The role of indigenous microorganisms in the biodegradation of naturally occurring petroleum, the reduction of iron, and the mobilization of arsenite from west bengal aquifer sediments.

High levels of naturally occurring arsenic are found in the shallow reducing aquifers of West Bengal, Bangladesh, and other areas of Southeast Asia. These aquifers are used extensively for drinking water and irrigation by the local population. Mechanisms for its release are unclear, although increasing evidence points to a microbial control. The type of organic matter present is of vital importance because it has a direct impact on the rate of microbial activity and on the amount of arsenic released into the ground water. The discovery of naturally occurring hydrocarbons in an arsenic-rich aquifer from West Bengal provides a source of potential electron donors for this process. Using microcosm-based techniques, seven sediments from a site containing naturally occurring hydrocarbons in West Bengal were incubated with synthetic ground water for 28 d under anaerobic conditions without the addition of an external electron donor. Arsenic release and Fe(III) reduction appeared to be microbially mediated, with variable rates of arsenic mobilization in comparison to Fe(III) reduction, suggesting that multiple processes are involved. All sediments showed a preferential loss of petroleum-sourced n-alkanes over terrestrially sourced sedimentary hydrocarbons n-alkanes during the incubation, implying that the use of petroleum-sourced n-alkanes could support, directly or indirectly, microbial Fe(III) reduction. Samples undergoing maximal release of As(III) contained a significant population of Sulfurospirillum sp., a known As(V)-reducing bacterium, providing the first evidence that such organisms may mediate arsenic release from West Bengali aquifers.

The serum bactericidal and opsonizing defect in sickle cell anaemia: restoration of activity by control serum.

Thirty-eight homozygous sickler sera were compared with a large pool of serum from healthy African non-sicklers with regard to bactericidal and phagocytic indices. One third of the sera showed reduced bactericidal activity against Salmonella enteritidis which was restored by the addition of 4% control serum; control serum provided both heat-labile (HL) and absorbable (ABS) serum factors. 76% of test sera showed greatly defective opsonization as indicated by ingestion by normal human neutrophils. Activity was not readily restored by the addition of control serum which provided only HL factors. Intracellular survival was increased when bacteria were ingested from sickler serum; activity was readily restored by control serum which provided both HL and ABS factors. In the presence of both serum and neutrophils 84% of test sera permitted increased bacterial survival; the defect was not readily reversed by the addition of control serum which provided both HL and ABS factors.

The bactericidal and opsonic effects of serum from patients with sickle cell anaemia.

The bactericidal and opsonic activity of serum from 12 homozygous sicklers was compared with that of a single control pool of healthy nonsickler African serum. Factorially designed experiments were used to calculate 4 indices which were expressed as the ratio of test to control. Using S. enteritidis and normal human neutrophils viability indices (VI) were calculated for serum, for ingested organisms and for cells + serum, together with a phagocytic index (PI) for cells. Only 1 of the 12 sickler sera gave values equal to that for the control, the remainder showing marked deviation. The survival of organisms in sickler serum was 3 times that in control serum. Phagocytosis by neutrophils in the presence of test sera was only 10% of that in control sera and survival of ingested bacteria was 6 times greater. In the presence of neutrophils overall bacterial survival was 22 times greater for sickler than for control serum.