Cleavage of cell junction proteins as a host invasion strategy in leptospirosis

Infection and invasion are the prerequisites for developing the disease symptoms in a host. While the probable mechanism of host invasion and pathogenesis is known in many pathogens, very little information is available on Leptospira invasion/pathogenesis. For causing systemic infection Leptospira must transmigrate across epithelial barriers, which is the most critical and challenging step. Extracellular and membrane-bound proteases play a crucial role in the invasion process. An extensive search for the proteins experimentally proven to be involved in the invasion process through cell junction cleavage in other pathogens has resulted in identifying 26 proteins. The similarity searches on the Leptospira genome for counterparts of these 26 pathogenesis-related proteins identified at least 12 probable coding sequences. The proteins were either extracellular or membrane-bound with a proteolytic domain to cleave the cell junction proteins. This review will emphasize our current understanding of the pathogenic aspects of host cell junction-pathogenic protein interactions involved in the invasion process. Further, potential candidate proteins with cell junction cleavage properties that may be exploited in the diagnostic/therapeutic aspects of leptospirosis will also be discussed. KEY POINTS: • The review focussed on the cell junction cleavage proteins in bacterial pathogenesis • Cell junction disruptors from Leptospira genome are identified using bioinformatics • The review provides insights into the therapeutic/diagnostic interventions possible.

Relative biochemical and physiological docking of cucumber varieties for supporting innate immunity against Podosphaera xanthii

Powdery mildew in cucumber is caused by the Podosphaera xanthii. No strategy for improving disease resistance can be successful in the absence of thorough insights into the physiological and biochemical responses of cucumber plants to powdery mildew. Therefore, a field experiment was executed to evaluate five commercial cucumber varieties (V1: Dynasty, V2: Long green, V3:Desi Kheera, V4:Thamin II, V5:Cucumber 363) for their inherent immunity to powdery mildew. Upon inoculating cucumber plants with Podosphaera xanthii, we noted differential responses among the varieties. Compared to other varieties, V1 and V2 showed higher values (P ≤ 0.05) for chlorophyll-a under control and pathogen-attacked plants respectively. The minimum value of anthocyanin content (-53.73%) was recorded in V3 as compared to other varieties post pathogen infection. All pathogen-infected cucumber varieties showed a considerable (P ≤ 0.05) loss in flavonoid content except V2. The maximum destruction for Phenolics under powdery mildew (179%) were recorded in V4, whereas V1 exhibited maximum phenolic content under control conditions. In pathogen-infected plants, the minimum AsA was recorded in V5 as compared to all other varieties. Pathogen invasion impacted significantly (P ≤ 0.05) the activity of superoxide dismutase (SOD). Besides, cucumber plants after pathogen inoculation resulted in a considerable (P ≤ 0.05) increase of peroxidase (POD) activity in V1 (5.02%), V2 (7.5%), and V3 (11%) in contrast to V4. Our results confirmed that cucumber varieties perform differently, which was brought on by distinct metabolic and physiological modifications that have an impact on growth and development. The changes in different attributes were correlated with cucumber resistance against powdery mildew. The results would help us fully harness the potential of these varieties to trigger disease management initiatives and defense responses.

Gene expression of TRPMLs and its regulation by pathogen stimulation

The transient receptor potential mucolipin (TRPML) subfamily in mammalian has three members, namely TRPML1, TRPML2, and TRPML3, who play key roles in regulating intracellular Ca²⁺ homeostasis, endosomal pH, membrane trafficking and autophagy. Previous studies had shown that three TRPMLs are closely related to the occurrence of pathogen invasion and immune regulation in some immune tissues or cells, but the relationship between TRPMLs expression and pathogen invasion in lung tissue or cell remains elusive. Here, we investigated the expression distribution of three TRPML channels in mouse different tissues by qRT-PCR, and then found that all three TRPMLs were highly expressed in the mouse lung tissue, as well as mouse spleen and kidney tissues. The expression of TRPML1 or TRPML3 in all three mouse tissues had a significant down-regulation after the treatment of Salmonella or LPS, but TRPML2 expression showed a remarkable increase. Consistently, TRPML1 or TRPML3 but not TRPML2 in A549 cells also displayed a decreased expression induced by LPS stimulation, which shared a similar regulation pattern in the mouse lung tissue. Furthermore, the treatment of the TRPML1 or TRPML3 specific activator induced a dose-dependent up-regulation of inflammatory factors IL-1β, IL-6 and TNFα, suggesting that TRPML1 and TRPML3 are likely to play an important role in immune and inflammatory regulation. Together, our study identified the gene expression of TRPMLs induced by pathogen stimulation in vivo and in vitro, which may provide novel targets for innate immunity or pathogen regulation.

Butyrate driven raft disruption trots off enteric pathogen invasion: possible mechanism of colonization resistance

The gut microbiome derived short chain fatty acids perform multitude of functions to maintain gut homeostasis. Here we studied how butyrate stymie enteric bacterial invasion in cell using a simplistic binary model. The surface of the mammalian cells is enriched with microdomains rich in cholesterol that are known as rafts and act as entry points for pathogens. We showed that sodium butyrate treated RAW264.7 cells displayed reduced membrane cholesterol and less cholera-toxin B binding coupled with increased membrane fluidity compared to untreated cells indicating that reduced membrane cholesterol caused disruption of lipid rafts. The implication of such cellular biophysical changes on the invasion of enteric pathogenic bacteria was assessed. Our study showed, in comparison to untreated cells, butyrate-treated cells significantly reduced the invasion of Shigella and Salmonella, and these effects were found to be reversed by liposomal cholesterol treatment, increasing the likelihood that the rafts' function against bacterial invasion. The credence of ex vivo studies found to be in concordance in butyrate fed mouse model as evident from the significant drift towards a protective phenotype against virulent enteric pathogen invasion as compared to untreated mice. To produce a cytokine balance towards anti-inflammation, butyrate-treated mice produced more of the gut tissue anti-inflammatory cytokine IL-10 and less of the pro-inflammatory cytokines TNF-α, IL-6, and IFN-γ. In histological studies of Shigella infected gut revealed a startling observation where number of neutrophils infiltration was noted which was correlated with the pathology and was essentially reversed by butyrate treatment. Our results ratchet up a new dimension of our understanding how butyrate imparts resistance to pathogen invasion in the gut.

Peptidoglycan recognition protein MsPGRP in largemouth bass (Micropterus salmoides) mediates immune functions with broad nonself recognition ability

Peptidoglycan (PGN) recognition proteins (PGRPs) are important immune factors in innate immunity that function in recognising pathogens and activating the immune system. These ubiquitous proteins are conserved in invertebrates and vertebrates. In this study, a PGRP gene (MsPGRP) from largemouth bass (Micropterus salmoides) was identified and characterised, and its transcription distribution was explored. Recombinant protein (rMsPGRP) exhibited dose-dependent binding to PGN and glucan (GLU), but weak binding to lipopolysaccharide (LPS). MsPGRP exhibited agglutinating activity against several Gram-negative bacteria, Gram-positive bacteria and fungi, and it promoted phagocytosis activity of leukocytes against Micrococcus luteus and Aeromonas hydrophila. The protein also possessed amidase activity in the presence of Zn²⁺, degraded PGN, and disrupted the M. luteus cell wall. The results suggest that MsPGRP plays an important role in pathogen recognition, and acts as a opsonin during immune system responses and elimination of invading pathogens.

Distribution of the potential pathogenic Alternaria on plant leaves determines foliar fungal communities around the disease spot

Plant leaves are colonized by a remarkably diverse fungal microbiome, which contributes to host plant growth and health. However, responses of foliar fungal community to phytopathogen invasion and measures of the fungal community taken to resist or assist pathogens remain elusive. By utilizing high-throughput sequencing of internal transcribed spacer (ITS) amplicons, we studied the relationships between the foliar fungal community around the disease spot and the pathogen of brown spot disease. The pathogenic Alternaria was found to follow a dramatically decreased trend from the disease spot to its surrounding fungal communities, whose community structure also diverged substantially away from the disease spot community. With the increase of pathogenic Alternaria, diversity indexes, including Shannon, Pielou and Simpson, showed a trend of increasing first and then decreasing. Total network links and the average path distance exhibited strong negative and positive correlations with Alternaria, respectively. Five keystone members showed direct interactions with pathogenic Alternaria. Members of Botryosphaeria, Paraphoma and Plectosphaerella might act as key 'pathogen facilitators' to increase the severity and development of brown spot disease, while Pleospora and Ochrocladosporium might be important 'pathogen antagonists' to suppress the expansion of pathogenic Alternaria. Our study provides new insights in developing new strategies for leaf disease prediction or prevention.

Managing Wildlife Faced with Pathogen Risks Involving Multi-Stable Outcomes

Most models designed to understand how to manage infected wildlife systems with bioeconomic multi-stability take the initial conditions as given, thereby treating pathogen invasion as unanticipated. We examine how ex ante management is an opportunity to influence the ex post conditions, which in turn affect the ex post optimal outcome. To capture these ex ante management choices, we extend the Poisson "collapse" model of Reed and Heras (Bull Math Biol 54:185-207, 1992) to allow for endogenous initial conditions and ex post multi-stability. We account for two uncertain processes: the introduction and establishment of the pathogen. Introduction is conditional on anthropogenic investments in prevention, and both random processes are conditional on how we manage the native population to provide natural prevention of invasion and natural insurance against establishment placing the system in an undesirable basin of attraction. We find that both multi-stability of the invaded system and these uncertainty processes can create economic non-convexities that yield multiple candidate solutions to the ex ante optimization problem. Additionally, we illustrate how the nature of natural protection against introduction and establishment risks can play an important role in the allocation of anthropogenic investments.