Search

Ti-6Al-4V (TC4) alloy is widely utilized as the structural material in marine industries owing to its low density, high specific strength, and favorable corrosion resistance. However, as biofouling drastically alters, some reported the major deleterious effect of bacteria has imposed a challenge to improve microbiologically influenced corrosion (MIC) resistance. A further opportunity for solving this problem is Cu micro-alloying, which was inspired by adding Cu for biomedical applications. Herein, a Ti-6Al-4V alloy with slight Cu addition (TC4-Cu) was exposed to 2216E media inoculated with Pseudomonas aeruginosa (P. A.), and then investigated compared to TC4. TC4-Cu exhibits lower corrosion current, more denser passive film, and lower weight loss with weaker pitting (a maximum pitting depth of 0.2 μm), compared to TC4 with a maximum pitting crater depth of 9.6 μm. Those demonstrated that the presence of Cu significantly improved the MIC resistance, and inhibited the proliferation of P. A., leading to a good antimicrobial efficacy against marine P. A. Moreover, besides the well-known bactericidal role, Cu ions were transferred to form Cu 2 O and CuO, constituting protective corrosion products, and thus improving the anti-microbial properties of TC4-Cu., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Highlights • Pseudomonas sp. CMR12a can efficiently control the cocoyam root rot disease (CRRD). • Phenazines, sessilins and orfamides function exclusively and additively in CRRD suppression. • Nanomolar levels of all three metabolites are sufficient to cause hyphal damage. • Compared to orfamides and phenazines, sessilins appear to have a different cell wall/membrane target. Abstract Root rot disease caused by Pythium myriotylum is the most devastating disease of the tropical tuber crop cocoyam (Xanthosoma sagittifolium) with production losses of up to 90%. This study was conducted in order to determine the role of phenazines (PCN), and two cyclic lipopeptides namely sessilins and orfamides, produced by Pseudomonas sp. CMR12a, in the suppression of the Cocoyam Root Rot Disease (CRRD). Previously generated biosynthetic mutants of CMR12a that were deficient in either one, two or all three metabolites were used in in vitro , microscopic and plant experiments. Using CMR12a and its biosynthetic mutants, plant experiments revealed that mutants, which produced sessilins, orfamides or phenazines alone or at least any two of the metabolites, could successfully suppress the cocoyam root rot disease caused by P. myriotylum albeit in varying capacities. In vitro assays using filter sterilized bacterial supernatants showed that besides the WT strain, all mutants except the null mutant, which makes none of the metabolites, could successfully inhibit P. myriotylum. Following contact between the mycelium of P. myriotylum and purified/semi-purified metabolites, microscopic analysis showed that a concentration of 1 nM and higher of crude sessilins resulted in cell damage including vacuolization and lysis whereas amounts of 25 nM PCN and higher could produce a similar phenotype including mycelial bloating. Treatments with orfamide at 10 nM and higher resulted in mycelial lysis. Interestingly, during plant experiments, the null mutant was able to give some level of disease suppression suggesting that CMR12a produces other compound(s) which could be antagonistic towards our target pathogen. In summary, phenazines, sessilins and orfamides, produced by Pseudomonas sp. CMR12a, can play independent and additive roles in the suppression of Pythium -mediated CRRD. [ABSTRACT FROM AUTHOR]

The rhizobacterium Pseudomonas aeruginosa 7NSK2 produces secondary metabolites such as pyochelin (Pch), its precursor salicylic acid (SA), and the phenazine compound pyocyanin. Both 7NSK2 and mutant KMPCH (Pch-negative, SA-positive) induced resistance to Botrytis cinerea in wild-type but not in transgenic NahG tomato. SA-negative mutants of both strains lost the capacity to induce resistance. On tomato roots, KMPCH produced SA and induced phenylalanine ammonia lyase activity, while this was not the case for 7NSK2. In 7NSK2, SA is probably very efficiently converted to Pch. However, Pch alone appeared not to be sufficient to induce resistance. In mammalian cells, Fe-Pch and pyocyanin can act synergistically to generate highly reactive hydroxyl radicals that cause cell damage. Reactive oxygen species are known to play an important role in plant defense. To study the role of pyocyanin in induced resistance, a pyocyanin-negative mutant of 7NSK2, PHZ1, was generated. PHZ1 is mutated in the phzM gene encoding an O-methyltransferase. PHZ1 was unable to induce resistance to B. cinerea, whereas complementation for pyocyanin production or co-inoculation with mutant 7NSK2-562 (Pch-negative, SA-negative, pyocyanin-positive) restored induced resistance. These results suggest that pyocyanin and Pch, rather than SA, are the determinants for induced resistance in wild-type P. aeruginosa 7NSK2.

Aim: To screen for novel antagonistic Pseudomonas strains producing both phenazines and biosurfactants that are as effective as Pseudomonas aeruginosa PNA1 in the biocontrol of cocoyam root rot caused by Pythium myriotylum. Material and Results: Forty pseudomonads were isolated from the rhizosphere of healthy white and red cocoyam plants appearing in natural, heavily infested fields in Cameroon. In vitro tests demonstrated that Py. myriotylum antagonists could be retrieved from the red cocoyam rhizosphere. Except for one isolate, all antagonistic isolates produced phenazines. Results from whole-cell protein profiling showed that the antagonistic isolates are different from other isolated pseudomonads, while BOX-PCR revealed high genomic similarity among them. 16S rDNA sequencing of two representative strains within this group of antagonists confirmed their relatively low similarity with validly described Pseudomonas species. These antagonists are thus provisionally labelled as unidentified Pseudomonas strains. Among the antagonists, Pseudomonas CMR5c and CMR12a were selected because of their combined production of phenazines and biosurfactants. For strain CMR5c also, production of pyrrolnitrin and pyoluteorin was demonstrated. Both CMR5c and CMR12a showed excellent in vivo biocontrol activity against Py. myriotylum to a similar level as Ps. aeruginosa PNA1 . Conclusion: Pseudomonas CMR5c and CMR12a were identified as novel and promising biocontrol agents of Py. myriotylum on cocoyam, producing an arsenal of antagonistic metabolites. Significance and Impact of the Study:  Present study reports the identification of two newly isolated fluorescent Pseudomonas strains that can replace the opportunistic human pathogen Ps. aeruginosa PNA1 in the biocontrol of cocoyam root rot and could be taken into account for the suppression of many plant pathogens. [ABSTRACT FROM AUTHOR]