic bacterium isolated from an acidic lake.

The heterotrophic, aerobic, facultatively anaerobic under denitrifying conditions, catalase- and oxidase-positive, non-motile strain MT-CBb6A5(T), which was isolated from an acidic lake located in Wisconsin (USA), was characterized. The strain grew on NSY medium over a temperature range of 15-30 °C and a NaCl range of 0.0-0.3 % (w/v). The predominant fatty acids were C(16 : 0), C(18 : 1)ω7c, 11-methyl C(18 : 1)ω7c, feature 3 (including C(16 : 1)ω7c), and feature 2 (including C(14 : 0) 3-OH). The DNA G+C content of the strain was 40.3 mol%. Phylogenetic analysis as well as strong similarities in phenotypic and chemotaxonomic traits indicated the affiliation with the genus Polynucleobacter. 16S rRNA gene sequence similarity values with the two described species of the genus Polynucleobacter ranged from 95.6 to 96.0 %. The strain differs from the two described species of the genus Polynucleobacter in the ability to assimilate oxalic and glycolic acids, and in the presence of the fatty acids C(15 : 1)ω8c and C(16 : 0) 3-OH as well as in quantitative differences in fatty acid composition. It has to be assumed that the strain shares with other free-living bacteria of the genus Polynucleobacter a planktonic lifestyle in the water column of freshwater habitats. Based on the phylogeny revealed and the chemotaxonomic and phenotypic differences from Polynucleobacter necessarius and Polynucleobacter cosmopolitanus, we propose to establish the novel species Polynucleobacter rarus sp. nov. with the type strain MT-CBb6A5(T) ( = DSM 21648(T)  = CIP 109928(T)).

Involvement of cell surface structures in size-independent grazing resistance of freshwater Actinobacteria.

We compared the influences of grazing by the bacterivorous nanoflagellate Poterioochromonas sp. strain DS on ultramicrobacterial Actinobacteria affiliated with the Luna-2 cluster and ultramicrobacterial Betaproteobacteria of the species Polynucleobacter cosmopolitanus. These bacteria were almost identical in size (<0.1 microm(3)) and shape. Predation on a Polynucleobacter strain resulted in a reduction of >86% relative to the initial bacterial cell numbers within 20 days, while in comparable predation experiments with nine actinobacterial strains, no significant decrease of cell numbers by predation was observed over the period of >or=39 days. The differences in predation mortality between the actinobacterial strains and the Polynucleobacter strain clearly demonstrated size-independent grazing resistance for the investigated Actinobacteria. Importantly, this size-independent grazing resistance is shared by all nine investigated Luna-2 strains and thus represents a group-specific trait. We investigated if an S-layer, previously observed in an ultrastructure study, was responsible for the grazing resistance of these strains. Experiments aiming for removal of the S-layer or modification of cell surface proteins of one of the grazing-resistant strains by treatment with lithium chloride, EDTA, or formaldehyde resulted in 4.2- to 5.2-fold higher grazing rates in comparison to the levels for untreated cells. These results indicate the protective role of a proteinaceous cell surface structure in the size-independent grazing resistance of the actinobacterial Luna-2 strains, which can be regarded as a group-specific trait.

Respiration and Carbon Balance of the Bacterium Pseudomonas sp., a Protozoan Tetrahymena thermophila, and a Fungus Trichoderma viride in a Food Chain System with Glass Beads.

The respiration rates per unit of microbial biomass (qCO(2)) of live cells were evaluated in inorganic medium using glass beads to which glucose was added at a rate of 50 µg C vial(-1) day(-1). The qCO(2) of live cells (g CO(2)-C (g biomass-C)(-1) day(-1)) was 0.23 in a pure culture of bacteria, 0.67 in a mixed culture of bacteria and protozoa, 0.16 in a mixed culture of bacteria and fungi, and 0.20 in a mixed culture of bacteria, protozoa and fungi. A culture system containing glass beads is a useful tool to estimate qCO(2) of live cells.

Effect of environmental factors on the relationship between concentrations of coprostanol and fecal indicator bacteria in tropical (Mekong Delta) and temperate (Tokyo) freshwaters.

A reliable assessment of microbial indicators of fecal pollution (total coliform, Escherichia coli, and fecal streptococcus) is critical in tropical environments. Therefore, we investigated the relationship between concentrations of indicator bacteria and a chemical indicator, coprostanol (5beta-cholestan-3beta-ol), in tropical and temperate regions. Water samples were collected from the Mekong Delta, Vietnam, during wet and dry seasons, and from Tokyo, Japan, during summer, the aftermath of a typhoon, and winter. During the wet season in the Mekong Delta, higher bacterial densities were observed in rivers, probably due to the higher bacterial inputs from soil particles with runoff. In Tokyo, higher bacterial densities were usually observed during summer, followed by those in the typhoon aftermath and winter. A strong logarithmic correlation between the concentrations of E. coli and coprostanol was demonstrated in all surveys. Distinctive seasonal fluctuations were observed, as concentrations of coprostanol corresponding to 1,000 CFU of E. coli/100 ml were at their lowest during the wet season in the Mekong Delta and the typhoon aftermath in Tokyo (30 ng/liter), followed by the dry season in the Mekong Delta and the summer in Tokyo (100 ng/liter), and they were much higher during the winter in Tokyo (400 ng/liter). These results suggested that E. coli is a specific indicator of fecal contamination in both tropical and temperate regions but that the densities are affected by elevated water temperature and input from runoff of soil particles. The concurrent determination of E. coli and coprostanol concentrations could provide a possible approach to assessing the reliability of fecal pollution monitoring data.

Quantitative application of fecal sterols using gas chromatography-mass spectrometry to investigate fecal pollution in tropical waters: western Malaysia and Mekong Delta, Vietnam.

This is the first report on fecal pollution using molecular markers in Southeast Asia where serious sewage pollution has occurred. A simple and sensitive analytical method using gas chromatography-mass spectrometry for 10 sterols in various environmental samples was developed to monitor extensive areas of tropical Asia. First, the method was applied to wastewater to confirm that >95% of sterols existed in the particulate phase. Then the approach was applied to a tropical Asian region, Malaysia and Vietnam, with a selection of 59 sampling stations in total. River water and sediment samples were collected and analyzed for chemical markers (coprostanol and other sterols) and microbiological markers (fecal coliforms and fecal streptococci). Particulate coprostanol concentrations ranged from <0.0001 to 13.47 microg/L in tropical river and estuarine waters, indicating severe fecal pollution in populous areas. Coprostanol concentrations in the sediments ranged from 0.005 to 15.5 microg/g-dry. The sedimentary coprostanol concentrations were lower than those reported in some urban areas of industrialized countries. This is probably because frequent heavy rain induces intensive input of eroded soil, which dilutes fecal material in river sediments. The relationship between the concentrations of fecal sterols and bacterial indicators was examined in an attempt to develop public health criteria for coprostanol levels applicable to the tropical region. Coprostanol concentrations of 30-100 ng/L or percent coprostanol levels of 2% corresponded to approximately 1000 fecal coliforms per 100 mL, which is set for secondary contact limit in many countries. These coprostanol concentrations were lower than those proposed as criteria in temperate countries, probably owing to greater survival of bacteria in warmer tropical waters. On the basis of these criteria, extensive monitoring of sediments suggests that poor sanitary conditions exist in most of the urbanized area of Malaysia and in several urban and rural sites in Vietnam.