Abstract

In order to promote the growth of photosynthetic bacteria (PB) for use as biofertilizers in organic saline paddy fields, a co-culture of selected PB and lactic acid bacterium strains was investigated. Using MRS agar medium (de Man Rogosa and Sharpe), a total of 46 LAB were isolated from the same source as the PB. The source was soil samples from organic saline paddy fields in 14 provinces of the Northeast region of Thailand that had been treated with straw to obtain soil and straw products (SSPs) and their average salinity was equivalent to 0.25% NaCl, about 4 dS/m. Over a 24 h strain L35 showed the highest ability to grow in MRS broth with 0.25% NaCl added, which was selected for co- culture. The PB strain used was Rhodopseudomonas palustris tk123 that had been previously selected for its ability to produce 5-aminolevelinic acid (ALA). Cultures were grown in Tryptic Soy Broth (TSB) medium with and without supplementation of 0.25% NaCl under aerobic dark and microaerobic light conditions. Both organisms grew best with microaerobic light conditions; however, a significant inhibition by the extra NaCl on growth was only observed with strain tk123, grown with microaerobic light conditions. This inhibition was removed by a co-culture with L35 and the significant increase of pH was observed when strain tk123 was grown by itself. This was also removed when co-cultured with L35. This synergism between LAB and PB occurred in a commercial complex medium (TSB) with high salinity. It is therefore most likely that a co-culture in rice straw medium will be possible for use as a tool for producing bio-fertilizers for use in organic saline paddy fields.

Key words: Photosynthetic bacteria (PB), lactic acid bacteria (LAB), co-culture, aerobic dark conditions, microaerobic light conditions