Abstract

Submersion of freshly harvested bamboo culms in water for a certain length of time is a traditional method of bamboo preservation followed in rural areas of India. A previous study has indicated a decrease in starch content of culms as a result of this treatment and the involvement of some microorganisms with starch depletion. The present study was conducted to investigate the rate of starch depletion in culms stored under water and the role of microbial population in the process. It was found that the starch stored in culm tissues was reduced by more than half in a two months period at a slow and gradual pace. Extending the length of submersion period by one more month led to further reduction in starch content. The activity of starch hydrolyzing enzyme a-amylase by microorganisms was responsible for the starch depletion. Even the water used in the submersion experiment showed amylase activity but it was low as compared to that in the tissue extract from submerged culms. The total microbial population comprising bacteria, fungi and actinomycetes within bamboo tissues increased drastically within 15 days after submersion. While aerobic microorganisms showed an early decline after 15th day, anaerobic organisms capable of starch degradation continued to increase up to 45th day. Increase of aerobic microorganisms in stagnant water was not considerable whereas their population increased in running water. Thus anaerobes were the most active starch degraders in stagnant water whereas, aerobes could degrade starch only in running water where oxygen is continuously replenished. About 75% of the bacteria were gram-positive spore forming Bacillus species, while 25% were gram negative cocci. There were a few actinomycetes but fungi were rare. The total anaerobes increased continuously even 60 days after keeping the bamboo pieces in stagnant water. But the population increase for aerobic as well as anaerobic starch degraders was not very rapid. The increasing populations of starch degraders within the submerged bamboo tissues and in bamboo-soaked water explain the decline in starch content when submerged under water. It is thus evident that water submersion treatment leads to depletion of storage starch in bamboo culms due to microbial activity and makes it less attractive to borers.