Bacillus strains isolated from the rhizosphere soil of potato roots were evaluated for the potential antagonistic activity against fungal pathogens in vitro and in vivo. Two bacterial isolates were identified as new Bacillus subtilis strains by 16S rRNA and GyrB gene sequencing and were designated GM2 and GM5, respectively. Strains were characterized by their ability to inhibit growth of a number of phytopathogenic fungi. It was shown that GM5 strain inhibited growth of phytopathogenic fungi more effectively than GM2 strain. Both strains were capable of producing a number of hydrolytic enzymes as well as antimicrobial metabolites (ammonia and HCN). In addition, GM2 strain also produced siderophores. Four genes encoding antimicrobial peptides were identified in the genome of GM2 strain: ituC, bmyB, bacA and srfA. Genome of GM5 contained two genes encoding for antimicrobial peptides, srfA and fenD. Purified lipopeptide fraction from GM5 but not from GM2 strain was able to control Fusarium solani spread in the plate assay. Furthermore, Bacillus subtilis strain GM2 promoted growth of wheat but only GM5 strain was able to protect wheat seedlings from Fusarium oxysporum infection.

Serratia marcescens is an emerging pathogen with increasing clinical importance due to its intrinsic resistance to several classes of antibiotics. The chromosomally encoded drug efflux pumps contribute to antibiotic resistance and represent a major challenge for the treatment of bacterial infections. The ABC-type efflux pump MacAB was previously linked to macrolide resistance in Escherichia coli and Salmonella enterica serovar Typhimurium. The role of the MacAB homolog in antibiotic resistance of S. marcescens is currently unknown. We found that an S. marcescens mutant lacking the MacAB pump did not show increased sensitivity to the macrolide antibiotic erythromycin but was significantly more sensitive to aminoglycoside antibiotics and polymyxins. We also showed that, in addition to its role in drug efflux, the MacAB efflux pump is required for swimming motility and biofilm formation. We propose that the motility defect of the ΔmacAB mutant is due, at least in part, to the loss of functional flagella on the bacterial surface. Furthermore, we found that the promoter of the MacAB efflux pump was active during the initial hours of growth in laboratory medium and that its activity was further elevated in the presence of hydrogen peroxide. Finally, we demonstrate a complete loss of ΔmacAB mutant viability in the presence of peroxide, which is fully restored by complementation. Thus, the S. marcescens MacAB efflux pump is essential for survival during oxidative stress and is involved in protection from polymyxins and aminoglycoside antibiotics. IMPORTANCE The opportunistic pathogen Serratia marcescens can cause urinary tract infections, respiratory infections, meningitis, and sepsis in immunocompromised individuals. These infections are challenging to treat due to the intrinsic resistance of S. marcescens to an extensive array of antibiotics. Efflux pumps play a crucial role in protection of bacteria from antimicrobials. The MacAB efflux pump, previously linked to efflux of macrolides in Escherichia coli and protection from oxidative stress in Salmonella enterica serovar Typhimurium, is not characterized in S. marcescens. We show the role of the MacAB efflux pump in S. marcescens protection from aminoglycoside antibiotics and polymyxins, modulation of bacterial motility, and biofilm formation, and we illustrate the essential role for this pump in bacterial survival during oxidative stress. Our findings make the MacAB efflux pump an attractive target for inhibition to gain control over S. marcescens infections.

This study investigated the impact of ferrihydrite on the pathway and rate of 2,4,6-trinitrotoluene (TNT) transformation by Yarrowia lipolytica AN-L15. The presence of ferrihydrite in the culture medium decreased the rate of TNT biotransformation but resulted in the accumulation of the same TNT metabolites as in the absence of ferrihydrite, albeit at slightly different concentrations. Transformation products observed included aromatic ring reduction products, such as hydride-Meisenheimer complexes, and nitro group reduction products, such as hydroxylamino- and amino-dinitrotoluenes. Independently of the presence of ferrihydrite the subsequent degradation of the hydride complex(es) resulted in the release of nitrite followed by its conversion to nitrate and nitric oxide at the low pH values observed during yeast cultivation. Nitric oxide generation was ascertained by electron spin resonance spectroscopy. In addition, increased Fe(3+)-reduction was observed in the presence of TNT and Y. lipolytica. This study demonstrates that in the presence of yeast cells, TNT-hydride complexes were formed at approximately the same level as in the presence of ferrihydrite, opening up the possibility of aromatic ring cleavage, instead of promoting the production of potentially toxic nitro group reduction products in the presence of iron minerals.

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Here we present a draft genome sequence of laboratory strain Serratia marcescens SM6. Using the antiSMASH 5.0 prediction tool, we identified five biosynthetic gene clusters involved in secondary metabolite production (two siderophores and a biosurfactant serratamolide, a glucosamine derivative, and a thiopeptide).

Endolithic microbial communities survive nutrient and energy deficient conditions while contributing to the weathering of their mineral substrate. This study examined the mineral composition and microbial communities of fully serpentinized weathered rock from 0.1 to 6.5 m depth at a site within the Khalilovsky massif, Orenburg Region, Southern Ural Mountains, Russia. The mineral composition includes a major content of serpentinite family (mostly consisting of lizardite and chrysotile), magnesium hydrocarbonates (hydromagnesite with lesser amounts of hydrotalcite and pyroaurite) concentrated in the upper layers, and clay minerals. We found that the deep-seated weathered serpentinites are chrysotile-type minerals, while the middle and surface serpentinites mostly consist of lizardite and chrysotile types. Microbial community analysis, based on 16S rRNA gene sequencing, showed a similar diversity of phyla throughout the depth profile. The dominant bacterial phyla were the Actinobacteria (of which unclassified genera in the orders Acidimicrobiales and Actinomycetales were most numerous), Chloroflexi (dominated by an uncultured P2-11E order) and the Proteobacteria (predominantly class Betaproteobacteria). Densities of several groups of bacteria were negatively correlated with depth. Occurrence of the orders Actinomycetales, Gaiellales, Solirubrobacterales, Rhizobiales and Burkholderiales were positively correlated with depth. Our findings show that endolithic microbial communities of the Khalilovsky massif have similar diversity to those of serpentine soils and rocks, but are substantially different from those of the aqueous environments of actively serpentinizing systems.

Serratia marcescens is ubiquitous in the environment and can survive in water, soil, plants, insects, and animals, and it can also cause infections in humans. In the face of disturbances such as oxidative or low-pH stress, bacteria adapt, survive, and recover through several mechanisms, including changes in their secretome.

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