During the past few years, an increasing awareness concerning the emission of an unexpected high number of bacterial volatiles has been registered. Humans sense, intensively and continuously, microbial volatiles that are released during food transformation and fermentation, e.g., the aroma of wine and cheese. Recent investigations have clearly demonstrated that bacteria also employ their volatiles during interactions with other organisms in order to influence populations and communities. This review summarizes the presently known bioactive compounds and lists the wide panoply of effects possessed by organisms such as fungi, plants, animals, and bacteria. Because bacteria often emit highly complex volatile mixtures, the determination of biologically relevant volatiles remains in its infancy. Part of the future goal is to unravel the structure of these volatiles and their biosynthesis. Nevertheless, bacterial volatiles represent a source for new natural compounds that are interesting for man, since they can be used, for example, to improve human health or to increase the productivity of agricultural products.

Bacterial volatiles and their action potential

Soil is one of the major habitats of bacteria and fungi. In this arena their interactions are part of a communication network that keeps microhabitats in balance. Prominent mediator molecules of these inter- and intraorganismic relationships are inorganic and organic microbial volatile compounds (mVOCs). In this review the state of the art regarding the wealth of mVOC emission is presented. To date, ca. 300 bacteria and fungi were described as VOC producers and approximately 800 mVOCs were compiled in DOVE-MO (database of volatiles emitted by microorganisms). Furthermore, this paper summarizes morphological and phenotypical alterations and reactions that occur in the organisms due to the presence of mVOCs. These effects might provide clues for elucidating the biological and ecological significance of mVOC emissions and will help to unravel the entirety of belowground‚ volatile-wired’ interactions.

Volatile Mediated Interactions Between Bacteria and Fungi in the Soil

Fungal volatile organic compounds: A review with emphasis on their biotechnological potential

Bacillus amyloliquefaciens NJN-6 produces volatile compounds (VOCs) that inhibit the growth and spore germination of Fusarium oxysporum f. sp. cubense. Among the total of 36 volatile compounds detected, 11 compounds completely inhibited fungal growth. The antifungal activity of these compounds suggested that VOCs can play important roles over short and long distances in the suppression of Fusarium oxysporum.

Antifungal Activity of Bacillus Amyloliquefaciens NJN-6 Volatile Compounds Against Fusarium Oxysporum F. Sp. Cubense

Soils may act as sources or sinks of volatile organic compounds (VOCs). Many of the formed VOCs are produced by microorganisms, and it would be a challenge to investigate soil microbial communities by studying their VOC profile. Such “volatilomics” would have the advantage of avoiding extraction steps that are often a limit in genomic or proteomic approaches. Abundant literature on microbially produced VOCs is available, and in particular novel detection methods allow additional insight. The aim of this paper was to give an overview on the current knowledge of microbial VOC emissions from soils.

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Volatile organic compounds (VOCs) in soils

Fungistasis is a widespread phenomenon that can be mediated by soil microorganisms and volatile organic compounds (VOCs). The relationship between soil microorganisms and VOCs is still unclear, however, and many fungistatic compounds remain to be identified. We assessed the effects of soils (soil direct fungistasis) and VOCs produced by natural soils (soil volatile fungistasis) on the spore germination of several fungi. Both strong soil direct fungistasis and soil volatile fungistasis were observed in a wide range of soils. Soil fungistasis and VOC fungistasis were significantly correlated ( P N , N -dimethyloctylamine and nonadecane, were produced by various fungistatic soils. Moreover, antifungal activity test of above VOCs showed that trimethylamine, benzaldehyde, and N , N -dimethyloctylamine have strong antifungal activity even at low levels (4–12 mg l −1 ).

Soil volatile fungistasis and volatile fungistatic compounds

An endospore-forming bacterium, strain B16, was isolated from a soil sample and identified as a Bacillus sp. The strain presented remarkable nematotoxic activity against nematode Panagrellus redivivus. The crude extracellular protein extract from culture supernatant of the bacteria killed about 80% of the tested nematodes within 24 h, suggesting the involvement of extracellular proteases. A homogeneous extracellular protease was purified by chromatography, and the hypothesis of proteinaceous pathogeny in the infection of B16 strain was confirmed by the experiments of killing living nematodes and by the degradation of purified nematode cuticle when treated with the homogenous protease. The gene for the virulence protease was cloned, and the nucleotide sequence was determined. The deduced amino acid sequence showed significant similarity with subtilisin BPN' but low homology with the other cuticle-degrading proteases previously reported in fungi. Characterization of the purified protease revealed the molecular mass of 28 kDa and the optimum activity at pH 10, 50°C. The purified protease can hydrolyze several native proteinaceous substrates, including collagen and nematode cuticle. To our knowledge, this is the first report of a serine protease from a Bacillus genus of bacteria that serves as a pathogenic factor against nematodes, an important step in understanding the relationship between bacterial pathogen and host and in improving the nematocidal activity in biological control.

Bacillus sp. B16 kills nematodes with a serine protease identified as a pathogenic factor

A neutral serine protease (designated Aoz1) was purified to homogeneity from a strain of Arthrobotrys oligospora, obtained from soil in Yunnan Province. The purified protein showed a molecular mass of approximately 38 000 Dalton, pI 4.9 and displayed optimal activity at 45 C and pH 6–8. The protein could hydrolyze gelatin, casein and the chromogenic substrate azocoll, and it could immobilize nematodes in vitro (Panagrellus redivivus L. [Goodey]). The level of activity in culture medium was found to increase with increasing gelatin concentration. Scanning electron micrographs demonstrated dramatic structural changes in nematode cuticle treated with the purified protease. A partial peptide sequence obtained by N-terminal sequence analysis was used to design degenerate primers for the isolation of a cDNA gene encoding the mature protease. Analysis of the cDNA and corresponding genomic sequence revealed 97% identity with PII, a gene previously described from A. oligospora, and we conclude that this gene is li...

Characterization of a neutral serine protease and its full-length cDNA from the nematode-trapping fungus Arthrobotrys oligospora

【Objective】Panax notoginseng, cultivated in Yunnan, China, is an important medicinal herb. Rot root disease is the most serious problem limiting the production of the herb. 【Method】 Panax notoginseng root rot disease was surveyed and sampled in the field. The pathogens of the root rot was isolated and identificated. Pathogenecity tests in vitro and in field were carried out. 【Result】A survey on the disease indicated that the symptoms of the disease are expressed as dry chap rot, medullary tissue rot, slowly yellow rot, stem base dry rot, suddenly wilt rot and wet rot. Among them, slowly yellow rot and suddenly wilt wet rot were the most popular ones. Dry chap rot, medullary tissue rot and stem base dry rot are new records for symptoms of the disease. Cylindrocarpon destructans, C. didynum, Fusarium solani, Phytophthora cactorum, Phoma herbarum, Monilia sp., Verticillium sp., Trichoderma sp., Rhizoctonia solani were involved in the disease. In vitro pathogenecity tests demonstrated that C. destructans, C. didynum, P. cactorum, P. herbarum and R. solani could result in the disease at different levels. Field inoculation tests showed that P. cactorum and P. herbarum were the most pathogenic fungi, leading to disease incidences at 48.4% and 50.0%, respectively. 【Conclusion】However, C. destructans and C. didynum were considered as two of the most important fungi causeing Panax notoginseng root-rot diseases because of their wide distribution, high frequency of isolation, and close relationship withdominant symptom.

The Causal Microorganisms of Panax notoginseng Root Rot Disease

A new (1) and a known (2) sphingolipid were isolated from mycelial cultures of Paraniesslia sp. YMF1.01400. The structures of these two isolates were elucidated as (2S,2'R,3R,3'E,4E,8E)-1-O-(beta-(D)-glucopyranosyl)-3-hydroxyl-2-[N-2'-hydroxyl-3'-eicosadecenoyl]amino-9-methyl-4,8-octadecadiene (1) and (2S,2'R,3R,3'E,4E,8E)-1-O(beta-(D)-glucopyranosyl)-3-hydroxyl-2-[N-2'-hydroxyl-3'-octadecenoyl]amino-9-methyl- 4,8-octadecadiene (2) by spectroscopic and chemical methods. In in vitro tests, both compounds showed moderate nematicidal activities against Bursaphelenchus xylophilus. This is the first report of secondary metabolites in a genus Paraniesslia aquatic fungus.

Zhang Keqin

Papers

Soil volatile fungistasis and volatile fungistatic compounds

Bacillus sp. B16 kills nematodes with a serine protease identified as a pathogenic factor

Characterization of a neutral serine protease and its full-length cDNA from the nematode-trapping fungus Arthrobotrys oligospora

The Causal Microorganisms of Panax notoginseng Root Rot Disease

Nematicidal sphingolipids from the freshwater fungus Paraniesslia sp. YMF1.01400