Biomedical subjects

Anushree Malik

Publications and source records attributed to Anushree Malik.

8 recordsLinked to original sources

PubMed2006

Environmental challenge vis a vis opportunity: the case of water hyacinth.

Water hyacinth (Eichhornia crassipes) is a noxious weed that has attracted worldwide attention due to its fast spread and congested growth, which lead to serious problems in navigation, irrigation, and power generation. On the other hand, when looked from a resource angle, it appears to be a valuable resource with several unique properties. As a result, research activity concerning control (especially biological control) and utilization (especially wastewater treatment or phytoremediation) of water hyacinth has boomed up in the last few decades. Investigations on biogas/compost production from water hyacinth have also come up very well mainly from few research groups in India. This review presents a comprehensive view of the research related to water hyacinth with special emphasis on the recent investigations on water hyacinth control and utilization technologies conducted in the last 2-3 decades. Based on these significant research achievements, now it is desirable to identify a management strategy so that the excessive growth can be controlled and the plant can be used in beneficial ways. In the rural areas, water hyacinth could be used in an integrated manner for decentralized wastewater treatment systems coupled to biogas and compost production from the resulting biomass. There is a need to work out the techno-economic viability of such integrated model systems.

Animals↗

PubMed2005

Effect of surfactants on stability of Acinetobacter johnsonii S35 and Oligotropha carboxidovorans S23 coaggregates.

The effect of anionic (sodium dodecyl sulphate or SDS) and cationic (cetyltrimethylammonium bromide or CTAB) surfactants on the stability of binary bacterial coaggregates comprising Acinetobacter johnsonii S35 and Oligotropha carboxidovorans S23 (both sewage sludge isolates) was studied and compared with that on the complex sewage sludge flocs. Both SDS and CTAB enhanced the bacterial coaggregation at their lower concentrations of 0.2 and 0.07 mg ml(-1), respectively. However, complete deflocculation of coaggregates was observed at 1 mg ml(-1) SDS and 0.3 mg l(-1) CTAB concentrations. Further, sewage sludge flocs did not deflocculate in the presence of CTAB, although a concentration-dependent deflocculation was observed in the presence of SDS. A. johnsonii S35 and O. carboxidovorans S23 cells were separately pretreated (prior to coaggregation) with the surfactants. In spite of the partial (complete) loss of viability during SDS (CTAB) pretreatment, washed cells still retained hydrophobic character and displayed significant coaggregation (aggregation index ranging from 84% to 97% in comparison to 96% in the case of non-treated cells), demonstrating reversibility of the surfactant induced deflocculation. Further, when exposed to lower concentration of surfactants (0.2 mg ml(-1) SDS), coaggregates were more resistant (76% viability) as compared to the individual partner (S35: 52%; S23: 39% viability). Since the coaggregates are stable and provide protection from surfactants at lower concentrations (those normally expected in the sewage treatment plants), their presence as well as a sustained role in the sewage sludge bioflocculation is evident.

Acinetobacter↗

PubMed2004

Metal bioremediation through growing cells.

Heavy-metal pollution represents an important environmental problem due to the toxic effects of metals, and their accumulation throughout the food chain leads to serious ecological and health problems. Metal remediation through common physico-chemical techniques is expensive and unsuitable in case of voluminous effluents containing complexing organic matter and low metal contamination. Biotechnological approaches that are designed to cover such niches have, therefore, received great deal of attention in the recent years. Biosorption studies involving low-cost and often dead/pretreated biomass have dominated the literature and, subsequently, extensive reviews focusing on equilibrium and kinetics of metal biosorption have also come up. However, the low binding capacity of biomass for certain recalcitrant metals such as Ni and failure to effectively remove metals from real industrial effluents due to presence of organic or inorganic ligands limit this approach. At times, when pure biosorptive metal removal is not feasible, application of a judicious consortium of growing metal-resistant cells can ensure better removal through a combination of bioprecipitation, biosorption and continuous metabolic uptake of metals after physical adsorption. Such approach may lead to simultaneous removal of toxic metals, organic loads and other inorganic impurities, as well as allow optimization through development of resistant species. However, sensitivity of living cells to extremes of pH or high metal concentration and need to furnish metabolic energy are some of the major constraints of employing growing cells for bioremediation. The efforts to meet such challenges via isolation of metal-resistant bacterial/fungal strains and exploitation of organic wastes as carbon substrates have began. Recent studies show that the strains (bacteria, yeast and fungi) isolated from contaminated sites possess excellent capability of metal scavenging. Some bacterial strains possess high tolerance to various metals and may be potential candidates for their simultaneous removal from wastes. Evidently, the stage has already been set for the application of metal-resistant growing microbial cells for metal harvesting. This review focuses on the applicability of growing bacterial/fungal/algal cells for metal removal and the efforts directed towards cell/process development to make this option technically/economically viable for the comprehensive treatment of metal-rich effluents.

Adsorption↗

PubMed2004

Stability of bacterial coaggregates in extreme environments.

The stability of coaggregates formed by the interaction of Acinetobacter johnsonii S35 and Oligotropha carboxidovorans S23, both of which are nonflocculating sludge bacteria, was evaluated by a spectrophotometric assay of aggregation index and phase contrast microscopy. Exposure of coaggregates to conditions of various pH (3-11) or temperature (10-5 degrees C) did not cause significant deflocculation and high aggregation index (85-93%) was still maintained as compared to 93.3% under normal conditions. Further, heat pretreatment of A. johnsonii S35 and O. carboxidovorans S23 cells at 60 or 80 degrees C did not prevent their subsequent coaggregation indicating that the interacting cell surface structures are heat-resistant. However, dual exposure of coaggregates to low temperature (10 degrees C) and extreme pH caused disruption of coaggregates coupled with the reduction in aggregation index below 28% (pH 3) and 49% (pH 11). Use of sterile filtrate of settled sewage (SFSS) in place of electrolyte solution as coaggregating medium produced usual large coaggregates (above 100 microm) indicating reproducibility of this coaggregation in sewage treatment plants. SFSS coaggregates incurred lesser deflocculation (50 and 85%, respectively) at extreme pH (3 and 11, respectively) and low temperature. This study demonstrated that although bacterial coaggregates are strong and stable against individual pH or temperature stress, a dual stress might deteriorate the performance and quality of treated waters.

Acinetobacter↗

PubMed2003

Intergeneric coaggregations among Oligotropha carboxidovorans and Acinetobacter species present in activated sludge.

The coaggregation traits of two pairs of sewage sludge bacteria were tested and characterized. Oligotropha carboxidovorans S23 coaggregated with two strains of the genus Acinetobacter viz. Acinetobacter junii S33 (56%) and Acinetobacter johnsonii S35 (99%). Coaggregates of O. carboxidovorans S23 and A. junii S33 were small (20-40 microm), weak and susceptible to EDTA and a commercial protease (Actinase E). Actinase/periodate pretreatment of the partners prior to coaggregation revealed that interaction in this case was mediated by protein surface components. Coaggregates of O. carboxidovorans S23 and A. johnsonii S35 were large (above 100 microm), strong and not deflocculated by EDTA or Actinase E. Only periodate pretreatment of A. johnsonii S35 prevented this coaggregation indicating a role for a carbohydrate-containing moiety without the involvement of protein components. The potential mechanisms and strength of bacterial coaggregations seem to be pair dependent.

Acinetobacter↗

PubMed2003

Pair-dependent co-aggregation behavior of non-flocculating sludge bacteria.

Two strains of non-flocculating sewage sludge bacteria (Xanthomonas sp. S53 and Microbacterium esteraromaticum S51) showed 91% and 77% co-aggregation, respectively, with Acinetobacter johnsonii S35 using a spectrophometric assay. The co-aggregates in case of Xanthomonas sp. S53 and A. johnsonii S35 were above 100 microm and stable against EDTA (2 mM) and a commercial protease (0.2 mg ml(-1)). Protease/periodate pretreatment of the partners did not affect this co-aggregation. On the other hand, co-aggregates of M. esteraromaticum S51 and A. johnsonii S35 (50-70 microm) were deflocculated by EDTA or protease. Protease pretreatment of M. esteraromaticum S51 and periodate pretreatment of A. johnsonii S35 prevented their co-aggregation with respective untreated partners. The potential co-aggregation mechanisms of A. johnsonii S35 varied depending upon the other partner involved.

Acinetobacter↗

PubMed2003

Coaggregation among nonflocculating bacteria isolated from activated sludge.

Thirty-two strains of nonflocculating bacteria isolated from sewage-activated sludge were tested by a spectrophotometric assay for their ability to coaggregate with one other in two-membered systems. Among these strains, eight showed significant (74 to 99%) coaggregation with Acinetobacter johnsonii S35 while only four strains coaggregated, to a lesser extent (43 to 65%), with Acinetobacter junii S33. The extent and pattern of coaggregation as well as the aggregate size showed good correlation with cellular characteristics of the coaggregating partners. These strains were identified by sequencing of full-length 16S rRNA genes. A. johnsonii S35 could coaggregate with strains of several genera, such as Oligotropha carboxidovorans, Microbacterium esteraromaticum, and Xanthomonas spp. The role of Acinetobacter isolates as bridging organisms in multigeneric coaggregates is indicated. This investigation revealed the role of much-neglected nonflocculating bacteria in floc formation in activated sludge.

Acinetobacter↗

PubMed2003

Coaggregation between Acinetobacter johnsonii S35 and Microbacterium esteraromaticum strains isolated from sewage activated sludge.

The extent and nature of intergeneric coaggregations among non-flocculating sludge bacteria were studied through examination of the coaggregation abilities of Acinetobacter johnsonii S35 with two other strains of non-flocculating sludge bacteria (Microbacterium esteraromaticum S38 and M. esteraromaticum S51). At first, the effect of electrolyte concentration as well as the addition of EDTA and proteases on coaggregation were studied. Changes in electrolyte concentration had little effect on the aggregation index (A.I.). However, the A.I. was reduced by 35-45% (addition of 2 mM EDTA) and 15-58% (addition of 0.2 mg/ml Actinase E) within 1 h depending upon the bacterial pair involved. Furthermore, the effect of pretreating either A. johnsonii S35 or its partners with Actinase E and periodate, respectively, was studied. The results indicate that these coaggregations involve a protein on the partner's surface that may interact with carbohydrate or a carbohydrate-containing moiety on the surface of A. johnsonii S35.

Journal Article↗