Marinospirillum perlucidum sp. nov., a novel helical bacterium isolated from a sea cucumber culture pond

Genomic insights into Marinospirillum alkalitolerans sp. nov., a novel PHB producing bacterium from an Indian impact crater, and an emended description of family Oceanospirillaceae

Two Gram-stain-negative bacterial strains (MEB164T and MEB148), were isolated from haloalkaline waters of Lonar, crater lake, India. The strains were helical, non-spore-forming and motile with polar tufts of flagella. Optimal growth occurred at 37 ℃, at pH 10 and with 3% (w/v) NaCl. 16S rRNA gene sequences of strains (MEB164T and MEB148) demonstrated the highest similarity with Marinospirillum alkaliphilum DSM 21637T (97.8%) followed by Marinospirillum celere DSM 18438T (96%). The genome size of strain MEB164T was determined to be 2.8 Mb with genomic DNA G + C contents of 53.1 mol %. ANI and dDDH values between strain MEB164T and the most closely related type strain M. alkaliphilum DSM 21637T were (72.3% and 21.4 ± 2.3%) while (AAI and POCP) values were (66.8 and 70.8%), respectively. Strain MEB164T exhibited potential for polyhydroxybutyrate (PHB) production, supported by key genes involved in PHB metabolism. Genome analysis further revealed presence of various pH tolerance genes, highlighting its adaptation to Lonar Lake. The predominant cellular fatty acids were summed feature 8 (C18:1 ω7c/C18:1 ω6c), C16:0 and summed feature 3 (C16:1 ω7c/C16:1 ω6c). The major respiratory quinone was ubiquinone-8. The prevalent polar lipids were diaminophosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, two unidentified amino phospholipids, three unidentified phospholipids and one unidentified lipid. Polyphasic analysis suggests that the two strains constitute a novel species within the genus Marinospirillum (family Oceanospirillaceae), proposed as Marinospirillum alkalitolerans sp. nov. The type strain is MEB164T (= JCM 35957T = MCC 5207T = NCIMB 15458T) and MEB148 (= JCM 35956 = MCC 5212 = NCIMB 15459) is an additional strain.

Assessment of Temporal Effects of a Mud Volcanic Eruption on the Bacterial Community and Their Predicted Metabolic Functions in the Mud Volcanic Sites of Niaosong, Southern Taiwan

The microbial communities inhabiting mud volcanoes have received more attention due to their noteworthy impact on the global methane cycle. However, the impact of temporal effects of volcanic eruptions on the microbial community’s diversity and functions remain poorly characterized. This study aimed to underpin the temporal variations in the bacterial community’s diversity and PICRUSt-predicted functional profile changes of mud volcanic sites located in southern Taiwan using 16S rRNA gene sequencing. The physicochemical analysis showed that the samples were slightly alkaline and had elevated levels of Na⁺, Cl⁻, and SO₄²⁻. Comparatively, the major and trace element contents were distinctly higher, and tended to be increased in the long-period samples. Alpha diversity metrics revealed that the bacterial diversity and abundance were lesser in the initial period, but increased over time. Instead, day 96 and 418 samples showed reduced bacterial abundance, which may have been due to the dry spell that occurred before each sampling. The initial-period samples were significantly abundant in haloalkaliphilic marine-inhabiting, hydrocarbon-degrading bacterial genera such as Marinobacter, Halomonas, Marinobacterium, and Oceanimonas. Sulfur-reducing bacteria such as Desulfurispirillum and Desulfofarcimen were found dominant in the mid-period samples, whereas the methanogenic archaeon Methanosarcina was abundant in the long-period samples. Unfortunately, heavy precipitation encountered during the mid and long periods may have polluted the volcanic site with animal pathogens such as Desulfofarcimen and Erysipelothrix. The functional prediction results showed that lipid biosynthesis and ubiquinol pathways were significantly abundant in the initial days, and the super pathway of glucose and xylose degradation was rich in the long-period samples. The findings of this study highlighted that the temporal effects of a mud volcanic eruption highly influenced the bacterial diversity, abundance, and functional profiles in our study site.

Sulfur and Methane-Oxidizing Microbial Community in a Terrestrial Mud Volcano Revealed by Metagenomics

Mud volcanoes are prominent geological structures where fluids and gases from the deep subsurface are discharged along a fracture network in tectonically active regions. Microbial communities responsible for sulfur and methane cycling and organic transformation in terrestrial mud volcanoes remain poorly characterized. Using a metagenomics approach, we analyzed the microbial community of bubbling fluids retrieved from an active mud volcano in eastern Crimea. The microbial community was dominated by chemolithoautotrophic Campylobacterota and Gammaproteobacteria, which are capable of sulfur oxidation coupled to aerobic and anaerobic respiration. Methane oxidation could be enabled by aerobic Methylococcales bacteria and anaerobic methanotrophic archaea (ANME), while methanogens were nearly absent. The ANME community was dominated by a novel species of Ca. Methanoperedenaceae that lacked nitrate reductase and probably couple methane oxidation to the reduction of metal oxides. Analysis of two Ca. Bathyarchaeota genomes revealed the lack of mcr genes and predicted that they could grow on fatty acids, sugars, and proteinaceous substrates performing fermentation. Thermophilic sulfate reducers indigenous to the deep subsurface, Thermodesulfovibrionales (Nitrospirae) and Ca. Desulforudis (Firmicutes), were found in minor amounts. Overall, the results obtained suggest that reduced compounds delivered from the deep subsurface support the development of autotrophic microorganisms using various electron acceptors for respiration.