In the cold regions of China, lignin-rich corn straw accumulates at high levels due to low temperatures. The application of psychrotrophic lignin-degrading bacteria should be an effective means of overcoming the low-temperature limit for lignin degradation and promoting the utilization of corn straw. However, this application is limited by the lack of suitable strains for decomposition of lignin; furthermore, the metabolic mechanism of psychrotrophic lignin-degrading bacteria is unclear. Here, the whole genome of the psychrotrophic lignin-degrading bacterium Arthrobacter sp. C2, isolated in our previous work, was sequenced. Comparative genomics revealed that C2 contained unique genes related to lignin degradation and low-temperature adaptability. DyP may participate in lignin degradation and may be a cold-adapted enzyme. Moreover, DyP was proven to catalyze lignin Cα-Cβ bond cleavage. Deletion and complementation of the DyP gene verified its ability to catalyze the first-step reaction of lignin degradation. Comparative transcriptomic analysis revealed that the transcriptional expression of the DyP gene was upregulated, and the genetic compensation mechanism allowed C2ΔDyP to degrade lignin, which provided novel insights into the survival strategy of the psychrotrophic mutant strain C2ΔdyP. This study improved our understanding of the metabolic mechanism of psychrotrophic lignin-degrading bacteria and provided potential application options for energy-saving production using cold-adapted lignin-degrading enzymes.

Steroidal estrogens (SEs) are mainly produced by animals, while bacteria are major consumers of SEs in the biosphere. However, the understanding of the gene clusters that participate in E1 degradation is still limited, and the enzymes involved in the biodegradation of E1 have not been well characterized.

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China has the largest blue honeysuckle (Lonicera caerulea L.) cultivation area globally. In June 2022, leaf spots were observed on approximately 10% of blue honeysuckle (cv. ‘Lanjingling’) leaves in a 0.03-ha field in Harbin (127.66°E, 45.61°N), Heilongjiang Province, China. The leaves of the affected plants displayed chlorotic to tan dieback with a darker brown margin along the leaftip and leave margins. Cross-sectional segments of approximately 3 mm were cut from 50 typical infected plant leaves. Their surfaces were sterilized with 75% ethanol for 30 s followed by 3 min in 5% sodium hypochlorite (NaOCl), rinsed three times with sterile water, and transferred to 9-cm Petri dishes containing 15 ml of sterile PDA growth medium. Five purified cultures with similar culture characteristics were finally obtained and their colonies were dark brown on the PDA plates. The pycnidia were subglobular and deep black and measured avg. 215.48 (135.30–331.20) μm × avg. 170.28 (99.90–282.90) μm (n = 50) (Chen et al., 2015; Huang et al., 2018). Conidia were single-celled, hyaline, and ellipsoidal and measured avg. 6.22 (5.40–7.20) µm × avg. 3.42 (2.70–3.90) µm (n = 50). For molecular verification, genomic DNA was extracted from a representative isolate, LD-75. The internal transcribed spacer region (ITS), the second-largest subunit of RNA polymerase II (rpb2), the partial 28S large subunit rDNA (LSU), beta-tubulin (TUB), and actin (ACT) genes were amplified with the primers ITS1/ITS4, RPB2f/RPB2r, LROR/LR7, TUB2Fd/TUB4Rd, and ACT512f/ACT783R, respectively (White et al. 1990; Carbone and Kohn, 1999; Staats et al., 2005; de Gruyter et al., 2009; Chen et al., 2015). BLAST results indicated that the genes of LD-75 (GenBank OP218870, OP264863, OQ561448, OQ597233, and OQ597232) shared 99%–100% identity with those of Didymella glomerata (OK485138, GU371781, EU754185, MZ073910, and MW963190, respectively). Therefore, based on morphological characteristics and molecular phylogeny, LD-75 was identified as D. glomerata. Six two-year-old healthy plants from the ‘Lanjingling’ cultivar were selected for a pathogenicity test. The leaves were surface disinfested with 75% ethanol and then wiped with sterilized water three times. All plants were cultured in a greenhouse at 28℃ under a 12-h light/dark cycle. Whole plants sprayed with conidial suspension of isolate LD-75 (106 spores/mL) (n = 3) displayed leaf spot symptoms after 14 d, while no symptoms were detected on whole plants sprayed with sterile water (n = 3). The same isolate, reisolated from infected leaves and with the same morphological and molecular traits, was also identified as D. glomerata, confirming Koch’s postulate. The fungus was previously reported in Cornus officinalis in Nanyang City, China (Huang et al., 2018). To our knowledge, this is the first report of blue honeysuckle leaf spot caused by D. glomerata in China. Reducing blue honeysuckle production losses caused by leaf spots is crucial for growers, and we hope that researchers will develop efficient control strategies for managing this emerging plant disease.

Relatively few studies investigating plant diseases in blue honeysuckle (Lonicera caerulea L.) have been conducted in China. In September 2021, a leaf spot disease was observed on approximately 10% of blue honeysuckle ‘Lanjingling’ leaves in a 0.02 ha field plantation in Tiekuang Street (124.36°E, 40.12°N) in Dandong City, Liaoning Province, China. The main symptom consisted of leaf spots with black mildew centers typically surrounded by yellow halos. Small pieces (3-4 mm) of the infected leaves were plated onto potato dextrose agar (PDA) medium as described by Wang et al. (2020) and six purified cultures were obtained through single spore culture on PDA. The observed conidia, consistent with the morphology of Alternaria alternata, were obpyriform and dark brown, measuring 5.8 to 15.3 μm × 7.9 to 42.5 μm, with 1-6 transverse septa and 0-3 longitudinal septa (n = 50) (Simmons 2007). For molecular verification, genomic DNA was extracted from a representative isolate LD-8. The ITS (GenBank OL454815), GPD (GenBank OL601993), TEF (GenBank OL538256), RPB2 (GenBank OL601966), and Alt (GenBank OL538257) genes were partially amplified with the respective primers ITS1/ITS4 (White et al. 1990), GPD1/GPD2 (Woudenberg et al. 2015), EFl-728F/EFI-986R (Carbone and Kohn 1999), RPB2-5F2/RPB2-7CR (Liu et al. 1999), and Alt-for/Alt-rev (Hong et al. 2005). BLAST analysis revealed that these genes shared 99%-100% identity with OK345332, MK451977, MN756011, KU933459, and MN655781, respectively. A greenhouse experiment was conducted using six, healthy two-year-old blue honeysuckle ‘Lanjingling’ plants to observe disease development (Mirzwa-Mróz et al. 2018). After 10 d, we noted typical leaf spot symptoms on inoculated leaves sprayed with a conidial suspension (106 spores/mL) while no symptoms were detected on uninoculated leaves. The same isolate, reisolated from infected leaves with the same morphological and molecular traits, was also identified as A. alternata, confirming Koch’s postulates. The fungus was previously reported in cockscomb plants in Heilongjiang Province, China (Wang et al. 2020). To our knowledge, this is the first report of leaf spot disease caused by A. alternata in blue honeysuckle grown in China. This study will provide a basis for future development of effective protection strategies against blue honeysuckle leaf spot in China.