The infection cycle of phage λ terminates in lysis mediated by three types of lysis proteins, each disrupting a layer in the bacterial envelope: the S105 holin, the R endolysin, and the Rz/Rz1 spanin ...complex targeting the inner membrane, cell wall or peptidoglycan, and the outer membrane, respectively. Video microscopy has shown that in most infections, lysis occurs as a sudden, explosive event at a cell pole, such that the initial product is a less refractile ghost that retains rod-shaped morphology. Here, we investigate the molecular basis of polar lysis using time-lapse fluorescence microscopy. The results indicate that the holin determines the morphology of lysis by suddenly forming two-dimensional rafts at the poles about 100 s prior to lysis. Given the physiological and biochemical similarities between the lambda holin and other class I holins, dynamic redistribution and sudden concentration may be common features of holins, probably reflecting the fitness advantage of all-or-nothing lysis regulation.IMPORTANCEIn this study, we use fluorescent video microscopy to track -green fluorescent protein (GFP)-labeled holin in the minutes prior to phage lysis. Our work contextualizes prior genetic and biochemical data, showing when hole formation starts and where holin oligomers form in relation to the site of lytic rupture. Furthermore, prior work showed that the morphology of lambda-infected cells is characterized by an explosive event starting at the cell pole; however, the basis for this was not clear. This study shows that holin most often oligomerizes at cell poles and that the site of the oligomerization is spatially correlated with the site of lytic blowout. Therefore, the holin is the key contributor to polar lysis morphology for phage lambda.
Phage P1 is a temperate phage which makes the lytic or lysogenic decision upon infecting bacteria. During the lytic cycle, progeny phages are produced and the cell lyses, and in the lysogenic cycle, ...P1 DNA exists as a low-copy-number plasmid and replicates autonomously. Previous studies at the bulk level showed that P1 lysogenization was independent of
ultiplicity
f
nfection (MOI; the number of phages infecting a cell), whereas lysogenization probability of the paradigmatic phage λ increases with MOI. However, the mechanism underlying the P1 behavior is unclear. In this work, using a fluorescent reporter system, we demonstrated this P1 MOI-independent lysogenic response at the single-cell level. We further observed that the activity of the major repressor of lytic functions (C1) is a determining factor for the final cell fate. Specifically, the repression activity of P1, which arises from a combination of C1, the anti-repressor Coi, and the corepressor Lxc, remains constant for different MOI, which results in the MOI-independent lysogenic response. Additionally, by increasing the distance between phages that infect a single cell, we were able to engineer a λ-like, MOI-dependent lysogenization upon P1 infection. This suggests that the large separation of coinfecting phages attenuates the effective communication between them, allowing them to make decisions independently of each other. Our work establishes a highly quantitative framework to describe P1 lysogeny establishment. This system plays an important role in disseminating antibiotic resistance by P1-like plasmids and provides an alternative to the lifestyle of phage λ.
Phage P1 has been shown potentially to play an important role in disseminating antibiotic resistance among bacteria during lysogenization, as evidenced by the prevalence of P1 phage-like elements in animal and human pathogens. In contrast to phage λ, a cell fate decision-making paradigm, P1 lysogenization was shown to be independent of MOI. In this work, we built a simple genetic model to elucidate this MOI independency based on the gene-regulatory circuitry of P1. We also proposed that the effective communication between coinfecting phages contributes to the lysis-lysogeny decision-making of P1 and highlighted the significance of spatial organization in the process of cell fate determination in a single-cell environment. Finally, our work provides new insights into different strategies acquired by viruses to interact with their bacterial hosts in different scenarios for their optimal survival.
Observations suggest that sudden canopy decline and death of widely dispersed individual trees, associated with wood-borer infestations, has recently expanded and intensified within high-elevation ...Eucalyptus pauciflora and E. lacrimans stands on the Kosciuszko massif, southeast Australia. Despite reports of insect infestations and associated tree decline over four decades, the phenomenon has been poorly understood and the identity of the associated wood-borer taxon only anecdotally resolved. We conducted a systematic study of sub-alpine forests in Kosciuszko National Park, NSW, with the intent of building a knowledge base of the phenomenon’s aetiology and guiding ongoing research priorities. Using 10-metre radius plots positioned on elevational transects in areas under shared management for snow-based recreation and conservation and areas managed for conservation-only, we found a strong association between increasing severity of wood-borer feeding galleries and decline of canopy condition. The presence of even the first indicators of insect infestation was associated with a three-fold increase in declining canopy condition. Two-way contingency analysis revealed that increasing severity of feeding galleries corresponded with a highly significant decline in canopy-condition. Indicators of wood-borer infestation held greater explanatory power for deteriorating crown condition, than the converse, indicating that wood-borer infestation more likely precede, than follow, canopy decline and death. Based on insect detections over three years and consistency between observed and previously described wood-borer damage, it is unambiguously clear that the native cerambycid species Phoracantha mastersi is principally responsible for insect galleries in affected trees. Detections were associated with warm daily temperature maxima. Modelling of the incidence and severity of infestations indicated elevation and land-management status were significant predictors for the probability of wood-borer infestation at stand and tree levels. The same predictors were significant for predicting the proportion of stand basal area affected. Combined with temporal patterns in insect detections, our modelling results suggest that low temperatures play a key role in limiting upward migration of infestations. While we suspect that fragmentation of forest cover within shared-management areas favours short-distance dispersal and local intensification, an increase in forest-edges may also account for both greater frequency and severity of stand-level infestations in shared-management areas. Mindful of an apparent lower limit to P. mastersi infestations at the interface of affected/unaffected eucalypt taxa, we advocate for greater understanding of physiological traits affecting tree-level vulnerability to infestation. Further, reflecting their roles in Phoracantha infestations elsewhere, we regard resolving the combined roles of temperature and drought stress in initiating outbreaks as particularly important. Similarly, consistent with the effect of land-management status on P. mastersi infestations, improved knowledge of the spatial and temporal attributes of Phoracantha-induced dieback in snow-gum forests is needed.
•A strong association exists between evidence of wood borers and canopy condition.•The native cerambycid species Phoracantha mastersi is principally responsible.•Elevation and land-management are significant predictors of infestation.•Declining temperature with elevation likely limits upward movement of wood borers.•Forest fragmentation may explain greater infestation severity in modified areas.
Removal of Pseudomonas type IV pili by a small RNA virus Thongchol, Jirapat; Yu, Zihao; Harb, Laith ...
Science (American Association for the Advancement of Science),
2024-Apr-05, 2024-04-05, 20240405, Volume:
384, Issue:
6691
Journal Article
Peer reviewed
The retractile type IV pilus (T4P) is important for virulence of the opportunistic human pathogen
. The single-stranded RNA (ssRNA) phage PP7 binds to T4P and is brought to the cell surface through ...pilus retraction. Using fluorescence microscopy, we discovered that PP7 detaches T4P, which impairs cell motility and restricts the pathogen's virulence. Using cryo-electron microscopy, mutagenesis, optical trapping, and Langevin dynamics simulation, we resolved the structure of PP7, T4P, and the PP7/T4P complex and showed that T4P detachment is driven by the affinity between the phage maturation protein and its bound pilin, plus the pilus retraction force and speed, and pilus bending. Pilus detachment may be widespread among other ssRNA phages and their retractile pilus systems and offers new prospects for antibacterial prophylaxis and therapeutics.
Increasing CO
2
may influence commercial crop and timber yield. While selection of genotypes sensitive to elevated CO
2
(eCO
2
) appears possible in agricultural crops, there is limited evidence ...for genotype-by-CO
2
(G × CO
2
) interactions in commercial tree species. We examined CO
2
responsiveness in 124 open-pollinated
Eucalyptus globulus
ssp.
globulus
(
E. globulus
) families with the aim of assessing whether G × CO
2
interactions are detectable in seedlings for early-age screening. Plants were grown in ambient (aCO
2
; ~ 405 μmol mol
−1
) and eCO
2
(640 μmol mol
−1
) and harvested 25 days after germination. Total, shoot, and root dry weights were determined for each plant. Carbon isotopic discrimination against
13
C (Δ
13
C) was determined at the family level. We observed highly significant (
p
< 0.0001) increases in mean total, shoot, and root dry weights. Mixed-model equations were used to estimate the main and interaction effects of the G × CO
2
for each mass trait. The main effects from the mixed-model output (CO
2
and individual-tree effects) were significant for all traits. However, CO
2
-by-individual tree interactions were non-significant for all traits, indicating little G × CO
2
interaction. A secondary aim was to examine the correlation between greenhouse and mature-age growth from breeding trials that use common families conducted under ambient CO
2
. These correlations were non-significant, suggesting early growth is not necessarily indicative of later-age responses. Our results suggest that while early growth of
E. globulus
is enhanced under eCO
2
, genotypes respond relatively uniformly to eCO
2
and little opportunity exists for seedling-based selection at the population level based upon the response of plants during the first weeks of growth.
Tad (tight adherence) pili, part of the type IV pili family, are crucial for mechanosensing, surface adherence, bacteriophage (phage) adsorption, and cell-cycle regulation. Unlike other type IV ...pilins, Tad pilins lack the typical globular β sheet domain responsible for pilus assembly and phage binding. The mechanisms of Tad pilus assembly and its interaction with phage ΦCb5 have been elusive. Using cryo-electron microscopy, we unveiled the Tad pilus assembly mechanism, featuring a unique network of hydrogen bonds at its core. We then identified the Tad pilus binding to the ΦCb5 maturation protein (Mat) through its β region. Notably, the amino terminus of ΦCb5 Mat is exposed outside the capsid and phage/pilus interface, enabling the attachment of fluorescent and affinity tags. These engineered ΦCb5 virions can be efficiently assembled and purified in
, maintaining infectivity against
, which presents promising applications, including RNA delivery and phage display.
Compaction of urban soil where stormwater infrastructures are built reduces infiltration, vegetation growth, and stormwater treatment capacity. Biochar—a carbonaceous porous material produced by ...pyrolysis of organic waste – can be used as a soil amendment to improve the function of stormwater infrastructure in addition to the proven benefit of increased pollutant removal. However, the benefits depend on the biochar’s properties such as particle size distribution and concentration. Further, because biochar’s particle size distribution is altered by compaction, the hydraulic functions of compacted biochar amended soil is unknown. Herein, we examined the effect of biochar concentrations (0-6% w/w) and particle sizes (unsieved, sieved to < 2mm, and to < 0.5 mm) on water retention and saturated or unsaturated hydraulic conductivity of compacted stormwater media amended with biochar. Our results show the particle size of biochar plays a critical role in whether or not compaction is alleviated: while increasing concentration of unsieved biochar increased hydraulic conductivity up to 3% biochar, increasing concentration of fine biochar (< 2 mm) resulted in consistent decline in hydraulic conductivity under compaction. The results indicate that large biochar particles can effectively dissipate the compaction energy, while the fine biochar under compaction increased clogging by generating more fines that occupy the pores. Water retention improved regardless of the size distribution of added biochar, indicating that addition of biochar would reduce the irrigation requirement to maintain plant health in dry climate or water-stressed conditions. Overall, the results indicate that biochar addition can be effective in mitigating the negative impacts of compaction on stormwater infrastructures, depending on the proportion of coarse biochar.
We examine climate sensitivity in tree-ring chronologies from Eucalyptus pauciflora Sieb. ex Spreng at three elevations—1,350, 1,475 and 1,600 m above the sea level. Consistent with the principle ...that the sensitivity of tree-ring chronologies increases with proximity to the limits of tree growth, statistics reflecting chronology reliability increased with elevation. Climatological analyses of the three elevation classes revealed that whilst ring width is significantly and positively correlated with maximum air temperature during spring (September-November) in the chronology from the highest elevation class, significant correlations with maximum temperature are not present at low elevations. Similarly, whilst ring width in the chronology from 1,350 m was significantly and positively correlated with precipitation during late summer and early autumn, no significant correlations are evident at higher elevations. Our results illustrate the importance of careful site selection in dendroclimatological studies of eucalypts and demonstrate the potential of E. pauciflora for climatological studies.
Enterotoxigenic
(ETEC) is an opportunistic pathogen that commonly causes foodborne illness. Study of bacteriophages against this pathogen could be useful to develop alternative treatment approaches. ...Here, we present the complete genome sequence of LL11, a T7-like podophage that infects ETEC.
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