Taxonomic Diversity and Lignin Biodegradation in Bacterial Community of Caatinga Soil. Taxonomic Diversity and Lignin Biodegradation in Bacterial Community of Caatinga Soil

The Caatinga is an exclusively brazilian biome, accounting for approximately 11% of the national territory and considered the most diverse semi-arid region of the world.On the other hand, it is the least protected biome conservation units in Brazil, and the leastscientifically explored among all other biomes of the country, with 41% of its territory eversampled. The semi-arid climate, low water availability and extremely variable rainfall attachgreat variability of adaptive mechanisms to the native biota of Caatinga, resulting fromresponses to extreme environmental conditions that characterize their regions. Soils representa major natural reservoir of genetical and biochemical diversity, as well as a variety of niches.However, the knowledge about the microbial diversity present in the soil of Caatinga and thebiotechnological potential associated with it is still incipient and scarce. Currently, millions oftons of lignin and related compounds are produced as waste from effluents of paper andcellulose pulp industries, with the forecast which this number will increase in the near future,given the recent development of alternative fuels generated from lignocellulosic biomass. Inparticular, microbial enzymes from the group of ligninases, which catalyze the bioconversionand biodegradation of lignin, have received much attention of scientists in recent decades.Among these enzymes, laccases has been highlighted by its phenolic oxidation of lignin,being exploited both industrially (paper and pulp mills, textile and biofuels industries) andenvironmentally (like detoxification of recalcitrant aromatic compounds and remediation ofcontaminated soils and rivers). In this sense, this work investigated native bacterialcommunities from soil of Caatinga under the influence of the addition of lignin, applying apolyphasic approach to the analysis of taxonomic diversity. At the same time, bacteria withligninolytic potential were isolated and cultivated for molecular and functional assays toscreening bacterial genes from laccases, hoping a future application in the treatment ofsewage and contaminated soils. During 27 days of sampling, 156 bacteria potentiallyligninolytic were isolated (39 derived directly from microcosms supplemented with 10%lignin), all of them grown in culture medium with 0.3% lignin (w/v). The data generated byIllumina sequencing of 16S rRNA gene showed that the introduction of lignin in themicrocosms provided changes in the abundance of taxa belonging to the bacterial communityover time, affecting the microbiota composition in the evaluated microcosms. While the mostbacterial taxonomic groups have been supressed, some genera such as Bacillus andStreptomyces showed significant increase in abundance under enrichment, as well as othergroups not described yet in the literature.

卡廷加生物群落（Caatinga）是巴西特有的生物群落，约占巴西国土总面积的11%，被认为是全球最多样化的半干旱区域。然而，它是巴西保护单元覆盖率最低的生物群落，也是该国所有生物群落中科学探索程度最低的，仅有41%的区域曾被采样调查。半干旱气候、水资源匮乏与极端多变的降水模式，使得卡廷加本土生物演化出高度多样的适应机制，这是对当地标志性极端环境条件的适应性演化结果。土壤是遗传与生化多样性以及多种生态位的重要天然储库。但目前学界对卡廷加土壤微生物多样性及其相关生物工程潜力的认知仍处于起步阶段，相关研究十分匮乏。当前，造纸与纤维素浆产业的废水会产生数以百万吨计的木质素及其相关副产物；随着近年来木质纤维素生物质基替代燃料的快速发展，该类废弃物的产量预计还将进一步增长。其中，能够催化木质素生物转化与生物降解的木质素酶类微生物酶制剂，近几十年来受到了科研人员的广泛关注。在这类酶中，漆酶（laccases）因可催化木质素的酚类氧化反应而备受瞩目，其应用场景涵盖工业（造纸与制浆、纺织及生物燃料产业）与环境治理（如难降解芳香族化合物的脱毒、污染土壤与河流的修复）两大领域。基于此，本研究以受木质素添加影响的卡廷加土壤原生细菌群落为研究对象，采用多相分析法对其分类多样性展开分析。同时，本研究分离并培养了具有木质素分解潜力的细菌，用于分子与功能实验以筛选漆酶相关的细菌基因，期望未来将其应用于污水与污染土壤的治理。在为期27天的采样周期内，研究人员共分离得到156株潜在木质素分解细菌（其中39株直接来自添加了10%木质素的微宇宙培养体系），所有菌株均在含0.3%（w/v）木质素的培养基中完成培养。通过对16S rRNA基因进行Illumina测序得到的数据显示，向微宇宙培养体系中添加木质素会随时间推移改变细菌群落类群的丰度，进而影响受试微宇宙的微生物群落组成。尽管多数细菌分类群的丰度受到抑制，但芽孢杆菌属（Bacillus）、链霉菌属（Streptomyces）等类群的丰度在富集培养后出现了显著提升，同时还发现了一些此前未在文献中被报道的细菌类群。