An antifungal phenazine pigment obtained from Pseudomonas aeruginosa inhibits the growth of Aspergillus ochraceus
Aspergillus ochraceus, a pathogenic mold frequently found in grains, soil, and dried food products. This mold can produce several toxins especially Ochratoxin A and B on infected crops. These toxins are associated with food intoxications both in humans and animals. This study aimed to evaluate the antifungal potentiality of a pigment produced by Pseudomonas aeruginosa, against A. ochraceus in-vitro. Primarily, the cross streak method showed P. aeruginosa (isolate PU8 and PU10) inhibits the growth of A. ochraceus. Then in the quantitative assay using crude extract of the isolate showed significant inhibitory (p<0.05) activities which were up to 72% inhibition by PU8 and 59% by PU10. Then the pigment was extracted, purified, and characterized. The UV spectrophotometry, FT-IR (Fourier Transform Infrared Spectrometry), TLC (Thin-Layer Chromatography) and microscopic analysis proved that the crude extract contained pyocyanin as a potent antifungal phenazine pigment. The adverse effects of chemical fungicides necessitated the use of eco-friendly biological control agents against fungi. Fortunately, from this study, we can infer that P. aeruginosa can produce an antifungal phenazine pigment pyocyanin that inhibits the growth of A. ochraceus and be used as a potential bio-control agent.
Fungi can produce various detrimental mycotoxins, which are potent causes of many diseases of humans, plants and cattle (Bouhet and Oswald 2005). Besides, spoilage of tons of crops and vegetables due to fungal infection is a worldwide alarming issue for agriculture rendering huge economic losses. Common fungal spoilage agents of fresh vegetables and fruits are various species of the genera Alternaria, Aspergillus, Cladosporium, Colletotrichum, Fusarium, Penicillium, Phytophthora, Pythium and Rhizopus spp (Tournas 2005 and Moss 2008). Out of these, a few organisms show a substrate preference whereas others such as Botrytis cinerea, Colletotrichum, Alternaria, Cladosporium, Phytophthora, and Rhizopus spp., can infect a wide variety of vegetables causing devastating losses (Tournas 2005). One of the early interventions which prevents mycotic infection is inhibition of fungal colonization by chemical fungicides or antimycotic agents. However, most of the time these fungicides are not eco-friendly and hazardous to human and cattle health. To tackle this problem in an eco-friendly way biological inhibition of those fungi using biocontrol agents opens a safe path to follow (Gupta 2016, 2018). One of the best actions of microorganisms in our environment is that they can kill each other in such a way which will not cause any diverse effect on the environment. Fortunately, the widely found bacteria named Pseudomonas aeruginosa, can kill fungi very incredibly by producing several antimicrobial coloring agents (Jayaseelan et al., 2014). They can inhibit a wide range of plant pathogenic fungi and control the spreading of various plant diseases (Morales et al., 2013). Previously it has been studied that phenazine pigment of P. aeruginosa named pyocyanin can inhibit the growth of aflatoxin producing A. flavus and other fungus species such as A. niger, Rhizoctonia solani and Candida albicans (Dharni et al., 2012; Morales et al., 2013).
To focus on the biological fungicidal activity of the bacteria, pathogenic fungi named A. ochraceus will be used in this study. A. ochraceus is a clinically important pathogen, which can produce several mycotoxins, such as ochratoxins, penicillic acid, xanthomegnin and viomellin (Pitt et al., 2009). Ochratoxin A (OTA) is a carcinogenic mycotoxin, generally a secondary metabolite produced by several A. ochraceus that contaminate grains, legumes, coffee, dried fruits, beer, wine, and meats (Bayman et al., 2002). The mode of action of this toxins are very complex but researches revealed that OTA inhibits protein synthesis of the infected cell by inhibiting the phenylalanine t-RNA synthetase and isocoumarin, and also enhances the production of oxygen freeradicals, apoptosis or necrosis to exert its toxic action (Kőszegi and Poór 2016; Dirheimer and Creppy 1991). In particular, this study aimed to biologically control the growth of A. ochraceus by phenazine pigmentproducing P. aeruginosa.
Source : An antifungal phenazine pigment obtained from Pseudomonas aeruginosa inhibits the growth of Aspergillus ochraceus
