Shushan Yan ^1,2 Tie Liu ³ Haobin Zhao ⁴ Zhao Chunbo ³ Yuxin Zhu ⁴ Wenqing Dai ⁴ Wenchang Sun ⁴ Junxi Sun ³ Lu Zhao ^4,5,6,7* Donghua Xu ^4*

• ¹ Department of Gastrointestinal and Anal Diseases Surgery the Affiliated Hospital, Shandong Second Medical University, Weifang, China
• ² Department of Microbiology and Immunology, Tulane University School of Medicine, New Orleans, American Samoa
• ³ Department of Anorectal Surgery of the First Affiliated Hospital, Shandong Second Medical University, Weifang, China
• ⁴ Central Laboratory of the First Affiliated Hospital, Shandong Second Medical University, Weifang, China
• ⁵ Weifang People's Hospital, Weifang, China
• ⁶ Department of Biostatistics, School of Public Health, Cheeloo College of Medicine, Shandong University, Jinan, China
• ⁷ Shandong Laibo Biotechnology Co., Ltd., Jinan, China

Accumulating evidence has supported that gut microbiota and the metabolite profiles play indispensable roles in the pathogenesis of colorectal cancer (CRC), which ranks as the third most common cancer and the second leading cause of cancer-related deaths worldwide. However, alterations in tumoral or circulating microbiomes in CRC remain incompletelyhave not been fully understood. It has been well documented that tissue or serum microbiomes with low microbial biomass could be screened by use of 2bRAD sequencing for microbiome (2bRAD-M) at the species resolution. In order to validateTo further confirm the microbial biomarkers distinguishing that differentiate CRC and the variations in differences of microorganisms present in serum and tumors, we performed 2bRAD-M to characterize the microbiomes in serum and cancer tissues from of CRC patients with and without lymph node or liver metastasis. The composition of dominated microbiota in serum was different from that of tissue samples, while the microbial community composition of tumors was similar to that of the tumor-adjacent tissues. The analysis of α-diversity and β-diversity has revealed notable variations inanalyses have implicated the significant serum microbiota diversities in CRC patients, particularly in patientsthose with liver metastasis. Multiple CRC-specific microbial species were identified particularly in serum, such as Moraxella A cinereus, Flavobacterium sp001800905, and Acinetobacter albensis, were identified in serum.Complicated functions and KEGG pathways were also confirmed in CRC according to the metastasis status. This study has found significant alterations in the microbial compositions and diversities in CRC and CRC-specific microbial species in both circulation and cancer tissues, which may serve as promising biomarkers for the screening, diagnosis and prognosis prediction of CRC. In particular, CRC-specific bacterial taxa are promising markers, holding transformative potentials in establishing personalized screening and risk stratification, refining non-invasive and much earlier non-invasive diagnostic approaches, and enhancing diagnostic sensitivity.