Plant growth promoting endophyte Burkholderia contaminans NZ antagonizes phytopathogen Macrophomina phaseolina through melanin synthesis and pyrrolnitrin inhibition

The endophytic bacterium Burkholderia contaminans NZ was isolated from jute, which is an important fiber-producing plant. This bacterium exhibits significant growth promotion activity in in vivo pot experiments, and like other plant growth-promoting (PGP) bacteria fixes nitrogen, produces indole acetic acid (IAA), siderophore, and 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. B. contaminans NZ is considered to exert a promising growth inhibitory effect on Macrophomina phaseolina, a phytopathogen responsible for infecting hundreds of crops worldwide. This study aimed to identify the possibility of B. contaminans NZ as a safe biocontrol agent and assess its effectiveness in suppressing phytopathogenic fungi, especially M. phaseolina. Co-culture of M. phaseolina with B. contaminans NZ on both solid and liquid media revealed appreciable growth suppression of M. phaseolina and its chromogenic aberration in liquid culture. Genome mining of B. contaminans NZ using NaPDoS and antiSMASH revealed gene clusters that displayed 100% similarity for cytotoxic and antifungal substances, such as pyrrolnitrin. GC-MS analysis of B. contaminans NZ culture extracts revealed various bioactive compounds, including catechol; 9,10-dihydro-12’-hydroxy-2’-methyl-5’-(phenylmethyl)- ergotaman 3’,6’,18-trione; 2,3-dihydro-3,5- dihydroxy-6-methyl-4H-pyran-4-one; 1-(1,6-Dioxooctadecyl)- pyrrolidine; 9-Octadecenamide; and 2- methoxy- phenol. These compounds reportedly exhibit tyrosinase inhibitory, antifungal, and antibiotic activities. Using a more targeted approach, an RP-HPLC purified fraction was analyzed by LC-MS, confirming the existence of pyrrolnitrin in the B. contaminans NZ extract. Secondary metabolites, such as catechol and ergotaman, have been predicted to inhibit melanin synthesis in M. phaseolina. Thus, B. contaminans NZ appears to inhibit phytopathogens by apparently impairing melanin synthesis and other potential biochemical pathways, exhibiting considerable fungistatic activity.

Altering Nitrogen Sources Affects Growth Carbon Costs in Vachellia nilotica Growing in Nutrient-Deficient Grassland Soils

Vachellianilotica (L.) Willd. Ex Del. is a multipurpose leguminous tree that is common in grassland and savanna ecosystems in southern and eastern Africa. These ecosystem soils are reported to be acidic and nutrient-limited, specifically with regards to nitrogen (N) and phosphorus (P). The presence of this plant in these terrestrial ecosystems improves soil fertility benefiting the surrounding vegetation due to its ability to fix atmospheric N. This study seeks to understand the N-fixing bacteria symbiosis and physiological adaptations of V. nilotica in these acidic and nutrient-deficient KwaZulu-Natal soils. The soils used for this study were collected from the Ukulinga Grassland Nutrient Experiment located at the Ukulinga research farm of the University of KwaZulu-Natal, Pietermaritzburg, South Africa. Due to long-term soil nutrient addition treatments, these soils offered a diverse nutrient variation for better understanding the effects of acidity and nutrient variation on microbial symbiosis, plant nutrition, and biomass accumulation of V. nilotica. V. nilotica was able to maintain growth by relying on both atmospheric and soil-derived N across all treatments decreasing carbon (C) growth costs. There was an increased reliance on atmospheric-derived N of un-nodulated high N-treated plants. The plants grown in high N + P soils were able to nodulate with various species from the Mesorhizobium genus, which resulted in increased biomass compared to other plants. The results of this study show that V. nilotica can alter N sources to reduce C growth costs. In addition, both nodulating and free-living soil N2 fixing bacteria such as Caulobacter rhizosphaerae, Sphingomonas sp. and Burkholderia contaminans identified in the experimental soils may play an important role under P-deficient conditions.

Outbreak of Burkholderia contaminans endophthalmitis traced to a clinic ventilation system

We describe the follow-up investigation of an outbreak of endophthalmitis due to Burkholderia contaminans following cataract surgery in a single clinic. Whole-genome sequence analysis of bacteria recovered from affected patients and the clinic identified the clinic’s ventilation system as the source of infection.

First Report of Shot-hole on Flowering Cherry Caused by Burkholderia contaminans and Pseudomonas syringae pv. syringae

The shot-hole disease (SH) is one of the most common and important diseases affecting the flowering cherry (FC; Prunus × yedoensis Matsumura; ‘Somei-yoshino’) trees in South Korea every year, resulting in premature defoliation and reduced flowering in the following year. However, pathogens associated with the disease remain unknown, which has rendered disease management challenging. Here, the pathogens associated with SH, their biochemical characteristics, and their host range were elucidated. Detached leaf and in planta assays revealed that two biofilm-forming bacteria, namely Burkholderia contaminans (Bc) and Pseudomonas syringae pv. syringae (Pss), caused SH of FC trees. These pathogens were recorded for the first time as the causes of SH of FC trees in South Korea. Additionally, the two pathogens induced similar disease symptoms in several stone fruits belonging to the genus Prunus, including peach (P. persica), plum (P. salicina), and apricot (P. mume), with peach being the most susceptible. These results indicate that Bc and Pss caused SH on FC trees and presented a broad spectrum of hosts. Furthermore, Xanthomonas arboricola pv. pruni, the causative agent of leaf spot on stone fruits, incited brown spots and shot holes on FC leaves. Therefore, FC trees are susceptible to infections by various pathogenic bacteria, including Bc, Pss, and Xap. These findings will be of great importance as a reference for effective management of SH in the face of possible cross-infection between Prunus species in the future.

Clinical course, treatment and visual outcome of an outbreak of Burkholderia contaminans endophthalmitis following cataract surgery

Background Postoperative endophthalmitis is a rare but dreaded complication of intraocular surgery and often results in severe visual impairment or blindness. The present study describes the clinical course, treatment and visual outcome of an outbreak of Burkholderia contaminans endophthalmitis following cataract surgery. Methods Among 290 patients who underwent uneventful phacoemulsification cataract surgery at one outpatient clinic between January 4th and 28th 2019, 6 cases developed Burkholderia contaminans endophthalmitis. Clinical data were collected by retrospective review of patient records. Microbiological samples from vitreous aspirates, intraocular lenses (IOL) and lens capsules were cultured, and recA and draft whole genome sequences analysed. Results The recA sequences of all Burkholderia contaminans isolates and the allelic profile of the isolates were identical. All cases had a similar clinical presentation with rapid development of endophthalmitis symptoms with variable time to onset. The mean time to admission was 34 days (12–112 days). All cases had a seemingly favourable response to intravitreal antibiotics. However, acute recurrences occurred after long time periods (12–71 days). The cases experienced between 0 and 3 recurrences. Due to persistent infection, the cases received between 5 and 15 treatments (mean 7.8) including IOL and lens capsule explantation in 5 of 6 cases. Burkholderia contaminans was detected in all explanted lens capsules. The final corrected distance visual acuity (CDVA, Snellen chart) was between 0.8 and 1.2 and all cases had final CDVA ≥0.8. Conclusions A persistent and intensive treatment approach including total lens capsule and IOL explantation is recommended for Burkholderia contaminans endophthalmitis following cataract surgery and may lead to a favourable visual result.

Improved Bio-Synthesis of 2,5-bis(hydroxymethyl)furan by Burkholderia contaminans NJPI-15 With Co-substrate

Upgrading of biomass derived 5-hydroxymethylfurfural (HMF) has attracted considerable interest recently. A new highly HMF-tolerant strain of Burkholderia contaminans NJPI-15 was isolated in this study, and the biocatalytic reduction of HMF into 2,5-bis(hydroxymethyl)furan (BHMF) using whole cells was reported. Co-substrate was applied to improve the BHMF yield and selectivity of this strain as well as HMF-tolerant level. The catalytic capacity of the cells can be substantially improved by Mn2+ ion. The strain exhibited good catalytic performance at a pH range of 6.0–9.0 and a temperature range of 25°C–35°C. In addition, 100 mM HMF could be reduced to BHMF by the B. contaminans NJPI-15 resting cells in presence of 70 mM glutamine and 30 mM sucrose, with a yield of 95%. In the fed-batch strategy, 656 mM BHMF was obtained within 48 h, giving a yield of 93.7%. The reported utilization of HMF to produce BHMF is a promising industrially sound biocatalytic process.

Key Parameters on the Antibacterial Activity of Silver Camphor Complexes

Nine new complexes with camphor imine or camphor sulfonimine ligands were synthesized and analytically and spectroscopically characterized, aiming to identify the key parameters that drive the antibacterial activity of the complexes with metal cores and imine substituents with distinct electronic and steric characteristics. The antimicrobial activity of all complexes was evaluated by determining their minimum inhibitory concentrations (MIC) against the Gram-negative Escherichia coli ATCC25922, Pseudomonas aeruginosa 477, and Burkholderia contaminans IST408, and the Gram-positive Staphylococcus aureus Newman. Camphor imine complexes based on the hydroxyl silver center ({Ag(OH)}) typically perform better than those based on the nitrate silver center ({Ag(NO3)}), while ligands prone to establish hydrogen bonding facilitate interactions with the bacterial cell surface structures. A different trend is observed for the silver camphor sulfonimine complexes that are almost non-sensitive to the nature of the metal cores {Ag(OH)} or {Ag(NO3)} and display low sensitivity to the Y substituent. The antibacterial activities of the Ag(I) camphor sulfonimine complexes are higher than those of the camphor imine analogues. All the complexes display higher activity towards Gram-negative strains than towards the Gram-positive strain.