The Occurrence and Persistence of Mixed Biofilms in Automobile Air Conditioning Systems

Twelve automobile air conditioner systems from six manufacturers and three countries, selected mostly because of complaints of unpleasant odors in the passenger compartment, were examined for microbial growth by direct microscopy and enrichment culture. Mixed populations of fungi and bacteria (with occasional protozoa) were observed in biofilms in at least some of the components from all used units. The aluminum heat exchanger fins from ten evaporators demonstrated bacterial biofilms that yielded Methylobacterium mesophilicum. Penicillium viridicatum colonized components from four units. These bacteria and fungi were recoverable repeatedly from these units during ‘dry’ storage of up to 27 months. This report associates a bacterial-fungal community with disagreeable air quality in some automobiles. Received: 24 March 1999 / Accepted: 13 April 1999     

Fungal colonization of automobile air conditioning systems

Air samples and swab samples of the air conditioning vents were collected from 29 automobiles in the metropolitan region of Atlanta, GA, and cultured for fungi. Among the fungi observed, species of Acremonium, Aspergillus, Alternaria, Aureobasidium, Cladosporium, and Penicillium were in the highest densities. Transparent adhesive tape imprints, SEM observations, and enrichment culture of components of five systems demonstrated fungal hyphae on the metal surfaces and within the matrix of various insulation materials. The evaporator removed from one automobile because of a series of complaints of noxious odors was densely colonized by Penicillium viridicatum. The amplification of known allergenic and odor-producing fungi occurred within the automobile air conditioning systems. Received 27 May 1997/ Accepted in revised form 16 July 1997     

Production of volatile organic compounds (VOCs) by yeasts isolated from the ascocarps of black (<Emphasis Type="Italic">Tuber melanosporum</Emphasis> Vitt.) and white (<Emphasis Type="Italic">Tuber magnatum</Emphasis> Pico) truffles

Twenty-nine yeast strains were isolated from the ascocarps of black and white truffles (Tuber melanosporum Vitt. and Tuber magnatum Pico, respectively), and identified using a polyphasic approach. According to the conventional taxonomic methods, MSP-PCR fingerprinting and sequencing of the D1/D2 domain of 26S rDNA, the strains were identified as Candida saitoana, Debaryomyces hansenii, Cryptococcus sp., Rhodotorula mucilaginosa, and Trichosporon moniliiforme. All isolates assimilated l-methionine as a sole nitrogen source and produced the volatile organic compounds (VOCs), 2-methyl butanol, 3-methyl butanol, methanethiol, S-methyl thioacetate, dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide, dihydro-2-methyl-3(2H)-thiophenone and 3-(methylthio)-1-propanol (MTP). ANOVA analysis of data showed significant (P<0.01) differences in VOCs produced by different yeasts, with MTP as the major component (produced at concentrations ranging from 19.8 to 225.6 mg/l). In addition, since some molecules produced by the isolates of this study are also characteristic of truffle complex aroma, it is possible to hypothesize a complementary role of yeasts associated with this ecosystem in contributing to final Tuber spp. aroma through the independent synthesis of yeast-specific volatile constituents.     

Effect of Volatile Organic Compounds from Bacteria on Nematodes

The five studied bacterial strains could produce volatile organic compounds (VOCs) that kill nematodes. Based on their 16S rRNA sequences, these strains were identified as Pseudochrobactrum saccharolyticum, Wautersiella falsenii, Proteus hauseri, Arthrobacter nicotianae, and Achromobacter xylosoxidans. The bacterial VOCs were extracted using solid‐phase micro‐extraction (SPME) and subsequently identified by GC/MS analysis. The VOCs covered a wide range of aldehydes, ketones, alkyls, alcohols, alkenes, esters, alkynes, acids, ethers, as well as heterocyclic and phenolic compounds. Among the 53 VOCs identified, 19 candidates, produced by different bacteria, were selected to test their nematicidal activity (NA) against Caenorhabditis elegans and Meloidogyne incognita. The seven compounds with the highest NAs were acetophenone, S‐methyl thiobutyrate, dimethyl disulfide, ethyl 3,3‐dimethylacrylate, nonan‐2‐one, 1‐methoxy‐4‐methylbenzene, and butyl isovalerate. Among them, S‐methyl thiobutyrate showed a stronger NA than the commercial insecticide dimethyl disulfide. It was reported for the first time here that the five bacterial strains as well as S‐methyl thiobutyrate, ethyl 3,3‐dimethylacrylate, 1‐methoxy‐4‐methylbenzene, and butyl isovalerate possess NA. These strains and compounds might provide new insights in the search for novel nematicides.     

The impact of post-harvest storage on sweet corn aroma

Fresh market sweet corn (Zea mays L.) is a high sugar, high moisture vegetable that, due to its fast metabolic rate, is susceptible to rapid post-harvest decay at ambient temperatures. Immediate cooling and storage at low but not freezing temperatures are well established industry practices for maintaining post-harvest sugar content. Less is known about how post-harvest storage temperature impacts other important sweet corn consumer traits, such as aroma. In this study we measure the production and stability of the cooked sweet corn aroma compounds dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide, 3-methyl furan, 3-methyl butanal and 2-methyl butanal. We reveal that these aroma compounds are also susceptible to post-harvest decay if sweet corn is stored at ambient rather than cool temperatures. Furthermore, the quantities and post-harvest decay rates of aroma volatiles vary among different sweet corn lines, indicating that sweet corn genetics can impact maintenance of post-harvest flavor.     

Identification of Volatile Metabolites from Five Fungal Species Cultivated on Two Media

Five fungal species, Aspergillus versicolor, Penicillium commune, Cladosporium cladosporioides, Paecilomyces variotii, and Phialophora fastigiata, were cultivated on two media, malt extract agar and dichloran glycerol agar. Culture flasks provided with inlet and outlet tubes were used and purified, and humidified air was constantly led through the flasks. Air samples from the cultures were sorbed on Tenax GR and analyzed by thermal desorption-gas chromatography. The produced volatile metabolites were analyzed by mass spectrometry. Various hydrocarbons, alcohols, ketones, ethers, esters, sulfur-containing compounds, and terpenes were identified. The most commonly produced substances were 2-methyl-1-propanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 3-methylfuran, and dimethyl disulfide. The production was highly dependent on both medium and species.     

Effects of Methylated, Organic, and Inorganic Substrates on Microbial Consumption of Dimethyl Sulfide in Estuarine Waters

We examined the effects of a variety of amendments on the consumption of [U-¹⁴C]dimethyl sulfide in a Georgia salt marsh. Methylated compounds, particularly those with dimethyl groups, significantly inhibited dimethyl sulfide consumption, while nonmethylated substrates had little effect. Dimethyl disulfide and dimethyl ether were the most effective inhibitors tested.     

Effects of growth conditions on production of methyl selenides in cultures of Rhodobacter sphaeroides

Rhodobacter sphaeroides 2.4.1 exposed to selenate or selenite produced volatile selenium compounds. Total amounts of dimethyl selenide, dimethyl diselenide, dimethyl sulfide and dimethyl disulfide in culture medium and headspace were determined. The highest selenate volatilization occurred in the late stationary phase of growth. However, cultures deprived of light in the stationary phase of growth produced much less of the volatile organo-selenium compounds. Lower culture pHs increased the rate of selenium volatilization. Low sulfate concentration limited biomass production and selenium volatilization; high sulfate concentrations had an enhancing effect on the release of organo-selenium compounds. Cultures of R. sphaeroides reacted very differently to amendments with increasing amounts of selenate and selenite. Only small amounts of selenite were volatilized; meanwhile high amounts of methylated selenides were found in selenate-poisoned cultures. Received 03 February 1997/ Accepted in revised form 16 May 1997     

The Ways of Plant Colonization by MethylobacteriumStrains and Properties of These Bacteria

The pink-pigmented facultative methylotrophic bacteria (PPFMB) of the genus Methylobacteriumare indispensible inhabitants of the plant phyllosphere. Using maize Zea maysas a model, the ways of plant colonization by PPFMB and some properties of the latter that might be beneficial to plants were studied. A marked strain, Methylobacterium mesophilicumAPR-8 (pULB113), was generated to facilitate the detection of the methylotrophic bacteria inoculated into the soil or applied to the maize leaves. Colonization of maize leaves by M. mesophilicumAPR-8 (pULB113) occurred only after the bacteria were applied onto the leaf surface. In this case, the number of PPFMB cells on inoculated leaves increased with plant growth. During seed germination, no colonization of maize leaves with M. mesophilicumcells occurred immediately from the soil inoculated with the marked strain. Thus, under natural conditions, colonization of plant leaves with PPFMB seems to occur via soil particle transfer to the leaves by air. PPFMB monocultures were not antagonistic to phytopathogenic bacteria. However, mixed cultures of epiphytic bacteria containing Methylobacterium mesophilicumor M. extorquensdid exhibit an antagonistic effect against the phytopathogenic bacteria studied (Xanthomonas campestris, Pseudomonas syringae, Erwinia carotovora, Clavibacter michiganense,andAgrobacterium tumifaciens). Neither epiphytic nor soil strains of Methylobacterium extorquens, M. organophillum, M. mesophilicum, andM. fujisawaensecatalyzed ice nucleation. Hence, they cause no frost injury to plants. Thus, the results indicate that the strains of the genus Methylobacteriumcan protect plants against adverse environmental factors.     

Über einige die Strahlenempfindlichkeit von Schimmelpilzen beeinflussende Faktoren

Zusammenfassung Der Einfluß der Nährmedien, der Inkubationstemperatur und des Kulturalters auf die Strahlenempfindlichkeit verschiedener Stämme von Penicillium viridicatum und Aspergillus flavus wird beschrieben. Die Reaktivierbarkeit bestrahlter Conidien war auf optimalen Nährmedien erhöht. Bei A. flavus wurde die Reaktivierbarkeit bestrahlter Conidien durch optimale Bebrütungstemperatur begünstigt, während die bestrahlten P. viridicatum-Stämme höchste relative Wachstumsraten bei suboptimalen Temperaturen zeigten. Die Strahlenempfindlichkeit der Conidien nahm mit deren Alter zu. Bei aktiv wachsenden Pilzkulturen war die Strahlenempfindlichkeit gegenüber älteren Kulturen erhöht.

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Some factors affecting the radiosensitivity of moulds

Summary The influence of the growth media, the incubation temperature, and the age of the cultures on the radiation sensitivity of different strains of Penicillium viridicatum and Aspergillus flavus is described. The recovery of irradiated conidia was higher on optimal media. The recovery of irradiated conidia of A. flavus was favored by optimal incubation temperature, while those of P. viridicatum showed highest relative growth rates at suboptimal temperatures. The radiosensitivity of the conidia increased with age. Actively growing cultures of the moulds were more sensitive to radiation than older ones.

     

Mold colonization during use of preservative-treated and untreated air filters, including HEPA filters from hospitals and commercial locations over an 8-year period (1996–2003)

High efficiency particulate arrestance (HEPA; 99.97% efficient at 0.3 m) filters, filters with ASHRAE particulate arrestance rating of 90–95% at 1 m (90–95% filters), and lower efficiency cellulosic-polyester filters from air conditioning systems in hospitals and commercial buildings were removed from the systems and examined microscopically for mold colonization. Cellulosic-type filters from systems with water entrainment problems typically were colonized, or became colonized upon incubation in moisture chambers. Species of Acremonium, Aspergillus, and Cladosporium were most common. With air filters of all types, treatment of filter media with an antimicrobial preservative tended to reduce or delay colonization. Mold colonization of HEPA and 90–95% filters was observed most often on the load surfaces, but two untreated HEPA filters were permeated with fungi, one with Aspergillus flavus, the other with Cladosporium sp. Air filters in heating, ventilating, and air conditioning (HVAC) systems, particularly those with chronic or periodic exposure to moisture, may serve as point sources for indoor molds.     

Conversion of the mycotoxin citrinin into dihydrocitrinone and ochratoxin A by Penicillium viridicatum

Summary The mycotoxin citrinin, produced by Penicillium viridicatum, was found to be unstable in broth culture. This instability was investigated using the techniques of ¹⁴C-labelling, mass spectrometry and thin layer chromatography. It was concluded that intracellular factors released by P. viridicatum were responsible for the instability of the mycotoxin. The major products resulting from the breakdown of citrinin were identified as 3,4-dihydro-6,8-dihydroxy-3,4,5-trimethyl-isocoumarin-7-carboxylic acid (dihydrocitrinone) and ochratoxin A.     

A Study on Low-boiling Compounds of Essential Oil of Geranium Species

From the first crop of P. graveolens and the first and third ones of P. roseum Bourbon, low-boiling compounds escaping during the steam distillation were collected, and examined through gas chromatography and the preparation of their derivatives. Nine hydrocarbons, five carbonyl compounds, three alcohols, two esters and one sulfide were identified. Among these twenty compounds, sixteen compounds except dimethyl sulfide, α-pinene, myrcene and limonene were newly identified in the geranium species. Appreciable variation between the species was observed in contents of methanol, acetone, dimethyl sulfide and terpene hydrocarbons.     

Chemical constituents and medicinal properties of Allium species

Allium species, belonging to Alliaceae family, are among the oldest cultivated vegetables used as food. Garlic, onions, leeks and chives, which belong to this family, have been reported to have medicinal properties. The Allium species constituents have been shown to have antibacterial and antioxidant activities, and, in addition, other biological properties. These activities are related to their rich organosulfur compounds. These organosulfur compounds are believed to prevent the development of cancer, cardiovascular, neurological, diabetes, liver diseases as well as allergy and arthritis. There have also been reports on toxicities of these compounds. The major active compounds of Allium species includes, diallyl disulfide, diallyl trisulfide, diallyl sulfide, dipropyl disulfide, dipropyl trisulfide, 1-propenylpropyl disulfide, allyl methyl disulfide and dimethyl disulfide. The aim of this review is to focus on a variety of experimental and clinical reports on the effectiveness, toxicities and possible mechanisms of actions of the active compounds of garlic, onions, leek and chives.

     

Production of volatile organic sulfur compounds (VOSCs) by basidiomycetous yeasts

Thirty-seven basidiomycetous yeasts belonging to 30 species of seven genera were grown on media containing l-cysteine or l-methionine as sole nitrogen sources with the objective of evaluating volatile organic sulfur compound (VOSC) production. The headspace of yeast cultures was analyzed by the solid-phase microextraction (SPME) sampling method, and volatile compounds were quantified and identified by GC-MS techniques. Ten strains assimilating L-methionine produced the following VOSCs: 3-(methylthio)-1-propanol, methanethiol, S-methyl thioacetate, dimethyl disulfide, dimethyl trisulfide, allyl methyl sulphide and 4,5-dihydro-3(2H)-thiophenone. Production was <1 mgl(-1) except for 3-(methylthio)-1-propanol of which between 40 and 400 mgl(-1) was synthesized. Higher alcohols (isobutyl alcohol, isoamyl alcohol and active amyl alcohol) and esters (ethyl acetate, ethyl propionate, n-propyl acetate, isobutyl acetate, n-propyl propionate, n-butyl acetate, isoamyl acetate, amyl acetate, isoamyl propionate, amyl propionate and 2-phenylmethyl acetate) were also sporadically produced. This is the first report of VOSCs production by basidiomycetous yeasts. Consequently, basidiomycetous yeasts may be considered an interesting new group of microbial VOSCs producers for the flavor industry.     

Major Volatile Components Formed from Casein during Roasting

The volatiles, produced from casein during roasting at 250°C for 1 hr, were fractionated and analyzed by various methods including the combination of gas chromatography and mass spectrometry. The following kinds of compounds were tentatively or conclusively identified: six aliphatic aldehydes, benzaldehyde, acetophenone, hydrogen sulfide, methanethiol, dimethyl disulfide, five primary alkylamines, piperidine, N-ethylcyclohexylamine, two alkylpyrazines, ethylmethylpyridine, three aliphatic carboxylic acids, pyruvic acid, benzoic acid, six aliphatic alcohols, and three aromatic hydrocarbons. α-Dicarbonyls were not formed in any detectable amount.

The results obtained above are discussed in comparison with those of pyrolysis of some kinds of α-amino acid and also with those of some roasted foods.     

Volatile Compounds Produced in Sterile Fish Muscle (Sebastes melanops) by Pseudomonas putrefaciens, Pseudomonas fluorescens, and an Achromobacter Species

Volatile compounds produced by Pseudomonas putrefaciens, P. fluorescens, and an Achromobacter species in sterile fish muscle (Sebastes melanops) were identified by combined gas-liquid chromatography and mass spectrometry. Compounds produced by P. putrefaciens included methyl mercaptan, dimethyl disulfide, dimethyl trisulfide, 3-methyl-1-butanol, and trimethylamine. With the exception of dimethyl trisulfide, the same compounds were produced by an Achromobacter species. Methyl mercaptan and dimethyl disulfide were the major sulfur-containing compounds produced by P. fluorescens.     

Transmission of <Emphasis Type="Italic">Methylobacterium mesophilicum</Emphasis> by <Emphasis Type="Italic">Bucephalogonia xanthophis</Emphasis> for paratransgenic control strategy of Citrus variegated chlorosis

Methylobacterium mesophilicum, originally isolated as an endophytic bacterium from citrus plants, was genetically transformed to express green fluorescent protein (GFP). The GFP-labeled strain of M. mesophilicum was inoculated into Catharanthus roseus (model plant) seedlings and further observed colonizing its xylem vessels. The transmission of this endophyte by Bucephalogonia xanthophis, one of the insect vectors that transmit Xylella fastidiosa subsp. pauca, was verified by insects feeding from fluids containing the GFP bacterium followed by transmission to plants and isolating the endophyte from C. roseus plants. Forty-five days after inoculation, the plants exhibited endophytic colonization by M. mesophilicum, confirming this bacterium as a nonpathogenic, xylem-associated endophyte. Our data demonstrate that M. mesophilicum not only occupy the same niche of X. fastidiosa subsp. pauca inside plants but also may be transmitted by B. xanthophis. The transmission, colonization, and genetic manipulation of M. mesophilicum is a prerequisite to examining the potential use of symbiotic control to interrupt the transmission of X. fastidiosa subsp. pauca, the bacterial pathogen causing Citrus variegated chlorosis by insect vectors.     

Production of Oil-Releasing Compounds by Microorganisms from the Daqing Oil Field,China

Twenty pure cultures isolated from formation waters of the Daqing oil field were studied with respect to their capacity to produce surface-active compounds in media with individual hydrocarbons, lower alcohols, and fatty acids. Aerobic saprotrophic bacteria belonging to the genera Bacillus, Brevibacillus, Rhodococcus, Dietzia, Kocuria, Gordonia, Cellulomonas, Clavibacter, Pseudomonas, and Acinetobacter decreased the surface tension of cultivation media from 55–63 to 28–44 mN/m. Strains of Bacillus cereus, Rhodococcus ruber, andBacillus licheniformis produced biosurfactants most actively. Bacteria of the genera Rhodococcus, Dietzia, Kocuria, and Gordonia produced exopolysaccharides in media with hydrocarbons. Culture liquids of the strains of R. ruberand B. licheniformis exhibited an oil-releasing effect. Thus, the Daqing oil field is inhabited by aerobic bacteria capable of producing effective oil-releasing agents.