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Moringa oleifera is hailed as the "miracle tree" for its impressive catalog of nutritional, medicinal, and water purification benefits. A (sub)tropical plant with a rapid growth rate (3-5 m in a single season), Moringa has proven beneficial in multiple ways in developing regions around the world. In addition to its high nutrient content and water clarifying properties, Moringa seed and leaf extracts have shown potential as natural antibacterial agents. Based on this, we anticipated that extracts from multiple species of Moringa would exhibit potentially useful antibacterial properties against a range of bacterial species. To explore this, both disk diffusion and minimum inhibitory concentration (MIC) culture techniques were employed to assess the inhibitory effects of seed and leaf extracts from M. oleifera and M. stenopetala against species of bacteria commonly used in research and teaching laboratories. Aqueous seed extracts from both Moringa species showed broad-spectrum activity but were especially effective at inhibiting the growth of Gram-positive bacteria, including species of Staphylococcus, Streptococcus, and Bacillus. Moringa leaf extracts also exhibited antibacterial activity, with ethanolic leaf extracts showing greater efficacy than aqueous leaf extracts in disk-diffusion assays. Temporary acidification (1 h at pH 2) of Moringa seed and leaf extracts had a detrimental effect on their antibacterial activity. MIC assays using Moringa leaf extracts also showed more pronounced inhibition of Gram-positive bacteria (MIC = 12.5% v/v) versus Gram-negative species (MIC = 25% v/v). These results are of particular relevance in tropical areas where pharmaceutical drugs are scarce but Moringa is widely available and often used as a nutritional supplement. Moreover, the rising threat of multi-drug resistant pathogens lends greater importance to the study of antibacterial plant products that ultimately may find application in the clinical setting. [ABSTRACT FROM AUTHOR]

Despite the fact that heliobacteria are the only phototrophic representatives of the bacterial phylum Firmicutes, genomic analyses of these organisms have yet to be reported. Here we describe the complete sequence and analysis of the genome of Heliobacterium modesticaldum, a thermophilic species belonging to this unique group of phototrophs. The genome is a single 3.1-Mb circular chromosome containing 3,138 open reading frames. As suspected from physiological studies of heliobacteria that have failed to show photoautotrophic growth, genes encoding enzymes for known autotrophic pathways in other phototrophic organisms, including ribulose bisphosphate carboxylase (Calvin cycle), citrate lyase (reverse citric acid cycle), and malyl coenzyme A lyase (3-hydroxypropionate pathway), are not present in the H. modesticaldum genome. Thus, heliobacteria appear to be the only known anaerobic anoxygenic phototrophs that are not capable of autotrophy. Although for some cellular activities, such as nitrogen fixation, there is a full complement of genes in H. modesticaldum, other processes, including carbon metabolism and endosporulation, are more genetically streamlined than they are in most other low-G+C gram-positive bacteria. Moreover, several genes encoding photosynthetic functions in phototrophic purple bacteria are not present in the heliobacteria. In contrast to the nutritional flexibility of many anoxygenic phototrophs, the complete genome sequence of H. modesticaldum reveals an organism with a notable degree of metabolic specialization and genomic reduction.

A report on the vertical distribution of cultivable strains of planktonic sulfur-oxidizing bacteria from the water column of the permanently ice-covered Lake Fryxell, Antarctica is described. The results support the hypothesis that biological sulfur cycling is occurring in this polar lake.

The populations of sulfate-reducing bacteria in Lake Fryxell, both 16 rRNA gene and metabolic primer sets targeting the dsrA gene for the dissimilatory sulfite reductase alpha subunit were employed to analyze environmental DNA obtained from the water column and sediments of Lake Fryxell were investigated. Several clone groups were highly localized with respect to lake depth and therefore experienced specific physiochemical conditions.

Research has been conducted on phototrophic purple bacteria from the permanently frozen Antarctic Lake Fryxell. The authors have investigated the biodiversity, ecology and metabolic activity of these phototrophs, and report that this lake is inhibited by a broad diversity of purple nonsulfur bacteria.

The cost of high-resolution water sampling devices for ecological studies and water quality analyses can be prohibitive. Moreover, the potential for operator error in the use of complicated sampling equipment can lead to inaccuracies. Here we describe the construction and operation of an inexpensive and easy-to-use water sampler that achieves a water column sampling resolution of approximately 1 cm. The device is driven by a peristaltic pump and is constructed entirely of non-corrosive and non-reactive materials. The sampler has no moving parts and was completely reliable in fieldwork on temperate and Antarctic lakes. The device is especially suited for the collection of water samples from calm or stagnant surface waters, such as lakes, ponds, reservoirs, and deep swamps or other wetlands. In addition, because its components are unaffected by corrosive salts and sulfides, the device is suitable for sampling calm inlet waters, including shallow bays and estuaries. Because of its low cost, simple construction, compact design, and precision performance, this water sampler is an excellent option for studying and monitoring shallow to moderately deep (<50 m) natural waters. [ABSTRACT FROM AUTHOR]

A novel, obligately anaerobic, fermentative bacterium, strain FCF9, was isolated from a 9-m water sample from permanently ice-covered, meromictic Lake Fryxell, Antarctica. A phylogenetic analysis based on 16S rRNA gene sequence identity clustered the Antarctic isolate within the Sporomusa−Pectinatus−Selenomonas phyletic group, where it was most closely related to Pelosinus fermentans (95.5% sequence identity). However, unlike species of Pelosinus, strain FCF9 was psychrophilic, with growth occurring optimally near 15 °C, and endospores were not produced. The metabolism of the new organism was strictly fermentative. The substrates fermented by strain FCF9 included only lactate and a few related organic acids. The major products from lactate fermentation were acetate and propionate. On the basis of phylogenetic, morphological, and physiological criteria, strain FCF9T is proposed as the type strain of a novel genus and species of psychrophilic-fermenting bacteria, Psychrosinus fermentans gen. nov., sp. nov. [ABSTRACT FROM AUTHOR]

Bacterial persistence is a state of metabolic dormancy among a small fraction (<1%) of a genetically identical population of cells that, as a result, becomes transiently resistant to environmental stressors. Such cells, called persisters, are able to survive indeterminate periods of exposure to challenging and even hostile environmental conditions, including nutrient deprivation, oxidative stress, or the presence of an antibiotic to which the bacterium would normally be susceptible. Subpopulations of cells having the persister phenotype is also a common feature of biofilms, in which limited space, hypoxia, and nutrient deficiencies all contribute to the onset of persistence. Microbiologists have been aware of bacterial persistence since the early days of antibiotic development. However, in recent years the significance of this phenomenon has been brought into new focus, as persistent bacterial infections that require multiple rounds of antibiotic treatment are becoming a more widespread clinical challenge. Here, we provide an overview of the major features of bacterial persistence, including the various conditions that precipitate persister formation and a discussion of several of the better-characterized molecular mechanisms that trigger this distinctive mode of bacterial dormancy., Competing Interests: Conflict of Interest: All authors declare no conflicts of interest in this paper.

Rhodoferax antarcticus is an Antarctic purple nonsulfur bacterium and the only characterized anoxygenic phototroph that grows best below 20 °C. We present here a high-quality draft genome of Rfx. antarcticus strain ANT.BR T , isolated from an Antarctic microbial mat. The circular chromosome (3.8 Mbp) of Rfx. antarcticus has a 59.1% guanine + cytosine (GC) content and contains 4036 open reading frames. In addition, the bacterium contains a sizable plasmid (198.6 kbp, 48.4% GC with 226 open reading frames) that comprises about 5% of the total genetic content. Surprisingly, genes encoding light-harvesting complexes 1 and 3 (LH1 and LH3), but not light-harvesting complex 2 (LH2), were identified in the photosynthesis gene cluster of the Rfx. antarcticus genome, a feature that is unique among purple phototrophs. Consistent with physiological studies that showed a strong capacity for nitrogen fixation in Rfx. antarcticus , a nitrogen fixation gene cluster encoding a molybdenum-type nitrogenase was present, but no alternative nitrogenases were identified despite the cold-active phenotype of this phototroph. Genes encoding two forms of ribulose 1,5-bisphosphate carboxylase/oxygenase were present in the Rfx. antarcticus genome, a feature that likely provides autotrophic flexibility under varying environmental conditions. Lastly, genes for assembly of both type IV pili and flagella are present, with the latter showing an unusual degree of clustering. This report represents the first genomic analysis of a psychrophilic anoxygenic phototroph and provides a glimpse of the genetic basis for maintaining a phototrophic lifestyle in a permanently cold, yet highly variable, environment.

The permanently ice-covered lakes of the McMurdo Dry Valleys, Antarctica are distinctive ecosystems that consist strictly of microbial communities. In this study, water samples were collected from Lake Vanda, a stratified Dry Valley lake whose upper waters (from just below the ice cover to nearly 60 m) are highly oligotrophic, and used to establish enrichment cultures. Six strains of psychrotolerant, heterotrophic bacteria were isolated from lake water samples from a depth of 50 or 55 m. Phylogenetic analyses showed the Lake Vanda strains to be species of Nocardiaceae, Caulobacteraceae, Sphingomonadaceae, and Bradyrhizobiaceae. All Lake Vanda strains grew at temperatures near or below 0 °C, but optimal growth occurred from 18 to 24 °C. Some strains showed significant halotolerance, but no strains required NaCl for growth. The isolates described herein include cold-active species not previously reported from Dry Valley lakes, and their physiological and phylogenetic characterization broadens our understanding of these limnologically unique lakes.