Integrating multi-platform assembly to recover MAGs from hot spring biofilms: insights into microbial diversity, biofilm formation, and carbohydrate degradation.

BACKGROUND: Hot spring biofilms provide a window into the survival strategies of microbial communities in extreme environments and offer potential for biotechnological applications. This study focused on green and brown biofilms thriving on submerged plant litter within the Sungai Klah hot spring in Malaysia, characterised by temperatures of 58-74 °C. Using Illumina shotgun metagenomics and Nanopore ligation sequencing, we investigated the microbial diversity and functional potential of metagenome-assembled genomes (MAGs) with specific focus on biofilm formation, heat stress response, and carbohydrate catabolism. RESULTS: Leveraging the power of both Illumina short-reads and Nanopore long-reads, we employed an Illumina-Nanopore hybrid assembly approach to construct MAGs with enhanced quality. The dereplication process, facilitated by the dRep tool, validated the efficiency of the hybrid assembly, yielding MAGs that reflected the intricate microbial diversity of these extreme ecosystems. The comprehensive analysis of these MAGs uncovered intriguing insights into the survival strategies of thermophilic taxa in the hot spring biofilms. Moreover, we examined the plant litter degradation potential within the biofilms, shedding light on the participation of diverse microbial taxa in the breakdown of starch, cellulose, and hemicellulose. We highlight that Chloroflexota and Armatimonadota MAGs exhibited a wide array of glycosyl hydrolases targeting various carbohydrate substrates, underscoring their metabolic versatility in utilisation of carbohydrates at elevated temperatures. CONCLUSIONS: This study advances understanding of microbial ecology on plant litter under elevated temperature by revealing the functional adaptation of MAGs from hot spring biofilms. In addition, our findings highlight potential for biotechnology application through identification of thermophilic lignocellulose-degrading enzymes. By demonstrating the efficiency of hybrid assembly utilising Illumina-Nanopore reads, we highlight the value of combining multiple sequencing methods for a more thorough exploration of complex microbial communities.

Community structure of thermophilic photosynthetic microbial mats and flocs at Sembawang Hot Spring, Singapore.

The Sembawang Hot Spring in Singapore lies at the foot of a major regional geological feature called the Bentong-Raub Suture Zone. Amid an extensively managed surface geothermal park, an undisturbed hot spring emerges with source water at 61°C, pH 6.8, and 1 mg/L dissolved sulfide. A small main pool at the source supported orange-green benthic flocs, whereas the outflow channel with gradually less extreme environmental stress supported extensive vivid green microbial mats. Microscopy revealed that cyanobacterial morphotypes were distinct in flocs and mats at several intervals along the environmental gradient, and we describe a spiraling pattern in the oscillatorian cyanobacteria that may reflect response to poly-extreme stress. Estimation of diversity using 16S rRNA gene sequencing revealed assemblages that were dominated by phototrophic bacteria. The most abundant taxa in flocs at 61°C/1 mg/L sulfide were Roseiflexus sp. and Thermosynechococcus elongatus, whilst the mats at 45.7-55.3°C/0-0.5 mg/L sulfide were dominated by Oscillatoriales cyanobacterium MTP1 and Chloroflexus sp. Occurrence of diverse chemoautotrophs and heterotrophs reflected known thermal ranges for taxa, and of note was the high abundance of thermophilic cellulolytic bacteria that likely reflected the large allochthonous leaf input. A clear shift in ASV-defined putative ecotypes occurred along the environmental stress gradient of the hot spring and overall diversity was inversely correlated to environmental stress. Significant correlations for abiotic variables with observed biotic diversity were identified for temperature, sulfide, and carbonate. A network analysis revealed three putative modules of biotic interactions that also reflected the taxonomic composition at intervals along the environmental gradient. Overall, the data indicated that three distinct microbial communities were supported within a small spatial scale along the poly-extreme environmental gradient. The findings add to the growing inventory of hot spring microbiomes and address an important biogeographic knowledge gap for the region.

Influence of native and exotic plant diet on the gut microbiome of the Gray's Malayan stick insect, Lonchodes brevipes.

Herbivorous insects require an active lignocellulolytic microbiome to process their diet. Stick insects (phasmids) are common in the tropics and display a cosmopolitan host plant feeding preference. The microbiomes of social insects are vertically transmitted to offspring, while for solitary species, such as phasmids, it has been assumed that microbiomes are acquired from their diet. This study reports the characterization of the gut microbiome for the Gray's Malayan stick insect, Lonchodes brevipes, reared on native and introduced species of host plants and compared to the microbiome of the host plant and surrounding soil to gain insight into possible sources of recruitment. Clear differences in the gut microbiome occurred between insects fed on native and exotic plant diets, and the native diet displayed a more species-rich fungal microbiome. While the findings suggest that phasmids may be capable of adapting their gut microbiome to changing diets, it is uncertain whether this may lead to any change in dietary efficiency or organismal fitness. Further insight in this regard may assist conservation and management decision-making.