Microbiology
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Item Pectobacterium carotovorum Phage vB_PcaM_P7_Pc Is a New Member of the Genus Certrevirus(Microbiology Spectrum, 2022) Naligama, K. N.; Halmillawewa, A. P.Pectobacterium carotovorum is an economically important phytopathogen and has been identified as the major causative agent of bacterial soft rot in carrots. Control of this phytopathogen is vital to minimizing carrot harvest losses. As fully effi- cient control measures to successfully avoid the disease are unavailable, the phage- mediated biocontrol of the pathogen has recently gained scientific attention. In this study, we present a comprehensive characterization of the P. carotovorum phage vB_PcaM_P7_Pc (abbreviated as P7_Pc) that was isolated from infected carrot samples with characteristic soft rot symptoms, which were obtained from storage facilities at market places in Gampaha District, Sri Lanka. P7_Pc is a myovirus, and it exhibits growth characteristics of an exclusively lytic life cycle. It showed visible lysis against four of the tested P. carotovorum strains and one Pectobacterium aroidearum strain. This phage also showed a longer latent period (125 min) than other related phages; however, this did not affect its high phage titter (.1010 PFU/mL). The final assembled genome of P7_Pc is 147,299 bp in length with a G1C content of 50.34%. Of the 298 predicted open reading frames (ORFs) of the genome of P7_Pc, putative functions were assigned to 53 ORFs. Seven tRNA-coding genes were predicted in the genome, while the genome lacked any major genes coding for lysogeny-related products, con- firming its virulent nature. The P7_Pc genome shares 96.12% and 95.74% average nu- cleotide identities with Cronobacter phages CR8 and PBES02, respectively. Phylogenetic and phylogenomic analyses of the genome revealed that P7_Pc clusters well within the clade with the members representing the genus Certrevirus. Currently, there are only 4 characterized Pectobacterium phages (P. atrosepticum phages phiTE and CB7 and Pectobacterium phages DU_PP_I and DU_PP_IV) that are classified under the genus, making the phage P7_Pc the first reported member of the genus isolated using the host bacterium P. carotovorum. The results of this study provide a detailed characteriza- tion of the phage P7_Pc, enabling its careful classification into the genus Certrevirus. The knowledge gathered on the phage based on the shared biology of the genus will further aid in the future selection of phage P7_Pc as a biocontrol agent.Item Identification of Potentially Hazardous Microorganisms and Assessment of Physicochemical Deterioration of Thermally Processed King Coconut (Cocos nucifera var. aurantiaca) Water under Different Processing Conditions in Sri Lanka(Journal of Food Quality, 2022) Jayasinghe, M. D.; Madage, S. S. K.; Hewajulige, I. G. N.; Jayawardana, T. M. D. A.; Halmillawewa, A. P.; Divisekera, D. M. W. D.King coconut water (KCW) is a sweet relish product that is more prone to rapid quality deterioration, and several safety concerns are emerging due to its inappropriate thermal processing. (erefore, the objective of this study was to identify the potential spoilage/ pathogenic microorganisms associated with the processing of KCW, with the assessment of possible physicochemical changes as providing preliminary information required for the thermal process validation of bottled KCW. Samples (n� 6, 150 ml/sample) were collected from three different KCW processing facilities at five critical processing steps (P1 − P5). A facility survey, physicochemical analyses, and microbial enumeration and isolation, along with their molecular identifications, were conducted. It was found that all tested physicochemical properties were significantly changed (p < 0.05) among sampling points at each processing facility.(ecolour of thermally processed KCW samples has significantly changed (p < 0.05) compared to the fresh KCW, which causes a distinct effect on the appealing quality of the final product. A pattern of initial lower counts with gradually increased microbial counts at intermediate processing steps (1.0 ×103–5.3×106 CFU/ml) and significantly lowered (p < 0.05) counts after thermal treatment was observed. Among the bacterial and fungal isolates identified, several potential pathogenic bacterial species, such as Pantoea dispersa, Bacillus siamensis, Pseudomonas stutzeri, and Acinetobacter lactucae; a few thermal resistant yeasts, Pichia kudriavzevii, Debaryomyces nepalensis, and Candida carpophila; and moulds, Penicillium citrinum, Microdochium fisheri, and Trichosporon asahii, have survived in the thermally processed KCW. Based on the results of the study, it is suggested that the thermal process validation of KCW should be targeted according to the revealed knowledge on the identified hazardous microorganisms, while adhering to Good Manufacturing and Hygienic Practices with minimized handling time to avoid rapid quality deterioration.