Search

The cell envelope is essential for viability in all domains of life. It retains enzymes and substrates within a confined space while providing a protective barrier to the external environment. Destabilising the envelope of bacterial pathogens is a common strategy employed by antimicrobial treatment. However, even in one of the best studied organisms, Escherichia coli, there remain gaps in our understanding of how the synthesis of the successive layers of the cell envelope are coordinated during growth and cell division. Here, we used a whole-genome phenotypic screen to identify mutants with a defective cell envelope. We report that loss of yhcB, a conserved gene of unknown function, results in loss of envelope stability, increased cell permeability and dysregulated control of cell size. Using whole genome transposon mutagenesis strategies, we report the comprehensive genetic interaction network of yhcB, revealing all genes with a synthetic negative and a synthetic positive relationship. These genes include those previously reported to have a role in cell envelope biogenesis. Surprisingly, we identified genes previously annotated as essential that became non-essential in a ΔyhcB background. Subsequent analyses suggest that YhcB functions at the junction of several envelope biosynthetic pathways coordinating the spatiotemporal growth of the cell, highlighting YhcB as an as yet unexplored antimicrobial target., Author summary All life depends on a cell envelope to enclose the chemical reactions that make life possible. But how do cell envelopes grow? How each component of the cell envelope is incorporated into the envelope at the correct amount, in the correct place, and at the correct time, to prevent cell death, has been a long-standing question in bacteriology. Using a unique combination of high throughput chemical genetic screens we identified yhcB, a conserved gene of unknown function, required for the maintenance of cell envelope integrity in Escherichia coli. Loss of YhcB results in aberrant cell size driven by the production of excess membrane phospholipids. Subsequent molecular and biochemical analyses suggest YhcB influences the spatiotemporal biogenesis of LPS, peptidoglycan and membrane phospholipids. Our data indicate YhcB is a key regulator of cell envelope growth in Gram-negative bacteria playing a crucial role in coordinating cell width, elongation, and division to maintain cell envelope integrity.

Desert rodents exhibit irruptive (boom–bust) population dynamics in response to pulses of primary productivity. Such unpredictable population dynamics are a challenge for monitoring population trends and managing populations, particularly for species in decline. We studied the population dynamics and occurrence of populations of the vulnerable plains mouse, Pseudomys australis (42-g body mass), during the low (bust) phase of the cycle in the Simpson Desert, Australia, to examine the use of refuges by the species and the predation pressure experienced from native and introduced predators. Specifically we investigated landscape-scale occurrence; body mass, reproduction, and population size; and presence of native and introduced predators. Our results demonstrate that P. australis contracted to discrete areas of the landscape (refuges) during the low phase and that these areas occupied a small proportion (~17%) of the range occupied during population peaks. Animals in refuge populations had comparable body mass, occurred at similar densities to populations during the boom phase, and continued to reproduce during dry conditions. Such refuges represented a significant concentration of biomass to predators in a resource-poor environment. Native predators were rare during the low phase, suggesting that refuges naturally experienced low predation levels. Two introduced predators, feral house cats and red foxes, persisted during the low phase and exploited refuge populations of P. australis, thus representing a significant threat to population persistence. We advocate a novel approach to management of rodents in arid systems that involves identifying the discrete parts of the landscape that function as drought refuges and then focusing threat management there. The relatively small size of these refuges increases the likelihood of cost-effective management.

The Princess Parrot (Polytelis alexandrae) is an Australian endemic that displays irruptive population dynamics. We studied a breeding event in the southern Northern Territory in 2010–11, which followed a peak in primary productivity stimulated by extended above average rainfall. Birds were present from mid-July 2010 to February 2011, with highest numbers in August–November 2010. The maximum count was 172 birds. Multiple nests, all in mature Marble Gum (Eucalyptus gongylocarpa), were detected monthly from August to November 2010 and a single nest in January 2011. Birds fed on flowers, seeds and other material of 11 plant species, both on the ground and within foliage. The decrease in abundance of Parrots over time coincided with a decrease in plant species richness and flower abundance and an increase in availability of seeds and fruit. The area had not been burnt since 2002 indicating that fire-stimulated primary production does not trigger breeding. Despite the time since fire there was evidence of severe effects of past fires. Management of the area now involves efforts to reduce the incidence of high-intensity fires, control of buffel grass (Cenchrus ciliaris) and annual monitoring for the presence of Princess Parrots. Our research highlights the importance of ecological information for making effective conservation management recommendations.

Dasycercus cristicauda and Dasycercus blythi are significant mesopredators in arid Australia and both species are threatened nationally. We investigated size dimorphism, habitat use, and population dynamics of sympatric populations during a low rainfall period in central Australia and examined congruence between morphological and molecular methods of species identification. Our molecular analyses confirmed the presence of two Dasycercus species in sympatry and showed that the descriptions of Woolley (2005) allowed confident identification of the two species in the field. We captured 23 D. cristicauda and 55 D. blythi over 39 months on 20 monitoring plots and another 49 survey sites stratified across five habitat types within a 7000 km2 area. Both species showed sexual dimorphism in body mass with males being significantly heavier. The species typically occupied non-overlapping habitat; D. cristicauda was restricted to sandridges (n = 4 sites) with an understorey dominated by spinifex (Triodia), whereas D. blythi occupied sand plain and gibber plain, the latter being a new habitat for the species. Capture rate of D. cristicauda peaked in autumn-winter 2008 and winter 2009. D. blythi exhibited similar variability with peaks in winter 2009 and summer-autumn 2010. We consider that the relatively low abundance of each species during low rainfall periods makes them vulnerable to predation by feral house cats and European red foxes.

The chlor-alkali industry is one of the world’s larger chemical processing industries in terms of product tonnage and value. The United States is the leading producing country with about 1/3 of the total; it is followed by West Germany with about 10 percent of the world’s production, and then Japan and USSR in that order. Global production of chlorine is currently in excess of 31 million metric tons per year from a total annual capacity of about 40 million tons. The United States has an annual capacity of 13.2 million tons of chlorine.