High antagonistic activity and antibiotic resistance of flavobacteria of polar microbial freshwater mats on King George Island in maritime Antarctica

Abstract

This is the first study to demonstrate a relationship between antagonistic interactions with antibiotic resistance within flavobacterial strains, a component of polar-region microbial mats. These strains were derived from ephemeral freshwater reservoirs, i.e. ponds and streams of the periglacial zone of Ecology Glacier (King George Island, maritime Antarctica). The study demonstrated the strains' surprisingly high phylogenetic diversity, with 20 species among 50 isolates. Flavobacteria were characterised by different patterns of antagonism and sensitivity to antimicrobials. 29 strains produced substances inhibiting the growth of other isolates, with 21 strains being sensitive to such compounds; 34 strains were multidrug-resistant (MDR). The antibiotic resistance index (ARI) demonstrated a significantly higher proportion of MDR strains and ARI ≥ 0.2 in stream mats (87%) as compared to the strains derived from pond mats (55%). A strong correlation was observed between the strains' antagonistic potential and antibiotic resistance. An important role in these phenomena is accomplished by the "super bacteria" strains that effectively accumulate numerous traits associated with antagonistic potential and can be involved in the potential transfer of these traits. The results of the study demonstrate that there are individual patterns of antagonistic interactions and antibiotic resistance among the biotic components of mats.

Keywords: Antagonistic activity; Antarctica; Antibiotic resistance; Flavobacteria; Microbial Mats.

Fig. 1

Location of the sampling area and sampling sites of streams (S1–S15) and ponds (P1–P5) microbial mats in the periglacial zone of Ecology Glacier, King George Island, maritime Antarctica. Characteristic of sampling sites is shown in Table 1 (https://www.npolar.no/quantarctica/; QGIS 3.40 Bratislava, http://www.qgis.org/).

Fig. 2

Macroscopic and microscopic (vertical cross section) structure of the microbial mats of the periglacial zone of Ecology Glacier; stream (a, b) and pond (c, d).

Fig. 3

Phylogenetic tree based on 16 S rRNA gene sequences comparison of the isolated flavobacteria strains among their closest related species within the genus Flavobacterium. The evolutionary history was inferred using the maximum likelihood method based on the Tamura-Nei distance with the gamma model. Bootstrap probability values (percentages of 1000 tree replications) greater than 50% are indicated at branch points. Bar, 0.01 substitutions per nucleotide position. Flavobacterial isolates are marked by a strain code number (S – strim, P – pond) and GenBank accession number (in brackets).

Fig. 4

Map of the antimicrobial resistance profiles (orange – resistant; grey – sensitive) and antagonistic activity data of flavobacteria isolates from the microbial mat of ponds and streams in the periglacial zone of Ecology Glacier. NAR – number of antibiotic resistance; ARI – antibiotic resistance index; I % – percentage of inhibited strains; R % – percentage of resistance to antagonistic interactions; ITP – interactive type profile: P – production of antibacterial compounds; R – resistance to antibacterial compounds; S – sensitivity to antibacterial compounds. Characteristics of antibiotics are listed in Table 3.

Fig. 5

Antibiotic resistance index (ARI) of flavobacteria to a selected group of antibiotics: inhibitors of cell wall synthesis (CW), proteins (P) and nucleic acids (NA). ARI index with p < 0.05 is indicated (*), and p < 0.01 is indicated with (**).

Fig. 6

Network analyses of antagonistic interactions and antibiotic resistance among flavobacteria isolated from microbial mats, (a) 20 × 20 array of tests among ponds isolates, (b) 30 × 30 array among streams isolates. Each node represents bacterial strains. Strains with the same type of antagonistic activity (ITP – interactive type profile) have the same fill colour: PR – green, PRS – blue, SR – purple, and R – orange. Each line represents an antagonistic interaction from an active strain (red dot) towards a sensitive strain (arrow). The number of red dots indicate range of antagonistic activity of strain, and number of arrows indicate range of sensitivity of strain. The size of the red ring indicates the antibiotic resistance range. The species names of the strains are listed in Fig. 4.

Fig. 7

Correlation between antibiotic resistance index (ARI) and antagonistic activity (a) and resistance to antagonistic reactions (b) of flavobacteria strains.