Science: Soil bacteria stop mosquitoes dead

时间:2019-03-01 04:04:02166网络整理admin

By LEIGH DAYTON in SYDNEY Common soil bacteria could soon be enlisted in the battle against malaria. Trials in India and Indonesia have already shown that preparations containing these bacteria kill the larvae of mosquitoes that carry the malaria parasite, without harming plants, animals or people. A company in Madras, India, expects to have a product on the market in the next six to nine months. The protozoan that causes malaria infects more than 300 million people each year, of whom between 1 and 3 million will die, mostly children in Africa. Increasingly, the parasite is becoming resistant to antimalarial drugs such as chloroquine. In parts of Thailand, for instance, it is immune to all drugs. Progress is being made on a malaria vaccine at the National University of Colombia in Bogota, but no effective vaccine is yet on the market (This Week, 19 February). Teams of researchers in Australia, the US, India and Indonesia are participating in a worldwide effort to exploit two strains of bacteria, Bacillus sphaericus (BS) and Bacillus thuringensis (BT), to kill the mosquitoes that transmit malaria. The mosquito larvae eat the bacteria, which produce protein crystals. These bind to the mid-gut of the larvae, causing paralysis and death. One strain of BT called B. thuringensis israelensis kills blackflies as well as mosquitoes. But the scientists are working mostly with strains of BS that affect only mosquitoes. ‘We tried BS with midges and bees and all sorts of things, and it doesn’t have any effect on those,’ says Peter Rogers at the University of New South Wales in Sydney, who is involved with the Indonesian trials. BS strains act against larvae of anopheles and culex mosquitoes, while BT is deadly to anopheles, the main carriers of malaria. Culex mosquitoes carry parasites which spread malaria, dengue fever and filariasis. In West Africa, the WHO has used BT to clear thousands of square kilometres of the flies which carry river blindness. The Indonesian trials, which began in 1992, are being conducted at a field station 150 kilometres from Yogyakarta in central Java. There, researchers sprayed stagnant ponds where mosquitoes breed with a powder of BS and bagasse, the fibrous by-product of sugar production. From early results it appears that the mixture kills nearly all the larvae and remains active for up to four weeks. There are hints that the bacteria may continue to reproduce after that. High levels of BS are unlikely to build up because there is not enough carbon and nitrogen in the water for the bacteria to feed on. In India, trials have been conducted since 1991 at sites in Cochin in Kerala and in Madras by Kunthala Jayaraman and his colleagues at the Anna University Centre for Biotechnology in Madras. Jayaraman’s team has developed a liquid preparation containing BS, a polymer filler and a food preservative. It, too, is sprayed over water where mosquitoes breed. After 24 to 48 hours, the number of larvae is ‘nearly zero’, says Jayara-man. Preparations of BT kill even faster – larvae begin dying within 10 minutes. ‘That’s too fast,’ says Jayara-man, who fears that there may be unknown hazards. ‘It’s best to avoid BT just in case.’ The Indian researchers have turned their BS formulation over to Tupicorin Akali Chemicals and Fertilisers for commercial development. Singer is screening other strains of BS which could be more active than those studied so far. Also,