Microbial colonization affects the efficiency of photovoltaic panels in a tropical environment.

Sub-aerial biofilm (SAB) development on solar panels was studied in São Paulo. After 6, 12 and 18 months' exposure, photovoltaic panels were covered by increasing proportions of organic matter (42%, 53% and 58%, respectively). Fungi were an important component of these biofilms; very few phototrophs were found. Major microorganisms detected were melanised meristematic ascomycetes and pigmented bacterial genera Arthrobacter and Tetracoccus. While diverse algae, cyanobacteria and bacteria were identified in biofilms at 6 and 12 months, diversity at a later stage was reduced to that typical for SAB: the only fungal group detected in 18 month biofilm was the meristematic Dothideomycetes and the only phototrophs Ulothrix and Chlorella. Photovoltaic modules showed significant power reductions after 6, 12 (both 7%) and 18 (11%) months. The lack of difference in power reduction between 6 and 12 months reflects the dual nature of soiling, which can result from the deposition of particulates as well as from SAB fouling. Although 12-month old SAB demonstrated an almost 10-fold increase in fungal colonization and a higher organic content, the larger non-microbial particles (above 10 µm), which were important for efficiency reduction of lightly-biofilmed panels, were removed by high rainfall just before the 12-month sampling.

A conductive polymer based electronic nose for early detection of Penicillium digitatum in post-harvest oranges.

We describe the construction of an electronic nose, comprising four chemiresistive sensors formed by the deposition of thin conductive polymer films onto interdigitated electrodes, attached to a personal computer via a data acquisition board. This e-nose was used to detect biodeterioration of oranges colonized by Penicillium digitatum. Significant responses were obtained after only 24 h of incubation i.e. at an early stage of biodeterioration, enabling remedial measures to be taken in storage facilities and efficiently distinguishing between good and poor quality fruits. The instrument has a very low analysis time of 40 s.

Fungal colonization and succession on newly painted buildings and the effect of biocide.

This report describes the sequence of fungal colonization and the influence of biocide incorporation on paint films, determined using quantitative methods. Two buildings were painted with an acrylic paint, with and without an experimental biocide formulation containing a carbamate (carbendazin), N-octyl-2H-isothiazolin-3-one and N-(3,4-dichlorophenyl)N,N-dimethyl urea (total biocide concentration 0.25% w/w). One week after painting, the major groups of organisms detected were yeasts and Cladosporium. The yeast population fell to undetectable levels after the third week and this microbial group was not detected again until the 31st week, after which they increased to high levels on the 42nd week. Aureobasidium showed a pattern similar to the yeasts. The main fungal genera detected over the 42-week period were Alternaria, Curvularia, Epicoccum, Helminthosporium, Coelomycetes (mainly Pestalotia/Pestalotiopsis), Monascus, Nigrospora, Aureobasidium and Cladosporium. The latter was the main fungal genus detected at all times. The physiological factors controlling colonization are discussed. Cladosporium, Aureobasidium, Tripospermum and yeasts on the painted surfaces were all able to grow on mineral salts agar containing 10% sodium chloride. This is the first time that the genus Tripospermum has been reported on painted buildings. The fungal population on biocide-containing surfaces was significantly lower than on non-biocide-containing paint after 13 weeks and continued so to 42 weeks after painting, but there was no statistically significant difference in the level of fungal biodiversity.