Page | 1 AROC in Pharmaceutical and Biotechnology, 2022, 2(1);01-08 https://doi.org/10.53858/arocpb02010108 ISSN: 2789-3928 Molecular characterization of xanthan gum producing Xanthomonas Campestris isolated from dark rot spotted leaves in Keffi, Nasarawa State, Nigeria Makwin Danladi Makut * , Kenneth Kit Madaiki, and Obumneme Smart Obiekezie Department of Microbiology, Nasarawa State University, P.M.B. 2022, Keffi, Nigeria ABSTRACT Background: Despite the wide application of Xanthan gum, its commercial production remains a global challenge. In recent years, considerable research has been carried out using agro-industrial wastes, which are renewable and abundantly available to produce value-added products. The present study was set out for molecular identification of Xanthomonas campestris from leaves of four different plants with indications of dark rot spots and evaluation of their xanthan gum production capacity. Methods: Twenty-five (25) samples of leaves from four different plants with indications of dark rot spots were collected from the study area and isolated for Xanthomonas campestris following standard microbiological methods. Cultural, morphological and biochemical tests were conducted to confirm the organism. Results: The results revealed that of the total 100 samples taken, 6 leaves (24%) were infected with Xanthomonas species in mint, 3(12%) were infected in mango, 1(4%) were infected in rice and 2(8%) were infected in pepper. Further molecular identification of the isolates was carried out to reveal Xanthomonas campestris pv. vesicatoria strain 85-10 and Xanthomonas perforans strain 91-118. These were further used for the production of xanthan gum using sugar cane molasses substrates extracted from sugar cane, which was used as fermentation medium for the production. Isolates from plants varying ability in Xanthan gum production, with the mint plant having the highest Xanthan gum production (0.10 ± 0.02 to 0.9 ± 0.00 g/l). Conclusion: The present study confirmed the high xanthan gum production capacity of Xanthomonas campestris from dark rot spots containing mint leaves and should be considered during local and industrial production of the xanthan gum Keywords: Xanthomonas campestris; xanthan gum; dark rot spots; molecular and phylogenic identification Received: 09 December 2021, Revised: 23 December 2021, Published: 08 January 2022 Citation: Makut, M.D., Madaiki, K.K., and Obiekezie, S.O. (2022). Molecular characterization of xanthan gum producing Xanthomonas Campestris isolated from dark rot spotted leaves in Keffi, Nasarawa State, Nigeria. AROC in Pharmaceutical and Biotechnology, 2(1);01-08, https://doi.org/10.53858/arocpb02010108 1.0 Introduction Xanthomonas campestris gram-negative bacteria, having a single polar flagellum [1], plant-associated bacteria that is generally pathogenic for plants belonging to the family Brassicaceae [2]. They cause huge problems in areas with a warm and wet climate [3]. Machinery and insects damage plants creating wound entry points for Xanthomonas bacteria [4]. The bacteria enter plant leaves through breathing pores (stomata) and water releasing pores (hydathodes) in the leaf surface. Once inside the plant, the bacteria reproduce and move around using the plant’s water transportation system (xylem) [5]. Xanthomonas bacteria feed on nutrients released from plant cells as they become leaky and start to die. They cause black rot disease where leaves become yellow and sticky, then wilt and die [5]. The bacteria are the causal agents of an assortment of persistent and periodic plant diseases [3], most strains are relatively common phytopathogenic bacteria which mainly infect crucifers and cause black rot which have high agronomic and economic importance-particularly in regions of subsistence agriculture and those with poor crop management resources [3]. X. campestris, is the most widely used for the industrial production of xanthan gum based on its high yield and the high-quality product suitable for many applications [6]. It is strictly aerobic bacteria, and the rate of oxygen transmission affects xanthan gum production [7]. Xanthan gum is produced by Xanthomonas campestris [1,8. It derived its name from the strain of bacteria used during fermentation process [9]. It AROC in Pharmaceutical and Biotechnology 2022, 2(1);01-08 https://doi.org/10.53858/arocpb02010108 Arocjournal.com RESEARCH ARTICLE *Corresponding author Prof. Makwin Danladi Makut Email: makmakwin@yahoo.com