Abstract
A novel Gram negative rod-shaped bacterium, designated strain MSh1T, was isolated from Southeast Pahang tropical peat swamp forest soil in Malaysia and characterized using a polyphasic taxonomy approach. The predominant cellular fatty acids (>10.0%) were C16:0 (31.7%), C17:0 cyclo (26.6%), and C19:0 cyclo ω8c (16.1%). The polar lipids detected were phosphatidylglycerol, phosphatidylethanolamine, and diphosphatidylglycerol. The predominant ubiquinone was Q-8. This revealed that strain MSh1T belongs to the genus Burkholderia. The type strain MSh1T can be differentiated from other Burkholderia cepacia complex (Bcc) species by phylogenetic analysis of 16S rRNA gene sequence, multilocus sequence analysis (MLSA), average nucleotide identity (ANI) and biochemical tests. DNA–DNA relatedness values between strain MSh1T and closely related type strains were below the 70% threshold value. Based on this polyphasic study of MSh1T, it can be concluded that this strain represents a novel species within the Bcc, for which the name Burkholderia paludis sp. nov. is proposed. The type strain is MSh1T (= DSM 100703T = MCCC 1K01245T). The dichloromethane extract of MSh1T exhibited antimicrobial activity against four Gram positive bacteria (Enterococcus faecalis ATCC 29212, E. faecalis ATCC 700802, Staphylococcus aureus ATCC 29213, S. aureus ATCC 700699) and a Gram negative bacteria (Escherichia coli ATCC 25922). Further purification work has led to the isolation of Compound 1, pyochelin. Pyochelin demonstrated antimicrobial activity against four S. aureus strains and three E. faecalis strains with MIC-values of 3.13 μg/ml and 6.26 μg/ml, respectively. SEM analysis showed that the cellular morphology of E. faecalis ATCC 700802 was not affected by pyochelin; suggesting that it might target the intracellular components. Pyochelin, a siderophore with antimicrobial activity might be useful in treating bacterial infections caused by S. aureus and E. faecalis, however further work has to be done.
Highlights
The misuse of antimicrobial compounds to treat infections has led to an increase in the prevalence of antimicrobial resistant bacteria (ARB), often associated with nosocomial infections (Mishra et al, 2012)
The DNA–DNA relatedness values between strain MSh1T with its close neighbor based on 16S rRNA phylogenetic analysis: B. arboris R-24201T (29.0 ± 3.7%), B. cenocepacia J2315T
Phylogenetic analysis of concatenated allele sequences demonstrated that strain MSh1T diverged from the other closely related Burkholderia cepacia complex (Bcc) type strains, supported by a bootstrap value of 86% (Figure 2)
Summary
The misuse of antimicrobial compounds to treat infections has led to an increase in the prevalence of antimicrobial resistant bacteria (ARB), often associated with nosocomial (hospital acquired) infections (Mishra et al, 2012). It was reported that nosocomial infections constitute the sixth leading cause of death in the United States and more than 70% of these nosocomial pathogens are resistant to at least one of the common antimicrobial drugs used to treat them (Iowa Department of Public Health) This is an alarming issue because ARB infections often result in increased mortality rates, limit treatment options and cause increased healthcare costs (Ammerlaan et al, 2016). Tropical peat swamp forests are unique wetland ecosystems characterized by their acidic (pH range of 2.9 to 4.5) and waterlogged conditions They are ombotrophic receiving nutrients solely from rain and atmospheric deposition which results in an extremely nutrient poor environment (Yule, 2010). Despite being such a harsh environment, we successfully isolated an antimicrobialproducing bacterium, belonging to the Burkholderia cepacia complex (Bcc) in a previous study (Ong et al, 2015)
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