New method for arbuscular mycorrhizal fungus spore separation using a microfluidic device based on manual temporary flow diversion

Arbuscular mycorrhizal fungi are beneficial components often included in biofertilizers. Studies of the biology and utilization of these fungi are key to their successful use in the biofertilizer industry. The acquisition of isolated spores is a required step in these studies; however, spore quality control and spore separation are bottlenecks. Filtered and centrifuged spores have to be hand-picked under a microscope. The conventional procedure is skill-demanding, labor-intensive, and time-consuming. Here, we developed a microfluidic device to aid manual separation of spores from a filtered and centrifuged suspension. The device is a single spore streamer equipped with a manual temporary flow diversion (MTFD) mechanism to select single spores. Users can press a switch to generate MTFD when the spore arrives at the selection site. The targeted spore flows in a stream to the collection chamber via temporary cross flow. Using the device, spore purity, the percentage of spore numbers against the total number of particles counted in the collecting chamber reached 96.62% (median, n = 10) which is greater than the spore purity obtained from the conventional method (88.89% (median, n = 10)).

Empowering rice seedling growth by endophytic Bradyrhizobium sp. SUTN9-2

Bradyrhizobium sp. strain SUTN9-2 was confirmed as rice endophytic bacteria and also as rice growth promotion agent. SUTN9-2 showed the capability of plant growth promotion characteristics, such as indole-3-acetic acid (IAA) and 1-amino-cyclopropane-1-carboxylic acid (ACC) deaminase productions and nitrogen fixation. In this study, the ability of SUTN9-2 to stimulate rice growth was investigated at different stages with N-free and NH₄ NO₃ under in vivo condition. The rice dry weight and chlorophyll content could be enhanced when SUTN9-2 was inoculated in N-free, especially at seedling stage (7 and 14 dai). The rice dry weight was also increased when SUTN9-2 was inoculated with NH₄ NO₃ at 7 and14 dai. The results of quantitative analysis of IAA and ACC deaminase were inconsistent with the expression of genes involved in IAA (nit) and ACC deaminase (acdS) productions. This inconsistently could implied that IAA and ACC deaminase produced from SUTN9-2 do not directly affect rice growth, but other factors resulting from the production of IAA and ACC deaminase could be involved. Moreover, the expression of genes involved in nitrogen fixation (nifH and nifV) of SUTN9-2 was also induced in rice tissues. This finding suggested that rice growth promotion may be supported by NH₄ NO₃ together with nitrogen fixation by SUTN9-2. SIGNIFICANCE AND IMPACT OF THE STUDY: Indole-3-acetic acid, 1-amino-cyclopropane-1-carboxylic acid deaminase productions and nitrogen fixation may play important roles in rice growth promotion by endophytic SUTN9-2, especially at early rice seedling growth stage, which has the potential to be used as rice seedling growth promoter in the system of rice intensification.