Burkholderia pseudomallei-absent soil bacterial community results in secondary metabolites that kill this pathogen

Dynamics and removal mechanisms of antibiotic and antibiotic resistance genes during the fermentation process of spectinomycin mycelial dregs: An integrated meta-omics study

Antibiotic mycelial dregs (AMDs) have been listed as industrial hazardous wastes. With the aim of reducing the environmental risk, the integrated-omics and qPCR approaches were used to reveal the dynamics and removal mechanisms of antibiotic and antibiotic resistance genes (ARGs) during the fermentation of different spectinomycin mycelial dregs (SMDs). The results showed that the removal efficiency of antibiotic in the fermentation of high moisture SMDs reached up to 98%. The high abundance of aadA1 gene encoded by Streptomyces, Lactobacillus, and Pseudomonas was associated with the efficient degradation of spectinomycin, and the inactivating enzymes secreted by degradative bacteria were identified. Furthermore, the dominant microbiota was impacted by moisture content significantly under high temperature environments. In the fermentation of low moisture SMDs, Saccharopolyspora was the dominant microbiota which secreted S8 endopeptidase, M14, M15, S10, S13 carboxypeptidases, M1, M28, S15 aminopeptidases, and antioxidant enzymes, while in the fermentation of high moisture SMDs, Bacillus and Cerasibacillus were dominant genera which mainly secreted S8 endopeptidase and antioxidant enzymes. The abundance of ARGs and mobile genetic elements decreased significantly at thermophilic phase, with maximum drops of 93.7% and 99.9%, respectively. Maintaining moisture content below 30% at the end phase could prevent the transmission of ARGs effectively.

The Burkholderia pseudomallei hmqA-G Locus Mediates Competitive Fitness against Environmental Gram-Positive Bacteria

Burkholderia pseudomallei is an opportunistic pathogen that is responsible for the disease melioidosis in humans and animals. The microbe is a tier 1 select agent because it is highly infectious by the aerosol route, it is inherently resistant to multiple antibiotics, and no licensed vaccine currently exists. Naturally acquired infections result from contact with contaminated soil or water sources in regions of endemicity. There have been few reports investigating the molecular mechanism(s) utilized by B. pseudomallei to survive and persist in ecological niches harboring microbial competitors. Here, we report the isolation of Gram-positive bacteria from multiple environmental sources and show that ∼45% of these isolates are inhibited by B. pseudomallei in head-to-head competition assays. Two competition-deficient B. pseudomallei transposon mutants were identified that contained insertion mutations in the hmqA-G operon. This large biosynthetic gene cluster encodes the enzymes that produce a family of secondary metabolites called 4-hydroxy-3-methyl-2-alkylquinolines (HMAQs). Liquid chromatography and mass spectrometry conducted on filter-sterilized culture supernatants revealed five HMAQs and N-oxide derivatives that were produced by the parental strain but were absent in an isogenic hmqD deletion mutant. The results demonstrate that B. pseudomallei inhibits the growth of environmental Gram-positive bacteria in a contact-independent manner via the production of HMAQs by the hmqA-G operon. IMPORTANCE Burkholderia pseudomallei naturally resides in water, soil, and the rhizosphere and its success as an opportunistic pathogen is dependent on the ability to persist in these harsh habitats long enough to come into contact with a susceptible host. In addition to adapting to limiting nutrients and diverse chemical and physical challenges, B. pseudomallei also has to interact with a variety of microbial competitors. Our research shows that one of the ways in which B. pseudomallei competes with Gram-positive environmental bacteria is by exporting a diverse array of closely related antimicrobial secondary metabolites.