Differential proteomic analysis of Acidithiobacillus ferrooxidans cells maintained in contact with bornite or chalcopyrite: Proteins involved with the early bacterial response

Adaptive response of the holdase chaperone network of Acidithiobacillus ferrooxidans ATCC 23270 to stresses and energy sources

Acidithiobacillus ferrooxidans is a chemolithoautotrophic acidophilic bacterium belonging to microbial communities involved in sulfide ore bioleaching. This microorganism possesses redundancy of genes encoding ATP-independent chaperone holdases like Hsp20 (hps20.1, hsp20.2, and hsp20.3), Hsp31, Hsp33, RidA (ridA.1 and ridA.2), and Lon (lon.1, lon.2, and lon.3), and single copy genes encoding SlyD and CnoX. We evaluated the response of these holdases to short and long-term stresses induced by changes in temperature (30° to 37 °C), pH (1.6 to 1.2 or 2.0), and oxidative status (1 mM H2O2) as well as to different energy sources (iron, sulfur, pyrite, sphalerite or chalcopyrite). Cells adapted under thermal and oxidative stress conditions showed a generalized upregulation of holdase genes, while short-term stress led to more discrete increases in transcript levels, with only hsp20.2 and hsp31 showing higher mRNA levels. hsp31 was also upregulated under acidic stresses, sulfur and sulfides. hsp20 variants showed different mRNA levels under different conditions, and cnoX was induced under oxidative conditions. Cells cultured on chalcopyrite had similar responses to those grown with peroxide. With some exceptions, stresses led to significant increases in intracellular ROS content, and decreases in ATP. These results pave the way to understanding proteostasis systems in extreme acidophilic bacteria.

Understanding Stress Response to High-Arsenic Gold-Bearing Sulfide Concentrate in Extremely Metal-Resistant Acidophile Sulfobacillus thermotolerans

Biooxidation of gold-bearing arsenopyrite concentrates, using acidophilic microbial communities, is among the largest commercial biohydrometallurgical processes. However, molecular mechanisms of microbial responses to sulfide raw materials have not been widely studied. The goal of this research was to gain insight into the defense strategies of the acidophilic bacterium Sulfobacillus thermotolerans, which dominates microbial communities functioning in industrial biooxidation processes at >35 °C, against the toxic effect of the high-arsenic gold-bearing sulfide concentrate. In addition to extreme metal resistance, this acidophile proved to be one of the most As-tolerant microorganisms. Comparative proteomic analysis indicated that 30 out of 33 differentially expressed proteins were upregulated in response to the ore concentrate, while the synthesis level of the functional proteins required for cell survival was not negatively affected. Despite a high level of cellular metal(loid) accumulation, no specific metal(loid)-resistant systems were regulated. Instead, several proteins involved in the metabolic pathways and stress response, including MBL fold metallo-hydrolase, sulfide:quinone oxidoreductase, and GroEL chaperonin, may play crucial roles in resistance to the sulfide ore concentrate and arsenic, in particular. This study provides the first data on the microbial responses to sulfide ore concentrates and advances our understanding of defense mechanisms against toxic compounds in acidophiles.

Comparative proteomic analysis of Xanthomonas citri ssp. citri periplasmic proteins reveals changes in cellular envelope metabolism during in vitro pathogenicity induction

Citrus canker is a plant disease caused by Gram-negative bacteria from the genus Xanthomonas. The most virulent species is Xanthomonas citri ssp. citri (XAC), which attacks a wide range of citrus hosts. Differential proteomic analysis of the periplasm-enriched fraction was performed for XAC cells grown in pathogenicity-inducing (XAM-M) and pathogenicity-non-inducing (nutrient broth) media using two-dimensional electrophoresis combined with liquid chromatography-tandem mass spectrometry. Amongst the 40 proteins identified, transglycosylase was detected in a highly abundant spot in XAC cells grown under inducing condition. Additional up-regulated proteins related to cellular envelope metabolism included glucose-1-phosphate thymidylyltransferase, dTDP-4-dehydrorhamnose-3,5-epimerase and peptidyl-prolyl cis-trans-isomerase. Phosphoglucomutase and superoxide dismutase proteins, known to be involved in pathogenicity in other Xanthomonas species or organisms, were also detected. Western blot and quantitative real-time polymerase chain reaction analyses for transglycosylase and superoxide dismutase confirmed that these proteins were up-regulated under inducing condition, consistent with the proteomic results. Multiple spots for the 60-kDa chaperonin and glyceraldehyde-3-phosphate dehydrogenase were identified, suggesting the presence of post-translational modifications. We propose that substantial alterations in cellular envelope metabolism occur during the XAC infectious process, which are related to several aspects, from defence against reactive oxygen species to exopolysaccharide synthesis. Our results provide new candidates for virulence-related proteins, whose abundance correlates with the induction of pathogenicity and virulence genes, such as hrpD6, hrpG, hrpB7, hpa1 and hrpX. The results present new potential targets against XAC to be investigated in further functional studies.

Development of a markerless gene replacement system for Acidithiobacillus ferrooxidans and construction of a pfkB mutant

The extremely acidophilic, chemolithoautotrophic Acidithiobacillus ferrooxidans is an important bioleaching bacterium of great value in the metallurgical industry and environmental protection. In this report, a mutagenesis system based on the homing endonuclease I-SceI was developed to produce targeted, unmarked gene deletions in the strain A. ferrooxidans ATCC 23270. A targeted phosphofructokinase (PFK) gene (pfkB) mutant of A. ferrooxidans ATCC 23270 was constructed by homologous recombination and identified by PCR with specific primers as well as Southern blot analysis. This potential pfkB gene (AFE_1807) was also characterized by expression in PFK-deficient Escherichia coli cells, and heteroexpression of the PFKB protein demonstrated that it had functional PFK activity, though it was significantly lower (about 800-fold) than that of phosphofructokinase-2 (PFK-B) expressed by the pfkB gene from E. coli K-12. The function of the potential PFKB protein in A. ferrooxidans was demonstrated by comparing the properties of the pfkB mutant with those of the wild type. The pfkB mutant strain displayed a relatively reduced growth capacity in S(0) medium (0.5% [wt/vol] elemental sulfur in 9K basal salts solution adjusted to pH 3.0 with H(2)SO(4)), but the mutation did not completely prevent A. ferrooxidans from assimilating exogenous glucose. The transcriptional analysis of some related genes in central carbohydrate metabolism in the wild-type and mutant strains with or without supplementation of glucose was carried out by quantitative reverse transcription-PCR. This report suggests that the markerless mutagenesis strategy could serve as a model for functional studies of other genes of interest from A. ferrooxidans and multiple mutations could be made in a single A. ferrooxidans strain.