Macroalgae and macroalgae-associated bacteria together constitute the most efficient metabolic cycling system in the ocean. Their interactions, especially the responses of macroalgae-associated bacteria communities to algae in different geographical locations, are mostly unknown. In this study, metagenomics was used to analyze the microbial diversity and associated algal-polysaccharide-degrading enzymes on the surface of red algae among three remote regions. There were significant differences in the macroalgae-associated bacteria community composition and diversity among the different regions. At the phylum level, Proteobacteria, Bacteroidetes, and Actinobacteria had a significantly high relative abundance among the regions. From the perspective of species diversity, samples from China had the highest macroalgae-associated bacteria diversity, followed by those from Antarctica and Indonesia. In addition, in the functional prediction of the bacterial community, genes associated with amino acid metabolism, carbohydrate metabolism, energy metabolism, metabolism of cofactors and vitamins, and membrane transport had a high relative abundance. Canonical correspondence analysis and redundancy analysis of environmental factors showed that, without considering algae species and composition, pH and temperature were the main environmental factors affecting bacterial community structure. Furthermore, there were significant differences in algal-polysaccharide-degrading enzymes among the regions. Samples from China and Antarctica had high abundances of algal-polysaccharide-degrading enzymes, while those from Indonesia had extremely low abundances. The environmental differences between these three regions may impose a strong geographic differentiation regarding the biodiversity of algal microbiomes and their expressed enzyme genes. This work expands our knowledge of algal microbial ecology, and contributes to an in-depth study of their metabolic characteristics, ecological functions, and applications.

Sibero MT, Frederick EH, Sabdono A, Wijayanti DP, Pringgenies D, Radjasa OK, Zilda DS, Murwani R. 2022. First report of seaweed-associated yeast from Indonesia: Species composition and screening of their polysaccharides-degrading enzymes. Biodiversitas 23: 1408-1419. Yeast has been widely utilized in various industries due to its enzyme properties. Therefore, plenty of studies focus on exploring yeast biodiversity from diverse sources. However, there are limited reports regarding marine yeast biodiversity and its potential from Indonesia. This study aimed to isolate and identify the seaweed-associated yeast from Jepara in Central Java and Sepanjang Beach in Gunung Kidul, Yogyakarta, then examined their potential to produce extracellular polysaccharides-degrading enzymes (EPEs). Marine yeasts were isolated using standard marine agar (STD) and potato dextrose agar (PDA). All isolates were characterized by their salinity tolerance, morphology, and species confirmation using DNA barcoding. Three EPEs consisting of agarase, alginate-lyase, and carrageenase were screened using polysaccharides-enriched agar media. A specific agarase encoding gene was detected with specific primers. In total, 21 seaweed-associated yeast were successfully isolated from 6 seaweeds and noted as facultative marine yeast. The DNA barcoding study discovered that these yeasts belonged to 5 genera, consisted of Aureobasidium, Candida, Debaryomyces, Hortaea, and Rhodotorula. Moreover, Candida was noted as the most abundant genus (71.42%). It was noted that Hortaea werneckii MTJ.11 and MTJ.13 were positive for all enzymes; Aureobasidium melanogenum MTGK.31 gave a positive result for agarase and carrageenase; while [Candida] zeylanoides MTGK.23 only exhibited alginate-lyase activity. Unfortunately, none of the primers used to detect the presence of genes encoding polysaccharide-degrading enzymes were successfully amplified.

Brown algae (Phaeophyceae) and red algae (Rhodophyta) are a group of seaweed that scattered all over the ocean. In addition, previous studies have reported the biotechnological potential of its associated fungi. However, there are only a few studies related to the extracellular enzyme of seaweed-associated fungi. The purposes of this research were to isolated brown algae and red algae associated fungi from Sepanjang Beach, GunungKidul, Yogyakarta, Indonesia, and screen its enzyme production. Padina sp., Asparagopsis sp., and Chondrophycussp. were collected from Sepanjang Beach, GunungKidul, Yogyakarta. Swab tap method on PDA medium and STD medium was conducted to isolate seaweed-associated fungi, while starch agar medium, agar medium, alginate agar medium, and carrageenan agar medium, was utilized to screen the enzyme activity with addition of povidone-iodine 10% reagent. The presence of clear zone around the colony indicated enzyme.

Bakteri kitinolitik yang mendegradasi kitin dan turunannya telah banyak diisolasi dari berbagai sumber seperti tanah, spons dan limbah udang dan rajungan. Sumber lain yang diduga potensial untuk isolasi bakteri kitinolitik adalah terasi yang merupakan produk fermentasi berbahan baku rebon. Kitosanase adalah enzim kitinolitik yang terlibat dalam produksi kitooligosakarida yang lebih larut air dan berguna dalam berbagai bidang seperti nutrasetikal, medik, dan farmasi. Isolat T5a1, salah satu isolat kitinolitik yang diisolasi dari terasi, ditumbuhkan pada medium minimal sintetik (MSM) dengan penambahan 0,5% koloidal kitin pada 37o C, 100 rpm, di inkubator goyang selama 24 jam untuk produksi kitosanase. Enzim kasar kemudian dipekatkan menggunakan amonium sulfat dan didialisis. Dari hasil karakterisasi, diketahui pH dan suhu optimum aktivitas enzim adalah 7 dan 50o C. Enzim stabil pada suhu 40o C selama lebih dari 200 menit. Penambahan ion Mg2+ dan Zn2+ menurunkan aktivitas enzim sampai 15% sementara penambahan ion Ca2+ meningkatkan aktivitas enzim sampai 37%.

Deep-sea polymetallic nodules, rich in cobalt, nickel and titanium, are valuable for electronics, aerospace and energy industries. However, the vertical distribution and ecological functions of prokaryotic communities in sediments beneath nodules from the Magellan seamounts, a unique microbial habitat characterized by ultra-slow sedimentation rates (0.4–4 mm ky ⁻¹ ) and heterogeneous metal gradients, remain poorly characterized. In our research, 16S rRNA gene amplicon sequencing and metagenomic analyses of sediment cores (0–20 cm) from the western Pacific polymetallic nodule province revealed statistically significant decreases in prokaryotic diversity (Shannon index: 9.446 to 2.288; P <0.001). Proteobacteria , Crenarchaeota , Chloroflexi and Bacteroidota were the dominant taxa. The microbial co-occurrence network in the surface layer had a longer mean path length (2.11 vs 1 in the bottom layer) and a larger network diameter (11 vs 1), indicating a loose community structure and greater resistance to disturbance, while the bottom microbial network had a higher density (0.037 vs 0.01) and clustering coefficient (0.32 vs 1), suggesting tight microbial interactions. The concentrations of MnO (6.96–9.41 µg g ⁻¹ ) and P₂O₅ (2.55–3.89 µg g ⁻¹ ) gradually decreased with increasing depth. The concentrations of Co and Pb were relatively high in the surface sediments (0–8 cm) but decreased significantly below 8 cm. In contrast, the concentrations of Fe₂O₃ and As increased with depth. The environmental factors depth, MnO, Fe₂O₃ and heavy metals (Cr, Zn and Cu) were found to be the main drivers of the microbial community structure. We assembled 122 metagenome-assembled genomes from the metagenomic data. Gene abundance analysis revealed that sox genes ( soxB / C / D / X / Y / Z ) and assimilatory sulphate reduction genes ( cysC and cysH ) were highly abundant in the surface sediment, whereas the abundance of dissimilatory sulphate reduction genes ( dsrA and dsrB ) was enhanced in the bottom layer, reflecting a hierarchical adaptive strategy for sulphur metabolism. Our study expands current knowledge on the vertical variations of microbial diversity and microbially driven biogeochemical cycling in deep-sea settings underneath polymetallic nodules. Characterizing the microbial community underneath those nodules may provide insights into microbial resilience in extreme oligotrophic environments and valuable insights for future deep-sea mining activities.