Characterization of arsenite tolerant Halomonas sp. Alang-4, originated from heavy metal polluted shore of Gulf of Cambay

Arsenic Pollution and Anaerobic Arsenic Metabolizing Bacteria in Lake Van, the World's Largest Soda Lake

Arsenic is responsible for water pollution in many places around the world and presents a serious health risk for people. Lake Van is the world's largest soda lake, and there are no studies on seasonal arsenic pollution and arsenic-resistant bacteria. We aimed to determine the amount of arsenic in the lake water and sediment, to isolate arsenic-metabolizing anaerobic bacteria and their identification, and determination of arsenic metabolism. Sampling was done from 7.5 m to represent the four seasons. Metal contents were determined by using ICP-MS. Pure cultures were obtained using the Hungate technique. Growth characteristics of the strains were determined at different conditions as well as at arsenate and arsenite concentrations. Molecular studies were also carried out for various resistance genes. Our results showed that Lake Van's total arsenic amount changes seasonally. As a result of 16S rRNA sequencing, it was determined that the isolates were members of 8 genera with arsC resistance genes. In conclusion, to sustain water resources, it is necessary to prevent chemical and microorganism-based pollution. It is thought that the arsenic-resistant bacteria obtained as a result of this study will contribute to the solution of environmental arsenic pollution problems, as they are the first data and provide the necessary basic data for the bioremediation studies of arsenic from contaminated environmental habitats. At the same time, the first data that will contribute to the creation of the seasonal arsenic map of Lake Van are obtained.

Biotechnological impacts of Halomonas: a promising cell factory for industrially relevant biomolecules

Extremophiles are the most fascinating life forms for their special adaptations and ability to offer unique extremozymes or bioactive molecules. Halophiles, the natural inhabitants of hypersaline environments, are one among them. Halomonas are the common genus of halophilic bacteria. To support growth in unusual environments, Halomonas produces various hydrolytic enzymes, compatible solutes, biopolymers like extracellular polysaccharides (EPS) and polyhydroxy alkaloates (PHA), antibiotics, biosurfactants, pigments, etc. Many of such molecules are being produced in large-scale bioreactors for commercial use. However, the prospect of the remaining bioactive molecules with industrial relevance is far from their application. Furthermore, the genetic engineering of the respective gene clusters could open up a new path to bio-prospect these molecules by overproducing their products through heterologous expression. The present survey on Halomonas highlights their ecological diversity, application potential of the their various industrially relevant biomolecules and impact of these biomolecules on respective fields.

Complete genome sequence of a multiple-stress-tolerant bacterium Halomonas piezotolerans NBT06E8T isolated from a deep-sea sediment sample of the New Britain Trench

Halomonas piezotolerans NBT06E8T is a Gram-stain-negative, moderately halophilic, piezotolerant, H2O2 and heavy metal-resistant bacterium, isolated from a deep-sea sediment sample collected from the New Britain Trench at depth of 8900 m. Growth of the strain was observed at 4-45 °C (optimum 30 °C), at pH 5-11 (optimum 8-9) and in 0.5-21% (w/v) NaCl (optimum 3-7%). The optimum pressure for growth was 0.1-30 MPa (megapascal) with tolerance up to 60 MPa. Under optimum growth conditions, the strain could tolerant 15 mM H2O2. Here, we report the complete genome of H. piezotolerans NBT06E8T, which consists of 3,945,801 bp (G + C content of 57.93%) with a single chromosome, 3509 protein-coding genes, 60 tRNAs and 6 rRNA operons. Genomic analysis revealed the capability of utilizing various carbon and nitrogen sources, the presence of multiple toxin-antitoxin systems and strain-specific type VI secretion system benefitting its adaptation to the oligotrophic hadal environments. Multiple respiratory chain components, especially the strain-specific anaerobic enzymes, could allow its survival in both surficial and buried sediments with variable oxygen concentrations. Gene function and metabolic pathway analysis showed that strain NBT06E8T encodes a series of genes related to high hydrostatic pressure tolerance, antioxidative stress and heavy metal resistance, which could also contribute to its deep-sea adaptation strategies. The complete genome sequence of H. piezotolerans NBT06E8T provides further insights into the stress adaptation strategies of deep-sea bacteria and potential biotechnological application of Halomonas species.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03283-3.

Concentration and Community of Airborne Bacteria in Response to Cyclical Haze Events During the Fall and Midwinter in Beijing, China

Since 2013, severe haze events frequently have occurred in Beijing between October and March, which have created a significant public health threat. Although variations in the chemical composition of these haze events have been studied widely, information pertaining to airborne bacteria in such haze events remains limited. In this study, we characterized the concentration, community structure, and composition of the airborne bacteria in response to nine haze events that occurred between October 1, 2015, and January 5, 2016. We also analyzed the correlations of airborne bacteria (concentration, community structure, and composition) with pollution levels and meteorological factors. The results indicated that airborne bacterial concentration showed a positive cyclical correlation with the haze events, but the bacterial concentration plateaued at the yellow pollution level. In addition, we found particulate matter (PM₁₀) and relative humidity to be key factors that significantly affected the airborne bacterial concentration and community structure. Moreover, Halomonas and Shewanella were enriched on haze days for all nine of the haze events. Finally, the correlations between haze pollution and airborne bacteria in midwinter were weaker than those in fall and early winter, indicating an obvious staged distinction among the effects of haze on airborne bacteria. Our study illuminated the dynamic variation of bioaerosols corresponding to the cyclical haze events and revealed the interactions among air pollution, climate factors (mainly relative humidity), and airborne bacteria. These results imply that different strategies should be applied to deal with the potential threat of airborne bacteria during haze events in different seasons.

A rapid and efficient electroporation method for transformation of Halomonas sp. O-1

Halomonas sp. O-1 is a halophilic bacterium with a high potential for industrial application due to its natural ability to produce polyhydroxyalkanoates (PHAs) using seawater-based media. However, a major barrier preventing industrial scale implementation of this organism is a lack of molecular methodologies capable of readily transforming members of the Halomonas genus. Currently, the only reliable method used for introducing DNA into Halomonas spp. is bacterial conjugation, a somewhat tedious and time-consuming technique compared to electroporation-based methodologies. Here we describe a rapid and reproducible method for the electroporation of Halomonas sp. O-1 with plasmid DNA. Electrocompetent cells were generated by growing Halomonas sp. O-1 in a yeast extract-tryptone medium with a final salinity of 3.5%, pH of 7.5, followed by several washes using 300mM sucrose. Results show that plasmids containing chloramphenicol (Cm(R)) and gentamicin (Gm(R)) resistance cassettes are suitable antibiotic selection markers for transformation and yields of 10(4) transformants per μg of DNA were obtained. This method is simple to perform and the materials used are readily available in most research labs. Additionally, this plasmid-based transformation procedure has the potential to be adapted for a number of applications including the creation of recombinant stains and the generation of deletion mutants of Halomonas spp.