Withania somnifera (L.) Dunal, a potential medicinal plant used for the treatment of nervous disorders, intestinal infection, leprosy, and cancer, is a perennial herb belonging to Solanaceae and distributed throughout the drier parts of India. Leaf blight disease of this plant generally occurs during March in various districts of South Bengal, India. At the initial stage of infection, symptoms appear as small, light brown spots, gradually becoming irregular, dark brown, concentrically zonate with a diffuse margin, frequently surrounded by light yellow haloes, conspicuous brownish concentric rings in the advance stage of infection. A species of Alternaria was isolated from the lesions. The pathogen was isolated on potato dextrose agar (PDA) media. On PDA, the fungus grew slowly with colonies reaching approximately 35 to 40 mm in diameter in 7 days when incubated at 30°C. Conidiophores arose singly or in groups, straight or flexous, cylindrical, septate, pale to olivaceous brown, as much as 155 μm long, 4 to 5.5 μm thick; conidia were straight, obclavate, pale olivaceous brown, smooth, with up to 15 transverse and rarely 1 or 2 longitudinal or oblique septa and measured 50 to 115 × 5 to 10 μm. Pathogenicity tests were carried out three times on 6-month-old plants (n = 10). Plants were sprayed with a conidial suspension of 105 conidia/ml; control plants were sprayed with sterilized water. Plants were covered with polyethylene bags for 10 days. Disease symptoms appeared after 12 ± 1 day after inoculation. Symptoms on the leaves were similar to those of a naturally occurring diseased plant. The fungal pathogen was consistently reisolated from inoculated plants. The pathogen was identified as Alternaria dianthicola and further confirmed by the Agharkar Research Institute, Pune, India. A literature survey reports the occurrence of some fungal diseases (1), but to our knowledge, this is the first report of A. dianthicola on W. somnifera. References: (1) P. Sinha et al. Page 14 in: Recent Progress in Medicinal Plants. Vol. 6 Diseases and their Management. Sci Tech Publishing LLC, Houston, TX, 2000.

Extracellular polymeric substances (EPS) of microbial origin are a complex mixture of biopolymers comprising polysaccharides, proteins, nucleic acids, uronic acids, humic substances, lipids, etc. Bacterial secretions, shedding of cell surface materials, cell lysates and adsorption of organic constituents from the environment result in EPS formation in a wide variety of free-living bacteria as well as microbial aggregates like biofi lms, biofl ocs and biogranules. Irrespective of origin, EPS may be loosely attached to the cell surface or bacteria may be embedded in EPS. Compositional variation exists amongst EPS extracted from pure bacterial cultures and heterogeneous microbial communities which are regulated by the organic and inorganic constituents of the microenvironment. Functionally, EPS aid in cell-to-cell aggregation, adhesion to substratum, formation of fl ocs, protection from dessication and resistance to harmful exogenous materials. In addition, exopolymers serve as biosorbing agents by accumulating nutrients from the surrounding environment and also play a crucial role in biosorption of heavy metals. Being polyanionic in nature, EPS forms complexes with metal cations resulting in metal immobilization within the exopolymeric matrix. These complexes generally result from electrostatic interactions between the metal ligands and negatively charged components of biopolymers. Moreover, enzymatic activities in EPS also assist detoxifi cation of heavy metals by transformation and subsequent precipitation in the polymeric mass. Although the core mechanism for metal binding and / or transformation using microbial exopolymer remains identical, the existence and complexity of EPS from pure bacterial cultures, biofi lms, biogranules and activated sludge systems differ signifi cantly, which in turn affects the EPS -metal interactions. This paper presents the features of EPS from various sources with a view to establish their role as central elements in bioremediation of heavy metals.

A group of 34 chromium-resistant bacteria were isolated from naturally occurring chromium percolated serpentine soil of Andaman (India). These isolates displayed different degrees of chromate reduction under aerobic conditions. One of the 34 isolates identified as Bacillus sphaericus was tolerant to 800 mgl(-1) Cr(VI) and reduced > 80% Cr(VI) during growth. In Vogel Bonner broth, B. sphaericus cells (10(10) cells ml(-1)) reduced 62% of 20mg l(-1) of Cr(VI) in 48h with concomitant discoloring of yellow medium to white one. Reduction of chromate was pronounced by the addition of glucose and yeast extract as electron donors. In the presence of 4.0 g l(-1) of glucose, 20mg l(-1) of Cr(VI) was reduced to 2.45mg l(-1) after 96h of incubation. Optimum pH and temperature for reduction were 6.0 and 25 degrees C, respectively. Increase in cell density and initial Cr(VI) concentration increased chromate reduction but was inhibited by metal ions like, Ni2+, Co2+, Cd2+ and Pb2+. Experiments with cell-free extracts indicated that the soluble fraction of the cell was responsible for aerobic reduction of Cr(VI) by this organism.

Cell-free extracts (CFEs) of chromium-resistant bacterium Bacillus sphaericus AND 303 isolated from serpentine soil of Andaman, India reduced Cr(VI) in in vitro condition, and the reductase activity was solely localized in the soluble cell-fractions (S12, S32, and S150). The enzyme was constitutive as the CFEs from cells grown in Cr(VI)-free and Cr(VI)-containing media reduced a more or less equal amount of Cr(VI). Optimum Cr(VI) reductase activity was obtained at an enzyme (S150) concentration equivalent to 4.56 mg protein/mL, 300 microM: Cr(VI) and pH 6.0 after 30 min incubation at 30 degrees C. The enzyme was heat labile; 80% of its activity was lost when exposed at 70 degrees C for 15 min. Kinetics of Cr(VI) reductase activity fit well with the linearized Lineweaver-Burk plot and showed a V(max) of 1.432 micromol Cr(VI)/mg protein/min and K(m) of 158.12 microM: Cr(VI). The presence of additional electron donors accelerated Cr(VI) reductase activity of CFE, and an increase of 28% activity over control was recorded with 1.0 microM: NADH. Heavy metal ions such as Ni(II), Cu(II), and Cd(II) were strong inhibitors of Cr(VI) reductase unlike that of 100 microM: Co(II), which retained 93% activity over control.

Serpentine soils collected from Saddle Hills, Chidyatapu and Rutland of Andaman Islands, India were analyzed for physico-chemical and microbiological characteristics and compared with those from adjacent non-serpentine localities. The serpentine soils contained high levels of nickel (1740.0-8033.4 mg/kg dry soil), cobalt (93.2-533.4 mg/kg dry soil) and chromium (302.9-4437.0 mg/kg dry soil), in addition to 62-152 g of iron and 37-60 g of magnesium per kg dry soil. Characteristically the serpentine soils showed low microbial density (6.2-11.3 x 10(6) colony forming unit/g soil) and activity (1.7-3.5 microg fluorescein/g dry soil/h) than non-serpentine outcrops. Serpentine microbial population was dominated by bacteria which represented 5.12 to 9.5 x 10(6) cfu/g of soil, while the fungal population ranged from 0.17 to 3.21 x 10(6) cfu/g of soil. A total of 342 (200 from serpentine and 142 from non-serpentine soils) isolates were compared for Ni, Co and Cr resistance. Serpentine microflora was in general, highly resistant than non-serpentine ones and showed a metal-resistance profile of Cr > Ni > Co. Amongst the serpentine isolates, 8 and 11 bacteria tolerated > 12.0 mM Ni and > 16.0 mM Cr respectively, while 6 fungal isolates showed a minimum inhibitory concentration (MIC) value > 8.0 mM Co. These 25 serpentine strains also showed co-resistance to Cu, Zn and Mn but were sensitive to Hg and Cd. The selected bacterial isolates were resistant to ampicillin, penicillin G and polymyxin B, whereas fungal strains showed resistance to amphotericin B, nystatin and fusidic acid.