Isolation of cellulase-producing Microbulbifer sp. from marine teleost blackfish (Girella melanichthys) intestine and the enzyme characterization

Construction and Effect Analysis of a Mixed Actinomycete Flora for Straw Returning to Albic Soil in Northeast China

This research targets straw return in Farm 852's albic soil, China. The soil is nutrient-poor with few microbes and slow straw decomposition. Through fixed-point sampling and bacterial screening, an actinomycete consortium consisting of four strains was assembled, and two of them were identified as new actinomycetes. After 7 days of fermentation, the lignocellulose degradation rates of this consortium outstripped those of single strains, with cellulose degraded at 69.07%, hemicellulose at 64.98%, and lignin at 68.95%. FTIR, XRD, and SEM verified the damage inflicted on the straw structure. Lab simulations found group D (with the consortium) had a higher straw weight loss rate than group C (with commercialized microbial agents) and controls. The compound actinomycetes stepped up the bacterial abundance with the passage of time. In contrast, their effect on fungal abundance was hardly noticeable, but they had markedly ameliorated the soil fertility. These findings prove that the microbial consortium effectively accelerates straw decomposition and boosts soil microbe abundance and fertility in albic soil. It shows great potential for straw return and provides a microbial solution for this field.

Cellulolytic enzymes in Microbulbifer sp. Strain GL-2, a marine fish intestinal bacterium, with emphasis on endo-1,4-β-glucanases Cel5A and Cel8

Cellulose is an abundant biomass on the planet. Various cellulases from environmental microbes have been explored for industrial use of cellulose. Marine fish intestine is of interest as one source of new enzymes. Here, we report the discovery of genes encoding two β-glucosidases (Bgl3A and Bgl3B) and four endo-1,4-β-glucanases (Cel5A, Cel8, Cel5B, and Cel9) as part of the genome sequence of a cellulolytic marine bacterium, Microbulbifer sp. Strain GL-2. Five of these six enzymes (excepting Cel5B) are presumed to localize to the periplasm or outer membrane. Transcriptional analysis demonstrated that all six genes were highly expressed in stationary phase. The transcription was induced by cello-oligosaccharides rather than by glucose, suggesting that the cellulases are produced primarily for nutrient acquisition following initial growth, facilitating the secondary growth phase. We cloned the genes encoding two of the endo-1,4-β-glucanases, Cel5A and Cel8, and purified the corresponding recombinant enzymes following expression in Escherichia coli. The activity of Cel5A was observed across a wide range of temperatures (10-40 ˚C) and pHs (6-8). This pattern differed from those of Cel8 and the commercial cellulase Enthiron, both of which exhibit decreased activities below 30 ˚C and at alkaline pHs. These characteristics suggest that Cel5A might find use in industrial applications. Overall, our results reinforce the hypothesis that marine bacteria remain a possible source of novel cellulolytic activities.

Polymer degrading marine Microbulbifer bacteria: an un(der)utilized source of chemical and biocatalytic novelty

Microbulbifer is a genus of halophilic bacteria that are commonly detected in the commensal marine microbiomes. These bacteria have been recognized for their ability to degrade polysaccharides and other polymeric materials. Increasingly, Microbulbifer genomes indicate these bacteria to be an untapped reservoir for novel natural product discovery and biosynthetic novelty. In this review, we summarize the distribution of Microbulbifer bacteria, activities of the various polymer degrading enzymes that these bacteria produce, and an up-to-date summary of the natural products that have been isolated from Microbulbifer strains. We argue that these bacteria have been hiding in plain sight, and contemporary efforts into their genome and metabolome mining are going to lead to a proliferation of Microbulbifer-derived natural products in the future. We also describe, where possible, the ecological interactions of these bacteria in marine microbiomes.

Draft genome sequence of Hahella sp. CR1 and its ability in producing cellulases for saccharifying agricultural biomass

Hahella is a genus that has not been well-studied, with only two identified species. The potential of this genus to produce cellulases is yet to be fully explored. The present study isolated Hahella sp. CR1 from mangrove soil in Tanjung Piai National Park, Malaysia, and performed whole genome sequencing (WGS) using NovaSeq 6000. The final assembled genome consists of 62 contigs, 7,106,771 bp, a GC ratio of 53.5%, and encoded for 6,397 genes. The CR1 strain exhibited the highest similarity with Hahella sp. HN01 compared to other available genomes, where the ANI, dDDH, AAI, and POCP were 97.04%, 75.2%, 97.95%, and 91.0%, respectively. In addition, the CAZymes analysis identified 88 GTs, 54 GHs, 11 CEs, 7 AAs, 2 PLs, and 48 CBMs in the genome of strain CR1. Among these proteins, 11 are related to cellulose degradation. The cellulases produced from strain CR1 were characterized and demonstrated optimal activity at 60 ℃, pH 7.0, and 15% (w/v) sodium chloride. The enzyme was activated by K+, Fe2+, Mg2+, Co2+, and Tween 40. Furthermore, cellulases from strain CR1 improved the saccharification efficiency of a commercial cellulase blend on the tested agricultural wastes, including empty fruit bunch, coconut husk, and sugarcane bagasse. This study provides new insights into the cellulases produced by strain CR1 and their potential to be used in lignocellulosic biomass pre-treatment.

Midgut Bacterial Microbiota of 12 Fish Species from a Marine Protected Area in the Aegean Sea (Greece)

Fish microbiome science is progressing fast, but it is biased toward farmed or laboratory fish species against natural fish populations, which remain considerably underinvestigated. We analyzed the midgut bacterial microbiota of 45 specimens of 12 fish species collected from the Gyaros Island marine protected area (Aegean Sea, Greece). The species belong to seven taxonomic families and are either herbivores or omnivores. Mucosa midgut bacterial diversity was assessed by amplicon metabarcoding of the 16S rRNA V3-V4 gene region. A total of 854 operational taxonomic units (OTUs) were identified. In each fish species, between 2 and 18 OTUs dominated with cumulative relative abundance ≥ 70%. Most of the dominating bacterial taxa have been reported to occur both in wild and farmed fish populations. The midgut bacterial communities were different among the 12 fish species, except for Pagrus pagrus and Pagellus erythrinus, which belong to the Sparidae family. No differentiation of the midgut bacterial microbiota was found based on feeding habits, i.e., omnivorous vs. carnivorous. Comparing wild and farmed P. pagrus midgut bacterial microbiota revealed considerable variation between them. Our results expand the gut microbiota of wild fish and support the host species effect as the more likely factor shaping intestinal bacterial microbiota.

Novel Polyhydroxybutyrate-Degrading Activity of the Microbulbifer Genus as Confirmed by Microbulbifer sp. SOL03 from the Marine Environment

Ever since bioplastics were globally introduced to a wide range of industries, the disposal of used products made with bioplastics has become an issue inseparable from their application. Unlike petroleum-based plastics, bioplastics can be completely decomposed into water and carbon dioxide by microorganisms in a relatively short time, which is an advantage. However, there is little information on the specific degraders and accelerating factors for biodegradation. To elucidate a new strain for biodegrading poly-3-hydroxybutyrate (PHB), we screened out one PHB-degrading bacterium, Microbulbifer sp. SOL03, which is the first reported strain from the Microbulbifer genus to show PHB degradation activity, although Microbulbifer species are known to be complex carbohydrate degraders found in high-salt environments. In this study, we evaluated its biodegradability using solid- and liquid-based methods in addition to examining the changes in physical properties throughout the biodegradation process. Furthermore, we established the optimal conditions for biodegradation with respect to temperature, salt concentration, and additional carbon and nitrogen sources; accordingly, a temperature of 37°C with the addition of 3% NaCl without additional carbon sources, was determined to be optimal. In summary, we found that Microbulbifer sp. SOL03 showed a PHB degradation yield of almost 97% after 10 days. To the best of our knowledge, this is the first study to investigate the potent bioplastic degradation activity of Microbulbifer sp., and we believe that it can contribute to the development of bioplastics from application to disposal.