Abstract
Microorganisms possess a variety of survival mechanisms, including the production of antimicrobials that function to kill and/or inhibit the growth of competing microorganisms. Studies of antimicrobial production have largely been driven by the medical community in response to the rise in antibiotic-resistant microorganisms and have involved isolated pure cultures under artificial laboratory conditions neglecting the important ecological roles of these compounds. The search for new natural products has extended to biofilms, soil, oceans, coral reefs, and shallow coastal sediments; however, the marine deep subsurface biosphere may be an untapped repository for novel antimicrobial discovery. Uniquely, prokaryotic survival in energy-limited extreme environments force microbial populations to either adapt their metabolism to outcompete or produce novel antimicrobials that inhibit competition. For example, subsurface sediments could yield novel antimicrobial genes, while at the same time answering important ecological questions about the microbial community.
Highlights
Microbes play fundamental roles in ecosystem functioning, through mediating biogeochemical cycles, yet we know very little about their interactions in nature
Freshwater Cyanobacteria encode diverse polyketide synthases (PKS) and non-ribosomal peptide synthases (NRPS) are and able to produce a wide array of antimicrobial compounds including cyclic peptides, macrolides, and terpenoids (Ehrenreich et al, 2005; Busti et al, 2006; Frangeul et al, 2008; Silva-Stenico et al, 2011; Swain et al, 2017)
There have been 260 compound families of Cyanobacteria secondary metabolite products and can have a range of activities including lethality, cytotoxicity, antibacterial, anti-microalgal, and enzyme inhibition (Demay et al, 2019). Due to their PKS and NRPS diversity (Brito et al, 2015; Mazard et al, 2016), Cyanobacteria will likely be the primary focus for future exploration of novel or unique antimicrobials in freshwater environments
Summary
Microbes play fundamental roles in ecosystem functioning, through mediating biogeochemical cycles, yet we know very little about their interactions in nature. One of the most common mechanisms for inhibition or elimination of competition is the production of antimicrobial compounds, including antibacterials and antifungals. These compounds can be toxic to the surrounding community, providing a selective advantage for nutrients, carbon, and space (Bibb, 2005; Rigali et al, 2008). This review will survey natural antimicrobials that have been isolated from Bacteria and putative antimicrobial production within different environments including continental soil, caves, freshwater, marine, and deep subsurface sediments. The overall purpose of this review is to highlight studies that have found natural antimicrobial producing genes from Bacteria and Archaea within various environments, as well as pinpoint areas that have yet to be explored
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