D. Chandramohan

Differential sensitivity of pigmented and non-pigmented marine bacteria to metals and antibiotics

Abstract The response of pigmented and non-pigmented marine bacteria to metals and antibiotics was investigated. The two groups responded differently to heavy metals and antibiotics. Pigmented bacteria were more resistant to metals. Among the metals, Zn and Hg were less toxic to pigmented bacteria than Cd. Pigmented strains were resistant to antibiotics, particularly at higher concentrations. All the strains, irrespective of their pigment, showed multiple metal and drug resistance.

Effect of lead, mercury and cadmium on a sulphate-reducing bacterium

A sulphate-reducing bacterial strain isolated from the south-west coast of India resembling Desulfosarcina in its physiology was tested for its behaviour towards HgCl(2), CdSO(4) and Pb(NO(3))(2). The order of toxicity to growth of these metal salts in a lactate-based medium at 50 microg ml(-1) concentrations was Cd>Pb>Hg and to respiration Pb>Cd>Hg. Inhibitory concentrations (viz. 100 microg ml(-1) of HgCl(2) and 200 microg ml(-1) of Pb(NO(3)(2)) had a stimulatory effect when the substrate was changed to acetate. With sodium acetate at 0.1% concentration, Hg and Pb had maximum stimulatory effect for growth and sulphide production. Experiments conducted directly with sediment slurries amended with lactate showed that all three metals (at levels below their inhibitory concentrations, i.e. 50 microg ml(-1) of metal salt for Cd and Hg and 100 microg ml(-1) for Pb) inhibited sulphate-reducing activity (SRA) with Pb decreasing the peak production by 68%. The order of toxicity in both lactate and acetate-amended slurry was Pb>Cd>Hg and Pb>Hg>Cd, respectively. With acetate, SRA in the presence of Cd and Hg was stimulated 110% and 27%, respectively. Pb inhibited SRA by 11%. There is a general reduction in the inhibition of sulphide production in slurries as compared with pure culture of the isolate.

Bacterial Growth Efficiency in a Tropical Estuary: Seasonal Variability Subsidized by Allochthonous Carbon

Bacterial growth efficiency (BGE) is a key factor in understanding bacterial influence on carbon flow in aquatic ecosystems. We report intra-annual variability in BGE, and bacteria-mediated carbon flow in the tropical Mandovi and Zuari estuaries (southwest India) and the adjoining coastal waters (Arabian Sea). BGE ranged from 3% to 61% and showed clear temporal variability with significantly (ANOVA, p < 0.01) higher values in the estuaries (mean, 28 ± 14%) than coastal waters (mean, 12 ± 6%). The greater variability of BGE in the estuaries than coastal waters suggest some systematic response to nutrient composition and the variability of dissolved organic matter pools, as BGE was governed by bacterial secondary production (BP). Monsoonal rains and its accompanied changes brought significant variability in BGE and bacterial productivity/primary productivity (BP/PP) ratio when compared to nonmonsoon seasons in the estuaries and coastal waters. High BP/PP ratio (>1) together with high carbon flux through bacteria (>100% of primary productivity) in the estuarine and coastal waters suggests that bacterioplankton consumed dissolved organic carbon in excess of the amount produced in situ by phytoplankton of this region, which led to the mismatch between primary production of carbon and amount of carbon consumed by bacteria. Despite the two systems being subsidized by allochthonous inputs, the low BGE in the coastal waters may be attributable to the nature and time interval in the supply of allochthonous carbon.

Bacteriology of ferromanganese nodules from the Indian Ocean

Abstract Bacteriological investigations of the ferromanganese nodules collected from the Indian Ocean indicate that the microbial populations associated with the nodules are, in general, comparable to those of the Pacific and Atlantic Oceans. Both Mn(II)‐oxidizing and MnO2‐reducing psychrotrophic bacteria were present in the nodules. The maximum percentage of oxidizers was noticed on the surface of the nodules. The sediments harbored more inactive forms. Members of Vibrio, Enterobacteriaceae, Bacillus, Micrococcus, Sta‐phylococcus, Arthrobacter, and coryneforms were encountered in the present study. Most of the isolates were able to grow on a wide range of sodium chloride concentrations (0 to 10%). The isolates elaborated a number of hydrolytic enzymes, namely, amylase, gelatinase, lipase, and phosphatase. The dominance of the gram‐positive group is attributed to terrigenous influences. The present study clearly indicates that Indian Ocean nodules also harbor a variety of heterotrophic bacteria capable of...

'Trade-off' in Antarctic bacteria: limnetic psychrotrophs concede multiple enzyme expressions for multiple metal resistance

The present study examines the metal and antibiotic resistant bacteria in ice and water from lakes east and west of the Indian base camp (Maitri) in Antarctica. The isolates from western and eastern lakes showed distinct geographical differences in properties like metal resistance and enzyme expression. This may be attributed to high organic loading in the lakes on the west of Maitri. However, there was no marked geopraphical distinction in antibiotic resistance between the lakes. Bacteria from the lakes on the eastern side showed resistance to three or more metals including mercury while, those from the western were resistant to only 1–2 metals excluding mercury. Multiple enzyme expression was more pronounced in the lakes on the western side. On the eastern side multiple metal resistance was encountered in bacterial isolates associated with fewer enzyme expressions suggesting a “trade-off”. Thus these Antarctic isolates from the east trade their ability to express multiple enzymes for developing resistance to multiple metals including mercury.

Effect of heavy metals on marine Bacillus sp. and Flavobacterium sp.

Responses to varying concentrations of Hg, Cd, and Zn were studied in two strains of bacterial isolates (Flavobacterium sp. and Bacillus sp.) from Indian coastal waters. Growth responses showed inhibition (in terms of percentage reduction with respect to control) and the order of inhibition was Hg>Zn>Cd in the case of Bacillus sp. and Hg>Cd>Zn in the case of Flavobacterium sp. With prolonged incubation Bacillus sp. overcame the inhibitory effect whereas Flavobacterium sp. did not. Higher concentrations of glucose in the growth medium increased the inhibitory effect of the metal. At lower concentrations (15μg ml-1) there was a stimulatory effect on [14C] glucose uptake on Flavobacterium sp. Our studies showed that the Gram positive isolate was less adaptable to metals than the Gram negative.