Browsing by Author "Pinaki Sar"

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Copper uptake and its compartmentalization in Pseudomonas aeruginosa strains: Chemical nature of cellular metal
(1999) Sufia K. Kazy; Pinaki Sar; R.K. Asthana; S.P. Singh
Copper-sensitive (Cu5) and copper-resistant (Cu1) strains of Pseudomonas aeruginosa were characterized in terms of Cu2+ sensitivity, uptake and its compartmentalization in the possible cell sectors. Minimum inhibitory concentrations (MICs) of Cu2+ for the Cur strain (3.2 mM and 0.12 mM in enriched- and in minimal-medium, respectively) were almost 5-fold higher over that of its sensitive counterpart. While Cu(s) strain accumulated Cu2+ to a maximum of 1.8 μmol mg-1 protein, Cu(r) strain increased it to 2.37 μmol mg-1 protein. Both the strains also demonstrated energy- and pH-dependent Cu2+ uptake through the broad-substrate range divalent cation (Zn2+, Mg2+, Co2+) uptake system as well as through the system specific for Cu2+. Cell-fractionation study revealed that in Cu(r) strain, periplasm and membrane are the main Cu2+ binding sites, whereas, in case of Cu(s) strain, it is the cytoplasm. The overall observations indicate that the Cur strain restricted Cu2+ sequestration exterior to the cytoplasm as the possible strategy for Cu-resistance. The chemical nature of Cu2+ deposition in the respective strains was also ascertained by X-ray powder diffraction analysis.
Extracellular polysaccharides of a copper-sensitive and a copper-resistant Pseudomonas aeruginosa strain: Synthesis, chemical nature and copper binding
(2002) Sufia K. Kazy; Pinaki Sar; S.P. Singh; Asish K. Sen; S.F. D'Souza
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 neutral- and amino-sugars. Acid content in the Cur EPS (480.54 mg g-1) was greater than that in the Cus EPS (442.0 mg g-1). Presence of Cu2+ 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 Cu2+ binding (320 mg g-1 EPS) compared to that of the sensitive type (270 mg g-1). The overall observations show the potential of the Cur EPS for its deployment in metal bioremediation.
Nickel uptake by Pseudomonas aeruginosa: Role of modifying factors
(1998) Pinaki Sar; Sufia K. Kazy; Ravi K. Asthana; Sureshwar P. Singh
Pseudomonas aeruginosa cells growing in minimal medium were 40-fold more sensitive to Ni2+ than cells growing in enriched medium, suggesting a possible protective role of medium ingredients. Likewise, cells pre-grown in enriched medium showed a high K(m) (6.15 mM) and increased Ni2+ uptake (950 nmol mg-1 protein, 1h) over cells pre-sown in minimal medium (K(m), 0.48 mM: 146 nmol mg-1 protein, 1 h). The overall pattern indicates that cells pre-grown in enriched medium were characterized by having lowered affinity towards Ni2+ than those with minimal medium background. The enhanced Ni2+ uptake by enriched medium-grown cells can be correlated with the improved metabolic state of the cells Ni2+ uptake was optimum at neutrality (pH 7.0). A major Ni2+ transport system was competitively inhibited by Mg2+, Zn2+, Cd2+, or Co2+ (400 μM each). Noticeably, a minor Ni2+ transport pathway was still operative even in the higher concentration range of Mg2+ (4 mM and 40 mM). The stimulation of Ni2+ uptake monitored in the presence of different carbon sources (0.5% wt/vol, each) showed the sequence: glucose (1.6-fold) > phenol = gallic acid (1.5 fold). Succinate, in comparison, reduced Ni2+ uptake (0.5-fold) possibly because of its acting as a metal chelator as well. Sensitivity of Ni2+ transport towards methyl viologen, azide, 2-4 DNP, and DCCD suggested that transport was energy- linked.