Influence of cations and anions on the induction of cell density-independent luminescence in Photorhabdus luminescens.

Bioluminescence is emitted by various living organisms, including bacteria. While the induction mechanism in marine luminescent bacteria, such as Vibrio fischeri and V. harveyi, has been well characterized, this mechanism has not been studied in detail in the non-marine luminescent bacterium Photorhabdus luminescens. Therefore, we investigated the effect of cations and anions on the induction of luminescence by P. luminescens. Cultivation of cells in an inorganic salts solution (ISS) containing KCl, CaCl2 , MgCl2 , NaHCO3 , and MgSO4 resulted in a rapid increase in luminescence intensity. Moreover, the induction of luminescence in the ISS medium was not dependent on cell density, since cell densities remained unchanged during 48 h. Furthermore, we found that compounds containing K(+) , Mg(2+) , and HCO3(-) were necessary to induce cell density-independent luminescence. The intensity of luminescence per cell cultured in medium containing KCl, MgCl2 , and NaHCO3 was approximately 100-fold higher than that cultured in NB. In contrast, when cells actively grew in normal growth condition, the intensity of luminescence per cell was not increased even in the presence of K(+) , Mg(2+) , and HCO3(-) . Thus, these results suggest that the luminescence of P. luminescens is regulated by 2 independent cell density-dependent and -independent mechanisms.

Selenium cannot substitute for sulfur in cell density-independent bioluminescence in Vibrio fischeri.

It has been proposed that selenium, an element chemically similar to sulfur, can participate in some of the same biological pathways as sulfur, although only a few studies have been confirmed this. In this study, we investigated the relationship between selenium and sulfur-dependent luminescence in Vibrio fischeri. The luminescence of V. fischeri was induced by the addition of sulfur-containing compounds such as Na2SO4 and L-cystine, and their luminescence was suppressed, in a dose-dependent manner, by the addition of the selenium-containing compounds Na2SeO4 and L-selenocystine. Since the viability of V. fischeri was not affected by the addition of low concentration of selenium-containing compounds, the decrease in luminescence intensity cannot be explained by cell death. Kinetic analysis performed using Lineweaver-Burk plots demonstrate that Na2SeO4 and L-selenocystine act as competitive suppressors in inorganic sulfur (Na2SeO4)-dependent luminescence. In contrast, these selenium-containing compounds act as uncompetitive suppressors in organic sulfur (L-cystine)-dependent luminescence.

The crucial role of single-stranded DNA binding in enhancing sensitivity to DNA-damaging agents for Schlafen 11 and Schlafen 13.

Schlafen (SLFN) 11 enhances cellular sensitivity to various DNA-damaging anticancer agents. Among the human SLFNs (SLFN5/11/12/13/14), SLFN11 is unique in its drug sensitivity and ability to block replication under DNA damage. In biochemical analysis, SLFN11 binds single-stranded DNA (ssDNA), and this binding is enhanced by the dephosphorylation of SLFN11. In this study, human cell-based assays demonstrated that a point mutation at the ssDNA-binding site of SLFN11 or a constitutive phosphorylation mutant abolished SLFN11-dependent drug sensitivity. Additionally, we discovered that nuclear SLFN13 with a point mutation mimicking the DNA-binding site of SLFN11 was recruited to chromatin, blocked replication, and enhanced drug sensitivity. Through generating multiple mutants and structure analyses of SLFN11 and SLFN13, we identified protein phosphatase 2A as a binding partner of SLFN11 and the putative binding motif in SLFN11. These findings provide crucial insights into the unique characteristics of SLFN11, contributing to a better understanding of its mechanisms.

Requirements for sulfur in cell density-independent induction of luminescence in Vibrio fischeri under nutrient-starved conditions.

Despite the universal requirement for sulfur in living organisms, it is not known whether the luminescence of Vibrio fischeri is sulfur-dependent and how sulfur affects the intensity of its luminescence. In this study, we investigated the requirement for sulfur in V. fischeri luminescence under nutrient-starved conditions. Full induction of V. fischeri luminescence required MgSO(4); in artificial seawater cultures that lacked sufficient MgSO(4), its luminescence was not fully induced. This induction of luminescence was not dependent on autoinduction because the cell density of V. fischeri did not reach the critical threshold concentration. In addition to MgSO(4), this cell density-independent luminescence was induced or maintained by nontoxic concentrations of l-cysteine, sulfate, sulfite, and thiosulfate. Moreover, the addition of N -3-oxo-hexanoyl homoserine lactone and N -octanoyl homoserine lactone, which are known autoinducers in V. fischeri, did not induce luminescence under these conditions. This result suggested that the underlying mechanism of luminescence may be different from the known autoinduction mechanism.

Interactions between bicarbonate, potassium, and magnesium, and sulfur-dependent induction of luminescence in Vibrio fischeri.

In spite of its central importance in research efforts, the relationship between seawater compounds and bacterial luminescence has not previously been investigated in detail. Thus, in this study, we investigated the effect of cations (Na(+) , K(+) , NH(4) (+) , Mg(2+) , and Ca(2+) ) and anions (Cl(-) , HCO(3) (-) , CO(3) (2-) , and NO(3) (-) ) on the induction of both inorganic (sulfate, sulfite, and thiosulfate) and organic (L-cysteine and L-cystine) sulfur-dependent luminescence in Vibrio fischeri. We found that HCO(3) (-) (bicarbonate) and CO(3) (2-) (carbonate), in the form of various compounds, had a stimulatory effect on sulfur-dependent luminescence. The luminescence induced by bicarbonate was further promoted by the addition of magnesium. Potassium also increased sulfur-dependent luminescence when sulfate or thiosulfate was supplied as the sole sulfur source, but not when sulfite, L-cysteine, or L-cystine was supplied. The positive effect of potassium was accelerated by the addition of magnesium and/or calcium. Furthermore, the additional supply of magnesium improved the induction of sulfite- or L-cysteine-dependent luminescence, but not the l-cystine-dependent type. These results suggest that sulfur-dependent luminescence of V. fischeri under nutrient-starved conditions is mainly controlled by bicarbonate, carbonate, and potassium. In addition, our results indicate that an additional supply of magnesium is effective for increasing V. fischeri luminescence.

Effects of magnesium sulfate on the luminescence of Vibrio fischeri under nutrient-starved conditions.

In this study, we investigated the relationship between MgSO(4) and luminescence in Vibrio fischeri under nutrient-starved conditions. When V. fischeri was cultured in an artificial seawater medium, the luminescence intensity was low relative to that observed under normal growth conditions. It decreased during the initial 14 h, and then increased slightly at 24 h. This regulation of luminescence was not dependent on the quorum-sensing mechanism, because the cell densities had not reached a critical threshold concentration. Under MgSO(4)-starved conditions, luminescence was not fully induced at 14 h, and decreased at 24 h. In contrast, induction of luminescence occurred under MgSO(4)-supplemented conditions, but MgSO(4) alone was insufficient to induce luminescence, and required NaHCO(3) or KCl. These results suggest that the luminescence of V. fischeri is controlled by an exogenous sulfur source under nutrient-starved conditions. In addition, they indicate that the induction of sulfur-dependent luminescence is regulated by the NaHCO(3) or KCl concentration.

Cr(VI) reduction from contaminated soils by Aspergillus sp. N2 and Penicillium sp. N3 isolated from chromium deposits.

Aspergillus sp. N2 and Penicillium sp. N3 are chromate-resistant filamentous fungi that were isolated from Cr(VI) contaminated soil based on their ability to decrease hexavalent chromium levels in the growth medium. After 120 h of growth in a medium containing 50 ppm Cr(VI) at near neutral pH, Aspergillus sp. N2 reduced the Cr(VI) concentration by about 75%. Penicillium sp. N3 was able to reduce the Cr(VI) concentration by only 35%. However, Penicillium sp. N3 reduced the Cr(VI) concentration in the medium by 93% under acidic conditions. Interestingly, the presence of Cu(II) enhanced the Cr(VI) reducing ability of Aspergillus sp. N2 and Penicillium sp. N3 at near neutral pH. Aspergillus sp. N2 and Penicillium sp. N3 reduced the Cr(VI) concentration in the growth medium to a virtually undetectable level within 120 h. For both Aspergillus sp. N2 and Penicillium sp. N3, mycelial seed cultures were more efficient at Cr(VI) reduction than conidium seed cultures. The mechanisms of Cr(VI) reduction in Aspergillus sp. N2 and Penicillium sp. N3 were enzymatic reduction and sorption to mycelia. Enzymatic activity contributed significantly to Cr(VI) reduction. Aspergillus sp. N2 and Penicillium sp. N3 reduced the levels of Cr(VI) in polluted soil samples, suggesting that these strains might be useful for cleaning up chromium-contaminated sites.

Effects of Practice and Psychological Pressure on Interpersonal Coordination Failures.

Although sports players in the same team try to manage their interpersonal coordination for improved performance, failures such as hesitations and collisions are often seen in interpersonal coordination between teammates. However, it is unclear what factors influence the occurrence of such hesitations and collisions. The purpose of this study was to examine the effects of practice and psychological pressure on the occurrence of hesitations and collisions. A total of 80 right-handed university students (aged 19.1 years ± 0.8; 32 males and 48 females) were randomly assigned into pairs and were instructed to perform a serial-tapping task cooperatively. An apparatus had five buttons in a row, which flashed once in each trial in a quasi-random order. When a flashing button was hit, a corresponding light went off and another button flashed. The participants were instructed that the task was to hit a flashing button as quickly and accurately as possible, and either member of the pair could hit the button. They performed 80 practice trials, 10 trials as a control test, and 10 trials as a pressure test. Before the pressure test, pressure was added by informing them about audience and confiscation of the prize if they could not fulfill a criterion. As a result, the occurrence rates of hesitations and collisions and the performance time significantly decreased from the first 40 trials to the next 40 trials of the practice session. Under pressure, state anxiety, the intention to cooperate, and the occurrence rates of hesitations and collisions increased, though heart rate and performance time did not change. These results suggested that interpersonal coordination improved with practice but deteriorated under pressure.