ALBERT

Description: R-type bacteriocins are contractile phage tail-like structures that are bactericidal towards related bacterial species. The C-terminal region of the phage tail fiber protein determines target-binding specificity. The mutualistic bacteria Xenorhabdus nematophila and X. bovienii produce R-type bacteriocins (xenorhabdicins) that are selectively active against different Xenorhabdus species. We analyzed the P2-type remnant prophage clusters in draft sequences of nine strains of X. bovienii . The C-terminal tail fiber region in each of the respective strains was unique and consisted of mosaics of modular units. The region between the main tail fiber gene ( xbpH1 ) and the sheath gene ( xbpS1 ) contained a variable number of modules encoding tail fiber fragments. DNA inversion and module exchange between strains was involved in generating tail fiber diversity. Xenorhabdicin-enriched fractions from three different X. bovienii strains isolated from the same nematode species displayed distinct activities against each other. In one set of strains, the strain that produced highly active xenorhabdicin was able to eliminate a sensitive strain. In contrast, xenorhabdicin activity was not a determining factor in the competitive fitness of a second set of strains. These findings suggest that related strains of X. bovienii use xenorhabdicin and additional antagonistic molecules to compete against each other.

Description: Anabaena PCC7120 has two annotated toxin–antitoxin systems: MazEF and HicAB. Overexpression of either of the toxins severely inhibited the growth of Escherichia coli BL21(p lysS )(DE3). Of the two Anabaena toxins, MazF exhibited higher toxicity than HicA as evidenced by (i) 100-fold lower viability upon overexpression of MazF compared to HicA; (ii) complete loss of cell viability within 1 h of induction of MazF expression, as against 〉10 3 colony forming units mL –1 in case of HicA; (iii) inability to maintain the MazF overexpressing plasmid in E. coli cells; and (iv) neutralisation of the toxin was effective at the molar ratio of 1:1.9 for MazF:MazE and 13:1 for HicA:HicB, indicating higher antitoxin requirement for neutralisation of MazF. The growth inhibitory effect of MazF was found to be higher in lag phase cultures compared to mid-logarithmic phase cultures of E. coli , while the reverse was true for HicA. The results suggest possible distinct roles for MazEF and HicAB systems of Anabaena .

Description: Animal-associated microbiotas form complex communities, which play crucial functions for their host, including susceptibility to infections. Despite increasing attention to bats as reservoirs of zoonotic pathogens, their microbiota is poorly documented, especially for samples potentially implicated in pathogen transmission such as urine and saliva. Here, using low-biomass individual samples, we examined the composition and structure of bacterial communities excreted by insectivorous bats, focusing on three body habitats (saliva, urine and faeces). We show that niche specialisation occurs as bacterial community composition was distinct across body habitats with the majority of phylotypes being body habitat specific. Our results suggest that urine harbours more diverse bacterial communities than saliva and faeces and reveal potentially zoonotic bacteria such as Leptospira , Rickettsia , Bartonella and Coxiella in all body habitats. Our study emphasised that, in addition to the traditional use of gut-associated samples such as faeces, both urine and saliva are also of interest because of their diverse microbiota and the potential transmission of pathogenic bacteria. Our results represent a critical baseline for future studies investigating the interactions between microbiota and infection dynamics in bats.

Description: Many toxic insecticides used worldwide as well as some chemical warfare agents are phosphotriester derivatives. Therefore, detoxification of organophosphorus compounds has become the subject of many studies and in particular bioremediation, based on the phosphotriesterase catalysed hydrolysis of these compounds, has shown to be an effective and ecological methodology. In order to identify new bacterial phosphotriesterases, a simple and sensitive fluorimetric screening method on solid media was employed that allowed the selection of six strains with phosphotriesterase activity. Since pH and temperature are important parameters for bioremediation of contaminated soils and waters, the influence of these variables on the rate of the enzymatic hydrolysis was assessed. This study afforded notable results, being the most remarkable one the increased activity exhibited by Nocardia asteroides and Streptomyces setonii strains at 50°C, 7 and 30 times higher than at 30°C, respectively. Compared with the results obtained with Brevundimonas diminuta , whose activity is usually considered as reference, an increase of 26 and 75 times is observed, respectively.

Description: Neonicotinoids are neurotoxic systemic insecticides used in plant protection worldwide. Unfortunately, application of neonicotinoids affects both beneficial and target insects indiscriminately. Being water soluble and persistent, these pesticides are capable of disrupting both food chains and biogeochemical cycles. This review focuses on the biodegradation of neonicotinoids in soil and water systems by the bacterial community. Several bacterial strains have been isolated and identified as capable of transforming neonicotinoids in the presence of an additional carbon source. Environmental parameters have been established for accelerated transformation in some of these strains. Studies have also indicated that enhanced biotransformation of these pesticides can be accomplished by mixed microbial populations under optimised environmental conditions. Substantial research into the identification of neonicotinoid-mineralising bacterial strains and identification of the genes and enzymes responsible for neonicotinoid degradation is still required to complete the understanding of microbial biodegradation pathways, and advance bioremediation efforts.

Description: This is the second of three papers investigating properties of titanohematite-bearing quartzo-feldspathic rocks that create a significant remanent magnetic anomaly in the Modum District, South Norway. The first paper provided initial magnetic results, mineralogical characterization and evidence for the presence of lamellar magnetism. In this paper, knowledge of lamellar magnetic properties is explored through experiments where ilmenite lamellae were magnetized below 57 K, and interact magnetically along interfaces with the titanohematite host. Samples with known NRM directions were placed in specific orientations in an MPMS then cooled in zero field to 5 K, where hysteresis loops were measured in fields up to 5 Tesla. This assured that results were ultimately related to the natural lamellar magnetism produced during cooling ~1 billion years ago. In a second set of experiments the same oriented samples, were subjected to a +5 Tesla (T) field then field cooled to 5 K before hysteresis experiments. The first experiments consistently produced asymmetric shifted hysteresis loops with two loop separations, one in a positive field and one in a negative field. Without exception, when the NRM was oriented toward the negative field end of the MPMS, the bimodal loop showed a dominant loop separation in a positive field. By contrast, when the NRM was oriented toward the positive field end of the MPMS, the bimodal loop showed a dominant loop separation in a negative field. Both observations are consistent with antiferromagnetic coupling between the hard magnetization of ilmenite and the more easily shifted lamellar magnetism of the hematite. The bimodal nature of the loops indicates that the NRMs are vector sums of natural lamellar moments, which are oriented both positively and negatively, and that these opposite moments control the orientations of ilmenite magnetizations when cooling through 57 K. Here, extreme exchange biases up to 1.68 T were measured. The second set of experiments produced asymmetric shifted hysteresis loops with one opening always in the negative field. These observations indicate that the +5 T field applied at room temperature rotated the hematite lamellar magnetism in a positive direction, so that upon cooling all the ilmenite lamellae acquired negative magnetic moments, thus causing unimodal negatively shifted loops. Here, the largest exchange bias among the unimodal loops was only 0.7 T. These results will be used in paper III to build a better understanding of lamellar magnetism at the atomic layer scale.

Description: The temperature dependence of magnetic susceptibility ( –T curves) and magnetization ( M–T curves) has been used as a routine rock magnetic tool to characterize the magnetic mineralogy and magnetic granulometry of Chinese loess/palaeosols. However, palaeoclimatic interpretation of these thermomagnetic analyses remains controversial. In the present study, total organic carbon (TOC), thermomagnetic and low-temperature magnetic experiments on Mid-Late Pleistocene loess/palaeosols in Central Asia and the Chinese Loess Plateau (CLP) have been conducted. We found that the M ( T ) cooling curves at room temperature were mostly lower than the corresponding heating curves, whereas for the ( T ) analyses the cooling curves at room temperature were always much higher than the heating curves. Low-temperature magnetic measurements demonstrated that a large amount of superparamagnetic ferrimagnetic particles were produced during the thermal treatment and resulted in the aforementioned differences. This finding further indicated that the use of the M–T curves to estimate the relative content of maghemite in the loess/palaeosols from the CLP was problematic. In addition, a positive correlation exists between the TOC and the frequency-dependent susceptibility ( FD ) in the CLP, suggesting that stronger pedogenesis would result in the simultaneous increase in the content of both maghemite and organic matter. Consequently, the parameters 1 (representing the relative content of pedogenic maghemite), 2 ([ ph – ] + 1 ) and ph (related to the organic matter concentration), which can be calculated from the –T analyses, can potentially be used as new indicators of pedogenesis and palaeoclimate in Central Asia and the CLP.

Description: This study aimed to evaluate the survival and gene expression of Vibrio harveyi under starvation conditions. The microcosms V. harveyi were incubated in sterilized seawater for 4 weeks at room temperature. Overall, the cell numeration declined rapidly about 10 3 CFU/ml during starvation, with a tiny rebound at day 21. Scanning electron microscopy revealed that rod-shaped cells became sphere with a rippled cell surface. By polymerase chain reaction (PCR) assay, nine genes, named lux R, tox R, vhh B, fla A, top A, fur , rpo S, mre B and fts Z, were detected in the non-starved cells. In the starved cells, the expression levels of the detected genes declined substantially ranging from 0.005-fold to 0.028-fold compared to the non-starved cells performed by reverse transcription quantitative real-time PCR with 16S rRNA as the internal control. In the recovering cells, the expression levels of the detected genes, except lux R and mre B, were upregulated dramatically compared to the wild, especially top A (23.720-fold), fur (39.400-fold) and tox R (9.837-fold), validating that the expressions of both the metabolism and virulence genes were important for growth and survival of V. harveyi. The results may shed a new light on understanding of stress adaptation in bacteria.

Description: Type 1 fimbriae (T1F) are well characterised cell surface organelles expressed by Escherichia coli and required for adherence to mannosylated host tissue. They satisfy molecular Koch's postulates as a virulence determinant and a host-adapted role has been reinforced by reports that T1F expression is repressed at submammalian temperatures. Analysis of a group of 136 environmental and animal E. coli isolates that express T1F at 37°C showed that 28% are also capable of expression at 20°C, in a phase variable manner. The heterogeneous proportions varied widely, and although growth temperature impacted the total proportion expressing T1F, there was no direct correlation between growth at 37°C and 20°C, indicative of differences in thermoregulation of the genetic switch ( fimS ) that controls phase variation. Specificities of the adhesin (FimH) also varied between the isolates: most bound to α-(1-3) mannan and yeast extracts as expected, but some recognised β-(1-4)-mannans and N -linked glycoproteins from plants, and T1F from two of the isolates mediated binding to plant roots. The results expand our view of a well-described adherence factor to show alternative expression profiles and adhesin specificities, which in turn may confer an advantage for certain isolates in alternative hosts and habitats.

Description: If the in situ growth rate of filamentous bacteria in activated sludge can be quantified, researchers can more accurately assess the effect of operating conditions on the growth of filaments and improve the mathematical modeling of filamentous bulking. We developed a method to quantify the in situ specific growth rate of Sphaerotilus natans (a model filament) in activated sludge using the species-specific 16S rRNA:rDNA ratio. Primers targeting the 16S rRNA of S. natans were designed, and real-time PCR and RT-PCR were used to quantify DNA and RNA levels of S. natans , respectively. A positive linear relationship was found between the rRNA:rDNA ratio (from 440 to 4500) and the specific growth rate of S. natans (from 0.036 to 0.172 h –1 ) using chemostat experiments. The in situ growth rates of S. natans in activated sludge samples from three water reclamation facilities were quantified, illustrating how the approach can be applied in a complex environment such as activated sludge.