Production of S -Methylthioacetate by Brevibacterium linens

Volatile Organic Compounds from Bacillus aryabhattai MCCC 1K02966 with Multiple Modes against Meloidogyne incognita

Plant-parasitic nematodes cause severe losses to crop production and economies all over the world. Bacillus aryabhattai MCCC 1K02966, a deep-sea bacterium, was obtained from the Southwest Indian Ocean and showed nematicidal and fumigant activities against Meloidogyne incognita in vitro. The nematicidal volatile organic compounds (VOCs) from the fermentation broth of B. aryabhattai MCCC 1K02966 were investigated further using solid-phase microextraction gas chromatography-mass spectrometry. Four VOCs, namely, pentane, 1-butanol, methyl thioacetate, and dimethyl disulfide, were identified in the fermentation broth. Among these VOCs, methyl thioacetate exhibited multiple nematicidal activities, including contact nematicidal, fumigant, and repellent activities against M. incognita. Methyl thioacetate showed a significant contact nematicidal activity with 87.90% mortality at 0.01 mg/mL by 72 h, fumigant activity in mortality 91.10% at 1 mg/mL by 48 h, and repellent activity at 0.01-10 mg/mL. In addition, methyl thioacetate exhibited 80-100% egg-hatching inhibition on the 7th day over the range of 0.5 mg/mL to 5 mg/mL. These results showed that methyl thioacetate from MCCC 1K02966 control M. incognita with multiple nematicidal modes and can be used as a potential biological control agent.

Olfactometry Profiles and Quantitation of Volatile Sulfur Compounds of Swiss Tilsit Cheeses

To establish the odor profiles of three differently fabricated commercial Swiss Tilsit cheeses, analyses were conducted using headspace solid-phase microextraction gas chromatography-mass spectrometry/pulsed flame photometric detection and gas chromatography-olfactometry to identify and quantitate volatile compounds. In addition, odor quality and the impact of target sulfur compounds on the overall odor of the cheeses were investigated. The odor profile was found to be mainly influenced by buttery-cheesy and sulfury odor notes in all cheeses. Buttery-cheesy odor notes were attributed to three main molecules: butanoic acid, 3-methylbutanoic acid, and butane-2,3-dione. Over a dozen volatile sulfur compounds were detected at parts per billion levels, but only a few influenced the odor profile of the cheeses: methanethiol, dimethyl disulfide, bis(methylthio)methane, dimethyl trisulfide, 3-(methylthio)propanal, and 2-methyltetrahydrothiophen-3-one (tentative). In conclusion, the conducted analyses allowed differentiation of the cheeses, and gas chromatography-olfactometry results confirmed that partially thermized milk cheese has a more intense and more multifaceted overall flavor.

Methionine metabolism: major pathways and enzymes involved and strategies for control and diversification of volatile sulfur compounds in cheese

For economical reasons and to accommodate current market trends, cheese manufacturers and product developers are increasingly interested in controlling cheese flavor formation and developing new flavors. Due to their low detection threshold and diversity, volatile sulfur compounds (VSCs) are of prime importance in the overall flavor of cheese and make a significant contribution to their typical flavors. Thus, the control of VSCs formation offers considerable potential for industrial applications. This paper gives an overview of the main VSCs found in cheese, along with the major pathways and key enzymes leading to the formation of methanethiol from methionine, which is subsequently converted into other sulfur-bearing compounds. As these compounds arise primarily from methionine, the metabolism of this amino acid and its regulation is presented. Attention is focused in the enzymatic potential of lactic acid bacteria (LAB) that are widely used as starter and adjunct cultures in cheese-making. In view of industrial applications, different strategies such as the enhancement of the abilities of LAB to produce high amounts and diversity of VSCs are highlighted as the principal future research trend.

Bacterial and fungal community composition over time in chicken litter with high or low moisture content

1. Changes in bacterial and fungal communities in chicken litter with high and low moisture content over a five week period during a single chicken grow out cycle in a poultry shed in subtropical Australia were investigated to study the association between specific microbes and odour production. 2. Microbial biomass, as indicated by DNA yields, was higher and community composition was more dynamic over time in moist compared with dry chicken litter. 3. Bacillus, Atopostipes and Aspergillus species increased in relative abundance in moist chicken litter samples over time reflecting the relatively high fitness and hence activity of these specific bacteria and this specific fungus in this environment.

Production of methanethiol in milk fat-coated microcapsules containingBrevibacterium linensand methionine

Milk fat-coated microcapsules containingBrevibacterium linensand methionine were used to produce methanethiol, one of the volatile sulphur compounds implicated in Cheddar cheese flavour. Production of methanethiol from methionine occurred aerobically and anaerobically, but the production was 3- to 4-fold greater aerobically with most of the methanethiol being oxidized to dimethyl disulphide. About 35% of the total methanethiol was absorbed by the milk fat capsules and about 65% detected in the headspace. Levels of methanethiol began to decline at 26 °C after 24 h in milk fat-coated microcapsules. However, low temperature, such as 4–12 °C, stabilized levels of methanethiol in microcapsules over an 8-d analysis period. Optimum pH and temperature for methanethiol production were 8 and 26 °C respectively. The antioxidants butylated hydroxytoluene, butylated hydroxyanisole and ascorbic acid had negligible effects on methanethiol production.

Irresistible bouquet of death--how are burying beetles (Coleoptera: Silphidae: Nicrophorus) attracted by carcasses

Chemical composition of volatiles emitted from fresh mouse carcasses (laboratory mice, Mus musculus) was studied using solid sample injection technique (solid-phase micro-extraction), two-dimensional gas chromatography with time of flight mass spectrometric detection and gas chromatography with electroantennographic detection. Electroantennography (EAG) and laboratory olfactometric behavioural observations were used to study the antennal sensitivity to identified infochemicals and their attractiveness for burying beetles Nicrophorus vespillo and Nicrophorus vespilloides (Silphidae: Nicrophorinae). Chemical analysis showed that immediately after death, emitted volatiles did not differ from those emitted by a living organism. However, in the course of time, sulphur-containing chemicals, specifically methanethiol, methyl thiolacetate, dimethyl sulphide, dimethyl disulphide and dimethyl trisulphide appear. EAG measurements revealed antennal sensitivity to these compounds. Behavioural tests in laboratory olfactometer showed that dimethyl sulphide, dimethyl disulphide and dimethyl trisulphide are highly attractive to both studied species. The data suggest that sulphur-containing chemicals are involved in mediating the fresh carcass attractiveness for N. vespillo and N. vespilloides.

Production of volatile aroma compounds by bacterial strains isolated from different surface-ripened French cheeses

Twelve bacterial strains belonging to eight taxonomic groups: Brevibacterium linens, Microbacterium foliorum, Arthrobacter arilaitensis, Staphylococcus cohnii, Staphylococcus equorum, Brachybacterium sp., Proteus vulgaris and Psychrobacter sp., isolated from different surface-ripened French cheeses, were investigated for their abilities to generate volatile aroma compounds. Out of 104 volatile compounds, 54 volatile compounds (identified using dynamic headspace technique coupled with gas chromatography-mass spectrometry [GC-MS]) appeared to be produced by the different bacteria on a casamino acid medium. Four out of eight species used in this study: B. linens, M. foliorum, P. vulgaris and Psychrobacter sp. showed a high flavouring potential. Among these four bacterial species, P. vulgaris had the greatest capacity to produce not only the widest varieties but also the highest quantities of volatile compounds having low olfactive thresholds such as sulphur compounds. Branched aldehydes, alcohols and esters were produced in large amounts by P. vulgaris and Psychrobacter sp. showing their capacity to breakdown the branched amino acids. This investigation shows that some common but rarely mentioned bacteria present on the surface of ripened cheeses could play a major role in cheese flavour formation and could be used to produce cheese flavours.

Aroma compound production in cheese curd by coculturing with selected yeast and bacteria

The microorganisms involved in cheese ripening produce various volatile compounds and induce typical flavors that contribute to cheese variety. To investigate aroma compound generation of cheese microflora, we used a dynamic headspace-gas chromatography-mass spectrometry analysis. To obtain good sensitivity and repeatability of quantification, dynamic headspace conditions and sample preparation were first optimized and led to an extraction set up in which samples were heated at 60 degrees C and diluted with water without pH adjustment. Then three different yeasts and three Geotrichum candidum commonly used in mold surface ripened cheeses were studied in pure culture in a cheese model medium. Thirty-nine cocultures of these three yeasts, the three G. candidum, and five bacteria were studied in the same medium to assess the interaction between microorganisms on aroma compound production. Twenty-four volatile compounds belonging to different chemical classes (alcohols, aldehydes, esters, sulfides, terpenes) were identified and quantified. Yeasts and especially Kluyveromyces lactis produced large amounts of alcohols, aldehydes, esters, and terpenes when cultured alone or in association. Geotrichum candidum and especially G. candidum strain G3 generated the largest amount of sulfides when cultured alone or in association. Finally, bacteria also produced aroma compounds but, except for Brevibacterium linens strain B5, which produced dimethyl trisulfide and ketones, no specific trend in the production of particular aroma compounds could be evidenced.

Enzymatic versus spontaneous S-methyl thioester synthesis in Geotrichum candidum

The synthesis of short chain S-methyl thioesters was investigated in Geotrichum candidum strain GcG. The results indicated the involvement of an enzymatic reaction in this microorganism that led to the synthesis of S-methyl thioacetate (MTA) when methanethiol and acetyl-CoA were used as substrates. MTA was generated from these substrates by enzymatic or spontaneous reactions, whose relative importance depended largely on pH and temperature. For longer chain acyl-CoA compounds (C3 to C6), thioester synthesis was primarily spontaneous. Short chain fatty acid activation by a CoA residue probably is a prerequisite for the synthesis of S-methyl thioesters.

Production of sulfur flavors by ten strains of Geotrichum candidum

Ten strains of Geotrichum candidum were studied on a liquid cheese model medium for the production of sulfur compounds which contribute to the aroma of cheeses. The volatile components produced by each cultured strain were extracted by dynamic headspace extractions, separated and quantified by gas chromatography (GC), and identified by GC-mass spectrometry. It was shown that four strains of this microorganism produced significant quantities of S-methyl thioacetate, S-methyl thiopropionate, S-methyl thiobutanoate, S-methyl thioisobutanoate, S-methyl thioisovalerate, and S-methyl thiohexanoate. This is the first example of the production of these compounds by a fungus. In addition, dimethyldisulfide, dimethyltrisulfide, dimethylsulfide, and methanethiol, which are more commonly associated with the development of cheese flavor in bacterial cultures, were also produced by G. candidum in various yields, depending on the strain selected. The potential application of these strains in cultured microbial associations to produce modified cheeses with more desirable organoleptic properties is discussed.

Aspects of enzymology and biochemical properties of Brevibacterium linens relevant to cheese ripening: a review

Brevibacterium linens is a major surface microorganism that is present in the smear of surface-ripened cheeses. The enzymology and biochemical characteristics of B. linens influence the ripening and final characteristics of smear surface-ripened cheeses. Proteolytic, peptidolytic, esterolytic, and lipolytic activities, which are of particular importance in the ripening process, are discussed in detail. This review also describes the production of volatile compounds, especially sulfur-containing ones, by B. linens, which are thought to be important in respect to the flavor of smear surface-ripened cheeses. The unique orange-colored carotenoids and the factors effecting their production by B. linens are also presented. The catabolism of aromatic amino acids, bacteriocin production, plasmids, and miscellaneous biochemical and physiological properties (peptidoglycan type, antibiotic resistance, insecticide degradation, and biotechnological applications) of B. linens are discussed. The problem associated with the current taxonomical classification of B. linens strains caused by strain variation is evaluated. Finally, the application of B. linens cell extracts or its proteolytic enzymes as cheese ripening accelerants for semi-hard or hard cheese varieties is considered.

Production of esters by Staphylococci

The ability of resting cells and extracellular concentrates of Staphylococci to synthesize ethyl esters was studied in the presence of ethanol and short chain acids considered individually. All the strains synthesized ethyl esters, S. warneri was the highest producer and S. carnosus the lowest. Resting cells esterified preferentially butanoic acid, extracellular concentrates esterified butanoic, valeric and hexanoic acids. Acetic, decanoic and branched acids were poorly esterified. The activity of the extracellular concentrates with ethanol and butanoic acid was not modified by the pH (pH 5.5 or 7.0); but it was decreased at a temperature of 14 degrees C compared to 24 degrees C. For the resting cells it was the opposite, the activity was inhibited by acid pH and was not influenced by the temperatures. So the Staphylococci could produce esters during sausage manufacture.

Growth reduction of Listeria spp. caused by undefined industrial red smear cheese cultures and bacteriocin-producing Brevibacterium lines as evaluated in situ on soft cheese

The undefined microbial floras derived from the surface of ripe cheese which are used for the ripening of commercial red smear cheeses have a strong impact on the growth of Listeria spp. In some cases, these microbial consortia inhibit Listeria almost completely. From such undefined industrial cheese-ripening floras, linocin M18-producing (lin+) (N. Valdés-Stauber and S. Scherer, Appl. Environ. Microbiol. 60:3809-3814, 1994) and -nonproducing Brevibacterium linens strains were isolated and used as single-strain starter cultures on model red smear cheeses to evaluate their potential inhibitory effects on Listeria strains in situ. On cheeses ripened with lin+ strains, a growth reduction of L. ivanovii and L. monocytogenes of 1 to 2 log units was observed compared to cheeses ripened with lin strains. Linocin M18 activity was detected in cheeses ripened with lin+ strains but was not found in those ripened with lin strains. We suggest that production of linocin M18 contributes to the growth reduction of Listeria observed on model red smear cheeses but is unsufficient to explain the almost complete inhibition of Listeria caused by some undefined microbial floras derived from the surface of ripe cheeses.

Behavior of Listeria monocytogenes during manufacture and ripening of brick cheese

Brick cheese was made by the washed-curd procedure from pasteurized whole milk inoculated to contain ca. 1 x 10(2) to 1 x 10(3) Listeria monocytogenes [strain Scott A, Ohio, V7, or California]/ml. Cheeses were ripened (15 degrees C/95% relative humidity) with a surface smear for 2, 3, or 4 wk to simulate production of mild, aged, or "Limburger-like" brick cheese, respectively, and then stored an additional 20 to 22 wk at 10 degrees C. Populations of strains Scott A, Ohio, V7, and California increased 1.89, 1.72, .83, and .86 orders of magnitude, respectively, following completion of brining ca. 32 h after the start of cheese making. All four L. monocytogenes strains leached from cheese into brine during 24 h and survived in brine at 10 degrees C at least 5 d after removal of cheese. Strains Scott A and Ohio grew rapidly during the initial 2 wk of smear development and attained maximum populations of ca. 6.6 and 6.2, 7.0 and 6.9, and 5.6 and 5.1 log10/g in 4-wk-old slice (pH 6.0 to 6.5), surface (pH 6.5 to 6.9), and interior (pH 5.6 to 6.2) samples of cheese, respectively. Numbers of strains Scott A and Ohio generally decreased 1- to 7-fold during 20 to 22 wk at 10 degrees C. Strains V7 and California failed to grow appreciably in any cheese during or after smear development, despite pH of 6.8 to 7.4 in fully ripened cheese; the strains were never isolated from 2- and 3-wk-old cheese and with direct plating were detected sporadically at levels generally less than or equal to 4.0 log10/g in cheese aged greater than or equal to 4 wk. Cold enrichment of slice, surface, and interior samples of cheeses aged greater than or equal to 4 wk generally yielded positive results for L. monocytogenes; strains V7 and California were detected in all cheeses after 20 to 22 wk at 10 degrees C. At 10 ppm, methyl sulfide, dimethyl disulfide, or methyl trisulfide (compounds commonly produced during ripening of brick and Limburger cheese) failed to inhibit appreciably growth of L. monocytogenes.

Influence of Oxygen and pH on Methanethiol Production from l -Methionine by Brevibacterium linens CNRZ 918

The effects of dissolved oxygen concentration and pH on the growth of Brevibacterium linens CNRZ 918 and its production of methanethiol from l -methionine were investigated. Optimal specific methanethiol production was obtained at 25% saturation of dissolved oxygen and at a pH between 8 and 9, whereas optimal cell growth occurred at 50% oxygen saturation and when the pH was maintained constantly at 7. Methanethiol production by nonproliferating bacteria required the presence of l -methionine (7 mM) in the culture medium. This was probably due to the induction of enzyme systems involved in the process. The intracellular concentration of l -methionine seemed to play a key role in this process. B. linens CNRZ 918 tolerated alkaline pHs with a maximal growth pH of approximately 9. Its orange pigmentation seemed to depend on the presence of l -methionine in the culture medium and on the concentration of dissolved oxygen.

Characteristics of viable Brevibacterium linens cells, methionine and cysteine in milkfat-coated microcapsules

The potential for microencapsulation of viable Brevibacterium linens with methionine or cysteine in milkfat to produce sulphur compounds was examined in this study. More than 80 per cent of B. linens cells were encapsulated and then numbers inside capsules increased about three-fold during 48 h at 26 degrees C under anaerobic conditions before a slow decline. Most of micro-organisms (7 x 10(7)/ml) were still viable in the capsules after 15 days. More than 90 per cent of cysteine and methionine were encapsulated and 90, 80 and 60 per cent of the encapsulated amino acids were maintained in the capsules at 4, 12 and 26 degrees C, respectively, after 24 h. Most of the cysteine was oxidized to cystine during microencapsulation but still available to micro-organisms whereas methionine remained in the reduced form. Partition coefficients of methionine and cysteine to milkfat were 0.117 and 0.275, respectively, indicating that most of these substrates would be available to cells of B. linens in the capsules.

Identification of Brevibacterium from clinical sources

Coryneform bacteria of the genus Brevibacterium occur on the normal skin surface, but reports of human infection with this genus are lacking. A number of cultures of coryneform bacteria sent to the National Collection of Type Cultures for identification have been identified as Brevibacterium spp on the basis of their cell wall composition and ability to produce methane-thiol from L-methionine. We describe a rapid method for the detection of methane-thiol and confirmatory tests which differentiate Brevibacterium from morphologically similar genera.