Extracellular Polysaccharides of a Copper-Sensitive and a Copper-Resistant Pseudomonas Aeruginosa Strain: Synthesis, Chemical Nature and Copper Binding

Extracellular polysaccharides (EPS) of a copper-sensitive (Cus) and a copper-resistant (Cur) Pseudomonas aeruginosa strain were investigated in terms of their production, chemical nature and response towards copper exposure. The extent of EPS synthesis by the resistant strain (4.78 mg mg)1 cell dry wt.) was considerably higher over its sensitive counterpart (2.78 mg mg)1 dry wt.). FTIR-spectroscopy and gas chromatography revealed that both the polymers were acidic in nature, containing alginate as the major component along with various neutraland amino-sugars. Acid content in the Cur EPS (480.54 mg g)1) was greater than that in the Cus EPS (442.0mg g)1). Presence of Cu2þ in the growth medium caused a dramatic stimulation (approximately 4-fold) in EPS synthesis by the Cur strain, while in a similar condition, the Cus failed to exhibit such response. The polymer of the resistant strain showed elevated Cu2þ binding (320mg g)1 EPS) compared to that of the sensitive type (270mg g)1). The overall observations show the potential of the Cur EPS for its deployment in metal bioremediation

Diversity, Metabolic Properties and Arsenic Mobilization Potential of Indigenous Bacteria in Arsenic Contaminated Groundwater of West Bengal, India

<div><p>Arsenic (As) mobilization in alluvial aquifers is caused by a complex interplay of hydro-geo-microbiological activities. Nevertheless, diversity and biogeochemical significance of indigenous bacteria in Bengal Delta Plain are not well documented. We have deciphered bacterial community compositions and metabolic properties in As contaminated groundwater of West Bengal to define their role in As mobilization. Groundwater samples showed characteristic high As, low organic carbon and reducing property. Culture-independent and -dependent analyses revealed presence of diverse, yet near consistent community composition mostly represented by genera <i>Pseudomonas</i>, <i>Flavobacterium</i>, <i>Brevundimonas</i>, <i>Polaromonas</i>, <i>Rhodococcus</i>, <i>Methyloversatilis</i> and <i>Methylotenera</i>. Along with As-resistance and -reductase activities, abilities to metabolize a wide range carbon substrates including long chain and polyaromatic hydrocarbons and HCO₃, As³⁺ as electron donor and As⁵⁺/Fe³⁺ as terminal electron acceptor during anaerobic growth were frequently observed within the cultivable bacteria. Genes encoding cytosolic As⁵⁺ reductase (<i>ars</i>C) and As³⁺ efflux/transporter [<i>ars</i>B and <i>acr</i>3(2)] were found to be more abundant than the dissimilatory As⁵⁺ reductase gene <i>arr</i>A. The observed metabolic characteristics showed a good agreement with the same derived from phylogenetic lineages of constituent populations. Selected bacterial strains incubated anaerobically over 300 days using natural orange sand of Pleistocene aquifer showed release of soluble As mostly as As³⁺ along with several other elements (Al, Fe, Mn, K, <i>etc</i>.). Together with the production of oxalic acid within the biotic microcosms, change in sediment composition and mineralogy indicated dissolution of orange sand coupled with As/Fe reduction. Presence of <i>ars</i>C gene, As⁵⁺ reductase activity and oxalic acid production by the bacteria were found to be closely related to their ability to mobilize sediment bound As. Overall observations suggest that indigenous bacteria in oligotrophic groundwater possess adequate catabolic ability to mobilize As by a cascade of reactions, mostly linked to bacterial necessity for essential nutrients and detoxification.</p></div

Consolidated profiles of all the metabolic properties tested within the bacterial strains isolated from six As contaminated samples.

<p>(a) Positive (red box) and negative (yellow box) responses obtained for various properties tested; (b) Percentage of positive response obtained for each property and (c) UPGMA based on metabolic properties of bacterial strains isolated from six As contaminated samples. Metabolic characters tested are (I) enzymes involved in As transformation: 1: arsenite oxidase; 2: arsenate reductase; (II) ability to utilize different carbon sources: 3: cacsin; 4: glycerol; 5: glucose; 6: acetate; 7: pyruvate; 8: lactate; 9: citrate; 10: starch; 11: sucrose; 12: ascorbic acid and (III) utilization of different terminal electron acceptors: 13: As⁵⁺; 14: Se⁶⁺; 15: SO₄²⁻; 16: S₂O₃²⁻; 17: SO₃²⁻; 18: NO₃⁻; 19: Fe³⁺; 20: O_2. Taxonomic affiliations of bacterial isolates are indicated using coloured bars presented right side of consolidated metabolic profiles.</p

Phylogenetic tree of deduced amino acid sequences of genes encoding As⁵⁺ reductase (<i>ars</i>C and <i>arr</i>A), As³⁺ oxidase (<i>aio</i>B), and As³⁺ efflux [<i>ars</i>B, and <i>acr</i>3(2)].

<p>Genes detected in this study are shown in bold font. Percentage values on each branch represent the corresponding bootstrap probability values obtained in 500 replications. Significant bootstrap values (>50%) of major branch points are shown in the tree.</p

Neighbor-joining phylogenetic tree of <i>β-Proteobacteria</i>.

<p>The tree is constructed based on 16S rRNA gene sequences by using Jukes-Cantor distances. 1000 bootstraps analyses are conducted and more than 50% are denoted in nodes. Sequences retrieved from As contaminated environment, groundwater and mercury contaminated sites are suffixed here as ‘A’, ‘G’, and ‘Hg’, respectively. Sequences represented in bold italic font are derived from clone libraries and bold italic font with a suffix ‘<i>i</i>’ are derived from isolated strains.</p

Concentrations of As (a and b), Fe (c and d) and other metals (Mn, K and Al) (e) detected within the aqueous phase of microcosms (after 300 days).

<p>Error bars indicate standard deviations (n = 3). Bacterial strains represented in X axis are as follows: CAS922i (<i>Rhodococcus</i> sp.), CAS4005i (<i>Brevundimonas</i> sp.), BAS108i (<i>Staphylococcus</i> sp.), BAS224i (<i>Phyllobacterium</i> sp.), CAS4101i (<i>Arthrobacter</i> sp.), BAS323i (<i>Pseudomonas</i> sp.), BAS123i (<i>Acinetobacter</i> sp.) and CAS907i (<i>Pseudomonas</i> sp.).</p

Correlation between the metabolic-genetic characteristics of bacterial strains used for microcosm study and release of As and Fe within different microcosms.

<p>Correlation between the metabolic-genetic characteristics of bacterial strains used for microcosm study and release of As and Fe within different microcosms.</p

Neighbor-joining phylogenetic tree of <i>δ-Proteobacteria</i>, <i>Actinobacteria</i>, <i>Cyanobacteria</i> and other groups.

<p>The tree is based on 16S rRNA gene sequences using by Jukes-Cantor distances. 1000 bootstraps analyses are conducted and more than 50% are denoted in nodes. Sequences retrieved from As contaminated environment and groundwater are suffixed here as ‘A’, and ‘G’, respectively. Sequences represented in bold italic font are derived from clone libraries and bold italic font with a suffix ‘<i>i</i>’ are derived from isolated strains.</p

Distribution of major phylogenetic groups of isolated bacteria.

<p>Abundance of bacterial groups is plotted with respect to their affiliation at (a) phylum level and (b) genus level. The horizontal bar indicates gradient of As concentrations as detected in six samples.</p

PCA, CCA and UPGMA based ordination plots on samples’ microbiological and geochemical properties.

<p>(a) Principal Component Analysis (PCA) of the samples based on geochemical parameters; (b) Canonical correspondence analysis (CCA) of samples geochemical properties and bacterial community compositions (c) ordination plots representing (i) comparative analysis of metabolic properties of the isolates obtained from six As contaminated samples, (ii) cumulative metabolic profiles represented by UPGMA for the isolates obtained from individual samples and (iii) UPGMA cluster analysis among the test metabolic properties.</p