Impact of Clay Minerals on Sulfate-Reducing Activity in Aquifers

Previous studies have shown that sulfate-reduction activity occurs in a heterogeneous manner throughout the terrestrial subsurface. Low-activity regions are often observed in the presence of clay minerals. Here we report that clays inhibit sulfate reduction activity in sediments and in a pure culture of Desulfovibrio vulgaris. Clay minerals including bentonite and kaolinite inhibited sulfate reduction by 70–90% in sediments. Intact clays and clay colloids or soluble components, capable of passing through a 0.2-µm filter, were also inhibitory to sulfate-reducing bacteria. Other adsorbent materials, including anion or cation exchangers and a zeolite, did not inhibit sulfate reduction in sediments, suggesting that the effect of clays was not due to their cation-exchange capacity. We observed a strong correlation between the Al₂O₃ content of clays and their relative ability to inhibit sulfate reduction in sediments (r² = 0.82). This suggested that inhibition might be a direct effect of Al³⁺ (aq) on the bacteria. We then tested pure aluminum oxide (Al₂O₃) and showed it to act in a similar manner to clay. As dissolved aluminum is known to be toxic to a variety of organisms at low concentrations, our results suggest that the effects of clay on sulfate-reducing bacteria may be directly due to aluminum. Thus, our experiments provide an explanation for the lack of sulfate-reduction activity in clay-rich regions and presents a mechanism for the effect.     

Central blockade of nitric oxide synthesis induces hyperthermia that is prevented by indomethacin in rats

The effect of blocking brain nitric oxide (NO) synthesis on body temperature regulation was tested in conscious rats. NO synthase was inhibited by administration of equivalent doses of N^G-nitro-L-arginine methyl ester (L-NAME) or N^G-monomethyl L-arginine monoacetate (L-NMMA) into a lateral cerebral ventricle (ICV) and core temperature was monitored. An ICV injection of 300 μg L-NAME increased colonic temperature in rats (n=8) by 1.9±0.1 °C (P<0.001). The increase in temperature in response to blockade of NO synthesis was significant by 1 h after injection and sustained for more than 3 h. The hyperthermic response to central NO blockade (using L-NMMA) was found to be dose-dependent between 2.8 to 282 μg. Intravenous administration of L-NAME at the highest dose used in the study (300 μg) had no effect on temperature, indicating that the mechanism was mediated by the brain. Pre-treatment with indomethacin (300 μg) blocked hyperthermic responses to ICV L-NAME (300 μg) administration. We conclude that, blockade of nitric oxide induces a cyclooxygenase-dependent hyperthermia in conscious rats that is mediated by the brain.     

Renal nerve inhibition by central NaCl and ANG II is abolished by lesions of the lamina terminalis

The lamina terminalis is situated in the anterior wall of the third ventricle and plays a major role in fluid and electrolyte homeostasis and cardiovascular regulation. The present study examined whether the effects of intracerebroventricular infusion of hypertonic saline and ANG II on renal sympathetic nerve activity (RSNA) were mediated by the lamina terminalis. In control, conscious sheep (n = 5), intracerebroventricular infusions of 0.6 M NaCl (1 ml/h for 20 min) and ANG II (10 nmol/h for 30 min) increased mean arterial pressure (MAP) by 6 +/- 1 (P < 0.001) and 14 +/- 3 mmHg (P < 0.001) and inhibited RSNA by 80 +/- 6 (P < 0.001) and 89 +/- 7% (P < 0.001), respectively. Both treatments reduced plasma renin concentration (PRC). Intracerebroventricular infusion of artificial cerebrospinal fluid (1 ml/h for 30 min) had no effect. In conscious sheep with lesions of the lamina terminalis (n = 6), all of the responses to intracerebroventricular hypertonic saline and ANG II were abolished. In conclusion, the effects of intracerebroventricular hypertonic saline and ANG II on RSNA, PRC, and MAP depend on the integrity of the lamina terminalis, indicating that this site plays an essential role in coordinating the homeostatic responses to changes in brain Na(+) concentration.     

Shifts in archaeal communities associated with lithological and geochemical variations in subsurface Cretaceous rock

Subsurface microbial community structure in relation to geochemical gradients and lithology was investigated using a combination of molecular phylogenetic and geochemical analyses. Discreet groundwater and substratum samples were obtained from depths ranging from 182 to 190 m beneath the surface at approximately 10-cm intervals using a multilevel sampler (MLS) that straddled Cretaceous shale and sandstone formations at a site in the southern San Juan Basin in New Mexico. DNA and RNA were extracted directly from quartzite sand substratum loaded into individual cells of the MLS and colonized in situ. Polymerase chain reaction (PCR)-mediated T-RFLP analysis of archaeal rRNA genes (rDNA) in conjunction with partial sequencing analysis of archaeal rDNA libraries and quantitative RNA hybridization with oligonucleotide probes were used to probe community structure and function. Although total microbial populations remained relatively constant over the entire depth interval sampled, significant shifts in archaeal populations, predominantly methanogens, were observed. These shifts coincided with the geochemical transition from relatively high methane (26 mM), low sulphate (< 3 mg l(-1)) conditions in the region adjacent to the organic matter-rich shale to relatively low-methane (< 0.5 mM), high-sulphate (48 mg l(-1)) conditions in the organic-poor sandstone beneath the shale. These results indicated that active, phylogenetically diverse archaeal communities were present in the subsurface Cretaceous rock environment at this site and that major archaeal clades shifted dramatically over scales of tens of centimetres, corresponding to changes in the lithology and geochemical gradients.     

Effects of training on stress-related behavior of the common marmoset (Callithrix jacchus) in relation to coping with routine husbandry procedures

Using positive reinforcement, J. McKinley trained 12 common marmosets (Callithrix jacchus) to provide urine samples on request. The study then exposed the marmosets to mildly stressful, routine husbandry procedures (i.e., capture and weighing). The nonhuman animals spent less time inactive poststressor as opposed to prestressor. L. Bassett collected matched behavioral data from 12 nontrained marmosets who were less accustomed to human interaction. These animals spent significantly more time self-scratching and locomoting as well as less time inactive, poststressor. Collapsed data from the 2 populations showed increased scent marking, poststressor. These results suggest that locomotion, self-scratching, and scent marking are useful, noninvasive behavioral measures of stress and, thus, reduced welfare in the common marmoset. Overall, nontrained animals showed more self-scratching than did their trained counterparts. It was not possible to collect urine from nontrained marmosets. In response to the stressor, however, trained animals showed no significant change in excreted urinary cortisol. These results suggest that training marmosets may allow them to cope better with routine laboratory procedures.     

Seasonal migrations and reproductive patterns in the lake sturgeon, Acipenser fulvescens, in the vicinity of hydroelectric stations in northern Ontario

This study was conducted in order to evaluate seasonal migratory behaviour and reproductive pattern of lake sturgeon in a confined region of the Mattagami River system in northern Ontario where river flow is regulated by hydroelectric works. Radio tracking and the systematic sampling of lake sturgeon using gill nets indicated that the distribution of fish throughout the study site varied on a seasonal basis. This distribution was related to the migration of individuals to potential spawning sites in the spring, a post-spawning dispersal to feeding areas and late summer migration to an area of concentration on the Groundhog River which is a tributary of the Mattagami River. There was a high proportion of fish (about 50%), within the size range of reproductively active fish, found in the vicinity of suitable spawning habitat during early May. Measurement of the gonadosomatic index (GSI) and plasma sex steroid hormone levels revealed a divergent pattern of reproductive development between the sexes. Female sturgeon exhibited a prolonged period of ovarian regression following spawning. Resumption of ovarian development was not evident until September and was characterized by an increased GSI and plasma levels of testosterone and 17β-estradiol. In contrast, male lake sturgeon began testicular recrudescence within one month of spawning with the GSI reaching prespawning levels by September; reproductive hormones were at prespawning levels by the end of June. It seems that hydroelectric works has complex effects on sturgeon in the Mattagami system. The extensive migratory behaviour of lake sturgeon within the study area make it prone to impingement or entrainment whereas the altered river flow appears to enhance reproductive development. This revised version was published online in August 2006 with corrections to the Cover Date.     

Particulate carbonic anhydrase in homogenates of human kidney.

About 2% of human kidney carbonic anhydrase (carbonate hydro-lyase, EC 4.2.1.1) has been found in particulate fractions. Its distribution in the particulate fractions obtained by differential centrifugation suggests that it may be concentrated in the brush border. The particulate enzyme is like red cell carbonic anhydrace C in its susceptibility to inhibition by anions. Particulate carbonic anhydrase is firmly bound to the membrane and is not released by incubation at pH 10.6 and 37 degrees C or by addition of Triton X-100 or deoxycholate. In 10% Triton X-100 at pH 11.3 and 37 degrees C, the particulate enzyme is inactivated with a half time of about 20 min, and this is at least an order of magnitude slower than the inactivation of soluble enzymes in the presence or absence of membranes. The soluble enzymes are inactivated within a few minutes at 25 degrees C in 3-4% sodium dodecyl sulfate, but the particulate enzyme is relatively stable under those conditions, and its half-time of inactivation at 14 degrees C with a detergent-protein ratio of 25 was about 24 h. Gel filtration with Ultragel AcA-44 in sodium dodecyl sulfate indicates that the membrane carbonic anhydrase has a molecular weight of less than 66 000, so its stability is not due to association with large membrane fragments or vesicles. These results suggest that the membrane enzyme may be a different isozyme than the soluble carbonic anhydrases. Although present in relatively small amounts, its localization on the membrane could give it functional significance.