Frouz J, Kristůfek V, Li X, Santrůcková H, Sustr V, Brune A
Institute of Soil Biology, Academy of Sciences of the Czech Republic, 370 05 Ceské Budĕjovice, Czechia.
Folia Microbiol (Praha). 2003;48(4):535-42. doi: 10.1007/BF02931337.
To elucidate the interaction between bacteria and saprophagous Diptera larvae, the amounts of bacteria in leaf litter, individual gut compartments, and feces of three species of Bibionidae (Bibio pomonae, Bibio marci, and Penthetria holosericea), feeding either directly on leaf litter or on fecal pellets produced from leaf litter by larvae of the same species, were assessed by determining total direct counts and viable counts on solid media at different pH. In P. holosericea, the effect of various cultivation temperatures on direct counts of bacteria in individual compartments was also demonstrated. In all species, the amount of bacteria in the anterior mesenteron was lower than in the consumed food, regardless of whether the larvae were feeding on leaf litter or feces, and increased again in the posterior part of the gut. The amount of bacteria in these compartments was generally higher in larvae feeding on feces than in those feeding on leaf litter, whereas the amount of bacteria found in the ceca varied. In B. marci, the amount of bacteria in the mesenteron sections able to grow on alkaline medium (pH 9) was higher than that of bacteria able to grow on slightly acidic medium (pH 5.5) during both the first and the second gut passage. In B. pomonae and P. holosericea, this increase was observed only during the second gut passage. The effect of gut passage in P. holosericea on changes in direct counts of bacteria was more pronounced when the larvae were fed at 5 degrees C as compared to 20 degrees C. Radiolabeled bacteria were digested in the gut and utilized as a source of energy and nutrients by the larvae; digested bacteria represented up to 10% of the material assimilated by the larvae. Lysozyme activity in whole-gut extracts of P. holosericea had a pH optimum of at pH 7, indicating a low in situ activity in the alkaline mesenteron. Proteinase activity, however, had an optimum at pH > 12, suggesting that the digestion of bacteria in the bibionid gut is caused by a combination of digestive proteinases and alkaline pH in the anterior mesenteron.
为阐明细菌与腐食性双翅目幼虫之间的相互作用，通过测定不同pH值固体培养基上的总直接计数和活菌计数，评估了三种毛蚊科昆虫（苹果毛蚊、三月毛蚊和全丝毛蚊）的落叶、各个肠道区域及粪便中的细菌数量，这些昆虫要么直接取食落叶，要么取食同物种幼虫由落叶产生的粪便颗粒。在全丝毛蚊中，还证明了不同培养温度对各个区域细菌直接计数的影响。在所有物种中，无论幼虫取食落叶还是粪便，中肠前部的细菌数量均低于所消耗食物中的细菌数量，且在肠道后部再次增加。取食粪便的幼虫这些区域的细菌数量通常高于取食落叶的幼虫，而盲肠中的细菌数量则有所不同。在三月毛蚊中，在肠道第一次和第二次通过期间，能够在碱性培养基（pH 9）上生长的中肠部分的细菌数量高于能够在微酸性培养基（pH 5.5）上生长的细菌数量。在苹果毛蚊和全丝毛蚊中，仅在肠道第二次通过期间观察到这种增加。与20℃相比，当幼虫在5℃取食时，全丝毛蚊肠道通过对细菌直接计数变化的影响更为明显。放射性标记的细菌在肠道中被消化，并被幼虫用作能量和营养来源；被消化的细菌占幼虫同化物质的10%。全丝毛蚊全肠提取物中的溶菌酶活性在pH 7时达到最佳，表明在碱性中肠中的原位活性较低。然而，蛋白酶活性在pH>12时达到最佳，这表明毛蚊肠道中细菌的消化是由消化蛋白酶和中肠前部的碱性pH共同作用引起的。
