A mercury resistant bacterial strain, SA2, was isolated from soil contaminated with mercury. The 16S rRNA gene sequence of this isolate showed 99% sequence similarity to the genera Sphingobium and Sphingomonas of α-proteobacteria group. However, the isolate formed a distinct phyletic line with the genus Sphingobium suggesting the strain belongs to Sphingobium sp. Toxicity studies indicated resistance to high levels of mercury with estimated EC50 values 4.5 mg L(-1) and 44.15 mg L(-1) and MIC values 5.1 mg L(-1) and 48.48 mg L(-1) in minimal and rich media, respectively. The strain SA2 was able to volatilize mercury by producing mercuric reductase enzyme which makes it potential candidate for remediating mercury. ICP-QQQ-MS analysis of Hg supplemented culture solutions confirmed that almost 79% mercury in the culture suspension was volatilized in 6 h. A very small amount of mercury was observed to accumulate in cell pellets which was also evident according to ESEM-EDX analysis. The mercuric reductase gene merA was amplified and sequenced. The deduced amino acid sequence demonstrated sequence homology with α-proteobacteria and Ascomycota group.

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In present study, the occurrence of Salmonella in local chicken eggs and their pattern of antibiotic resistance were determined. 100 egg samples collected from different locations of Dhaka city were analysed and Salmonella spp were found in 8% of the samples. Among all presumptive Salmonella isolates, 8 isolates were confirmed as Salmonella enterica subsp. salamae (4%), Salmonella enterica subsp. indica (1%), Salmonella Paratyphi-A (1%), Salmonella bongori (1%) and Salmonella Choleraesuis (1%) on the basis of serotyping and biochemical analysis. These isolates were subjected to susceptibility test against 10 antibiotic disks. All the isolates were found chloramphenicol sensitive. The highest percentage of resistance (87.5%) was found to amoxicillin and ampicillin. Resistance against erythromycin, cephalexin, doxycycline hydrochloride, ceftazidime, doxycycline and nalidixic acid was also found significant ranging from 25% to 62.5%. Salmonella isolated from egg shell surface were found more antibiotic resistant than that of egg yolk and white. The present study suggests that poultry eggs are potential reservoir of antibiotic resistant Salmonellae.Keywords: Egg; Salmonella; Characterization; Antibiotic resistance.© 2011 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.doi:10.3329/jsr.v3i1.6109                J. Sci. Res. 3 (1), 191-196  (2011)

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Different organs of a host represent distinct microenvironments resulting in the establishment of multiple discrete bacterial communities within a host. These discrete bacterial communities can also vary according to geographical location. For the Pacific oyster, Crassostrea gigas, the factors governing bacterial diversity and abundance of different oyster microenvironments are poorly understood. In this study, the factors shaping bacterial abundance, diversity and composition associated with the C. gigas mantle, gill, adductor muscle and digestive gland were characterised using 16S (V3-V4) rRNA amplicon sequencing across six discrete estuaries. Both location and tissue-type, with tissue-type being the stronger determinant, were factors driving bacterial community composition. Bacterial communities from wave-dominated estuaries had similar compositions and higher bacterial abundance despite being geographically distant from one another, possibly indicating that functional estuarine morphology characteristics are a factor shaping the oyster bacterial community. Despite the bacterial community heterogeneity, examinations of the core bacterial community identified Spirochaetaceae bacteria as conserved across all sites and samples. Whereas members of the Vulcaniibacterium, Spirochaetaceae and Margulisbacteria, and Polynucleobacter were regionally conserved members of the digestive gland, gill and mantle bacterial communities, respectively. This indicates that baseline bacterial community profiles for specific locations are necessary when investigating bacterial communities in oyster health.

Contamination of land and water caused by heavy metal mercury (Hg) poses a serious threat to biota worldwide. The seriousness of toxicity of this neurotoxin is characterized by its ability to augment in food chains and bind to thiol groups in living tissue. Therefore, different remediation approaches have been implemented to rehabilitate Hg-contaminated sites. Bioremediation is considered as cheaper and greener technology than the conventional physico-chemical means. Large-scale use of Hg-volatilizing bacteria are used to clean up Hg-contaminated waters, but there is no such approach to remediate Hg-contaminated soils. This review focuses on recent uses of Hg-resistant bacteria in bioremediation of mercury-contaminated sites, limitation and advantages of this approach, and identifies the gaps in existing research.

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KR Mahbub added as the First author on 08/08/2012 and corrected PDF loaded on 08/08/2012.The aim of the study was to assess the microbiological quality of Dhaka WASA drinking water. A total of 45 samples were collected from different outlets of WASA water supply chain. Among the these samples 29 samples were collected from house tap, 5 samples from street pipe line tap and 11 samples from WASA source pump. The results of the Total Viable Count (TVC) showed that 62 % samples of house tap water, 60 % pipeline water and 45.45 % WASA pump water were exceeded the BDS standard (1240:2001) and WHO Guideline for drinking. The highest count was 2 × 106 cfu/ml in the house tap water of Gandaria. Total coliform and E. coli count ranged from <1.8 (MPN) /100 ml to >1600 (MPN)/100 ml. Among all the tested samples, 57.78 % water samples were positive for coliform and 51.11 % samples were positive for E. coli bacteria. Out of twenty three E. coli isolates, 8 isolates were subjected to biochemical and microscopic examination for confirmation. All 8 isolates were detected as E. coli based on biochemical parameters. The antibiotic sensitivity pattern of those isolates was determined. Most of them were found resistant to Ampicillin, Amoxicillin, kanamycin, Penicillin, Sulphomethoxazole antibiotics. Nearly all of them were found sensitive to Gentamycin and Nalidixic acid. The samples collected from different house tap water and road side tap water were more contaminated than WASA source pump water. It may therefore be concluded that distribution lines of Dhaka WASA supply chain might be the main source of microbiological contamination of drinking water. In this regard further investigations with more representatively drawn samples are required.DOI: http://dx.doi.org/10.3329/jesnr.v4i2.10133J. Environ. Sci. & Natural Resources, 4(2): 41-49, 2011