Uncovering the chitin degradation potential of the microbiomes of marine sponges and octocorals

Rúben João Rodrigues da Silva

Informações chave

Autores:

Rúben João Rodrigues da Silva (Rúben João Rodrigues da Silva)

Orientadores:

Rodrigo da Silva Costa (Rodrigo da Silva Costa), Cymon J. Cox, Tina Keller-Costa (Tina Keller Costa)

Publicado em

06/07/2023

Resumo

A quitina é o polissacárido mais abundante nos oceanos e o segundo mais abundante do planeta, depois da celulose. O conhecimento atual sobre os microrganismos, enzimas catalíticas, proteínas acessórias e vias metabólicas envolvidas na degradação de quitina deriva maioritariamente de estudos dependentes de cultivo e continua a ser limitado no que respeita aos ambientes marinhos. No entanto, recentes estudos ligados à investigação metagenómica sugerem que muitos dos micróbios capazes de degradar quitina são até agora incultiváveis. Desta forma, o entendimento atual da comunidade científica sobre o processamento de quitina na natureza poderá representar apenas a escassa ponta de um imenso icebergue por desvendar, apesar da relevância deste biopolímero para fisiologia dos organismos e funcionamento dos ecossistemas. Neste contexto, surgiu esta tese que junta métodos dependentes e independentes de cultivo, utilizando microrganismos associados a microbiomas marinhos de esponjas, corais, sedimentos e água do mar envolvente, com o intuito de aumentar o conhecimento atual sobre esta temática e investigar o potencial destes ecossistemas na degradação e transformação de quitina em compostos mais simples e de elevado valor biotecnológico, comparativamente com os atuais processos enzimáticos comerciais e industriais e, eventualmente, acrescentando valor ao sector da biotecnologia azul. Marine environments are an untapped source of novel enzymes with biotechnological potential across several fields. A group of enzymes attracting recent research interest are the chitinases, as their substrate, chitin, ranks as the most abundant polysaccharide in the oceans being widespread in nature and among several living organisms. Moreover, the products of chitinolytic activity, chito-oligosaccharides, possess several properties of interest in applied biotechnology. However, knowledge of the structure and diversity of chitin-degrading communities across marine microhabitats is scarce. This thesis integrates cultivationdependent and -independent approaches to shed light on the chitin processing potential within the microbiomes of marine sponges, octocorals, sediments and seawater, placing emphasis on the discovery and inferred metabolism of chitin-degrading symbionts of the abovementioned animals. Cultivatable host-associated bacteria from several genera including Aquimarina and Vibrio were found to be able to degrade colloidal chitin in vitro. Vibrio and Aquimarina species, particularly, possessed several endo- and exo-chitinase-encoding genes underlying their capacity to cleave the large polymer, while Alphaproteobacteria species were found to specialize in the utilization of N-acetylglucosamine more often. A cultivation-independent approach relying on the functional profiling of unassembled reads from the microbial metagenomes of sponges, octocorals, seawater and sediments revealed distinctive abundance distributions of genes involved in chitin metabolism across the surveyed microbiomes. While an enrichment of polysaccharide deacetylase encoding genes was unveiled in the Spongia officinalis microbiome, suggesting capability of transforming chitin into its deacetylated – and biotechnologically valuable – form chitosan, the relative abundance of endo-chitinase and chitin-binding proteins was more pronounced in the octocoral microbiome, indicating that the degradation of chitin via hydrolysis may be a relevant process in these symbiotic communities.