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Lời Cam Đoan

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Lời Cam Đoan i LỜI CAM ĐOAN Tôi xin cam đoan rằng: số liệu và kết quả nghiên cứu trong luận văn là trung thực và chưa từng được sử dụng để bảo vệ một học vị nào. Tôi xin cam đoan rằng mọi sự giúp đỡ cho việc thực hiện luận văn này đã được cảm ơn và các thông tin trích dẫn trong luận văn đều đã được ghi rõ nguồn gốc. Thừa Thiên Huế, ngày tháng 7 năm 2016 Tác giả Nguyễn Văn Sỹ ii LỜI CẢM ƠN Để hoàn thành luận văn này tôi xin chân thành cảm ơn: Tiến sĩ Nguyễn Ngọc Phước đã tận tình hướng dẫn, tạo mọi điều kiện cho em học tập, nghiên cứu và hoàn thành luận văn. Các thầy giáo, cô giáo Khoa Thủy sản – Trường Đại học Nông Lâm Huế đã giúp đỡ và truyền dạy cho em những kiến thức quý báu trong suốt thời gian học tập tại trường. Ban giám đốc Trung tâm giống thủy sản Quảng Bình, các anh chị, các bạn đồng nghiệp đã tạo mọi điều kiện thuận lợi cho tôi trong suốt thời gian học tập và nghiên cứu vừa qua. Gia đình và bạn bè đã động viên, giúp đỡ tôi trong quá trình học tập cũng như thực hiện đề tài. Thừa Thiên Huế, ngày tháng 7 năm 2016 Tác giả Nguyễn Văn Sỹ iii TÓM TẮT Vi khuẩn quang hợp (Phototropic bacteria) là một nhóm vi sinh vật có khả năng phân giải NH3 và H2S dưới tác dụng ánh sáng mặt trời, trong điều kiện kỵ khí nên có thể sử dụng để xử lý ô nhiễm trong các ao nuôi tôm. Nghiên cứu này đã phân lập được 8 chủng vi khuẩn quang hợp từ bùn các ao nuôi tôm thẻ chân trắng tại tỉnh Thừa Thiên Huế. Sau quá trình nuôi cấy trên môi trường DSMZ 27 lỏng, trong điều kiện kỵ khí, chiếu sáng liên tục đã lựa chọn được 2 chủng có mức độ tích lũy sinh khối cao nhất, được ký hiệu DL11, PH21 để tiến hành nghiên cứu đặc điểm sinh hoá, sinh lý và khả năng chuyển hoá lưu huỳnh. Quan sát đặc điểm hình thái, sinh lý sinh hoá của hai chủng vi khuẩn quang hợp cho thấy khuẩn lạc của chủng DL11 có màu cam nâu và khuẩn lạc chủng PH21 có màu vàng. Cả hai chủng PH21 và DL11 đều là vi khuẩn Gram (-), có dạng hình que và phản ứng âm tính (-) với oxidase. Chủng vi khuẩn DL11 có khả năng lên men đường sucrose, chuyển hoá tốt với nguồn sulfide. Chủng PH21 có thể sử dụng các nguồn cacbon khác nhau như citrate, glucose, succose. Kết quả định danh qua phân tích gen mã hóa 16S– rRNA của 2 chủng PH21 và DL11 có thể khẳng định: chủng DL11 là Allochromatium sp, chủng PH21 là Marichromatium sp. Khoảng nồng độ muối của 2 chủng Allochromatium sp và Marichromatium sp tương đồng nhau: sinh trưởng và phát triển tốt ở nồng độ 10‰ - 20‰. Nồng độ pH tối ưu cho 2 chủng này phát triển trong khoảng 6 – 7. Việc bổ sung nồng độ cao nấm men vào môi trường nuôi cấy kích thích khả năng sinh trưởng của 2 chủng Allochromatium sp và Marichromatium sp, điều này thể hiện ở nồng độ cao nấm men càng cao thì tăng sinh của vi khuẩn càng cao. Ở điều kiện chiếu sáng, nuôi kị khí, cả 2 chủng đều có khả năng loại bỏ sulfide cao. Các chủng vi khuẩn quang hợp được tuyển chọn hoạt động tốt nhất ở nồng độ sulfide từ 10 - 20 mg/L. Kết quả nghiên cứu cho thấy cả hai chủng PH21 và DL11 có khả năng làm giảm hàm lượng khí độc H2S trong ao nuôi tôm. iv MỤC LỤC LỜI CAM ĐOAN ........................................................................................................ i LỜI CẢM ƠN ............................................................................................................. ii TÓM TẮT .................................................................................................................. iii MỤC LỤC ................................................................................................................. iv DANH MỤC CÁC KÝ HIỆU, CHỬ VIẾT TẮT..................................................... vii DANH MỤC CÁC BẢNG ...................................................................................... viii DANH MỤC CÁC HÌNH VẺ, ĐỒ THỊ .................................................................... ix MỞ ĐẦU .................................................................................................................... 1 1. Đặt vấn đề ............................................................................................................... 1 2. Mục đích của đề tài ................................................................................................. 2 3. Ý nghĩa khoa học và thực tiễn ................................................................................ 2 3.1 Ý nghĩa khoa học .................................................................................................. 2 3.2 Ý nghĩa thực tiễn ................................................................................................... 3 CHƯƠNG 1. TỔNG QUAN CÁC VẤN ĐỀ NGHIÊN CỨU ................................... 4 1.1. Tổng quan về vi khuẩn quang hợp ....................................................................... 4 1.1.1. Vi khuẩn quang hợp tía ..................................................................................... 4 1.1.2. Ảnh hưởng của các nhân tố lý hóa đến sinh trưởng và phát triển của vi khuẩn tía ... 10 1.2. Tổng quan về tôm thẻ chân trắng (Litopenaeus vannamei) ............................... 11 1.2.1. Hệ thống phân loại, phân bố ........................................................................... 11 1.2.2. Tập tính sống, khả năng thích nghi với môi trường sống ............................... 13 1.2.3. Đặc điểm dinh dưỡng ...................................................................................... 14 1.2.4. Đặc điểm sinh trưởng ...................................................................................... 14 1.2.5. Đặc điểm sinh sản ........................................................................................... 16 1.3. Tình hình nuôi tôm thẻ chân trắng trên thế giới và tại Việt Nam ...................... 17 1.3.1. Tình hình nuôi tôm thẻ chân trắng trên thế giới ............................................. 17 1.3.2. Tình hình nuôi tôm thẻ chân trắng tại Viêt Nam ............................................ 19 v 1.3.3. Tình hình nuôi tôm thẻ chân trắng tại tỉnh Thừa Thiên Huế .......................... 22 1.4. Vấn đề ô nhiểm môi trường nước trong hoạt động thủy sản ............................. 23 1.4.1. Ô nhiểm môi trường nước do hoạt động chế biến thủy sản............................ 24 1.4.2. Ô nhiễm môi trường biển, ven bờ do các hoạt động hàng hải ........................ 25 1.4.3. Ô nhiểm nguồn nước do tác động của nuôi trồng thủy sản ............................ 25 1.4.4. Ô nhiễm do việc sử dụng thuốc và các hóa chất trong nuôi tôm .................... 27 1.5. Một số nghiên cứu về vi khuẩn quang hợp và ứng dụng của chúng trong nuôi trồng thủy sản ............................................................................................................ 28 1.6. Một số ứng dụng khác của vi khuẩn quang hợp tía ........................................... 30 1.6.1. Sản xuất protein đơn bào ................................................................................ 30 1.6.2. Sản xuất ubiquinone........................................................................................ 30 1.6.3. Sản xuất hoocmon thực vật ............................................................................. 31 1.6.4. Sản xuất các chất kháng sinh .......................................................................... 31 1.6.5. Sử dụng vi khuẩn quang hợp tía trong xử lý nước thải .................................. 31 1.7. Ảnh hưởng của H2S trong nuôi trồng thủy sản .................................................. 32 1.7.1. Bản chất của khí H2S ...................................................................................... 32 1.7.2. Tác hại của khí H2S ........................................................................................ 32 1.8. Giải pháp giảm ô nhiễm môi trường bằng chế phẩm vi sinh ............................. 33 1.8.1. Phòng ngừa dịch bệnh..................................................................................... 33 1.8.2. Kích thích tôm phát triển ................................................................................ 34 1.8.3. Ngăn ngừa, làm giảm thiểu ô nhiễm và chất độc trong ao ............................. 34 CHƯƠNG 2. NỘI DUNG VÀ PHƯƠNG PHÁP NGHIÊN CỨU .......................... 36 2.1. Phạm vi, đối tượng nghiên cứu .......................................................................... 36 2.1.1. Phạm vi nghiên cứu ........................................................................................ 36 2.1.2. Đối tượng nghiên cứu ..................................................................................... 36 2.2. Môi trường hóa chất ........................................................................................... 36 2.3. Phương pháp nghiên cứu và theo dõi các chỉ tiêu ............................................. 37 vi 2.3.1. Phương pháp thu mẩu bùn đáy ao nuôi tôm ................................................... 37 2.3.2. Phương pháp pha loảng mẩu nuôi cấy vi khuẩn ............................................. 38 2.3.3. Nuôi cấy vi khuẩn ........................................................................................... 38 2.3.4. Phương pháp làm giàu và phân lập vi khuẩn quang hợp tía ........................... 39 2.3.5. Quan sát hình thái tế bào ................................................................................ 40 2.3.6. Xác định khả năng sinh trưởng ....................................................................... 40 2.3.7. Đánh giá ảnh hưởng của pH và nồng độ NaCl lên sự phát triển của vi khuẩn quang hợp. ................................................................................................................
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