Bubble biofilm: Bacterial colonization of air-air interface.

Microbial mats or biofilms are known to colonize a wide range of substrates in aquatic environments. These dense benthic communities efficiently recycle nutrients and often exhibit high tolerance to environmental stressors, characteristics that enable them to inhabit harsh ecological niches. In some special cases, floating biofilms form at the air-water interface residing on top of a hydrophobic microlayer. Here, we describe biofilms that reside at the air-air interface by forming gas bubbles (bubble biofilms) in the former Ytterby mine, Sweden. The bubbles are built by micrometer thick membrane-like biofilm that holds enough water to sustain microbial activity. Molecular identification shows that the biofilm communities are dominated by the neuston bacterium Nevskia. Gas bubbles contain mostly air with a slightly elevated concentration of carbon dioxide. Biofilm formation and development was monitored in situ using a time-lapse camera over one year, taking one image every second hour. The bubbles were stable over long periods of time (weeks, even months) and gas build-up occurred in pulses as if the bedrock suddenly exhaled. The result was however not a passive inflation of a dying biofilm becoming more fragile with time (as a result of overstretching of the organic material). To the contrary, microbial growth lead to a more robust, hydrophobic bubble biofilm that kept the bubbles inflated for extended periods (several weeks, and in some cases even months).

Mycelial pellet formation by Penicillium ochrochloron species due to exposure to pyrene.

Five indigenous fungal strains with characteristics of the genus Penicillium capable of degrading and utilizing pyrene, as sole carbon source were isolated from soil of a former gas work site. Two strains were identified as Penicillium ochrochloron. One of the strains was able to degrade a maximum of 75% of 50 mg l(-1) pyrene at 22 degrees C during 28 days of incubation. The presence of pyrene in the medium resulted in an aggregation of hyphae into pellets by the two Penicillium ochrochloron strains. Formation of pellets was observed after 48 h of incubation with difference in size and texture between the two strains. This indicated the individual variation within the same genus of fungi. However, remaining strains did not show this behavior even though they were capable of utilizing pyrene as sole carbon source. The macro- and microscopic morphology of fungal pellets was studied using scanning electron microscopy. It was found that the addition of varying concentration of pyrene ranging from 10 to 50 mg l(-1) in the medium influenced shape and structure of the mycelial pellets. A two-fold increase in hyphal branching (with concomitant decrease in the average hyphal growth unit) was observed at a concentration of 10mg l(-1). The relevance of fungal growth and morphology for bioremediation of polycyclic aromatic hydrocarbons (PAHs) contaminated sites are discussed.

Degradation of pyrene by indigenous fungi from a former gasworks site.

Indigenous fungi isolated from soil of a former gasworks site were investigated in submerged cultures with pyrene as the sole carbon source. Five fungal strains capable of degrading pyrene included one strain of Trichoderma harzianum and four strains with characteristics of the genus Penicillium. These are identified as Penicillium simplicissimum, Penicillium janthinellum, Penicillium funiculosum and Penicillium terrestre. A maximum of 75% of 50 mg l(-1) and 67% of 100 mg l(-1) of pyrene was removed by the fast degrading strain P. terrestre at 22 degrees C during 28 days of incubation. The slower degrader P. janthinellum was able to remove 57% of 50 mg l(-1) and about 31.5% of 100 mg l(-1) pyrene. Degradation of pyrene is directly correlated with biomass development. To the best of our knowledge, this is the first time that fungi have been reported to use pyrene as the sole carbon and energy source. They may be ideal candidates for effective bioremediation of polycyclic aromatic hydrocarbons.