Silver nanoparticles (AgNPs), embedded into a specific polysaccharide (EPS), were biogenerated by Klebsiella oxytoca DSM 29614 under aerobic (AgNPs-EPSaer) and anaerobic conditions (AgNPs-EPSanaer). Both AgNPs-EPS matrices were tested by MTT assay for cytotoxic activity against human breast (SKBR3 and 8701-BC) and colon (HT-29, HCT 116 and Caco-2) cancer cell lines, revealing AgNPs-EPSaer as the most active, in terms of IC50, with a more pronounced efficacy against breast cancer cell lines. Therefore, colony forming capability, morphological changes, generation of reactive oxygen species (ROS), induction of apoptosis and autophagy, inhibition of migratory and invasive capabilities and proteomic changes were investigated using SKBR3 breast cancer cells with the aim to elucidate AgNPs-EPSaer mode of action. In particular, AgNPs-EPSaer induced a significant decrease of cell motility and MMP-2 and MMP-9 activity and a significant increase of ROS generation, which, in turn, supported cell death mainly through autophagy and in a minor extend through apoptosis. Consistently, TEM micrographs and the determination of total silver in subcellular fractions indicated that the Ag+ accumulated preferentially in mitochondria and in smaller concentrations in nucleus, where interact with DNA. Interestingly, these evidences were confirmed by a differential proteomic analysis that highlighted important pathways involved in AgNPs-EPSaer toxicity, including endoplasmic reticulum stress, oxidative stress and mitochondrial impairment triggering cell death trough apoptosis and/or autophagy activation.

During primary colonization of rock substrates by plants, mineral weathering is strongly accelerated under plant roots, but little is known on how it affects soil ecosystem development before plant establishment. Here we show that rock mineral weathering mediated by chemolithoautotrophic bacteria is associated to plant community formation in sites recently released by permanent glacier ice cover in the Midtre Lovénbreen glacier moraine (78 degrees 53'N), Svalbard. Increased soil fertility fosters growth of prokaryotes and plants at the boundary between sites of intense bacterial mediated chemolithotrophic iron-sulfur oxidation and pH decrease, and the common moraine substrate where carbon and nitrogen are fixed by cyanobacteria. Microbial iron oxidizing activity determines acidity and corresponding fertility gradients, where water retention, cation exchange capacity and nutrient availability are increased. This fertilization is enabled by abundant mineral nutrients and reduced forms of iron and sulfur in pyrite minerals within a conglomerate type of moraine rock. Such an interaction between microorganisms and moraine minerals determines a peculiar, not yet described model for soil genesis and plant ecosystem formation with potential past and present analogues in other harsh environments with similar geochemical settings.

Two strains of Desulfovibrio desufunrcans, one known to synthesize monomethylmercury from ionic mercury, were grown to determine methylmercury toxicity and for comparison with an anaerobic strain of Clostridium pasteurianum, a H2 producer, and with the broad-spectrum mercury-resistant Pseudomonas putida strain FB-1, capable of degrading 1 pg of methylmercury to methane and elemental mercury in 2 h. The CH3HgCl resistance of D. desulfuricans strains was 10 times that of P. putida FB-1 and 100 times that of C. pasteurianum. The methylmercury resistance of D. desulfuricans was related to the disappearance of methylmercury from cultures by transformation to dimethylmercury, metacinnabar, methane, and traces of ionic mercury. During a 15-day experiment the kinetics of the two volatile compounds dimethylmercury [(CH3)2HgJ and methane were monitored in the liquid by a specific new technique with purge-and-trap gas * Corresponding author.

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ABSTRACT-During the massive mucllage event in the northern Adriatic Sea in July 1991 samples of macroaggregate were fixed in different ways: with formaldehyde, deep frozen and freeze-dried. Conventional microscopy (light and epifluorescence) revealed different autotrophic species embedded in gelatinous matl-ix. Cyanobacteria and heterotrophic bacteria were also identified. Scanning confocal laser microscopy (SCLMI and fluorescent m o l e c~~l a r probes (the lectins concanavalin A and UEA-I) showed wall-free cytoplasm and particulate polysacchar~des leaklng from the envelopes of broken cells in the matrix. The extensive cell lysis was supported by the observation of cytoplasn1-free cytoskeletons, stained by the molecular probe phalloidin High concentrations of triglycerides (30Y0 of total lipids) and free fatty aclds (22'2%) along with very low concentrations of phospholipids ( 2 % ) also indicated massive cell degradation in freeze-dried material. The mucllage observations were compared with those of a natural plankton community grown under hlgh nutrlent conditions using the same techniques. Free polysaccharides were observed as globular flocs (marine snow) during in situ enrichment experiments and inti-acellular polysaccharides as carbon storage materials In autotrophic organisms. No strings, filaments, layers, cell lysis or lipid classes indicating strong cell biodeterioration were observed in a 1 mo controlled experiment during a n algal bloom.

The enterobacterium Klebsiella oxytoca strain BAS-10 was isolated from sediments under an iron mat formed in a stream receiving leached waters from pyrite mine tailings. Under anaerobic laboratory conditions, BAS-10 fermented Fe(III)-citrate and Na-citrate giving CH(3)COOH and CO(2). In the presence of ferric citrate, BAS-10 secreted quantities of a thick gel containing glucose and/or mannose, if not other sugars. Sugar residues were observed in microbial aggregates using the sugar-specific concanavalin A lectin conjugated with fluorescein and imaged by a scanning confocal laser microscope. The gel bound Fe(III) which quickly precipitated. During fermentation, however, half the initial Fe(III) concentration was reduced to Fe(II) which did not bind to the gel and remained in solution. BAS-10 showed a high tolerance to heavy metals. Its growth was not inhibited by 1 mM Zn-, Pb- or Cd-acetate. These cations also co-precipitated with the iron gel, suggesting a possible application of this strain for abatement of toxic metals under anaerobic conditions.

A bacterial strain ANT-3b was isolated at the sea-ice seawater interface from Terra Nova Bay station, Ross Sea, Antarctica. It was isolated on mineral medium supplemented with 2% diesel fuel as a sole carbon and energy source and grown routinely on 2% n-hexadecane. Analysis of 16S rRNA gene sequence indicates that the strain has 99.8% sequence similarity with Halomonas neptunia. The strain ANT-3b was grown in mineral medium supplemented with n-hexadecane between 4 and 20 degrees C, but not at 30 degrees C. The maximum degradation rate of the n-alkane was measured at 15 degrees C, with 5.6+/-1.7 mg O2 microg(-1) protein d(-1). The strain ANT-3b produced emulsifying compounds when grown on n-hexadecane, but not on mineral medium supplemented with D-fructose. A preliminary characterisation of the emulsifier was carried out. The lipid moiety contained a mixture of fatty acids with a following composition in molar ratio: caprylic acid 18.85, myristic acid 1.0, palmitic acid 9.68, palmitoleic acid 5.69 and oleic acid 1.26. The polysaccharide moiety also contained a mixture of sugars with the following molar ratio: mannose 1.71, galactose 1.00 and glucose 2.96. The molecular weight of the glycolipid component determined by gel permeation chromatography was in the 18 kDa range and contained smaller fragments, possibly oligomeric contaminants. Transmission electron microscopy showed contact between the glycolipid secreted by the strain and n-hexadecane broken down to nanodroplets at the water interface, to form a material with mesophase (liquid crystal) organisation.