Toxic Neighborhood: Bacterial populations are often considered to be driven by gene-centric, selfish dynamics. Superficially, antibiotic production fits this picture as individuals can gain most benefit by inhibiting or killing close relatives with high niche overlap. Contrary to that notion, Cordero et al. (p. 1228 ; see the Perspective by Morlon ) show that bacteria in the wild form social units in which antibiotic production and resistance leads to cooperation within, and antagonism between, populations. A combination of high-throughput interaction screening, molecular genetics, and genomics revealed that antibiotics are produced by only a few members of each population, while all other members are resistant. In the past, lack of knowledge of the ecological structure of microbial populations has led to interpretations of antibiotic production and resistance as being largely driven by short-lived, cyclic invasions of populations by antibiotic-producing resistant bacteria. This work shows that structured, socially cohesive bacterial populations exist in the wild and form organizational patterns similar to those of animal and plant populations.

Proteorhodopsins (PRs) phototrophy was recently discovered in oceanic surface waters. PRs have been observed in different marine environments and in diverse taxa, including the ubiquitous marine alphaproteobacterial SAR11 group and the uncultured gammaproteobacterial SAR86 group. Previously, two SAR86 PR subgroups, discovered in the Pacific Ocean, were shown to absorb light with different maxima, _max 527 nm (green) and _max 490 nm (blue) and their distribution was explained by prevailing light conditions – green pigments at the surface and blue in deeper waters. Here, we show that PRs display high diversity in geographically distinct patterns despite similar physical water column properties such as mixing and light penetration. We compared summer and winter samples representing stratified and mixed conditions from both the Mediterranean and Sargasso Sea. As expected, in the Mediterranean Sea, green pigments were mainly confined to the surface and the percentage of blue pigments increased toward deeper samples; in the Sargasso Sea, unexpectedly, all PRs were of the blue type. As an additional result, both locations show seasonal dependence in the distribution of different PR families. Finally, spectral tuning was not restricted to a single PR family as previously reported but occurs across the sampled PR families from various microbial taxa. The distribution of tunable PRs across the PR tree suggests that ready adaptability has been distributed widely among microorganisms, and may be a reason that PRs are abundant and taxonomically widely dispersed.

Acinetobacter baumannii is a nosocomial bacterial pathogen, and infections attributed to this species are further complicated by a remarkable ability to acquire antimicrobial resistance genes and to survive in a desiccated state. While the antibiotic resistance and biofilm formation of A. baumannii is well-documented, less is known about the virulence attributes of this organism. Recent studies reported A. baumannii strains display a motility phenotype, which appears to be partially dependent upon Type IV pili, autoinducer molecules, and the response to blue light. In this study, we wanted to determine the prevalence of this trait in genetically diverse clinical isolates, and any additional required factors, and environmental cues that regulate motility. When strains are subjected to a wide array of stress conditions, A. baumannii motility is significantly reduced. In contrast, when extracellular iron is provided or salinity is reduced, motility is significantly enhanced. We further investigated whether the genes required for the production of lipopolysaccharide (lpsB) and K1 capsule (epsA/ptk) are required for motility as demonstrated in other Gram-negative bacteria. Transposon mutagenesis resulted in reduced motility by the insertion derivatives of each of these genes. The presence of the parental allele provided in trans, in the insertion mutant background, could only restore motility in the lpsB mutant. The production of core LPS directly contributes to the motility phenotype, while capsular polysaccharide may have an indirect effect. Further, the data suggest motility is regulated by extracellular conditions, indicating that A. baumannii is actively sensing the environment and responding accordingly.

Multidrug-resistant (MDR) Acinetobacter baumannii infections are of particular concern within medical treatment facilities, yet the gene assemblages that give rise to this phenotype remain poorly characterized. In this study, we tested 97 clinical A. baumannii isolates collected from military treatment facilities (MTFs) from 2003 to 2009 by using a molecular epidemiological approach that enabled for the simultaneous screening of 236 antimicrobial resistance genes. Overall, 80% of the isolates were found to be MDR, each strain harbored between one and 17 resistant determinants, and a total of 52 unique resistance determinants or gene families were detected which are known to confer resistance to β-lactam (e.g., bla _GES-11 , bla _TEM , bla _OXA-58 ), aminoglycoside (e.g., aphA1 , aacC1 , armA ), macrolide ( msrA , msrB ), tetracycline [e.g., tet (A), tet (B), tet (39)], phenicol (e.g., cmlA4 , catA1 , cat4 ), quaternary amine ( qacE , qacE Δ 1 ), streptothricin ( sat2 ), sulfonamide ( sul1 , sul2 ), and diaminopyrimidine ( dfrA1 , dfrA7 , dfrA19 ) antimicrobial compounds. Importantly, 91% of the isolates harbored bla _OXA-51-like carbapenemase genes (including six new variants), 40% harbored the bla _OXA-23 carbapenemase gene, and 89% contained a variety of aminoglycoside resistance determinants with up to six unique determinants identified per strain. Many of the resistance determinants were found in potentially mobile gene cassettes; 45% and 7% of the isolates contained class 1 and class 2 integrons, respectively. Combined, the results demonstrate a facile approach that supports a more complete understanding of the genetic underpinnings of antimicrobial resistance to better assess the load, transmission, and evolution of MDR in MTF-associated A. baumannii .