Aneuploidy is not induced by ethanol during spermatogenesis in the Chinese hamster

Aneuploidy was scored in spermatogonial stages and at both meiotic divisions in male Chinese hamsters exposed to alcohol in vivo. After light ether anesthetization, the animals were intubated (by gastric tube) with 1.5 ml of 12.5% ethanol, whereas controls were given 1.5 ml of distilled water. Gonadectomy was performed 3.5-24 h after ethanol exposure. Ethanol-dosed animals were obviously intoxicated, as evidenced by a rolling gait; serum alcohol levels in 10 animals that were tested peaked 1-2 h after exposure. Among the animals exposed to ethanol, no significant difference over time in the rates of aneuploidy was observed. These data were pooled, and, when compared to control rates, no significant difference could be attributed to ethanol exposure. The aneuploidy found could therefore be interpreted as background rates, and these compared well with data previously published for the Chinese hamster. Several artifactual phenomena were observed: Up to 15% aneuploid spermatogonial metaphases were seen in test and control animals. These were attributed to the mechanical breaking-up of closely apposed groups of diploid spermatogonia. Significant numbers of artifactual diploid MII figures and hypohaploid MI and MII figures were also recorded. To address the possibility that a spermatogonial or other long-term effect could be detected, two animals (with controls) were dosed with 12.5% ethanol daily for 13 and 16 days before sacrifice. No aneuploidy attributable to ethanol was found at MII in these animals either.     

Frequency doubling in the cyanobacterial circadian clock

Organisms use circadian clocks to generate 24‐h rhythms in gene expression. However, the clock can interact with other pathways to generate shorter period oscillations. It remains unclear how these different frequencies are generated. Here, we examine this problem by studying the coupling of the clock to the alternative sigma factor sigC in the cyanobacterium Synechococcus elongatus. Using single‐cell microscopy, we find that psbAI, a key photosynthesis gene regulated by both sigC and the clock, is activated with two peaks of gene expression every circadian cycle under constant low light. This two‐peak oscillation is dependent on sigC, without which psbAI rhythms revert to one oscillatory peak per day. We also observe two circadian peaks of elongation rate, which are dependent on sigC, suggesting a role for the frequency doubling in modulating growth. We propose that the two‐peak rhythm in psbAI expression is generated by an incoherent feedforward loop between the clock, sigC and psbAI. Modelling and experiments suggest that this could be a general network motif to allow frequency doubling of outputs.     

Dual-bioaugmentation strategy to enhance remediation of cocontaminated soil.

Although metals are thought to inhibit the ability of microorganisms to degrade organic pollutants, several microbial mechanisms of resistance to metal are known to exist. This study examined the potential of cadmium-resistant microorganisms to reduce soluble cadmium levels to enhance degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) under conditions of cocontamination. Four cadmium-resistant soil microorganisms were examined in this study. Resistant up to a cadmium concentration of 275 microg ml(-1), these isolates represented the common soil genera Arthrobacter, Bacillus, and Pseudomonas. Isolates Pseudomonas sp. strain H1 and Bacillus sp. strain H9 had a plasmid-dependent intracellular mechanism of cadmium detoxification, reducing soluble cadmium levels by 36%. Isolates Arthrobacter strain D9 and Pseudomonas strain I1a both produced an extracellular polymer layer that bound and reduced soluble cadmium levels by 22 and 11%, respectively. Although none of the cadmium-resistant isolates could degrade 2,4-D, results of dual-bioaugmentation studies conducted with both pure culture and laboratory soil microcosms showed that each of four cadmium-resistant isolates supported the degradation of 500-microg ml(-1) 2,4-D by the cadmium-sensitive 2,4-D degrader Ralstonia eutropha JMP134. Degradation occurred in the presence of up to 24 microg of cadmium ml(-1) in pure culture and up to 60 microg of cadmium g(-1) in amended soil microcosms. In a pilot field study conducted with 5-gallon soil bioreactors, the dual-bioaugmentation strategy was again evaluated. Here, the cadmium-resistant isolate Pseudomonas strain H1 enhanced degradation of 2,4-D in reactors inoculated with R. eutropha JMP134 in the presence of 60 microg of cadmium g(-1). Overall, dual bioaugmentation appears to be a viable approach in the remediation of cocontaminated soils.     

Isoform switching facilitates period control in the Neurospora crassa circadian clock

A striking and defining feature of circadian clocks is the small variation in period over a physiological range of temperatures. This is referred to as temperature compensation, although recent work has suggested that the variation observed is a specific, adaptive control of period. Moreover, given that many biological rate constants have a Q₁₀ of around 2, it is remarkable that such clocks remain rhythmic under significant temperature changes. We introduce a new mathematical model for the Neurospora crassa circadian network incorporating experimental work showing that temperature alters the balance of translation between a short and long form of the FREQUENCY (FRQ) protein. This is used to discuss period control and functionality for the Neurospora system. The model reproduces a broad range of key experimental data on temperature dependence and rhythmicity, both in wild‐type and mutant strains. We present a simple mechanism utilising the presence of the FRQ isoforms (isoform switching) by which period control could have evolved, and argue that this regulatory structure may also increase the temperature range where the clock is robustly rhythmic.     

Differential responses of a mine tailings Pseudomonas isolate to cadmium and lead exposures

We examined cadmium and lead resistance in Pseudomonas sp. S8A, an isolate obtained from mine tailings-contaminated soil. Resistant to soluble metal concentrations up to 200 mg l⁻¹ cadmium and 300 mg l⁻¹ lead, S8A produced both exopolymer and biosurfactant. Upon growth, this pseudomonad diverged into two morphologically distinct colony subtypes; small and round or large and flat. In the presence of lead and in the no metal control the large morphotype appeared only in late stationary phase. With cadmium the large morphotype appeared immediately following exposure. Results show that the large morphotype produced greater amounts of surfactant than the small morphotype, suggesting a unique subpopulation response to cadmium toxicity. Results also indicate that an unidentified 28 kDa protein was expressed following exposure to >10 mg l⁻¹ cadmium. This study demonstrates new links between surfactant production, differential subpopulation response and metal exposure.