Microbial community dynamics during start‐up operation of flowerpot‐using fed‐batch reactors for composting of household biowaste

Abstract

Microbial community changes during start-up operation of flowerpot-using fed-batch reactors for composting of household biowaste were studied by quinone profiling, rRNA-targeted fluorescence in situ hybridization (FISH) and cultivation methods. Total and plate counts of bacteria and quinone contents in the reactors increased sharply with time during the start-up period. These increase patterns had two phases; the first increase occurred during 3-4 weeks from the start of waste loading and the second increase was found during the subsequent 4 weeks. The microbial biomass was temporally reduced between the two succession phases. Ubiquinones predominated at the beginning of operation but decreased sharply with time, whereas partially saturated menaquinones became predominant at the fully acclimated stage. These data indicated that the major constituents of microbial populations changed from ubiquinone-containing Proteobacteria to Actinobacteria during the period of operation. Neighbour-joining dendrograms constructed based on the quinone profile data suggested that at least one month is required to establish a stable community structure with the Actinobacteria predominating. The characteristic population shift in the start-up process was also demonstrated by FISH probing and 16S rDNA sequence comparisons of bacterial strains isolated.

Water Availability Is a Critical Determinant of a Population Shift from Proteobacteria to Actinobacteria during Start-Up Operation of Mesophilic Fed-Batch Composting

“…In this study, we have entirely confirmed our previous observations that a population shift from ubiquinone-containing Proteobacteria to Actinobacteria takes place during the start-up operation of the mesophilic FBC process 12,23,25) . That is, the SCM in the FBC reactors during the early phases of operation contained ubiquinones as the major class of quinone, whereas partially hydrogenated menaquinones became predominant under steady-state conditions.…”

“…In addition, bacterial strains isolated previously from FBC systems (strains TUT1003 to TUT1096 and TUT1200 to TUT1296) 12,25) were used. For this test, PBYG agar plates having different levels of aw were prepared by mixing with different concentrations of PEG 300 solution.…”

“…To confirm the universality of the aforementioned phenomena, several bacterial strains previously isolated from different FBC processes and identified with a wide variety of genera of Actinobacteria, Firmicutes, and Proteobacteria 12,25) were also tested for growth response to low aw. Combined data on the phylogenetic positions, quinone systems, and growth response to low a w of these isolates are shown in Fig.…”

“…Therefore, there may be a need to consider a characteristic microbiological basis for the mesophilic FBC process different from that for the conventional composting system. In recent years, the FBC process for the biotreatment of garbage and food waste has been studied from a microbiological as well as kinetic point of view 1,8,[12][13][14]17,[22][23][24][25][26][27]31) . In previous studies on mesophilic FBC reactors for garbage treatment, we found that a population shift from members of the phylum Proteobacteria to those of the phylum Actinobacteria took place during the start-up period of operation 12,23,25) .…”

“…It has been shown that the solid waste-compost mixture (SCM) in FBC reactors operating under steady-state conditions has 30-40% moisture 12,23,25) , at which the microorganisms present exhibited the highest protease activity 25) . Biologically, water availability is more critical than moisture.…”