Identification of New Halomonas Strains from Food-related Environments

Advances and challenges in polyhydroxyalkanoates (PHA) production using Halomonas species: A review

Plastic waste pollution is one of the major threats to sustainable development. Biodegradable polymers and biopolymers such as polyhydroxyalkanoates (PHAs) offer suitable alternatives for replacing synthetic plastics. PHAs are produced by diverse bacteria species and archaea as storage compounds for utilization as carbon and energy sources. Halomonas species have emerged as attractive microbial cell factories for biosynthesis of PHAs due to their metabolic versality, ability to valorize diverse feedstock materials, and tolerance to high salinity and pH that allows fermentation in contamination-resistant conditions. In recent years, there has been great attention to the use of Halomonas species in PHA biosynthesis and genetic engineering efforts for enhanced production. This article provides a discussion of the current state of knowledge on production of polyhydroxyalkanoates by Halomonas species. It includes an overview of PHA biosynthesis mechanisms, fermentation strategies, production with cheap substrates, exploitation of open and unsterile conditions, co-production of PHAs and other products, and advances genetic engineering efforts.

A multi-omics investigation of the lung injury induced by PM2.5 at environmental levels via the lung-gut axis

Long-term exposure to fine particulate matter (PM2.5) posed injury for gastrointestinal and respiratory systems, ascribing with the lung-gut axis. However, the cross-talk mechanisms remain unclear. Here, we attempted to establish the response networks of lung-gut axis in mice exposed to PM2.5 at environmental levels. Male Balb/c mice were exposed to PM2.5 (dose of 0.1, 0.5, and 1.0 mg/kg) collected from Chengdu, China for 10 weeks, through intratracheally instillation, and examined the effect of PM2.5 on lung functions of mice. The changes of lung and gut microbiota and metabolic profiles of mice in different groups were determined. Furthermore, the results of multi-omics were conjointly analyzed to elucidate the primary microbes and the associated metabolites in lung and gut responsible for PM2.5 exposure. Accordingly, the cross-talk network and key pathways between lung-gut axis were established. The results indicated that exposed to PM2.5 0.1 mg/kg induced obvious inflammations in mice lung, while emphysema was observed at 1.0 mg/kg. The levels of metabolites guanosine, hypoxanthine, and hepoxilin B3 increased in the lung might contribute to lung inflammations in exposure groups. For microbiotas in lung, PM2.5 exposure significantly declined the proportions of Halomonas and Lactobacillus. Meanwhile, the metabolites in gut including L-tryptophan, serotonin, and spermidine were up-regulated in exposure groups, which were linked to the decreasing of Oscillospira and Helicobacter in gut. Via lung-gut axis, the activations of pathways including Tryptophan metabolism, ABC transporters, Serotonergic synapse, and Linoleic acid metabolism contributed to the cross-talk between lung and gut tissues of mice mediated by PM2.5. In summary, the microbes including Lactobacillus, Oscillospira, and Parabacteroides, and metabolites including hepoxilin B3, guanosine, hypoxanthine, L-tryptophan, and spermidine were the main drivers. In this lung-gut axis study, we elucidated some pro- and pre-biotics in lung and gut microenvironments contributed to the adverse effects on lung functions induced by PM2.5 exposure.

Taxonomic Diversity and Functional Traits of Soil Bacterial Communities under Radioactive Contamination: A Review

Studies investigating the taxonomic diversity and structure of soil bacteria in areas with enhanced radioactive backgrounds have been ongoing for three decades. An analysis of data published from 1996 to 2024 reveals changes in the taxonomic structure of radioactively contaminated soils compared to the reference, showing that these changes are not exclusively dependent on contamination rates or pollutant compositions. High levels of radioactive exposure from external irradiation and a high radionuclide content lead to a decrease in the alpha diversity of soil bacterial communities, both in laboratory settings and environmental conditions. The effects of low or moderate exposure are not consistently pronounced or unidirectional. Functional differences among taxonomic groups that dominate in contaminated soil indicate a variety of adaptation strategies. Bacteria identified as multiple-stress tolerant; exhibiting tolerance to metals and antibiotics; producing antioxidant enzymes, low-molecular antioxidants, and radioprotectors; participating in redox reactions; and possessing thermophilic characteristics play a significant role. Changes in the taxonomic and functional structure, resulting from increased soil radionuclide content, are influenced by the combined effects of ionizing radiation, the chemical toxicity of radionuclides and co-contaminants, as well as the physical and chemical properties of the soil and the initial bacterial community composition. Currently, the quantification of the differential contributions of these factors based on the existing published studies presents a challenge.

Halophilic Plant-Associated Bacteria with Plant-Growth-Promoting Potential

The salinization of soils is a growing agricultural concern worldwide. Irrigation practices, drought, and climate change are leading to elevated salinity levels in many regions, resulting in reduced crop yields. However, there is potential for a solution in the microbiome of halophytes, which are naturally salt-tolerant plants. These plants harbor a salt-tolerant microbiome in their rhizosphere (around roots) and endosphere (within plant tissue). These bacteria may play a significant role in conferring salt tolerance to the host plants. This leads to the possibility of transferring these beneficial bacteria, known as salt-tolerant plant-growth-promoting bacteria (ST-PGPB), to salt-sensitive plants, enabling them to grow in salt-affected areas to improve crop productivity. In this review, the background of salt-tolerant microbiomes is discussed and their potential use as ST-PGPB inocula is explored. We focus on two Gram-negative bacterial genera, Halomonas and Kushneria, which are commonly found in highly saline environments. These genera have been found to be associated with some halophytes, suggesting their potential for facilitating ST-PGPB activity. The study of salt-tolerant microbiomes and their use as PGPB holds promise for addressing the challenges posed by soil salinity in the context of efforts to improve crop growth in salt-affected areas.

Agarase, Amylase and Xylanase from Halomonas meridiana: A Study on Optimization of Coproduction for Biomass Saccharification

Coproduction of multienzymes from single potential microbe has captivated contemplation in industries. Bacterial strain, Halomonas meridiana VITSVRP14, isolated from seaweed was labored to produce amylase, agarase and xylanase conjointly using submerged fermentation. The optimum production conditions clinched by classical optimization were: pH 8; 1.5% inoculum; 24 h incubation, 40 °C; 8% NaCl (sodium chloride); 1% lactose and NaNO3 (sodium nitrate). The preponderant variables (pH, temperature, lactose) and their interaction effect on enzyme production were studied by Plackett-Burman design and Response Surface Methodology (RSM). There were 3.29, 1.81 and 2.08 fold increase in enzyme activity with respect to agarase, amylase and xylanase after optimization against basal medium. After 24 h of enzymatic treatment, the saccharification rates of the coproduced enzyme mixture were 38.96% on rice bran, 49.85% on wheat bran, 61.2% on cassava bagasse and 57.82% on corn cob. Thus, the coproduced enzyme mixture from a bacterium with halotolerance is plausible in pretreated lignocellulose degradation. The ability of this single microbe Halomonas meridiana VITSVRP14, in coproducing agarase, amylase and xylanase give the nod for its application in biomass saccharification by subsiding cost, energy and time involved in the process.

Establishment of genetic tools for genomic DNA engineering of Halomonas sp. KM-1, a bacterium with potential for biochemical production

Halomonas species are halophilic and alkaliphilic bacteria, which exhibit potential for industrial production of a variety of chemicals, such as polyhydroxyalkanoates and ectoine, by fermentation because of their favorable characteristics, including high-density culturing capacity and low risk of contamination. However, genetic tools to modify the metabolism of Halomonas for suitable fermentation performance are limited. In this study, we developed two independent basic vectors for Halomonas, named pUCpHAw and pHA1AT_32, consisting of ori regions from two plasmids isolated from Halomonas sp. A020, and chloramphenicol- and tetracycline-resistant genes as cloning markers, respectively. These vectors can independently transform and co-transform the Halomonas sp. KM-1 (KM-1). A protein that was highly and constitutively accumulated was identified as a hemolysin coregulated protein (Hcp) based on proteome analysis of KM-1. Using the hcp promoter, various genes, such as phaA and EGFP, were highly expressed. To establish a gene disruption system, the Streptococcus pyogenes cas9 gene and guide RNA for the pyrF gene, a yeast URA3 homologue, were expressed in pUCpHAw and pHA1AT_32, respectively. As a result, gene disruption mutants were isolated based on phenotypes, 5-fluoroorotic acid resistance, and uracil auxotrophy. A combination of KM-1 and these vectors could be a suitable platform for industrial chemical and protein production.