This study investigated genomic differences in Australian and Indian Pseudomonas aeruginosa isolates from keratitis (infection of the cornea). Overall, the Indian isolates were resistant to more antibiotics, with some of those isolates being multi-drug resistant. Acquired genes were related to resistance to fluoroquinolones, aminoglycosides, beta-lactams, macrolides, sulphonamides, and tetracycline and were more frequent in Indian (96%) than in Australian (35%) isolates (p = 0.02). Indian isolates had large numbers of gene variations (median 50,006, IQR = 26,967–50,600) compared to Australian isolates (median 26,317, IQR = 25,681–33,780). There were a larger number of mutations in the mutL and uvrD genes associated with the mismatch repair (MMR) system in Indian isolates, which may result in strains losing their efficacy for DNA repair. The number of gene variations were greater in isolates carrying MMR system genes or exoU. In the phylogenetic division, the number of core genes were similar in both groups, but Indian isolates had larger numbers of pan genes (median 6518, IQR = 6040–6935). Clones related to three different sequence types—ST308, ST316, and ST491—were found among Indian isolates. Only one clone, ST233, containing two strains was present in Australian isolates. The most striking differences between Australian and Indian isolates were carriage of exoU (that encodes a cytolytic phospholipase) in Indian isolates and exoS (that encodes for GTPase activator activity) in Australian isolates, large number of acquired resistance genes, greater changes to MMR genes, and a larger pan genome as well as increased overall genetic variation in the Indian isolates.

In this study we report the formation of marine oil snow (MOS), its associated microbial community, the factors influencing its formation, and the microbial response to crude oil in surface waters of the Faroe-Shetland Channel (FSC). The FSC is a subarctic region that is hydrodynamically complex located in the northeast Atlantic where oil extraction is currently occurring and where exploration is likely to expand into its deeper waters (>500 m). A major oil spill in this region may mirror the aftermath that ensued following the Deepwater Horizon blowout in the Gulf of Mexico, where the massive influx of Macondo crude oil triggered the formation of copious quantities of rapidly sinking MOS and successional blooms of opportunistic oil-degrading bacteria. In laboratory experiments, we simulated environmental conditions in sea surface waters of the FSC using water collected from this site during the winter of 2015. We demonstrated that the presence of dispersant triggers the formation of MOS, and that nutrient amendments magnify this. Illumina MiSeq sequencing revealed the enrichment on MOS of associated oil-degrading (Cycloclasticus, Thalassolituus, Marinobacter) and EPS-producing (Halomonas, Pseudoalteromonas, Alteromonas) bacteria, and included major representation by Psychrobacter and Cobetia with putative oil-degrading/EPS-producing qualities. The formation of marine snow, in the absence of crude oil and dispersant, in seawater amended with nutrients alone indicated that the de novo synthesis of bacterial EPS is a key factor in MOS formation, and the glycoprotein composition of the MOS aggregates confirmed that its amorphous biopolymeric matrix was of microbial (likely bacterial) origin. The presence of dispersants and crude oil with/without nutrients resulted in distinct microbial responses marked by intermittent, and in some cases short-lived, blooms of opportunistic heterotrophs, principally obligate hydrocarbonoclastic (Alcanivorax, Cycloclasticus, Thalassolituus, Marinobacter) and EPS-producing (Halomonas, Alteromonas, Pseudoalteromonas) bacteria. Interestingly, members of the Vibrionales (principally the genus Vibrio) were strongly enriched by crude oil (with/without dispersant or nutrients), highlighting a putative importance for these organisms in crude oil biodegradation in the FSC. Our findings mirror those observed at Deepwater Horizon and hence underscore their broad relevance.

Silicate weathering improves soils by releasing bioessential nutrients from the bedrock to the soil ecosystem. However, whether bacteria are capable

Biofilms in nature often exist as communities. In this study, an experimental mixed-species community consisting of Pseudomonas aeruginosa, Pseudomonas protegens and Klebsiella pneumoniae was used to investigate how AI-2 transporters affect interspecies interactions and composition. The K. pneumoniae lsrB/lsrD deletion mutants had a 10–25-fold higher concentration of extracellular AI-2 compared to the wild-type. Although these deletion mutants produced monospecies biofilms of similar biomass, the substitution of these mutants for the parental strain significantly altered composition. Dual-species biofilm assays demonstrated that the changes in composition were due to the cumulative effect of pairwise interactions. It was further revealed that K. pneumoniae being present physically in the consortium was important in AI-2 mediating composition in the consortium, and that AI-2 transporters were crucial in achieving maximum biomass in the community. In conclusion, these findings demonstrate that AI-2 transporters mediate interspecies interactions and is important in maintaining the compositional equilibrium of the community.