The potential of Ordinary Compost and Vermicompost bacterial Isolates in Reducing the Harmful Bloom of Microcystis Aeruginosoa

Maria Sheila K. Ramos

(PhD Graduated: 2nd Sem 2010-2011)

Abstract

Freshwater resources are threatened by the presence and increase of harmful algal blooms (HABs) all over the world. These toxinogenic blooms especially those which are caused by Microcystis aeruginosa, a hepatotoxin producing microalga, have been epidemiologically linked to high incidence of liver cancer through drinking microcystin contaminated water from rivers, ditches, and ponds; and were further positively associated with the incidence of colorectal cancer in some provinces in China. M. aeruginosa is one of the dominant species in Laguna de Bay, Philippines and its bloom is a yearly occurrence in the lake. Sadly, the Laguna Lake Development Authority (LLDA) is not monitoring the toxin associated with these bloom occurrences. Countermeasures have been proposed and implemented to manage HABs with varying levels of success. These control measures include the mechanical removal of the hyperscum and the application of chemical algicides but both measures are costly. Algicides lyse cyanobacterial cells which leads to the release of cyanobacteria toxins into the surrounding water. Algicides accumulate in sediments and may cause long term damage to the lake ecology. Thus, the development of environment friendly, safe non-chemical control measures such as biological control offers potential to the management of HABs.

This work focuses on the isolation and identification of microorganisms present in ordinary compost and vermicompost that are suppressive to the growth of M. aeruginosa. These microorganisms were isolated, identified through their 16S rRNA genes, their cyanolytic properties were evaluated and their lytic mechanisms had been elaborated. In this study, we are presenting three novel bacteria out of the six that we have isolated from vermicompost samples.

The novel inhibitory isolates are identified as Stenotrophomonas maltophilia strain Biyaya0827, Stenotrophomonas maltophilia strain Megumi0711 and Bacillus sp. Strain RNR0410. They exhibited high lytic abilities against M. aeruginosa and are potential biocontrol agents against its harmful blooms. The cyanolytic bacterial exudates of the two Stenotrophomonas strains are proteinaceous and most probably are enzymes while those of the Bacillus isolate are non-proteinaceous and most probably are antibiotic analogues. Acute toxicity test with Daphnia magna showed that the EC50 of the cyanolytic extracellular substances of SmB 0827, Sm M0711 and Bacillus sp. RNR0410 may not pose adverse effect on actual lake environment.

This is the first time that suppressive bacteria from vermicompost are implicated in the suppression of growth of M. aeruginosa.

Keywords: Bacillus sp. Strain RNR0410, cyanolytic activity, extracellular substances, Microcystis aeruginosa, Stenotrophomonas maltophilia strain Biyaya0827, Stenotrophomonas maltophilia strain Megumi0711, vermicompost

Subject Index : Vermicomposting, Microcystis Aeruginosoa