Alex Gonzalez

AHL signaling molecules with a large acyl chain enhance biofilm formation on sulfur and metal sulfides by the bioleaching bacterium Acidithiobacillus ferrooxidans.

Biofilm formation plays a pivotal role in bioleaching activities of bacteria in both industrial and natural environments. Here, by visualizing attached bacterial cells on energetic substrates with different microscopy techniques, we obtained the first direct evidence that it is possible to positively modulate biofilm formation of the extremophilic bacterium Acidithiobacillus ferrooxidans on sulfur and pyrite surfaces by using Quorum Sensing molecules of the N-acylhomoserine lactone type (AHLs). Our results revealed that AHL-signaling molecules with a long acyl chain (12 or 14 carbons) increased the adhesion of A. ferrooxidans cells to these substrates. In addition, Card-Fish experiments demonstrated that C14-AHL improved the adhesion of indigenous A. ferrooxidans cells from a mixed bioleaching community to pyrite. Finally, we demonstrated that this improvement of cell adhesion is correlated with an increased production of extracellular polymeric substances. Our results open up a promising means to develop new strategies for the improvement of bioleaching efficiency and metal recovery, which could also be used to control environmental damage caused by acid mine/rock drainage.

Draft genome sequence of the Chilean isolate Aeromonas salmonicida strain CBA100

We report the draft genome sequence from Aeromonas salmonicida sp. strain CBA100, which was characterized as an antibiotic-resistant bacterium isolated from infected rainbow trout. The total size of the genome is 4,788,109 bp, with a G + C content of 60.55%. Comparison of its open reading frames shows that the closest homologue to one third of the genes of strain CBA100 are found in A. hydrophila. The strain contains several efflux pumps and putative genes that confer resistance to multiclass antibiotics, including macrolide, β-lactamics, florfenicol and quinolones. The antibiogram profile suggests that efflux pumps are the main mechanism of resistance to non-β-lactamic antibiotics. This is the first genome of a Chilean isolate of A. salmonicida, which should shed light on the design of strain-specific vaccines against this pathogen and reduce the use of antibiotics for preventive treatment in Chilean aquaculture.

Isolation and molecular characterization of Thraustochytrium strain isolated from Antarctic Peninsula and its biotechnological potential in the production of fatty acids

Thraustochytrids are unicellular protists belonging to the Labyrinthulomycetes class, which are characterized by the presence of a high lipid content that could replace conventional fatty acids. They show a wide geographic distribution, however their diversity in the Antarctic Region is rather scarce. The analysis based on the complete sequence of 18S rRNA gene showed that strain 34-2 belongs to the species Thraustochytrium kinnei, with 99% identity. The total lipid profile shows a wide range of saturated fatty acids with abundance of palmitic acid (16:0), showing a range of 16.1–19.7%. On the other hand, long-chain polyunsaturated fatty acids, mainly docosahexaenoic acid and eicosapentaenoic acid are present in a range of 24–48% and 6.1–9.3%, respectively. All factors analyzed in cells (biomass, carbon consumption and lipid content) changed with variations of culture temperature (10 °C and 25 °C). The growth in glucose at a temperature of 10 °C presented the most favorable conditions to produce omega-3fatty acid. This research provides the identification and characterization of a Thraustochytrids strain, with a total lipid content that presents potential applications in the production of nutritional supplements and as well biofuels.

Draft Genome Sequence of a Copper-Resistant Marine Bacterium, Pantoea agglomerans Strain LMAE-2, a Bacterial Strain with Potential Use in Bioremediation

ABSTRACT Pantoea agglomerans LMAE-2 was isolated from seabed sediment moderately contaminated with Cu2+. Here, we report its draft genome sequence, which has a size of 4.98 Mb. The presence of cop genes related with copper homeostasis in its genome may explain the resistance and strengthen its potential for use as bioremediation agent.

DEGRADATION OF FOOD MANUFACTURING WASTES BY A FUNGAL ISOLATE

Food manufacturing wastes, such as olive mill solid waste, tomato pomace and grape pomace are three wastes produced by food industries in the Region of Maule. One of the simplest strategies for the proper disposal of these residues is to directly eliminate them by cultivation with degrading mesophilic microorganisms, which use these wastes as their sole carbon source. A fungal strain was isolated from tomato peel and used to degrade food manufacturing wastes. This strain was effective in degrading olive mill solid waste, but partially degraded both grape and tomato pomace. Based on mycelium morphology, sequence of part of the ribosomal and internal transcribed spacer (ITS) DNA, the strain most probably belongs to Botrytis genera. This is the first report that uses a strain similar to Botrytis in degrading food manufacturing wastes from the Region of Maule.

Proteomic Studies in Acidthiobacillus ferrooxidans Cells Induced by Synthetic Acyl-Homoserine Lactones

Quorum sensing (QS) is a widespread phenomenon that enables bacterial cells to establish cell-to-cell communication and to regulate the expression of specific genes in response to local changes in cell density. In Gram-negative bacteria the signal molecules used for this cell-cell communication, frequently referred to as autoinducers (AI), are mainly N-acyl homoserine lactones (AHLs). A. ferrooxidans was the first acidophilic chemolithotrophic γ-proteobacteria involved in biomining in which a functional QS system has been identified (Farah et. al., 2005, Appl. Environ. Microbiol. 71: 7033-40). Analysis of culture supernatants revealed that A. ferrooxidans produce nine different kinds of AHLs. This microorganism develops biofilm structures on mineral surfaces which are essential for the bioleaching process. As in many bacteria QS regulates the biofilm formation, we decided to study the proteomic changes of A. ferroxidans cells induced by synthetic AHLs and grown in different energetic substrates to identify proteins whose expression are regulated by this QS system. The proteomic studies were made by 2D-PAGE assisted by computational analysis with the Delta 2D software. Preliminary results revealed changes in respect to the control condition without AHL induction. The amino-terminal sequence identifications of these proteins is currently in progress and should allow us to understand which physiological function(s) is(are) controlled by QS in A. ferrooxidans and if biofilm production is one of them.

Is the Quorum Sensing Type AI-1 System of Acidithiobacillus ferrooxidans Involved in its Attachment to Mineral Surfaces?

Biofilm development plays a pivotal role in the bioleaching process. The attachment of the acidophilic chemolithotrophic Acidithiobacillus ferrooxidans to mineral surfaces is mediated by extracellular polymeric substances (EPS) involved in biofilm development. Previous work suggests that EPS composition of A. ferrooxidans is adapted to the energy source and, accordingly, the bacterium must be able to sense the surface to which attachment occurs with the consequent triggering of the expression of different EPS-genes. Quorum sensing (QS) is recognized as one of the main regulators of biofilm formation. A. ferrooxidans possesses a functional QS type AI-1 system and the analysis of culture supernatants revealed us that this bacterium is able to synthesize nine different homoserine lactones (AHLs) whose acyl-chain lengths oscillate between 8 and 16 carbons and include an alcohol or a ketone function at the C3 position. The transcription levels of the afeI gene encoding for the AHL synthase are higher in cells grown in sulfur and thiosulfate media than in iron-grown cells, suggesting that biofilm formation in A. ferrooxidans would be regulated by the QS type AI-1 system. In the present study, the effect of several synthetic AHLs and analogues on the attachment of A. ferrooxidans to pyrite was analyzed. Preliminary results suggest that some of these molecules are changing the bacterial attachment to pyrite.